Effects of insulin, glucagon, and somatostatin on the release of somatostatin-25 and somatostatin-14 from rainbow trout, Oncorhynchus mykiss, pancreatic islets in vitro.

Somatostatins are a diverse family of peptides known to modulate insulin and glucagon secretion as well as to stimulate glycogenolysis and lipolysis in salmonid fish. In this study, Brockmann bodies (bisected to yield hemi-islets) isolated from rainbow trout, Oncorhynchus mykiss, were used to study the effects of insulin, glucagon, and somatostatin at various concentrations of glucose (1, 5, and 10 mM) on pancreatic somatostatin release. The release of somatostatin-25, the most predominate form of somatostatin in salmonid pancreas, was stimulated by insulin in the presence of 1 and 5 mM glucose but not in the presence of 10 mM glucose, whereas glucagon stimulated somatostatin-25 release only in the presence of high (10 mM) glucose. Somatostatin-25 release also was stimulated by somatostatin-14. The secretion of somatostatin-14 was suppressed by insulin in the presence of 5 and 10 mM glucose and was stimulated by glucagon in the presence of high (10 mM) glucose. These results indicate that insulin, glucagon, and somatostatin-14 are regulators of somatostatin-14 and somatostatin-25 pancreatic release in rainbow trout and that these effects are modulated by glucose.