Effects of growth hormone on insulin release in the rat

Abstract

Summary. Growth hormone injected intravenously in the rat elicited a 6-fold spike change in immunoreactive insulin with little variation in glucose. Subcutaneous administration of growth hormone for 4 days augmented by 56% the insulin-secretory response to glucose of isolated islets from hypophysectomised rats but not the response of control rat islets. When islets were cultured in the presence of growth hormone, the glucose-induced insulin release was increased by 35 % in batch incubations of islets from both normal and hypophysectomised rats and by 70-110% in perifused islets. Thus the capacity for stimulated release of insulin is limited by hypophysectomy, and growth hormone is capable of directly influencing the secretory function of the/3-cell.

Effects of hypophysectomy and growth hormone on cultured islets of Langerhans of the rat

“…This observation may suggest that the lack of pituitary factors beside growth hormone contributes directly or indirectly to the diminished secretory response of islets from hypophysectomised rats. Earlier studies have shown that glucose-stimulated insulin release is impaired in islets from hypophysectomised rats [2][3][4][5] and the impairment is counteracted by injection of growth hormone [2,4]. The enhancing effect of growth hormone added to the culture medium on the insulin secretory responses to glucose of islets from both normal and hypophysectomised rats was previously noted [2]: in the present study, the use of rat growth hormone permitted the demonstration of these effects of growth hormone at a lower concentration than that of the bovine growth hormone used earlier [2].…”

“…In neither group was this ratio significantly affected by the presence of growth hormone in the culture medium. The combination of decreased insulin biosynthesis with decreased insulin secretion may underlie the reported lack of effect of hypophysectomy on the islet content of insulin [2]. In freshly prepared rat islets, insulin biosynthesis was decreased by hypophysectomy of the donor rats but the incorporation of {3H}-uridine into islet total RNA was unaffected [16].…”

“…Hypophysectomised rats were purchased from Charles River Laboratories and used after 4-5weeks from hypophysectomy. Islets were cultured for 4 days as described previously [2]. The culture medium was RPM1 1640 [8] containing glucose (6mmol/1), penicillin (0.1 mg/ml), streptomycin (0.1 mg/ml) and 10% (v/v) inactivated calf serum (Wellcome, Beckenham, Kent, UK) and was supplemented, where stated, with rat growth hormone 1 .ug/ml (National Institutes of Health, Bethesda, USA, lot GH-B-6); the pH was buffered at 7.4 with N-2-hydroxyethylpiperazine-N'-2-ethane sulphonate (Hepes) 25mmol/1.…”

“…In addition B-cell secretory * Present address: Department of Physiology, Vargas School of Medicine, Central University of Venezuela, Caracas, Venezuela function is influenced chronically by experimental manipulations such as starvation [1] or hypophysectomy [2][3][4][5], and in pregnancy [6]. We have shown that the impaired insulin secretory response of islets from hypophysectomised rats persists following 4-day culture of the islets and may be reversed by the addition of growth hormone to the culture medium [2]. To investigate the mechanisms involved, we have measured other parameters of islet function in normal and hypophysectomised rat islets cultured in the absence or presence of rat growth hormone.…”

“…We have shown that the impaired insulin secretory response of islets from hypophysectomised rats persists following 4-day culture of the islets and may be reversed by the addition of growth hormone to the culture medium [2]. To investigate the mechanisms involved, we have measured other parameters of islet function in normal and hypophysectomised rat islets cultured in the absence or presence of rat growth hormone.…”