Human Biochemistry, Volume 2 - Murray R. 1993

Biochemistry of Intracellular and Intercellular Communications
Pancreatic Hormones
Somatostatin

Somatostatin was so named because it was first isolated from the Hypothalamus as a factor inhibiting Growth Hormone secretion. Somatostatin is a cyclic peptide synthesized as a large prohormone (mol. wt. approximately 11,500) in the D Cells of the pancreatic islets. The METABOLISM/31.html">Transcription rate of the prosomatostatin Gene is significantly enhanced by cAMP. The prohormone is first converted into a 28-member peptide and ultimately into a molecule with a mol. wt. of 1,640 containing 14 amino acid residues (Fig. 51.19). All forms of the hormone exhibit biological activity.

In addition to the hypothalamus and pancreatic islets, somatostatin has been detected in numerous Tissues of the gastrointestinal tract, where it presumably regulates a variety of Functions, as well as in various Regions of the Central Nervous system (where it may act as a neurotransmitter).

Somatostatin inhibits the secretion of other islet Cell Hormones via a paracrine mechanism. In pharmacological doses, it significantly reduces the Ketosis associated with Insulin deficiency. This is presumably due to its ability to suppress Glucagon secretion caused by insulinopenia. It also decreases The entry of nutrients from the gastrointestinal tract into the bloodstream by: 1) delaying gastric emptying, 2) inhibiting gastrin secretion and, consequently, Hydrochloric acid production, 3) suppressing the exocrine function of the Pancreas (secretion of digestive Enzymes), 4) reducing Blood FLOW IN the Abdominal cavity, and 5) lowering the absorption of sugars. The biochemical and molecular effects of this hormone remain insufficiently studied.