title: Adrenergic receptors of isolated snake atria.
abstract: Cardiac adrenergic receptors in snakes were examined using an isolated atria preparation of Naja naja and Ptyas korros. Treatments included an examination of the atrial responses to selective alpha- and beta-adrenergic agonists and antagonists. In both species, both phenylephrine and isoproterenol produced dose-dependent increases in the atrial beating rate and tension. Phenylephrine-induced increases were characterized with a high affinity and low affinity components. These positive chronotropic and inotropic effects produced by phenylephrine and isoproterenol were abolished with propranolol and in the phenylephrine-induced response phentolamine also attenuated the low affinity response and blocked the high affinity response. With catecholamines depletion via 6-OH dopamine or reserpine, the high affinity component in the phenylephrine-induced response was no longer observed. It is concluded that beta-adrenoceptors are the predominant post-synaptic adrenoceptors in snake atria. Stimulatory presynaptic alpha-adrenoceptors for modulating noradrenaline release may also be present.
authors.forename: K W
authors.initials: KW
authors.lastname: Chiu
authors.forename: J S
authors.initials: JS
authors.lastname: Sham
mesh_terms: D000818:Animals; D005260:Female; D006325:Heart Atria / Q000187:drug effects / Q000378:metabolism; D006339:Heart Rate / Q000187:drug effects; D006892:Hydroxydopamines / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D016627:Oxidopamine; D010646:Phentolamine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000378:metabolism*; D012110:Reserpine / Q000494:pharmacology; D012911:Snakes / Q000378:metabolism*
chemical_list: D006892:Hydroxydopamines; D011941:Receptors, Adrenergic; D010656:Phenylephrine; D012110:Reserpine; D016627:Oxidopamine; D011433:Propranolol; D007545:Isoproterenol; D010646:Phentolamine