Utilization of adenosine as a tool in studies on the regulation of liver glycogen biosynthesis

An eightfold increase in the active form of liver glycogen synthetase activity was detected in normal rats 1 hr after the intraperitoneal injection of adenosine. Such an increase is the highest yet observed after the administration of a specific hormone or compound. However, no change was detected in the total quantity of a plus b forms of the enzyme present in the liver. Previous administration of actinomycin or cycloheximide prevented increases in the active form of glycogen synthetase activity ordinarily provoked by the injection of the nucleoside. The addition of adenosine to rat liver homogenates did not cause a change in the active or total glycogen synthetase activity as compared to the control. The effect of adenosine was not mediated by insulin sincein diabetic rats the injection of the nucleoside was also followed by an increase in the active form of liver glycogen synthetase activity. Variation in the levels of blood glucose and serum inorganic phosphate and changes in the levels of inorganic phosphate in liver cells were also observed after adenosine administration. The maximum changes preceded the increase in the active form of hepatic glycogen synthetase in vivo. It is postulated that in the liver the synthetase phosphatase responsible for the conversion of the b into the a form of glycogen synthetase is the important point of regulation of glycogen biosynthesis.