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

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). The pA₂ 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. pA₂ 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. 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. 1974 British Pharmacological Society