Somatostatin

Somatostatin, also known as growth hormone-inhibiting hormone, is a naturally-occurring peptide hormone of 14 or 28 amino acid residues that regulates the endocrine system. It is secreted by the D cells of the islets to inhibit the release of insulin and glucagon, and is also generated in the hypothalamus, where it inhibits the release of growth hormone and thyroid-stimulating hormones from the anterior pituitary . Somatostatin is initially secreted as a 116 amino acid precursor, preprosomatostatin, which undergoes endoproteolytic cleavage to prosomastatin. Prosomastatin is further process into two active forms, somatostatin-14 (SST-14) and somatostatin-28 (SST-28), an extended SST-14 sequence to the N-terminus . The actions of somatostatin are mediated via signalling pathways of G protein-coupled somatostatin receptors. Antineoplastic effects and potential uses of somatostatin on various tumours, including pituitary adenomas, GEP-NETs, paragangliomas, carcinoids, breast cancers, malignant lymphoma and small-cell lung cancers, have been extensively investigated . Somatostatin has been used in the clinical setting for the diagnosis of acromegaly and gastrointestinal tract tumours. Its analogues have been developed to achieve more favourable kinetics for efficiency use in the management of acute conditions, such as esophageal varices. Octreotide is a long-acting analogue of somatostatin that inhibits the release of a number of hormones, and is clinically used to relieve symptoms of uncommon gastroenteropancreatic endocrine tumours, as well as treat acromegaly .