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Meeting Abstracts  |   January 1996
Interaction of Nondepolarizing Muscle Relaxants with M2and M3Muscarinic Receptors in Guinea Pig Lung and Heart
Author Notes
  • (Okanlami) Fellow, Department of Anesthesiology and Critical Care Medicine.
  • (Fryer) Assistant Professor, Department of Environmental Health Sciences, School of Hygiene and Public Health.
  • (Hirshman) Professor, Departments of Anesthesiology, Environmental Health Sciences, and Medicine.
  • Received from the Departments of Anesthesiology and Environmental Health Sciences, The Johns Hopkins University, Baltimore, Maryland. Submitted for publication April 6, 1995. Accepted for publication September 29, 1995. Supported by National Institutes of Health grants HL-44727 and HL-10342 and by grants from the Council for Tobacco Research and the American Thoracic Society.
  • Address reprint requests to Dr. Hirshman: The Johns Hopkins School of Hygiene and Public Health, Division of Physiology/Room 7006, 615 North Wolfe Street, Baltimore, Maryland 21205.
Article Information
Meeting Abstracts   |   January 1996
Interaction of Nondepolarizing Muscle Relaxants with M2and M3Muscarinic Receptors in Guinea Pig Lung and Heart
Anesthesiology 1 1996, Vol.84, 155-161. doi:
Anesthesiology 1 1996, Vol.84, 155-161. doi:
ALTHOUGH neuromuscular blocking drugs are designed to specifically block nicotinic cholinergic receptors at the neuromuscular junction, many bind to muscarinic cholinergic receptors on ganglia, nerve endings, and smooth muscle, and alter parasympathetically mediated airway caliber and heart rate. [1] At least three muscarinic receptor subtypes have been identified pharmacologically and five molecular forms have been delineated. [2] The heart contains a homogeneous population of M2muscarinic receptors, activation of which induces bradycardia. [3] In the airways, acetylcholine (ACh) administered either exogenously or released from postganglionic parasympathetic nerve endings, induces bronchoconstriction by activating M3muscarinic receptors on airway smooth muscle. [4] In addition, ACh release from parasympathetic postganglionic nerves is under local control of muscarinic M2receptors on prejunctional postganglionic parasympathetic nerves. [5] .
Under physiologic conditions, M2muscarinic receptor activation inhibits ACh release, limiting vagally induced bronchoconstriction. Therefore, blockade of cardiac M2muscarinic receptors increases heart rate, [6–8] while in the lungs, blockade of the prejunctional M2muscarinic receptors potentiates vagally induced bronchoconstriction. [8,9] Conversely, blockade of M3muscarinic receptors on airway smooth muscle inhibits vagally induced bronchoconstriction. [4] Gallamine, atracurium, and low concentrations of pancuronium are M2receptor blockers. [8,9] Higher concentrations of pancuronium block M3receptors [8] while vecuronium does not appear to have either M2- or M3-blocking properties. [9] .
A new generation of nondepolarizing muscle relaxants is currently available for clinical use. Their effects on muscarinic receptors in heart and lung are not known. These experiments were designed to compare the effects of the new nondepolarizing muscle relaxants pipecuronium, doxacurium, and mivacurium to that of pancuronium on pulmonary and cardiac muscarinic receptors. We therefore determined the relative effects of prejunctional and postjunctional muscarinic receptor blockade with pancuronium, mivacurium, pipecuronium, and doxacurium on bronchoconstriction and the decrease in heart rate induced by vagal nerve stimulation and by intravenous ACh in anesthetized guinea pigs.
Materials and Methods
Dunkin-Hartley guinea pigs weighing 350–450 g were used. Guinea pigs were handled in accordance with the standards established by the United States Animal Welfare Acts set forth in the National Institutes of Health guidelines and the Policy and Procedures Manual published by the Johns Hopkins University School of Hygiene and Public Health Animal Care and Use Committee.
Animal Preparation
The guinea pigs were anesthetized with urethane (1.5 g/kg) injected intraperitoneally. The carotid artery was cannulated and connected to a Spectromed DTX pressure transducer (Spectromed, Oxnard, CA) for monitoring heart rate and blood pressure. Both jugular veins were cannulated for the administration of drugs. Both vagus nerves were cut and the distal ends were placed on shielded electrodes immersed in a pool of liquid paraffin. The animal's body temperature was maintained at 37 degrees C using a heating blanket. The animals were treated with guanethedine (10 mg/kg intravenous) to deplete norepinephrine, paralyzed with succinylcholine (infused at 10 micro gram *symbol* kg sup -1 *symbol* min sup -1), and their lungs artificially ventilated via a tracheal cannula using a positive pressure, constant volume animal ventilator (Harvard Apparatus Co., South Natick, MA; tidal volume 2.5–3.5 ml, 100–120 breaths/min). In this preparation, succinylcholine has been shown previously to have no effect on baseline pulmonary inflation pressure (Ppi), heart rate, or blood pressure [5] and no effect on vagally induced increases in Ppi. [5] Pulmonary inflation pressure was measured at the trachea with a Spectromed DTX pressure transducer. All signals were displayed on a Grass polygraph (Grass Instruments, Quincy, MA). Partial pressure of oxygen and partial pressure of carbon dioxide were measured from arterial blood samples at the beginning and the end of each experiment (Corning 170 pH/blood gas analyzer; Corning Glass, Medfield, MA).
