Acidotic depression of cyclic AMP accumulation and phosphorylase b to a transformation in skeletal muscle of man.

Abstract

I.v. infusion of adrenaline [epinephrine] was performed in 3 healthy subjects on 2 occasions. In 1 case, subjects performed a maximal isometric contraction before infusion. Biopsies were taken from the quadriceps femoris muscle before and after infusion for 0.5 and 2.0 min and analyzed for muscle pH, cAMP, metabolites and activities of glycogen phosphorylase and synthetase. Isometric contraction resulted in a decrease of muscle pH to 6.60 (normal value at rest 7.0-7.1). By this experimental procedure, the effect of adrenaline infusion could be studied on a muscle with normal or low pH. cAMP increased from 3 to .apprx. 9.5 .mu.mol/kg dry wt after 0.5 min of adrenaline infusion. When isometric contraction preceded the infusion, cAMP increased more slowly and was .apprx. 5.5 .mu.mol/kg dry wt after the same time of infusion. Phosphorylase a constituted .apprx. 22% of total phosphorylase in resting muscle but increased rapidly to 80% after 0.5 min infusion. When exercise preceded infusion phosphorylase a decreased and was still lower after 2 min infusion. The results can be explained by inhibition of adenylate cyclase and phosphorylase b kinase at low muscle pH.