Somatostatin and Its Analogues
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Direct answer
Somatostatin, released from the hypothalamus, pancreas and gut, is a universal inhibitory peptide that suppresses growth hormone, TSH, insulin, glucagon, gastrin, VIP and most gastrointestinal secretions, and reduces splanchnic blood flow. Its native form lasts only two to three minutes, so the synthetic analogues octreotide (subcutaneous action one to two hours, or monthly depot) and lanreotide are used therapeutically, with pasireotide for Cushing disease. Clinically, analogues are first-line medical therapy for acromegaly, control hormone hypersecretion in carcinoid and VIPoma syndromes, and octreotide is a standard vasoactive drug in acute variceal bleeding alongside endoscopy.
What you must remember
- Actions: inhibition of growth hormone (its original name was growth hormone release-inhibiting hormone), insulin, glucagon, TSH, gastrin, VIP, secretin and motilin, reduced splanchnic and portal flow, and reduced intestinal secretion and motility.
- Pharmacokinetics: native somatostatin half-life two to three minutes; octreotide about one to two hours subcutaneously with monthly intramuscular depot (LAR) formulations; lanreotide autogel monthly.
- Acromegaly: analogues lower growth hormone and IGF-1 in most patients and shrink tumours in a proportion; they are used after failed surgery, before surgery, or as primary therapy when surgery is unsuitable.
- Neuroendocrine tumours: control diarrhoea and flushing of carcinoid syndrome and the watery diarrhoea of VIPoma; they control symptoms rather than cure the tumour.
- Variceal bleeding: octreotide (50 microgram bolus then infusion for up to five days in standard protocols) as adjunct to endoscopic therapy; safer than terlipressin in cardiac disease.
- Other uses: pancreatic and enterocutaneous fistulas, refractory diarrhoea, dumping syndrome, postoperative ileus, and TSH-secreting adenoma; somatostatin receptor scintigraphy and peptide receptor radionuclide therapy (lutetium-177 DOTATATE) exploit receptor expression.
- Adverse effects: gallbladder sludge and stones (the classic exam point, from suppressed cholecystokinin and gallbladder stasis), steatorrhoea, hyper- or hypoglycaemia, bradycardia, nausea and injection-site pain; pasireotide prominently causes hyperglycaemia.
Common confusion
Octreotide does not improve outcomes in acute pancreatitis — it was historically given, but current guidance does not support it; the pancreas-related indications are fistula control and complication prevention after pancreatic surgery. Students also confuse octreotide with terlipressin in variceal bleeding: both lower portal pressure, but terlipressin is a vasopressin V1 agonist with cardiac and ischaemic cautions, while octreotide is the safer companion drug in comorbidity-laden cirrhotics.
Exam-focused takeaway
Expect stems on the acromegalic patient on monthly depot injections, the carcinoid crisis prevented by pre-treatment octreotide, gallstones developing during therapy, and the drug choice for a cirrhotic with cardiac disease and variceal haemorrhage. Mechanism questions hinge on the phrase universal inhibitor — a single peptide suppressing multiple hormones. One-liners on the two-to-three-minute native half-life and the diagnostic Octreoscan complete the pattern.
Frequently asked questions
Why does octreotide cause gallstones?
It inhibits cholecystokinin release and gallbladder contractility, producing biliary stasis, sludge and ultimately stones in a substantial fraction of long-term users.
What is the role of octreotide in variceal bleeding?
It reduces splanchnic blood flow and portal pressure and is given with endoscopic therapy for up to five days to prevent early rebleeding.
Which somatostatin analogue is used in Cushing disease?
Pasireotide, which suppresses ACTH from corticotroph adenomas; hyperglycaemia is its principal adverse effect.
Why is native somatostatin not used therapeutically?
Its half-life of two to three minutes and simultaneous inhibition of insulin and glucagon make it impractical; analogues are longer acting and more growth-hormone selective.
How does octreotide help VIPoma?
It blocks vasoactive intestinal peptide secretion and action, controlling the profuse watery diarrhoea, hypokalaemia and dehydration of the Verner-Morrison syndrome.