Colocalization of somatostatin receptor sst5 and insulin in rat pancreaticbeta-cells

Somatostatin, also known as somatotropin release-inhibiting factor (SRIF), is secreted by pancreatic delta-cells and inhibits the secretion of both in sulin and glucagon. SRIF initiates its actions by binding to a family of si x G protein-coupled receptors (sst1, -2A, -2B, -3, -4, and -5) encoded by f ive genes. Messenger RNA for both sst2 and sst5 have been reported in the r at pancreas, and the sst2A receptor protein has been localized to rat pancr eatic a and pancreatic polypeptide-secreting cells in the islets as well as to pancreatic acinar cells. In this study we have used double immunostaini ng to show that the sst5 protein is expressed exclusively in the beta-cells of rat pancreatic islets and localizes with insulin-secreting alpha-cells. The sst5 receptor is not colocalized with sst2A. Thus, in the rat SRIF inh ibits pancreatic insulin and glucagon secretion via different sst receptor subtypes.