Abstract

The effects of the ephedrine isomers were studied in the isolated guinea-pig tracheal chain preparation (which is believed to contain only beta adrenergic receptors). Cumulative dose-response curves were determined in the presence of methacholine-induced tone. The relaxation produced by the isomers was converted into percentage values with maximal effect as produced by isoproterenol or papaverine considered as 100%. In the normal preparation the isomers showed no striking differences in potency, although L(+)- ephednine was the least potent. In preparations from reserpine-pretreated animals (5 mg/ kg i.p., 16-24 hr) the effects of the D(-) isomers were not reduced but the effects of the L(+) isomers were. In similar preparations propranolol reduced the effects of all isomers. The results indicate that in the guinea-pig trachea D(-)-ephedrine and D(-)-pseudo-ephedrine are essentially directly acting drugs, whereas L(+)-ephedrine and L(+)-pseudo-ephedrine possess an appreciable indirect component in their action and that all four isomers probably act at beta adrenergic receptors.