Glucose-6-Phosphatase and Phosphorylase Activities in Mice Bearing Corticotropin-Secreting Tumors

The activity of hepatic glucose-6-phosphatase, the enzyme catalyzing the conversion of glucose-6-phosphate to glucose, has been measured under normal conditions as well as in a number of situations in which carbohydrate metabolism is disturbed.Cori and Cori (1) found an almost complete absence of this enzyme in the livers of two fatal cases of von Gierke's (glycogen storage) disease and levels below normal in four surviving subjects.Ashmore et al. ( 2) and Langdon and Weakley (3) have demonstrated that the activity of glucose-6-phosphatase is greatly increased in the livers of rats made diabetic by alloxan.The activity of this enzyme could be brought toward normal by the administration of insulin in vivo but not by the addition of this hormone in vitro.Both of these groups of workers, as well as Weber and Canter0 (4), reported an increase in this enzyme per gm. of tissue in the fasted animal, a condition in which the carbohydrate metabolism is similar to that in the diabetic state.In subsequent experiments by Weber et al. ( 5) and Ashmore et al. ( 6) the hormonal regulation of glucose-6-phosphatase has been studied.Weber and colleagues found that the administration of cortisone to rats in vivo caused a 49 per cent increase in the hepatic glucose-6-phosphatase per unit weight of wet liver.Ashmore and coworkers found that diabetic, adrenalectomized rats had normal liver glucose-6-phosphatase activity.The administration of 17-hydroxycorticosterone in vivo increased, while insulin administration decreased the activity of this enzyme.In contrast, Langdon and Weakley observed only unimpressive increases in hepatic glucose-6-phosphatase in rats treated with cortisone or adrenal cortical extracts.