LACK OF EVIDENCE FOR ACUTE EFFECTS OF GROWTH HORMONE-RELEASING HORMONE ON SERUM-INSULIN AND GLUCOSE-LEVELS IN NORMAL AND HYPOPHYSECTOMIZED RATS

Growth hormone (GH) is diabetogenic but has also been suggested to sti mulate insulin release. Our aim was to study whether acute effects of GH on serum insulin and glucose concentrations can be observed when GH release is physiologically induced by GH-releasing hormone (GHRH), wh ich is known to stimulate insulin secretion. We also studied the acute effects of GHRH as such on insulin release in vivo and in vitro. Fema le Sprague-Dawley rats were hypophysectomized (hyper) at 40 days of ag e. At day 188, rats received 1 mu g GHRH(1-29)/100 g body weight i.v. In sham-operated rats, GHRH induced a rise in serum GH from 36.5 +/- 1 .9 ng/ml (time 0 min) to 560.0 +/- 13.3 ng/ml (5 min;) (n = 6; p < 0.0 01). In hyper rats, no measurable serum levels of GH were detected eit her before or after GHRH treatment. Serum insulin was unaffected by GH RH in both groups of animals. Serum glucose was higher in sham operate d than in hyper rats (7.3 +/- 0.4 vs. 6.3 +/- 0.1 mM at 0 min; p < 0.0 1). Serum glucose did not rise following GHRH injection. In isolated r at islets, cultured for 3 days at 11.1 mM glucose, 0.1-10 nM GHRH stim ulated basal insulin release at 3 mM glucose. To summarize, GHRH at hi gh concentrations stimulates insulin release in vitro, but neither GHR H, at a concentration where GH secretion is greatly stimulated, nor GH RH-induced GH release, have any acute effects on serum insulin or gluc ose levels.