Control of Rat Liver Phosphorylase, Glucose-6-Phosphatase andPhosphoenolpyruvate Carboxykinase Activities by Insulin andGlucagon during the Perinatal Period

Abstract

Liver glucose-6-phosphatase and phosphoenolpyruvate carboxykinase (PEPCK) activities were increased by glucagon injection into 18.5–21.5-day-old rat fetuses. Liver phosphorylase activity, liver glycogen breakdown and blood glucose level were not increased by glucagon injection in rat fetus before day 20.5 of gestation. Treatment of rat fetus with hydrocortisone on day 18.5 allowed activation of phosphorylase by glucagon to occur prematurely, on day 19.5 of gestation. Insulin injection at birth prevented the normal development of liver glucose-6-phosphatase and PEPCK activities but was without any effect on liver phosphorylase activity and liver glycogen breakdown. Glucose administration at birth inhibited the increase of the three liver enzyme activities and liver glycogen degradation. Adrenalectomy at birth or treatment with adrenergic-blocking drugs had little if any effect on liver glycogen breakdown. Cortisol administration at birth did not impair or accelerate liver glycogenolysis. These results are discussed in view of the effect of these hormones on liver 3’,5’-adenosine monophosphate (cAMP) and in relation to the secretory pattern of insulin and glucagon at birth.