Somatostatin

Somatostatin
Identifiers
Symbol	SST
Entrez	6750
HUGO	11329
OMIM	182450
RefSeq	NM_001048
UniProt	P61278
Other data
Locus	Chr. 3 q28

Somatostatin (also known as growth hormone inhibiting hormone (GHIH) or somatotropin release-inhibiting hormone (SRIF)) 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.^[1]

Production

Digestive system

Somatostatin is secreted in several locations in the digestive system:

• stomach
• intestine
• delta cells of the pancreas^[2]

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 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.

Actions

Somatostatin is classified as an inhibitory hormone,^[1] whose main actions are to:

• Inhibit the release of growth hormone (GH)^[3] (thus opposing the effects of Growth Hormone-Releasing Hormone (GHRH))
• Inhibit the release of thyroid-stimulating hormone (TSH)
• Suppress the release of gastrointestinal hormones
  • Gastrin
  • Cholecystokinin (CCK)
  • Secretin
  • Motilin
  • Vasoactive intestinal peptide (VIP)
  • Gastric inhibitory polypeptide (GIP)
  • Enteroglucagon (GIP)
• Lowers the rate of gastric emptying, and reduces smooth muscle contractions and blood flow within the intestine^[3]
• Suppress the release of pancreatic hormones
  • Inhibit the release of insulin^[4]
  • Inhibit the release of glucagon^[4]
• Suppress the exocrine secretory action of pancreas.

Synthetic substitutes

Octreotide (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.

References

1. ^ ^{a b} Physiology at MCG 5/5ch4/s5ch4_16
2. ^ Costanzo, LS. Board Review Series: Physiology 3rd Ed. Lippincott, Williams & Wilkins. 2003. p. 280.
3. ^ ^{a b} http://www.vivo.colostate.edu/hbooks/pathphys/ endocrine/otherendo/somatostatin.html
4. ^ ^{a b} Physiology at MCG 5/5ch4/s5ch4_17

v • d • e Endocrine system: hormones/endocrine glands (Peptide hormones, Steroid hormones)
Hypothalamic-pituitary	Hypothalamus: TRH, CRH , GnRH, GHRH, somatostatin, dopamine - Posterior pituitary: vasopressin, oxytocin - Anterior pituitary: α (FSH, LH, TSH), GH, prolactin, POMC (ACTH, MSH, endorphins, lipotropin)
Adrenal axis	Adrenal medulla: epinephrine, norepinephrine - Adrenal cortex: aldosterone, cortisol, DHEA
Thyroid axis	Thyroid: thyroid hormone (T3 and T4) - calcitonin - Parathyroid: PTH
Gonadal axis	Testis: testosterone, AMH, inhibin - Ovary: estradiol, progesterone, inhibin/activin, relaxin (pregnancy)
Other end. glands	Pancreas: glucagon, insulin, somatostatin - Pineal gland: melatonin
Non-end. glands	Placenta: hCG, HPL, estrogen, progesterone - Kidney: renin, EPO, calcitriol, prostaglandin - Heart atrium: ANP - Stomach: gastrin, ghrelin - Duodenum: CCK, GIP, secretin, motilin, VIP - Ileum: enteroglucagon - Adipose tissue: leptin, adiponectin, resistin - Thymus: Thymosin - Thymopoietin - Liver/other: Insulin-like growth factor (IGF-1, IGF-2)
Target-derived	NGF, BDNF, NT-3

v • d • e Digestive system, physiology: gastrointestinal physiology
Enteric nervous system	Meissner's plexus - Auerbach's plexus
Exocrine	Chief cells (Pepsinogen) - Parietal cells (Gastric acid, Intrinsic factor) - Goblet cells (Mucus)
Endocrine/paracrine	G cells (gastrin), D cells (somatostatin) - ECL cells (Histamine) - enterogastrone: I cells (CCK), K cells (GIP), S cells (secretin)
Border	Brunner's glands - Paneth cells - Enterocytes
Fluids	Saliva - Bile - Intestinal juice - Gastric juice - Pancreatic juice
Processes	Swallowing - Vomiting - Peristalsis (Interstitial cell of Cajal) - Migrating motor complex - Borborygmus - Gastrocolic reflex - Segmentation contractions - Defecation

v • d • e Peptides: neuropeptides
Hypothalamic	Somatostatin - CRH - GnRH - GHRH - Orexins - TRH - POMC (ACTH, MSH, Lipotropin)
Gastrointestinal hormones	Cholecystokinin - Gastric inhibitory polypeptide - Gastrin - Motilin - Secretin - Vasoactive intestinal peptide
Other hormones	Vasopressin - Calcitonin -
Other	Angiotensin - Bombesin/Neuromedin B - Calcitonin gene-related peptide - Carnosine - Delta sleep-inducing peptide - FMRFamide - Galanin - Gastrin releasing peptide - Kinins (Bradykinin, Tachykinins ) - Neuropeptide Y - Neurophysins - Neurotensin - Opioid peptide - Pancreatic polypeptide - Pituitary adenylate cyclase activating peptide