Differential regulation of the multiple insulin and insulin receptor mRNAs by somatostatin.

We used rainbow trout as a model to study the regulation of the multiple and distinct insulin (INS) and insulin receptor (IR) mRNAs by somatostatin (SS). Implantation of SS reduced growth of animals without affecting food intake. SS decreased INS1 and INS2 expression in Brockmann bodies, but increased INS1 and INS2 expression in adipose and INS1 expression in brain. SS reduced mRNA levels of IR 2 and IR 3 in adipose tissue; of IR1 and IR 4 in Brockmann bodies; of IR1, IR2, IR3, and IR4 in cardiac muscle; of IR2 and IR4 in liver; of IR 3 and IR 4 in gill; and of IR4 in skeletal muscle. The direct effects of SS were examined in Brockmann bodies and liver in vitro. SS decreased INS and IR mRNAs in both tissues in a concentration-, time-, and isoform/subtype-dependent manner. These results indicate that SS regulates the expression of INS- and IR-encoding mRNAs and that independent mechanisms may serve to regulate the various INS isoforms and IR subtypes.