Role of hormones in glucose-6-phosphate dehydrogenase adaptation of rat liver

¹ Department of Pharmacology, State University of New York, Upstate Medical Center, Syracuse, New York

The hepatic enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase increase markedly in activity on refeeding after a 48-hr fast in the intact rat, but fail to do so in the hypophysectomized animal. Treatment with somatotrophin, cortisone, and thyroid hormone individually and in pairs failed to restore this adaptation to refeeding, but a combination of the three repaired the defect. Similar observations were made on increases in these enzymes in response to fructose feeding in ad libitum-fed hypophysectomized rats. Triple hormone-treated animals in which the enzyme increase in response to fructose feeding was restored were the only ones which gained weight. To rule out possible effects of variations in food intake as a determining factor in the response, hypophysectomized rats fed measured amounts of a starch-fructose diet by stomach tube were compared with suitable controls. A striking increase in enzyme activity occurred in these animals even when no hormone treatment was given, and no additional increase could be induced by treating with the three hormones. It is concluded that the liver cell of the hypophysectomized rat has an autonomous capacity to modify its enzyme profile selectively without the direction or support of hormones of pituitary origin. These hormones may exert their effects in ad libitum-fed animals by influencing food intake and intestinal hexose absorption rates.

Note:
With the Technical Assistance of Janet M. DeWitt and Andrew Branch