title: Effect of selective muscarinic antagonists on peristaltic contractions in opossum smooth muscle.
abstract: In this study we examined the role of M1- and M2-muscarinic receptors in the mediation of circular smooth muscle esophageal contractions elicited by pharmacological cholinergic stimulation and during peristalsis in anesthetized opossums. Esophageal-body contractions were induced by bethanechol administration, whereas peristalsis was elicited by pharyngeal stroking or cervical vagal stimulation. Contractions were measured by a low-compliance manometric recording system. The incidence and amplitude of bethanechol-induced contractions were antagonized by 4-diphenylacetoxy-n-methylpiperidine (4-DAMP) and atropine but not pirenzepine. 4-DAMP and atropine caused an increased velocity, decreased amplitude, and preferential reduction of the incidence of primary peristaltic contractions in the proximal smooth muscle esophagus. During long-train vagal stimulation, intra-stimulus A-waves had a velocity similar to primary peristalsis, whereas poststimulus B-waves showed a velocity considerably faster than primary peristalsis. Short-train vagal stimulation produced a contraction sequence, termed an "S-wave," that had a velocity similar to that of the A-wave. At low doses 4-DAMP increased the velocity and decreased the amplitude of A-wave and S-wave contractions, and at high doses 4-DAMP abolished both the A-wave and S-wave contractions. B-wave contractions were minimally affected by 4-DAMP. Pirenzepine had no effect on contractions induced by swallows or vagal stimulation. We conclude that M2-muscarinic receptors mediate esophageal contractions in the circular smooth muscle during primary peristalsis and during A-waves and S-waves induced by vagal stimulation, and M1-receptors do not have any important role in the excitatory neural pathway to the esophagus.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.forename: R J
authors.initials: RJ
authors.lastname: Gilbert
authors.forename: W J
authors.initials: WJ
authors.lastname: Dodds
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001570:Benzodiazepinones / Q000494:pharmacology; D018723:Bethanechol; D001626:Bethanechol Compounds / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004947:Esophagus / Q000502:physiology; D005260:Female; D008297:Male; D008365:Manometry; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009893:Opossums; D010528:Peristalsis / Q000187:drug effects; D010880:Piperidines / Q000494:pharmacology; D010890:Pirenzepine; D011976:Receptors, Muscarinic / Q000378:metabolism; D014630:Vagus Nerve / Q000502:physiology
chemical_list: D001570:Benzodiazepinones; D001626:Bethanechol Compounds; D010880:Piperidines; D011976:Receptors, Muscarinic; D018723:Bethanechol; D010890:Pirenzepine; D001285:Atropine; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium