title: Reversible antagonism between acetylcholine and phenoxybenzamine in isolated atria of guinea-pigs.
abstract: The antagonism between acetylcholine and phenoxybenzamine on isolated driven left atria of guinea-pigs has been examined. Phenoxybenzamine (10(-6) and 2.5 X 10(-6)M), added to the bath fluid 5 minutes before the administration of acetylcholine (10(-7) - 10(-6)M), caused an almost parallel shift (to the right) in the log dose-response curve of acetylcholine on isolated driven left atria of guinea-pigs. There was no fall in the maximum attainable response induced by acetylcholine. These results were taken to imply a reversible, competitive antagonism between acetylcholine and phenoxybenzamine in isolated atria of guinea-pigs. It is suggested that phenoxybenzamine probably combines reversibly (like atropine) with the muscarinic cholinoceptors on the atrial muscle to antagonise, in a competitive manner, the inhibitory action of acetylcholine on isolated atrial myocardium.
mesh_terms: D000109:Acetylcholine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D006168:Guinea Pigs; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D010643:Phenoxybenzamine / Q000037:antagonists & inhibitors / Q000494:pharmacology*
chemical_list: D010643:Phenoxybenzamine; D001285:Atropine; D000109:Acetylcholine