Physiologic Measurements
Basal Ppi was produced by positive pressure ventilation of the guinea pigs' lungs. Bronchoconstriction was measured as an increase in Ppi over the basal pressure produced by the ventilator. [10] The sensitivity of the method was increased by taking the output Ppi signal from the driver to the input of the preamplifier of a second channel on the polygraph. Thus, baseline Ppi was recorded on one channel and increases in Ppi above the baseline were recorded on a second channel at a greater sensitivity. With this method, increases in Ppi as small as 2–3 mmH2O could be amplified and recorded accurately.
Electrical stimulation of both vagus nerves (15 Hz, 0.2 ms, 45 pulses/train) produced increases in Ppi and bradycardia. The voltage was selected within a range of 5–30 V to yield similar increases in Ppi between animals. The nerves were stimulated at 1-min intervals, and at regular intervals, ACh (1 or 2 micro gram/kg) was administered intravenously to monitor the function of the postjunctional muscarinic receptors on the heart and airway smooth muscle.
In separate experiments, cumulative doses of pancuronium (0.01–3.0 mg/kg), mivacurium (0.01–5.0 mg/kg), pipecuronium (0.01–3.0 mg/kg), and doxacurium (0.01–1.0 mg/kg) were administered to guinea pigs. The doses used were based on the ED95(effective dose, 95% of subjects) of each drug for neuromuscular relaxation. All drugs were administered intravenously at 5-min intervals and the effects were measured immediately after administration. The effects of each muscle relaxant on pulmonary and cardiac M2muscarinic receptor function were tested by comparing the magnitude of vagally induced bronchoconstriction and bradycardia before and after each dose of the drug. The effect of each drug on postjunctional M3muscarinic receptors was also tested by measuring ACh-induced bronchoconstriction and bradycardia responses before and after each dose of the muscle relaxant. Results are expressed as the ratio of the maximum bronchoconstriction (or bradycardia) after a particular dose of a muscle relaxant to the response before that dose of drug.
At the end of each experiment, intravenous atropine (1 mg/kg), was given to determine whether responses were mediated via muscarinic receptors. In the animals given mivacurium, the histamine-1 receptor antagonist pyrilamine (5 mg/kg intravenous) was administered after the atropine to determine whether the remaining airway and/or cardiac changes seen were related to the release of histamine by mivacurium.
Drugs
The drugs used in these experiments were: urethane, guanethidine, succinylcholine, pyrilamine, pancuronium, atropine, and ACh, all purchased from Sigma Chemical (St. Louis, MO). Pipecuronium was a gift from Organon (West Orange, NJ) and doxacurium and mivacurium were gifts from Burroughs Wellcome (Research Triangle Park, NC). All drugs were dissolved and diluted in 0.9% NaCl.
Statistics
All data were expressed as mean+/-SEM. Control responses to vagal stimulation or ACh between groups of guinea pigs were compared using Student's t test for unpaired samples. Dose-response curves were analyzed by analysis of variance with repeated measures. A P value of less than 0.05 was considered significant. Appropriate ED50's (effective dose, 50% of subjects) were obtained from Figure 1, Figure 2, Figure 3, and Figure 4.
Figure 1. Pancuronium (0.01–1.0 mg/kg intravenous) potentiates vagally induced bronchoconstriction in the lungs (closed squares; left) but inhibits acetylcholine-induced bronchoconstriction (open triangles). In the heart, pancuronium inhibits bradycardia induced by vagal stimulation (closed squares; right) and by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of pancuronium to the response in the absence of pancuronium. In the absence of pancuronium the increase in pulmonary inflation pressure with vagal stimulation was 34.7+/-6.4 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 39.0 +/-9.0 mmH2O. These responses were not significantly different from each other. In the heart, in the absence of pancuronium, the decrease in heart rate with vagal stimulation was 83.6+/-22.3 beats/min, the decrease in heart rate with intravenous acetylcholine was 91.7+/-28.6 beats/min. These responses also were not significantly different from each other (n = 4).
Figure 1. Pancuronium (0.01–1.0 mg/kg intravenous) potentiates vagally induced bronchoconstriction in the lungs (closed squares; left) but inhibits acetylcholine-induced bronchoconstriction (open triangles). In the heart, pancuronium inhibits bradycardia induced by vagal stimulation (closed squares; right) and by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of pancuronium to the response in the absence of pancuronium. In the absence of pancuronium the increase in pulmonary inflation pressure with vagal stimulation was 34.7+/-6.4 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 39.0 +/-9.0 mmH2O. These responses were not significantly different from each other. In the heart, in the absence of pancuronium, the decrease in heart rate with vagal stimulation was 83.6+/-22.3 beats/min, the decrease in heart rate with intravenous acetylcholine was 91.7+/-28.6 beats/min. These responses also were not significantly different from each other (n = 4).
Figure 1. Pancuronium (0.01–1.0 mg/kg intravenous) potentiates vagally induced bronchoconstriction in the lungs (closed squares; left) but inhibits acetylcholine-induced bronchoconstriction (open triangles). In the heart, pancuronium inhibits bradycardia induced by vagal stimulation (closed squares; right) and by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of pancuronium to the response in the absence of pancuronium. In the absence of pancuronium the increase in pulmonary inflation pressure with vagal stimulation was 34.7+/-6.4 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 39.0 +/-9.0 mmH2O. These responses were not significantly different from each other. In the heart, in the absence of pancuronium, the decrease in heart rate with vagal stimulation was 83.6+/-22.3 beats/min, the decrease in heart rate with intravenous acetylcholine was 91.7+/-28.6 beats/min. These responses also were not significantly different from each other (n = 4).
