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

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Abstract
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 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. 3 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. 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.

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