The pancreatic glands from six male Wistar rats weighing between 200 and 250 g were isolated and perfused. After 30-min equilibration and 20-min basal periods, perfusion with 0.2 mg/ml of morphine for 20 min resulted in a significant (P < 0.05) increase in insulin release, with no changes in release of gucagon or somatostatin. After a recovery period of 20 min, a higher morphine concentration of 2 mg/ml was introduced for another 20-min period. With this morphine dose there were significant increases in release of insulin (P < 0.05), glucagon (P < 0.01) and somatostatin (P < 0.05). This shows that morphine induces the release of insulin, glucagon and somatostatin from pancreas in a dose-dependent way, and that release of insulin and glucagon is not primarily affected by regulation of somatostatin levels.

Serum contains insulin degrading components. We have evaluated the insulin and somatostatin secretion from isolated rat pancreatic islets during a 2-wk culture period using three different serum-containing media, and one serum-free medium with a synthetic serum replacement. Islets incubated in serum-free medium elicited significantly higher daily insulin and somatostatin secretions than islets incubated in the serum-containing media. After a 2-wk culture period, islets from the serum-free medium secreted significantly more insulin and somatostatin than islets cultured in other media when stimulated with 25 mmol/liter glucose together with 15 mmol/liter theophylline. We conclude that the serum-free medium is superior for long-term culture of rat pancreatic islets.