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Figure 2. Mivacurium (0.01–0.3 mg/kg intravenous) inhibits both vagally induced (closed squares; left side) and acetylcholine-induced (open triangles) bronchoconstriction in the lungs. Doses higher than 1.0 mg/kg increase only vagally induced bronchoconstriction. In the heart, mivacurium (0.01–3.0 mg/kg intravenous) inhibits bradycardia induced by vagal stimulation (closed squares; right) or by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of mivacurium to the response in the absence of mivacurium. In the absence of mivacurium the increase in pulmonary inflation pressure with vagal stimulation was 35.8+/-6.4 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 46.7+/-9.6 mmH2O. These responses were not significantly different from each other. In the heart, in the absence of mivacurium, the decrease in heart rate with vagal stimulation was 80.9 +/-31.2 beats/min, the decrease in heart rate with intravenous acetylcholine was 128+/-37.5 beats/min. These responses also were not significantly different from each other (n = 8).
Figure 2. Mivacurium (0.01–0.3 mg/kg intravenous) inhibits both vagally induced (closed squares; left side) and acetylcholine-induced (open triangles) bronchoconstriction in the lungs. Doses higher than 1.0 mg/kg increase only vagally induced bronchoconstriction. In the heart, mivacurium (0.01–3.0 mg/kg intravenous) inhibits bradycardia induced by vagal stimulation (closed squares; right) or by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of mivacurium to the response in the absence of mivacurium. In the absence of mivacurium the increase in pulmonary inflation pressure with vagal stimulation was 35.8+/-6.4 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 46.7+/-9.6 mmH2O. These responses were not significantly different from each other. In the heart, in the absence of mivacurium, the decrease in heart rate with vagal stimulation was 80.9 +/-31.2 beats/min, the decrease in heart rate with intravenous acetylcholine was 128+/-37.5 beats/min. These responses also were not significantly different from each other (n = 8).
Figure 2. Mivacurium (0.01–0.3 mg/kg intravenous) inhibits both vagally induced (closed squares; left side) and acetylcholine-induced (open triangles) bronchoconstriction in the lungs. Doses higher than 1.0 mg/kg increase only vagally induced bronchoconstriction. In the heart, mivacurium (0.01–3.0 mg/kg intravenous) inhibits bradycardia induced by vagal stimulation (closed squares; right) or by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of mivacurium to the response in the absence of mivacurium. In the absence of mivacurium the increase in pulmonary inflation pressure with vagal stimulation was 35.8+/-6.4 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 46.7+/-9.6 mmH2O. These responses were not significantly different from each other. In the heart, in the absence of mivacurium, the decrease in heart rate with vagal stimulation was 80.9 +/-31.2 beats/min, the decrease in heart rate with intravenous acetylcholine was 128+/-37.5 beats/min. These responses also were not significantly different from each other (n = 8).
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Figure 3. Pipecuronium (0.01–3.0 mg/kg intravenous) potentiates vagally induced bronchoconstriction in the lungs (closed squares; left) but has no effect on acetylcholine-induced bronchoconstriction (open triangles). In the heart, pipecuronium inhibits bradycardia induced by vagal stimulation (closed squares; right) and by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of pipecuronium to the response in the absence of pipecuronium. In the absence of pipecuronium the increase in pulmonary inflation pressure with vagal stimulation was 30.8+/-0.7 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 28.4+/-7.4 mmH2O. These responses were not significantly different from each other. In the heart in the absence of pipecuronium, the decrease in heart rate with vagal stimulation was 74.9 +/-20.7 beats/min, the decrease in heart rate with intravenous acetylcholine was 79.8.7+/-33.7 beats/min. These responses also were not significantly different from each other (n = 5).
Figure 3. Pipecuronium (0.01–3.0 mg/kg intravenous) potentiates vagally induced bronchoconstriction in the lungs (closed squares; left) but has no effect on acetylcholine-induced bronchoconstriction (open triangles). In the heart, pipecuronium inhibits bradycardia induced by vagal stimulation (closed squares; right) and by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of pipecuronium to the response in the absence of pipecuronium. In the absence of pipecuronium the increase in pulmonary inflation pressure with vagal stimulation was 30.8+/-0.7 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 28.4+/-7.4 mmH2O. These responses were not significantly different from each other. In the heart in the absence of pipecuronium, the decrease in heart rate with vagal stimulation was 74.9 +/-20.7 beats/min, the decrease in heart rate with intravenous acetylcholine was 79.8.7+/-33.7 beats/min. These responses also were not significantly different from each other (n = 5).
Figure 3. Pipecuronium (0.01–3.0 mg/kg intravenous) potentiates vagally induced bronchoconstriction in the lungs (closed squares; left) but has no effect on acetylcholine-induced bronchoconstriction (open triangles). In the heart, pipecuronium inhibits bradycardia induced by vagal stimulation (closed squares; right) and by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of pipecuronium to the response in the absence of pipecuronium. In the absence of pipecuronium the increase in pulmonary inflation pressure with vagal stimulation was 30.8+/-0.7 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 28.4+/-7.4 mmH2O. These responses were not significantly different from each other. In the heart in the absence of pipecuronium, the decrease in heart rate with vagal stimulation was 74.9 +/-20.7 beats/min, the decrease in heart rate with intravenous acetylcholine was 79.8.7+/-33.7 beats/min. These responses also were not significantly different from each other (n = 5).
