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What is the mechanism of action of somatostatin?
Octreotide is a synthetic analog of somatostatin, which is a natural growth inhibitor that also competitively inhibits release of several hormones. It decreases serotonin levels and relieves the symptoms of carcinoid syndrome. Somatostatin has been shown to suppress diarrhea associated with VIP tumors. It has a transient half-life; therefore, intravenous infusions are required for treatment of acute crises. For preoperative prophylaxis, octreotide 50–150 μg every 8 hours subcutaneously is recommended. If patients are on long-term therapy, the dose can be adjusted accordingly. Side-effects include ascending cholangitis or cholelithiasis because somatostatin inhibits gallbladder contractions. Other side-effects include nausea, vomiting, pain, diarrhea, and bradycardia. This occurs more commonly with larger doses. Symptoms are variable in different patients. Steatorrhea is occasionally observed, but this is generally mild and not associated with significant nutritional impairment. Somatostatin suppresses the response of leutinizing hormone (LH) to gonadotropic releasing hor-mone (GnRH). It decreases splanchnic blood flow and inhibits the release of serotonin, gastrin, VIP, and pancre-atic polypeptide. VIP-omas tend to cause watery diarrhea rather than steatorrhea, which is common with metastatic carcinoid tumors. Octreotide reduces growth hormone levels in patients with acromegaly as well.
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