Regulation of pancreatic somatostatin gene expression by insulin and glucagon

Rainbow trout were used as a model system to study the effects of insulin and glucagon on the expression of preprosomatostatins (PPSS). We previously showed that the endocrine pancreas of trout contains three mRNAs that encode for distinct somatostatin-containing peptides: PPSS I, which contains somatostain-14 (SS-14) at its C-terminus, and two separate PPSS IIs, PPSS II′ and PPSS II″, each containing [Tyr⁷, Gly ¹⁰]-SS-14 at their C-terminus. Rainbow trout injected (100 ng/g body weight) with insulin displayed elevated expression of PPSS II′ and PPSS II″ mRNAs. Glucagon-injected (100 ng/g body weight) animals displayed elevated pancreatic expression of all PPSS mRNAs compared to saline-injected control animals. Insulin directly stimulated the expression of pancreatic PPSS II′ and PPSS II″ mRNAs in vitro in a dose-dependent manner in the presence of 4 mM glucose. Glucagon, in the presence of 10 mM glucose, directly stimulated the expression of all PPSS mRNAs in a dose-dependent manner in vitro. These results indicate that the pancreatic expression of PPSS mRNAs is differentially regulated by insulin and glucagon and that the regulatory pattern is dependent on glucose concentration.