THE EFFECT OF ADRENALINE ON THE PHOSPHORYLASE ACTIVITY OF THE HEART IN THE OPEN-CHEST RAT

Abstract

Activity of heart phosphorylase was determined in the open-chest rat under various experimental conditions affecting the autonomic function. Exposure, manipulation or freezing of the heart significantly lowered the percent activity of phosphorylase a. The activity of phosphorylase a and total phosphorylase was higher in winter than in summer. In hypothermic rats epinephrine increased the phosphorylase a activity despite the manifestation of the negative inotropism. In atropinized and vagotomized open-chest rats a small dose of epinephrine increased the percent activity of phosphorylase a considerably more than a large dose of epinephrine in the untreated open-chest rats. A marked increase in the enzyme activity was still observed 2 hours after injection of epinephrine. From the results it may be suggested that the sympathetic discharge activates the heart phosphorylase; the endogenously liberated acetylcholine inhibits the phosphorylase-stimulating action of epinephrine in situ and the long-lasting elevation of the heart phosphorylase a activity even after disappearance of the positive inotropic action of epinephrine may be related to the uptake and storage of epinephrine in the cardiac tissue.