Direct effects of rat growth hormone in rat islets of langerhans in tissues culture.

The effects of rat growth hormone (1 microgram/ml) on the synthesis and release of insulin by isolated rat islets of Langerhans were studied. There was no effect of growth hormone on the release of insulin from freshly isolated islets during 30 min incubation periods. By contrast, islets previously cultured for 16h with growth hormone exhibited at 40% increase in the release of insulin in response to glucose or to glucose and theophylline. These islets also showed specific increases in basal and glucose-stimulated insulin synthesis of 16% and 21% respectively, together with a 22% increase in the basal rate of total protein synthesis. The total insulin content of islets was not affected by culture with growth hormone. The adenylate cyclase activity of islet homogenates was unaffected by the presence of growth hormone during 30 min incubations. When homogenates from islets previously cultured with growth hormone were studied, basal adenylate cyclase activity was unchanged, while fluoride-stimulated adenylate cyclase activity was increased by 37%. It is concluded that growth hormone can directly affect the synthesis and release of insulin in islets of Langerhans, without relation to its metabolic activities in other target organs.