[Pharmacologic analysis of the mechanisms of adrenergic modulation in the parasympathetic inhibition of myocardial contractile activity].

In the sinus-atrium preparation of the frog heart, exogenous adrenaline was shown to induce an ambiguous effect upon the inhibition of spontaneous contractile activity of the atrium in vagal stimulation. Obsidan did not affect the duration of the parasympathetic inhibition whereas adrenaline, against the obsidan background, considerably elongated the inhibition. Against the background of iochimbin, adrenaline practically eliminated the parasympathetic inhibition. Isadrin acted similarly to adrenaline against the background of blockade of alpha 2-adrenoreceptors. Clofellin increased the arrest of the contractile activity due to vagal stimulation. The pharmacological analysis suggests existence of alpha 2-and beta-adrenoreceptors at presynaptic endings of extracardiac parasympathetic nerves. Adrenaline modulates the cholinergic transmitter process through these adrenoreceptors.