ACCELERATED GLYCOGENOLYSIS IN UREMIA AND UNDER SUCROSE FEEDING - ROLEOF PHOSPHORYLASE-ALPHA REGULATORS

To understand the mechanism of hepatic glycogen depletion found in ure mia and under sucrose feeding, we examined net hepatic glycogenolysis- associated active enzymes and metabolites during fasting. Liver was ta ken 2, 7, and 18 h after food removal in uremic and pair-fed control r ats fed either a sucrose or cornstarch diet for 21 days. Other uremic and control rats fasted for 18 h were refed a sucrose meal to measure glycogen increment. Glycogen storage in uremia was normal, suggesting effective glycogen synthesis. During a short fast, sucrose feeding and uremia enhanced net glycogenolysis through different but additive mec hanisms. Under sucrose feeding, there were high phosphorylase a levels associated with hepatic insulin resistance. In uremia, phosphorylase a levels were low, but the enzyme was probably activated in vivo by a fall of inhibitors (ATP, alpha-glycerophosphate, fructose-1,6-diphosph ate, and glucose) and a rise of P-i, as verified in vitro. Enhanced gl uconeogenesis was also suggested, but excessive hepatic glucose produc tion was unlikely in uremia. During fasting, hypoglycemia occurred in uremia due to reduced glycogenolysis, inefficient hepatic gluconeogene sis, and impaired renal gluconeogenesis. This may be relevant to poor fasting tolerance in uremia, which could be aggravated under excessive sucrose intake.