Insulin release in rats 1 and 5 days after hypophysectomy

In the present experiments the effect of an intravenous glucose (0.5 g/kg body weight) and an intravenous glibenclamide (1 mg/kg body weight) injection on insulin release was studied in conscious rats shortly after hypophysectomy. 1 and 5 days after removal of the pituitary gland both the fasting blood glucose and the serum insulin concentrations were significantly lower when compared with control rats as was the insulin response to the stimulation by glucose or glibenclamide. In order to elucidate the contribution of the lower fasting blood glucose to the decreased insulin release, the effect of a continuous glucose infusion (2 ml/h of a 40% glucose solution) was studied in hypophysectomy rats. The artificial hyperglycemia for 4 1/2 days did not alter the low glucose-induced insulin release in these animals. The results clearly show that under appropriate in vivo conditions the diminished B-cell function can be detected very shortly after hypophysectomy. Furthermore, it appears that the depressed insulin release in hypophysectomized rats is not related to the lower blood glucose concentration.