ADRENOTROPIC RECEPTORS IN THE FROG

¹ Department of Pharmacology, Instituto N. de Cardiologia, Mexico, D. F., México

The relative potencies of a group of adrenergic agents, tested for chronotropic and inotropic effects in the perfused frog heart, were; isoproterenol > epinephrine > norepinephrine > phenylephrine. Methoxamine had no effects or depressed the heart. In the Laewen-Trendelenburg preparation, the order of vasoconstrictor potency was: epinephrine > norepinephrine > phenylephrine > methoxamine. Isoproterenol had no effects or caused vasodilatation.

DCI, a beta adrenergic blocking agent, prevented the effects of epinephrine in the heart, but not in the blood vessels. The alpha adrenergic blocking agents used were: dibozane, phenoxybenzamine and Hydergine. Dibozane and phenoxybenzamine antagonized the vasoconstriction caused by epinephrine but not its cardias effects. Hydergine blocked the effects of epinephrine in both the heart and the blood vessels. The evidence indicates that in the frog, as in the mammal, the myocardial responses to adrenergic stimuli are mediated by the beta adrenergic receptor, while the receptor involved in their vasoconstrictor action is of the alpha type.