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Figure 4. Doxacurium (0.01–1.0 mg/kg intravenous) had no effect on bronchoconstriction induced either by stimulation of the vagus nerve (closed squares; left) or by intravenous acetylcholine (open triangles). Likewise, in the heart, doxacurium also had no effect on bradycardia induced by either vagal stimulation (closed squares; right) or by intravenous acetylcholine (open triangles). Data are expressed as the mean +/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of doxacurium to the response in the absence of doxacurium. In the absence of doxacurium, the increase in pulmonary inflation pressure with vagal stimulation was 29.8+/- 1.0 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 49.0+/-16.5 mmH2O. These responses were not significantly different from each other. In the heart in the absence of doxacurium the decrease in heart rate with vagal stimulation was 46.9+/-7.5 beats/min, the decrease in heart rate with intravenous acetylcholine was 83.6+/-45.7 beats/min. These responses also were not significantly different from each other (n = 5).
Figure 4. Doxacurium (0.01–1.0 mg/kg intravenous) had no effect on bronchoconstriction induced either by stimulation of the vagus nerve (closed squares; left) or by intravenous acetylcholine (open triangles). Likewise, in the heart, doxacurium also had no effect on bradycardia induced by either vagal stimulation (closed squares; right) or by intravenous acetylcholine (open triangles). Data are expressed as the mean +/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of doxacurium to the response in the absence of doxacurium. In the absence of doxacurium, the increase in pulmonary inflation pressure with vagal stimulation was 29.8+/- 1.0 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 49.0+/-16.5 mmH2O. These responses were not significantly different from each other. In the heart in the absence of doxacurium the decrease in heart rate with vagal stimulation was 46.9+/-7.5 beats/min, the decrease in heart rate with intravenous acetylcholine was 83.6+/-45.7 beats/min. These responses also were not significantly different from each other (n = 5).
Figure 4. Doxacurium (0.01–1.0 mg/kg intravenous) had no effect on bronchoconstriction induced either by stimulation of the vagus nerve (closed squares; left) or by intravenous acetylcholine (open triangles). Likewise, in the heart, doxacurium also had no effect on bradycardia induced by either vagal stimulation (closed squares; right) or by intravenous acetylcholine (open triangles). Data are expressed as the mean +/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of doxacurium to the response in the absence of doxacurium. In the absence of doxacurium, the increase in pulmonary inflation pressure with vagal stimulation was 29.8+/- 1.0 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 49.0+/-16.5 mmH2O. These responses were not significantly different from each other. In the heart in the absence of doxacurium the decrease in heart rate with vagal stimulation was 46.9+/-7.5 beats/min, the decrease in heart rate with intravenous acetylcholine was 83.6+/-45.7 beats/min. These responses also were not significantly different from each other (n = 5).
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Results
At the beginning of each experiment, baseline pulmonary inflation pressure (range 9.6–11.5 cmH2O), heart rate (range 260–300 beats/min) and blood pressure (systolic range 43–50 mmHg; diastolic range 21–26 mmHg) were not different between groups. None of the drug treatments, except mivacurium, had any effect on these parameters.
Electrical stimulation of the vagus nerves (15 Hz, 0.2 ms, 5–40 V, 45 pulses/train) caused an increase in Ppi. Intravenous injection of ACh (1 or 2 micro gram/kg) also caused an increase in Ppi. Atropine (1 mg/kg intravenous) given at the end of each experiment blocked increases in Ppi induced by both electrical stimulation of the vagus nerves and intravenous ACh, indicating that these responses are mediated by muscarinic receptors. In the heart, vagal stimulation and intravenously administered ACh caused bradycardia (measured as a decrease in heart rate) via stimulation of M2muscarinic receptors on cardiac muscle.
Pancuronium at doses of 0.01–1.0 mg/kg potentiated the vagally induced increase in Ppi (P = 0.05). However, at the highest concentration used, 3.0 mg/kg, pancuronium inhibited vagally induced increases in Ppi by 40%(Figure 1, left). This inhibition is probably a result of the large, coincident blockade of M3muscarinic receptors because at this dose, increases in Ppi induced by intravenous ACh (and therefore mediated solely by M3receptors) are almost completely inhibited (open triangles). At all doses used, pancuronium caused an inhibition of ACh-induced increase in Ppi (P = 0.009). This effect of pancuronium on M3receptors was dose-dependent with a maximal inhibition (at 3 mg *symbol* kg sup -1 pancuronium) of 74%. In the heart, pancuronium (0.01–3.0 mg *symbol* kg sup -1 intravenous) inhibited both vagally induced (P = 0.0001) and ACh-induced (P = 0.0001) bradycardia (Figure 1, right). This effect of pancuronium in the heart was dose-related. After administration of 1 mg/kg or more of pancuronium, no bradycardia could be elicited either by vagal stimulation or by intravenous ACh. Atropine (1 mg/kg) abolished the vagally induced and ACh-induced increase in Ppi and bradycardia provoked by pancuronium.
Mivacurium, at doses of 1–5 mg/kg, increased baseline Ppi (Table 1). Pyrilamine, but not atropine, prevented the increase in baseline Ppi (Table 1), indicating that this increase was mediated via histamine release, rather than via a muscarinic receptor. In separate experiments, mivacurium (0.01–1.0 mg/kg) inhibited both vagally induced and ACh-induced increases in Ppi (Figure 2, left). Larger doses of mivacurium (1 and 3 mg/kg) reversed the inhibition of vagally induced, but not ACh-induced increases in Ppi (Figure 2, left). Vagally induced changes in Ppi were not measured at doses larger than 3 mg/kg because of large postjunctional effects of atracurium at these doses. In the heart, mivacurium inhibited both vagally induced (P = 0.0001) and ACh-induced (P = 0.0002) bradycardia similarly in a dose-related manner (Figure 2, right).
