Somatostatin
Overview
Somatostatin, also known as growth hormone-inhibiting hormone (GHIH) or by several other names, 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.
Discovery
Somatostatin was discovered in 1973 by Roger Guillemin and Andrew V. Schally, two neuroendocrinologists who were studying the hypothalamus in the context of growth hormone regulation. They isolated a peptide from sheep hypothalamus after hypothalamic extracts were shown to inhibit growth hormone secretion from the anterior pituitary, and they named this peptide "somatostatin".
Structure and Isoforms
Somatostatin is a peptide hormone, composed of a short chain of amino acids. It exists in two active isoforms: SRIF-14 and SRIF-28. SRIF-14 is a linear peptide composed of 14 amino acids, while SRIF-28 is a 28-amino acid peptide that is an extension of the SRIF-14 molecule.
Function
Somatostatin has many physiological effects. It inhibits the release of a variety of hormones, including growth hormone, thyroid-stimulating hormone, and insulin. It also suppresses the release of gastrointestinal hormones, including gastrin, cholecystokinin, secretin, motilin, vasoactive intestinal peptide, gastric inhibitory polypeptide, enteroglucagon, and pancreatic polypeptide. Furthermore, it decreases the rate of gastric emptying, and reduces smooth muscle contractions and blood flow within the intestine.
Clinical Significance
In medicine, somatostatin is used in a synthetic form (octreotide or lanreotide) for the treatment of acromegaly, a disorder caused by excessive production of growth hormone, and various types of neuroendocrine tumors. It can also be used to treat severe, refractory diarrhea caused by some types of endocrine tumors.