Beta-adrenoceptor blocking agents and responses to adrenaline and 5-hydroxytryptamine in rat isolated stomach and...

1 Four beta-adrenoceptor blocking agents, (+/-)- and (+)-propranolol, practolol and oxprenolol, were found to antagonize, apparently competitively, the responses of both the rat isolated stomach and uterus to 5-hydroxytryptamine (5-HT).2 The pA(2) values for each of these agents as antagonists of the contractile action of 5-HT on the rat stomach were found to be: (+/-)-propranolol, 6.08; (+)-propranolol, 4.94; practolol, 3.43; and oxprenolol, 5.99. These values were very similar to the corresponding figures for antagonism of 5-HT-induced contractions of the uterus.3 pA(2) values for antagonism of adrenaline-induced relaxations by the four blocking agents on the rat stomach and uterus did not differ from the values for 5-HT blockade.4 To antagonize contractile responses to acetylcholine of the rat stomach it was necessary to give 100 times more (+/-)-propranolol than was needed to antagonize responses to 5-HT.