The effect of adrenaline infusion on the regulation of glycogenolysis in human muscle during isometric contraction.

The regulation of glycogenolysis in human muscle during isometric contraction without and with adrenaline infusion has been investigated. The content of cAMP in muscle increased three-fold during the infusion. Total glycogen phosphorylase and synthetase activities were unchanged during contraction without and with adrenaline infusion. The fraction of phosphorylase in the a form was in resting muscle 26% and at the end of contraction 24%. During adrenaline infusion phosphorylase a increased to 80%. Contraction during continued infusion resulted in a decrease of phosphorylase a to 42%, despite persistently increased cAMP content in muscle. The activity of synthetase I decreased to about half of the initial value during adrenaline infusion and contraction both without and with the infusion. The rate of glycogenolysis in muscle during contraction was not significantly changed by the infusion. Phosphocreatine (PCr) decreased during the contraction and the decrease was similar without and with adrenaline infusion. The amount of inorganic phosphate (Pi) accumulated in muscle during contraction was lower when adrenaline was given due to a greater accumulation of hexose-monophosphates. It is concluded that the rate of glycogenolysis in muscle during contraction without and with adrenaline infusion is a function both of phosphorylase in the form a form and the availability of Pi at the active site of the enzyme.