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Somatostatin (also known as growth hormone-inhibiting hormone (GHIH) or somatotropin release-inhibiting factor (SRIF)) or somatotropin release-inhibiting hormone[citation needed] is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G-protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones.

Somatostatin has two active forms produced by alternative cleavage of a single preproprotein: one of 14 amino acids, the other of 28 amino acids.

Production Digestive system

Somatostatin is secreted in several locations in the digestive system:

stomach intestine delta cells of the pancreas[4]

Brain

Somatostatin is produced by neuroendocrine neurons of the periventricular nucleus of the hypothalamus. These neurons project to the median eminence, where somatostatin is released from neurosecretory nerve endings into the hypothalamo-hypophysial system through neuron axons. Somatostatin is then carried to the anterior pituitary gland, where it inhibits the secretion of growth hormone from somatotrope cells. The somatostatin neurons in the periventricular nucleus mediate negative feedback effects of growth hormone on its own release; the somatostatin neurons respond to high circulating concentrations of growth hormone and somatomedins by increasing the release of somatostatin, so reducing the rate of secretion of growth hormone.

Somatostatin is also produced by several other populations that project centrally, i.e., to other areas of the brain, and somatostatin receptors are expressed at many different sites in the brain. In particular, there are populations of somatostatin neurons in the arcuate nucleus[citation needed], the hippocampus[citation needed], and the brainstem nucleus of the solitary tract[citation needed]. Actions D cell is visible at upper-right, and somatostatinis represented by middle arrow pointing left

Somatostatin is classified as an inhibitory hormone] whose actions are spread to different parts of the body: Anterior pituitary

In the anterior pituitary gland, the effects of somatostatin are:

Inhibit the release of growth hormone (GH)[5] (thus opposing the effects of Growth Hormone-Releasing Hormone (GHRH)) Inhibit the release of thyroid-stimulating hormone (TSH)[6] It is induced by low pH. Inhibit adenylyl cyclase in parietal cells.

Gastrointestinal system

Somatostatin is homologous with cortistatin (see somatostatin family) and suppresses the release of gastrointestinal hormones Gastrin Cholecystokinin (CCK) Secretin Motilin Vasoactive intestinal peptide (VIP) Gastric inhibitory polypeptide (GIP) Enteroglucagon Decrease rate of gastric emptying, and reduces smooth muscle contractions and blood flow within the intestine[5] Suppresses the release of pancreatic hormones Inhibits insulin release when somatostatin is released from delta cells of pancreas[7] Inhibits the release of glucagon[7] Suppresses the exocrine secretory action of pancreas.