(also known as growth hormone inhibiting hormone
) or somatotropin release-inhibiting factor
)) 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.
Somatostatin is secreted in several locations in the digestive system:
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 portal circulation. These blood vessels carry somatostatin to the anterior pituitary gland
, where somatostatin 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, the hippocampus and the brainstem nucleus of the solitary tract.
Somatostatin is classified as an inhibitory hormone, whose actions are spread to different parts of the body:
In the anterior pituitary gland
, the effects of somatostatin are:
- Somatostatin suppresses the release of gastrointestinal hormones
- Lowers the rate of gastric emptying, and reduces smooth muscle contractions and blood flow within the intestine
- Suppresses the release of pancreatic hormones
- Suppresses the exocrine secretory action of pancreas.
(brand name Sandostatin
, Novartis Pharmaceuticals
) is an octopeptide
that mimics natural somatostatin pharmacologically, though is a more potent inhibitor of growth hormone
, glucagon, and insulin
than the natural hormone.