The effect of hypophysectomy on rat liver gluocokinase activity and on plasma glucose, insulin and nonesterified fatty acid concentrations

Abstract

1. 1. The relationship of rat liver glucokinase (ATP- d-glucose 6-phosphotransferance, EC 2.7.1.2) activity to plasma insulin level has been examined in hypophysectomized rats. 2. 2. Glucokinase activity was found to be depressed by at least 50% after hypophysectomy when compared with age, weight, sham-operated and pair-fed controls. 3. 3. The plasma insulin level in hypophysectomized rats was found to be lower than in all control animals. 4. 4. Attempts have been made to restore to normal the low glucokinase activity by hormone injections. 5. 5. Thyroxine and growth hormone had no effect on either the glucokinase activity or the plasma insulin. 6. 6. Hydrocortisone raised the plasma insulin in 12 h and the enzyme activity in 24 h. Administration of growth hormone with the hydrocortisone produced a more rapid response in the rise in plasma insulin, a change being detected 6 h after the injection. Glucokinase activity was raised by injection with both hormones, a slight rise was seen after 12 h. 7. 7. Phosphofructokinase (EC 2.7.1.11) and pyruvate kinase (EC 2.7.1.40) were also assayed in livers from hypophysectomized rats; pyruvate kinase activity was approx. 50% of the control value whereas phosphofructokinase activity was unchanged by the operation.