Abstract
It was reported by the present author in the preceding paper that the increase in liver glucokinase (GK) activity in steroid-diabetic rats is presumed to arise through an oversecretion of insulin and also that cortisol does not inhibit the GK-inducing effect of insulin. The present work was undertaken to investigate possible effects of hypophysectomy, thyroidectomy, and thyroxine, ACTH and growth hormone administration on the GK and hexokinase (HK) activity of rat liver, and also to know whether or not administration of each of these hormones yields an antagonizing action on the GK-inducing effect of insulin.
1. Upon administration of thyroxine to normal rats, the liver HK activity was increased significantly, but the GK activity remained unchanged.
2. Following thyroidectomy, the GK activity showed a significant decrease, while the HK activity remained unaltered. When T4 was administered to such ectomized animals, the GK activity showed a tendency to restoration.
3. Growth hormone administration to normal rats did not bring any significant change in the activity of these two enzymes.
4. In the liver of hypophysectomized rats, the GK activity was significantly lower than normal. After growth hormone or ACTH administration to these animals, no tendency to the recovery of this enzyme activity was observed.
5. The decreased level of the liver GK activity in alloxan-diabetic animals was raised almost to the normal by insulin treatment, but simultaneous administration of T4 or of growth hormone together with insulin did not bring any enhancement in the increase. This result may indicate the fact that neither T4 nor growth hormone blocks the GK-inducing effect of insulin.
