Somatostatin receptors

Somatostatin is a neuropeptide produced by neuroendocrine, inflammatory and immune cells in response to different stimuli, Somatostatin inhibits vario us cellular functions including secretions, motility and proliferation, Its action is mediated by five specific somatostatin receptors (sst1-sst5) whi ch belong to the G protein-coupled receptor family, The five receptors bind the natural pep tide with high affinity but only sst2, sst5 and sst3 bind the short synthetic analogues used to treat patients with neuroendocrine tu mors. The five receptors are expressed in various normal and tumor cells, t he expression of each receptor being receptor subtype and cell-type specifi c, In neuroendocrine tumors, sst2 is highly expressed whereas in advanced p ancreatic adenocarcinoma as well as high-grade colorectal carcinomas, its e xpression is lost, Each receptor subtype is coupled to different signal tra nsduction pathways through G protein-dependent and -independent mechanisms. The synthesis of selective agonists for each receptor and the recent devel opment of genetic animal models with selective deletion of receptor subtype provide tools for establishing some of the biological roles of the recepto rs. sst1, 2 and 5 mediate inhibition of GH secretion whereas sst2 and sst5 mediate inhibition of glucagon secretion and insulin secretion, respectivel y, Copyright (C) 2000 S. Karger AG, Basel.