β‐ADRENOCEPTOR BLOCKING AGENTS AND RESPONSES TO ADRENALINE AND 5‐HYDROXYTRYPTAMINE IN RAT ISOLATED STOMACH AND UTERUS

1 Four β‐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.