Effect of hypophysectomy on liver enzymes involved in glycogenolysis and in glucogenesis

Abstract

The effect of fasting on liver enzymes involved in glucose-6-phosphate production by glycogenolysis (phosphoglucomutase) and by gluconeogenesis (phosphohexoseisomerase, fructose-1, 6-diphosphatase) was studied in normal and hypophysectomized rats. In normal animals the nitrogen content of the average liver cell decreased to 56% at the end of 6 days starvation. In hypophysectomized rats, however, 1-day fasting was sufficient to decrease nitrogen content to 50%. Liver fructose-1,6-diphosphatase activity was preferentially maintained in normal animals as compared to nitrogen level during 6 days fasting. Hypophysectomy abolished this preferential maintenance and the enzyme dropped after 24 hours fasting below the level observed in normal animals after 6-day fast. One-day fasting in hypophysectomized animals reduced phosphohexoseisomerase and phosphoglucomutase activities to the level reached after 6-day fasting in normal rats. It appears that the breakdown in the normal metabolic adaptation to acute starvation is reflected in the ability to maintain the level of liver enzymes which produce glucose-6-phosphate. The physiological maintenance of hepatic fructose-1,6-diphosphatase, phosphohexoseisomerase and phosphoglucomutase depends, partially at least, on pituitary function.