Table 1. Effect of Mivacurium of Baseline Pulmonary Inflation Pressure
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Table 1. Effect of Mivacurium of Baseline Pulmonary Inflation Pressure
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Pipecuronium (0.01–3.0 mg/kg) potentiated vagally induced increases in Ppi (P = 0.02) but did not alter ACh-induced increases in Ppi (Figure 3, left). The maximum effect, a 2.5-fold potentiation, was obtained in response to 1.0 mg/kg pipecuronium. Both vagally (P = 0.0001) and ACh-induced (P = 0.0001) bradycardia were inhibited in a dose-related fashion by pipecuronium (Figure 3, right). Atropine (1 mg/kg) abolished vagally induced and ACh-induced increases in Ppi and bradycardia provoked by pipecuronium. Doxacurium (0.01–1.0 mg/kg) had no significant effect on either vagally induced or ACh-induced increases in Ppi or bradycardia (Figure 4).
The relative order of potency for the M2receptor was pancuronium > pipecuronium > mivacurium > doxacurium (Table 2). The relative order of potency for the M3receptor was pancuronium > mivacurium. Pipecuronium and doxacurium had no effect on M3muscarinic receptors at the doses used (Table 2).
Table 2. Approximate ED50of Nondepolarizing Muscle Relaxants at Postjunctional M2and M3Muscarinic Receptors in Guinea Pig Heart and Lung and ED95at Skeletal Muscle Nicotinic Receptors in Humans
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Table 2. Approximate ED50of Nondepolarizing Muscle Relaxants at Postjunctional M2and M3Muscarinic Receptors in Guinea Pig Heart and Lung and ED95at Skeletal Muscle Nicotinic Receptors in Humans
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Discussion
Vagal nerve stimulation in animals is an accepted model to study drug effects on bronchoconstriction. [8,9] The increase in pulmonary inflation pressure over the basal inflation pressure produced by the ventilator was used as our measure of bronchoconstriction, [10,11] because increases in pulmonary inflation pressure during vagal stimulation reflect primarily an increase in lung resistance with little change in dynamic compliance. [12,13] Cholinergic efferent nerve fibers of the parasympathetic nervous system pass down the vagus nerve and synapse in the smooth muscle of the airway wall. In the human lung, the parasympathetic nervous system regulates airway caliber, both in the baseline state and after mechanical, chemical, or physical stimulation, via release of ACh onto postjunctional muscarinic M3receptors of airway smooth muscle. However, previous studies from this laboratory have demonstrated the presence of prejunctional M2receptors, which inhibit ACh release, thus limiting vagally induced bronchoconstriction. [5] Thus, blockade of M3receptors inhibits bronchoconstriction induced by either vagal nerve stimulation or intravenous ACh, whereas blockade of M2receptors potentiates bronchoconstriction induced by vagal nerve stimulation. The net effect of a muscarinic antagonist on bronchoconstriction provoked by vagal nerve stimulation depends on its relative potency as an M2or M3antagonist. M2, but not M sub 3, antagonists inhibit bradycardia induced by either vagal nerve stimulation or intravenous ACh.
Our current study demonstrates that pancuronium is a potent antagonist for both M2and M3receptors, thus confirming previous studies in guinea pigs [8] and dogs. [9] In the lungs, the M2antagonist effect must predominate between 0.03 mg/kg and 1 mg/kg, resulting in potentiation of vagally induced bronchoconstriction. At clinical doses for humans, 0.05–0.1 mg/kg, [14] the potentiation would be small (1.2-fold;Figure 1), assuming that the dose-response relationship of the human and guinea pig airway are similar. At larger doses, the M3effect predominates and the potentiation is reversed. Pancuronium also inhibited vagally mediated bradycardia consistent with its M2-blocking properties.
Our findings that mivacurium inhibited bradycardia and bronchoconstriction (measured as an increase in Ppi), induced by either intravenous ACh or vagal nerve stimulation, suggest that mivacurium blocks both M2and M3receptors. It appears to be less potent than pancuronium as an M2antagonist. Thus, mivacurium does not potentiate vagally induced bronchoconstriction at doses between 0.03 and 0.3 mg/kg. The potentiation of vagally induced, but not ACh-induced, bronchoconstriction at 1- and 3-mg/kg doses could be caused by blockade of M2receptors. However, it is more likely caused by enhanced ACh release by histamine, [15,16] because this effect occurred at doses at which histamine was released [17] and was prevented by atropine. The increase in baseline airway tone at these same concentrations is likely a result of the direct effects of histamine on H1receptors on airway smooth muscle, because this effect occurred at doses at which histamine is released [17] and was prevented by pyrilamine, an H1receptor antagonist.
Our findings that pipecuronium potentiated bronchoconstriction induced by vagal stimulation, with no effect on bronchoconstriction induced by intravenous ACh, and inhibited bradycardia, suggest that pipecuronium is selective for M2muscarinic receptors. Pipecuronium, however, is less potent than pancuronium as an M2antagonist, only producing significant potentiation of vagally induced bronchoconstriction at doses greater than 0.3 mg/kg. Because the concentrations of pipecuronium used clinically are tenfold less, it is unlikely that pipecuronium will have any clinically relevant effects on muscarinic receptors. Our results with doxacurium showing neither potentiation nor inhibition of bronchoconstriction or bradycardia suggest that doxacurium has no effect on either M2or M3receptors at doses up to 1 mg/kg.
ACh release from vagal nerve stimulation may be inhibited by prejunctional beta-adrenoceptors. [13] Thus, inhibition of these receptors by pancuronium and pipecuronium could explain our results. However, all animals were pretreated with guanethidine to deplete norepinephrine, which rules out the possibility that pancuronium and pipecuronium potentiated bronchoconstriction by inhibiting prejunctional beta adrenoceptors.
