Somatostatin is a peptide that is distributed widely in endocrine and neural tissues. It was initially discovered in the hypothalamus as the factor that inhibited GH release. At this site, it occurs predominantlyas a fourteen amino-acid cyclic peptide that is linked by a disulphide bond. In the gastrointestinal tract, it occurs as fourteen and twenty-eight amino-acid peptides; both have an identical carboxy-terminal sequence, which is the biologically active region.
Somatostatin is secreted by specific endocrine cells in the gastric and intestinal mucosa, and by the D cells on the inner rim of the pancreatic islets.
