Somatostatin, also called somatotropin release-inhibiting factor (SRIF), is the inhibitory counterpart to GHRH in the growth hormone axis. It exists in two bioactive forms cleaved from a common precursor — somatostatin-14 and the N-terminally extended somatostatin-28 — and both carry a disulfide bridge that constrains the active loop.
Where it acts
Somatostatin is produced in the hypothalamic periventricular nucleus, in pancreatic islet delta-cells, and throughout the gastrointestinal tract. It signals through five class A GPCRs, SSTR1 to SSTR5, coupling through Gi to inhibit adenylate cyclase. Reported actions are broadly inhibitory: suppression of pituitary growth hormone and TSH release, of insulin and glucagon secretion, and of gastrointestinal exocrine output. Native somatostatin has a plasma half-life of roughly three minutes, which is why clinical analogs such as octreotide and lanreotide were developed as protease-resistant cyclic derivatives.
Why it matters
Somatostatin tone is the feedback brake that gives secretagogue research its ceiling. Growth hormone release evoked by a GHRP or GHRH analog depends on where in the somatostatin rhythm the stimulus lands, which is a common source of variability between studies.
Related terms
IGF-1. See the somatostatin research family and the pituitary and hypothalamus hub.