M2and M3antagonist activity by the neuromuscular blockers studied generally occurred at concentrations that were higher than the ED95for the nicotinic receptor on skeletal muscle, except for pancuronium (Table 2). Although pancuronium is a potent antagonist of the M2receptor, it is also a potent antagonist of M3receptors in the clinical range, inhibiting bronchoconstriction. Thus, the net effect of pancuronium on any potential irritant-induced bronchoconstriction would be expected to be small. Mivacurium is a more potent M3than M2antagonist, and should not potentiate irritant-induced bronchoconstriction in the clinical range. In contrast, pipecuronium is not an antagonist for M3receptors but does inhibit M2receptor function. However, this occurs only at doses larger than are used clinically.
In summary, the most important findings of this study are: mivacurium is a muscarinic antagonist with similar potencies for both M sub 2 and M3receptors; pipecuronium is an antagonist for M2but not M3muscarinic receptors; and doxacurium has no effect on either M2or M3receptors. Although pipecuronium is an M2receptor antagonist and can potentiate reflex-induced bronchoconstriction, this effect occurs only at doses that are larger than those used clinically. If these studies in the guinea pig are relevant to the clinical situation in humans, pipecuronium, mivacurium, and doxacurium, in concentrations in the clinical range, should have few adverse effects on airway tone and reactivity in humans.
REFERENCES
Bowman WC: Non-relaxant properties of neuromuscular blocking drugs. Br J Anaesth 54:147-60, 1982.
Goyal RK: Muscarinic receptor subtypes: Physiology and clinical implications. N Engl J Med 321:1022-9, 1989.
DiFrancesco D, Ducouret P, Robinson RB: Muscarinic modulation of cardiac rate at low acetylcholine concentrations. Science 243:669-71, 1989.
Roffel AF, Meurs H, Elzinger CRS, Zaagsma J: Characterization of the muscarinic receptor subtype involved in phosphoinositide metabolism in bovine tracheal smooth muscle. Br J Pharmacol 99:293-6, 1990.
Fryer AD, Maclagan J: Muscarinic inhibitory receptors in pulmonary parasympathetic nerves in the guinea pig. Br J Pharmacol 83:973-8, 1984.
Riker WF, Wescoe WC: The pharmacology of Flaxedil with observations on certain analogs. Ann NY Acad Sci 54:373-92, 1951.
Leung E, Mitchelson F: The interaction of pancuronium with cardiac and ileal muscarinic receptors. Eur J Pharmacol 80:1-9, 1982.
Fryer AD, Maclagan J: Pancuronium and gallamine are antagonists for pre- and post-junctional muscarinic receptors in the guinea pig lung. Naunyn-Schmiedeberg's Arch Pharmacol 335:367-71, 1987.
Vettermann J, Beck KC, Lindahl SGG, Brichant JF, Rehder K: Actions of enflurane, isoflurane, vecuronium, atracurium and pancuronium on pulmonary resistance in dogs. ANESTHESIOLOGY 69:688-95, 1988.
Dixon WE, Brody TG: Contributions to the physiology of the lungs: 1. The bronchial muscles and their innervation and the action of drugs upon them. J Physiol (Lond) 29:97-173, 1903.
Hirshman CA, Downes H: Experimental asthma in animals, Bronchial Asthma: Mechanisms and Therapeutics. Edited by Weiss EW, Segal MS, Stein M. Boston, Little Brown, 1993, p 383.
Blaber LC, Fryer AD, Maclagan J: Neuronal muscarinic receptors attenuate vagally-induced contraction of feline bronchial smooth muscle. Br J Pharmacol 86:723-8, 1985.
Danser AHJ, van den Ende R, Lorenz RR, Flavahan NA, Vanhoutte PM: Prejunctional/beta sub 1 -adrenoceptors inhibit cholinergic transmission in canine bronchi. J Appl Physiol 62:785-90, 1987.
Basta SJ: Pharmacology of neuromuscular blocking agents, Principles and Practice of Anesthesiology. Edited by Rogers MC, Tinker JH, Covino BG, Longnecker DE. St. Louis, Mosby, 1993, pp 1518-40.
Benson MK, Graf PD: Bronchial reactivity: Interaction between vagal stimulation and inhaled histamine. J Appl Physiol Respir Environ Exercise Physiol 43:643-7, 1977.
Kikuchi Y, Okayama H, Okayama M, Sasaki H, Takishima T: Interaction between histamine and vagal stimulation on tracheal smooth muscle in dogs. J Appl Physiol Respir Environ Exercise Physiol 56:590-5, 1984.
Basta SJ: Clinical pharmacology of mivacurium chloride: A review. J Clin Anesth 4:153-63, 1992.
Wierda JMKH, Richardson FJ, Agoston S: Dose-response relation and time course of action of pipecuronium bromide in humans anesthetized with nitrous oxide and isoflurane, halothane, or droperidol and fentanyl. Anesth Analg 68:208-13, 1989.
Basta SJ, Saverese JJ, Ali HH, Embree BB, Schwartz AF, Rudd GD, Wastilaw B: Clinical pharmacology of doxacurium chloride, a new long-acting nondepolarizing muscle relaxant. ANESTHESIOLOGY 69:478-86, 1988.
