THE EFFECT OF EPINEPHRINE AND AMINOPHYLLINE ON THE PHOSPHORYLASE ACTIVITY OF PERFUSED CONTRACTING HEART MUSCLE

¹ Laboratory of Pharmacology, University of Pennsylvania, Philadelphia

Phosphorylase activity was determined in extracts from isolated perfused rat hearts. Such extracts exhibited a high degree of activity in the absence of added adenylic acid and an increase in activity on the addition of adenylic acid. These observations indicate that phosphorylases are present in heart muscle which are similar to phosphorylase a and b of skeletal muscle. Additions of epinephrine or aminophylline to the perfusion fluid in concentrations that stimulated the mechanical activity of the muscle had little or no effect on phosphonylase activity when measured in the presence of adenylic acid but increased the activity in the absence of added adenylic acid. It appears that simultaneously with the increase in mechanical activity of the heart caused by epinephrine or aminophylline there occurred a transformation of phosphorylase b to phosphorylase a. The significance of these findings has been discussed.