Detailed Explanation
Somatostatin (also called somatotropin release-inhibiting factor, SRIF) is a cyclic peptide hormone that acts as a broad inhibitor of secretion throughout the body. It exists in two active forms: somatostatin-14 (14 amino acids) and somatostatin-28 (28 amino acids, with somatostatin-14 at its C-terminus). Both contain a disulfide bridge between Cys3 and Cys14 that forms the ring structure essential for biological activity. Somatostatin is produced by delta cells in the pancreatic islets, by neurons in the hypothalamus, and by D-cells throughout the gastrointestinal tract.
Somatostatin's defining characteristic is inhibition. In the hypothalamus, it suppresses growth hormone (GH) release from the pituitary — hence the name 'somatostatin' (soma = body, statin = inhibiting). In the pancreas, it inhibits both insulin (from beta cells) and glucagon (from alpha cells). In the gut, it suppresses gastrin, secretin, cholecystokinin, and other GI hormones, slows gastric emptying, reduces intestinal motility, and decreases splanchnic blood flow. This broad inhibitory profile makes it a master brake on secretory and proliferative processes.
Native somatostatin has a very short half-life (~3 minutes), making it impractical as a drug. Synthetic analogs with improved stability are widely used: octreotide (Sandostatin, 8 amino acids) and lanreotide (Somatuline, 8 amino acids) treat acromegaly (GH excess), neuroendocrine tumors, and severe diarrhea. Pasireotide (Signifor) is a newer multi-receptor analog for Cushing's disease. Radiolabeled somatostatin analogs (¹⁷⁷Lu-DOTATATE/Lutathera) are used for peptide receptor radionuclide therapy (PRRT) of neuroendocrine tumors — delivering targeted radiation directly to tumor cells expressing somatostatin receptors.
Key Facts
- Two forms: somatostatin-14 and somatostatin-28
- Cyclic peptide with Cys3–Cys14 disulfide bridge
- Inhibits GH, insulin, glucagon, gastrin, secretin, CCK
- Native half-life: ~3 minutes
- Analogs: octreotide (Sandostatin), lanreotide (Somatuline), pasireotide (Signifor)
- ¹⁷⁷Lu-DOTATATE (Lutathera): targeted radionuclide therapy for neuroendocrine tumors
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PeptideDefinition.com provides educational content about peptide science. Not medical advice. Consult a licensed healthcare provider for medical decisions.