Figure 1. Pancuronium (0.01–1.0 mg/kg intravenous) potentiates vagally induced bronchoconstriction in the lungs (closed squares; left) but inhibits acetylcholine-induced bronchoconstriction (open triangles). In the heart, pancuronium inhibits bradycardia induced by vagal stimulation (closed squares; right) and by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of pancuronium to the response in the absence of pancuronium. In the absence of pancuronium the increase in pulmonary inflation pressure with vagal stimulation was 34.7+/-6.4 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 39.0 +/-9.0 mmH2O. These responses were not significantly different from each other. In the heart, in the absence of pancuronium, the decrease in heart rate with vagal stimulation was 83.6+/-22.3 beats/min, the decrease in heart rate with intravenous acetylcholine was 91.7+/-28.6 beats/min. These responses also were not significantly different from each other (n = 4).
Figure 1. Pancuronium (0.01–1.0 mg/kg intravenous) potentiates vagally induced bronchoconstriction in the lungs (closed squares; left) but inhibits acetylcholine-induced bronchoconstriction (open triangles). In the heart, pancuronium inhibits bradycardia induced by vagal stimulation (closed squares; right) and by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of pancuronium to the response in the absence of pancuronium. In the absence of pancuronium the increase in pulmonary inflation pressure with vagal stimulation was 34.7+/-6.4 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 39.0 +/-9.0 mmH2O. These responses were not significantly different from each other. In the heart, in the absence of pancuronium, the decrease in heart rate with vagal stimulation was 83.6+/-22.3 beats/min, the decrease in heart rate with intravenous acetylcholine was 91.7+/-28.6 beats/min. These responses also were not significantly different from each other (n = 4).
Figure 1. Pancuronium (0.01–1.0 mg/kg intravenous) potentiates vagally induced bronchoconstriction in the lungs (closed squares; left) but inhibits acetylcholine-induced bronchoconstriction (open triangles). In the heart, pancuronium inhibits bradycardia induced by vagal stimulation (closed squares; right) and by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of pancuronium to the response in the absence of pancuronium. In the absence of pancuronium the increase in pulmonary inflation pressure with vagal stimulation was 34.7+/-6.4 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 39.0 +/-9.0 mmH2O. These responses were not significantly different from each other. In the heart, in the absence of pancuronium, the decrease in heart rate with vagal stimulation was 83.6+/-22.3 beats/min, the decrease in heart rate with intravenous acetylcholine was 91.7+/-28.6 beats/min. These responses also were not significantly different from each other (n = 4).
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Figure 2. Mivacurium (0.01–0.3 mg/kg intravenous) inhibits both vagally induced (closed squares; left side) and acetylcholine-induced (open triangles) bronchoconstriction in the lungs. Doses higher than 1.0 mg/kg increase only vagally induced bronchoconstriction. In the heart, mivacurium (0.01–3.0 mg/kg intravenous) inhibits bradycardia induced by vagal stimulation (closed squares; right) or by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of mivacurium to the response in the absence of mivacurium. In the absence of mivacurium the increase in pulmonary inflation pressure with vagal stimulation was 35.8+/-6.4 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 46.7+/-9.6 mmH2O. These responses were not significantly different from each other. In the heart, in the absence of mivacurium, the decrease in heart rate with vagal stimulation was 80.9 +/-31.2 beats/min, the decrease in heart rate with intravenous acetylcholine was 128+/-37.5 beats/min. These responses also were not significantly different from each other (n = 8).
Figure 2. Mivacurium (0.01–0.3 mg/kg intravenous) inhibits both vagally induced (closed squares; left side) and acetylcholine-induced (open triangles) bronchoconstriction in the lungs. Doses higher than 1.0 mg/kg increase only vagally induced bronchoconstriction. In the heart, mivacurium (0.01–3.0 mg/kg intravenous) inhibits bradycardia induced by vagal stimulation (closed squares; right) or by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of mivacurium to the response in the absence of mivacurium. In the absence of mivacurium the increase in pulmonary inflation pressure with vagal stimulation was 35.8+/-6.4 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 46.7+/-9.6 mmH2O. These responses were not significantly different from each other. In the heart, in the absence of mivacurium, the decrease in heart rate with vagal stimulation was 80.9 +/-31.2 beats/min, the decrease in heart rate with intravenous acetylcholine was 128+/-37.5 beats/min. These responses also were not significantly different from each other (n = 8).
Figure 2. Mivacurium (0.01–0.3 mg/kg intravenous) inhibits both vagally induced (closed squares; left side) and acetylcholine-induced (open triangles) bronchoconstriction in the lungs. Doses higher than 1.0 mg/kg increase only vagally induced bronchoconstriction. In the heart, mivacurium (0.01–3.0 mg/kg intravenous) inhibits bradycardia induced by vagal stimulation (closed squares; right) or by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of mivacurium to the response in the absence of mivacurium. In the absence of mivacurium the increase in pulmonary inflation pressure with vagal stimulation was 35.8+/-6.4 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 46.7+/-9.6 mmH2O. These responses were not significantly different from each other. In the heart, in the absence of mivacurium, the decrease in heart rate with vagal stimulation was 80.9 +/-31.2 beats/min, the decrease in heart rate with intravenous acetylcholine was 128+/-37.5 beats/min. These responses also were not significantly different from each other (n = 8).
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Figure 3. Pipecuronium (0.01–3.0 mg/kg intravenous) potentiates vagally induced bronchoconstriction in the lungs (closed squares; left) but has no effect on acetylcholine-induced bronchoconstriction (open triangles). In the heart, pipecuronium inhibits bradycardia induced by vagal stimulation (closed squares; right) and by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of pipecuronium to the response in the absence of pipecuronium. In the absence of pipecuronium the increase in pulmonary inflation pressure with vagal stimulation was 30.8+/-0.7 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 28.4+/-7.4 mmH2O. These responses were not significantly different from each other. In the heart in the absence of pipecuronium, the decrease in heart rate with vagal stimulation was 74.9 +/-20.7 beats/min, the decrease in heart rate with intravenous acetylcholine was 79.8.7+/-33.7 beats/min. These responses also were not significantly different from each other (n = 5).
