PANCREATIC SOMATOSTATIN-14 AND SOMATOSTATIN-25 RELEASE IN RAINBOW-TROUT IS STIMULATED BY GLUCOSE AND ARGININE

Previous work suggested that teleost fish possess two somatostatin (SS) genes. Regulation of differential secretion of SS gene I (SS-25) and SS gene II products (SS-14) by nutrients was studied using rainbow trout. Hemi-islets were cultured in medium containing different concentrations of glucose and arginine. SS-14 and insulin were determined by radioimmunoassay; SS-25 was determined by a novel enzyme-linked immunosorbent assay. Glucose stimulated SS-25 release in a concentration-related manner, with 10 mM being the most effective concentration; at higher (25 mM) glucose, release decreased. Insulin levels in the medium also were found to be more elevated from islets incubated in 10 mM glucose than those incubated in 25 mM glucose. Maximum SS-14 release was observed at lower (1-5 mM) glucose concentrations. Arginine stimulated SS release so that maximum release of both SS forms occurred at the lowest glucose concentrations (I mM). A concentration-related effect of arginine was observed on SS-25 release. The results of this study indicate that glucose and arginine regulate secretion of both pancreatic SS gene I and gene II products from rainbow trout islets, suggesting that two different pancreatic SS interact in nutrient homeostasis in this species.