title: Effects of cholinomimetic drugs on reptilian atrial muscles.
abstract: The effects of some cholinomimetic drugs have been examined on isolated atria of rainbow lizards (Agama agama Linn.) and land tortoises (Kinixys spp. Linn.). Acetylcholine (ACh, 10(-8) - 5 X 10(-5) M) caused concentration-dependent, atropine-sensitive, negative chronotropic or inotropic responses in isolated spontaneously-beating right or electrically-driven left atria of rainbow lizards and land tortoises. This prototype cholinergic drug (ACh, 10(-8) 5 X 10(-5) M) also induced atropine-sensitive, concentration-related negative chronotropic or inotropic responses in isolated atrial muscles taken from guinea-pigs. Histamine (10(-8) - 5 X 10(-5) M) produced concentration-related positive chronotropic or inotropic responses in isolated spontaneously-beating right or electrically-driven left atria of rainbow lizards and guinea-pigs without significantly affecting (P greater than 0.05) the tortoise atria. 5-Hydroxytryptamine (5-HT, 10(-7) - 5 X 10(-5) M) induced concentration-dependent positive chronotropic or inotropic responses in isolated, spontaneously-beating right or electrically-driven left atria of rainbow lizards, tortoises and guinea-pigs. Nicotine (10(-8) - 5 X 10(-5) M) had no effect on the rate of beating of the lizard or tortoise isolated right atria, but caused concentration-dependent positive chronotropic responses in spontaneously-beating isolated right atria of the guinea-pig. Furthermore, nicotine (10(-8) - 5 X 10(-5) M) had no effect on contractile tension of isolated, electrically-driven left atria of the tortoise; it induced a biphasic inotropic response in driven left atria of the rainbow lizard and produced a concentration-related positive inotropic response in electrically-driven isolated left atria of the guinea-pig.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D004558:Electric Stimulation; D005260:Female; D006168:Guinea Pigs; D006325:Heart Atria / Q000187:drug effects; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D008116:Lizards; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D009538:Nicotine / Q000494:pharmacology; D010277:Parasympathomimetics / Q000494:pharmacology*; D012701:Serotonin / Q000494:pharmacology; D013045:Species Specificity; D014426:Turtles
chemical_list: D010277:Parasympathomimetics; D012701:Serotonin; D009538:Nicotine; D006632:Histamine; D000109:Acetylcholine