Figure 3. Pipecuronium (0.01–3.0 mg/kg intravenous) potentiates vagally induced bronchoconstriction in the lungs (closed squares; left) but has no effect on acetylcholine-induced bronchoconstriction (open triangles). In the heart, pipecuronium inhibits bradycardia induced by vagal stimulation (closed squares; right) and by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of pipecuronium to the response in the absence of pipecuronium. In the absence of pipecuronium the increase in pulmonary inflation pressure with vagal stimulation was 30.8+/-0.7 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 28.4+/-7.4 mmH2O. These responses were not significantly different from each other. In the heart in the absence of pipecuronium, the decrease in heart rate with vagal stimulation was 74.9 +/-20.7 beats/min, the decrease in heart rate with intravenous acetylcholine was 79.8.7+/-33.7 beats/min. These responses also were not significantly different from each other (n = 5).
Figure 3. Pipecuronium (0.01–3.0 mg/kg intravenous) potentiates vagally induced bronchoconstriction in the lungs (closed squares; left) but has no effect on acetylcholine-induced bronchoconstriction (open triangles). In the heart, pipecuronium inhibits bradycardia induced by vagal stimulation (closed squares; right) and by intravenous acetylcholine equally (open triangles). Data are expressed as the mean+/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of pipecuronium to the response in the absence of pipecuronium. In the absence of pipecuronium the increase in pulmonary inflation pressure with vagal stimulation was 30.8+/-0.7 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 28.4+/-7.4 mmH2O. These responses were not significantly different from each other. In the heart in the absence of pipecuronium, the decrease in heart rate with vagal stimulation was 74.9 +/-20.7 beats/min, the decrease in heart rate with intravenous acetylcholine was 79.8.7+/-33.7 beats/min. These responses also were not significantly different from each other (n = 5).
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Figure 4. Doxacurium (0.01–1.0 mg/kg intravenous) had no effect on bronchoconstriction induced either by stimulation of the vagus nerve (closed squares; left) or by intravenous acetylcholine (open triangles). Likewise, in the heart, doxacurium also had no effect on bradycardia induced by either vagal stimulation (closed squares; right) or by intravenous acetylcholine (open triangles). Data are expressed as the mean +/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of doxacurium to the response in the absence of doxacurium. In the absence of doxacurium, the increase in pulmonary inflation pressure with vagal stimulation was 29.8+/- 1.0 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 49.0+/-16.5 mmH2O. These responses were not significantly different from each other. In the heart in the absence of doxacurium the decrease in heart rate with vagal stimulation was 46.9+/-7.5 beats/min, the decrease in heart rate with intravenous acetylcholine was 83.6+/-45.7 beats/min. These responses also were not significantly different from each other (n = 5).
Figure 4. Doxacurium (0.01–1.0 mg/kg intravenous) had no effect on bronchoconstriction induced either by stimulation of the vagus nerve (closed squares; left) or by intravenous acetylcholine (open triangles). Likewise, in the heart, doxacurium also had no effect on bradycardia induced by either vagal stimulation (closed squares; right) or by intravenous acetylcholine (open triangles). Data are expressed as the mean +/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of doxacurium to the response in the absence of doxacurium. In the absence of doxacurium, the increase in pulmonary inflation pressure with vagal stimulation was 29.8+/- 1.0 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 49.0+/-16.5 mmH2O. These responses were not significantly different from each other. In the heart in the absence of doxacurium the decrease in heart rate with vagal stimulation was 46.9+/-7.5 beats/min, the decrease in heart rate with intravenous acetylcholine was 83.6+/-45.7 beats/min. These responses also were not significantly different from each other (n = 5).
Figure 4. Doxacurium (0.01–1.0 mg/kg intravenous) had no effect on bronchoconstriction induced either by stimulation of the vagus nerve (closed squares; left) or by intravenous acetylcholine (open triangles). Likewise, in the heart, doxacurium also had no effect on bradycardia induced by either vagal stimulation (closed squares; right) or by intravenous acetylcholine (open triangles). Data are expressed as the mean +/-SEM of the ratio of the response to vagal stimulation or intravenous acetylcholine in the presence of doxacurium to the response in the absence of doxacurium. In the absence of doxacurium, the increase in pulmonary inflation pressure with vagal stimulation was 29.8+/- 1.0 mmH2O, the increase in pulmonary inflation pressure with intravenous acetylcholine was 49.0+/-16.5 mmH2O. These responses were not significantly different from each other. In the heart in the absence of doxacurium the decrease in heart rate with vagal stimulation was 46.9+/-7.5 beats/min, the decrease in heart rate with intravenous acetylcholine was 83.6+/-45.7 beats/min. These responses also were not significantly different from each other (n = 5).
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Table 1. Effect of Mivacurium of Baseline Pulmonary Inflation Pressure
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Table 1. Effect of Mivacurium of Baseline Pulmonary Inflation Pressure
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Table 2. Approximate ED50of Nondepolarizing Muscle Relaxants at Postjunctional M2and M3Muscarinic Receptors in Guinea Pig Heart and Lung and ED95at Skeletal Muscle Nicotinic Receptors in Humans
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Table 2. Approximate ED50of Nondepolarizing Muscle Relaxants at Postjunctional M2and M3Muscarinic Receptors in Guinea Pig Heart and Lung and ED95at Skeletal Muscle Nicotinic Receptors in Humans
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