The Permissive Effects of Glucocorticoid on Hepatic Gluconeogenesis. Glucagon Stimulation of Glucose-suppressed Gluconeogenesis and Inhibition of 6-phosphofructo-1-kinase in Hepatocytes from Fasted Rats

Production of [14C]glucose from [14C]lactate in the perfused livers of 24-h fasted adrenalectomized rats was not stimulated by 1 nM glucagon but was significantly increased by 10 nM hormone. Crossover analysis of glycolytic intermediates in these livers revealed a significant reduction in glucagon action at site(s) between fructose 6-phosphate and fructose 1,6-bisphosphate as a result of adrenalectomy. Site(s) between pyruvate and P-enolpyruvate was not affected. In isolated hepatocytes, adrenalectomy reduced glucagon response in gluconeogenesis while not affecting glucagon inactivation of pyruvate kinase. A distinct lack of glucagon action on 6-phosphofructo-1-kinase activity was noted in these cells. When hepatocytes were incubated with 30 mM glucose, lactate gluconeogenesis was greatly stimulated by glucagon. A reduction in both sensitivity and responsiveness to the hormone in gluconeogenesis was seen in the adrenalectomized rat. These changes were well correlated with similar impairment in glucagon action on 6-phosphofructo-1-kinase activity and fructose 2,6-bisphosphate content in hepatocytes from adrenalectomized rats incubated with 30 mM glucose. These results suggest that adrenalectomy impaired the gluconeogenic action of glucagon in livers of fasted rats at the level of regulation of 6-phosphofructo-1-kinase and/or fructose 2,6-bisphosphate content.