Abstract
Recently, reports have appeared, which indicate that the positive inotropic action of catecholamines on the heart is closely related to an activation of the cyclic 3', 5'-AMP formation with the subsequent conversion of phosphorylase b to a. Kukovetz et al. (1) and Hess et al. (2) noted a positive correlation between the increased force of cardiac contraction produced by sympathomimetic amines and phosphorylase a activity. Mayer and Moran (3), Belford and Feinleib (4) and Lacroix and Leusen (5) have published extensive studies on the relationship between the contractile force and the enzyme activity of the heart muscle in vivo and in vitro.
Other reports have given indications that there is no relationship between increased force of contraction and phosphorylase a in the heart. Mayer et al. (6) have recently reported that intravenous injection of adrenaline (0.5 μg/kg) does not produce significant change in the heart phosphorylase a but produces marked positive inotropic effect in the open-chest dog. Considering that cardiovascular reflexes and neurohumoral factors may affect the heart phosphorylase in the open-chest animal (7), Hess et al. (8) have studied the role of the autonomic nervous system in the regulation of heart phosphorylase in the open-chest rat, and showed that cholinergic stimulation of the heart decreases the enzyme activity. Vincent and Ellis (9) have concluded that acetylcholine opposes the glycogenolytic action of adrenaline, since simultaneous infusion of acetylcholine and adrenaline results in no increases in glycogenolysis, and in a marked reduction of chronotropic and inotropic action of adrenaline. Murad et al. (10) confirmed an inhibitory effect of acetylcholine and carbachol on the cyclic 3', 5'-AMP formation in the dog and rabbit heart. If it is certain that the formation of cyclic 3', 5'-AMP is affected by the infused acetylcholine, the endogenous acetylcholine released by a number of agents into the circulating blood may also influence the activity of phosphorylase a in the heart.
It is the purpose of this paper to report the intravenously administered adrenaline on the activity of heart phosphorylase in the open-chest rat.
