Somatostatin
A naturally occurring peptide hormone (14 or 28 amino acids) that broadly inhibits the release of growth hormone, insulin, glucagon, and multiple gastrointestinal hormones. Natural somatostatin has a half-life of only 1-3 minutes. Octreotide, lanreotide, and pasireotide are synthetic analogues with much longer durations of action.
Technical Context
Somatostatin exists in two bioactive forms: SRIF-14 (14 aa) and SRIF-28 (28 aa, N-terminally extended). Both are cyclic peptides with a Cys3-Cys14 disulphide bridge. Somatostatin has remarkably broad inhibitory effects: suppresses GH, TSH, and prolactin from the pituitary; insulin, glucagon, and VIP from the pancreas; gastrin, secretin, CCK, and gastric acid from the GI tract; and inhibits angiogenesis and cell proliferation. This breadth is due to expression of five somatostatin receptor subtypes (SSTR1-5) across diverse tissues. The half-life of 1-3 minutes renders native somatostatin therapeutically impractical, driving development of metabolically stable analogues that selectively engage specific SSTR subtypes.