The large decreases in hepatic glycogen associated with alloxan diabetes in fed rats were accompanied by apparent decreases in total activities of glycogen synthase, phosphorylase, protein kinase and synthase phosphatase determined on 8000 × g supernatants of liver homogenates. A review of recent studies of plasma glucagon and insulin levels reveals that the insulin:glucagon ratio (I/G) varies inversely with need for endogenous glucose production, being lowest in total starvation and highest during loading with exogenous carbohydrate. Glycogen was localized in eyes of streptozotocin-induced diabetic and control rats using light microscopic histochemistry and electron microscopy, and correlated with immunohistochemical staining for glycogen phosphorylase and phosphorylated glycogen synthase (pGS). GSK-3 inhibition caused a 41 +/- 2% (P < 0.001) and 26 +/- 4% (P < 0.05) reduction in the area under the glucose and insulin concentration curves, respectively, during the OGTT. Epinephrine produced similar changes in cyclic AMP accumulation, protein kinase activation, and phosphorylase kinase activation in perfused hearts of BB/W control and diabetic rats. Both phosphorylase a and total phosphorylase activities were also elevated by 5 wk, reaching levels twofold higher than controls. This results in a build up of abnormal amounts or types of glycogen in tissues. The factors promoting glycogen accumulation in vivo are related to the abundance of glucose and glucose-6-phosphate as substrates for glycogen synthesis, which may also cause an increase in the activity ratio glycogen synthase a/phosphorylase a.