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Pathophysiology of Carcinoid Syndrome

المؤلف:  Wass, J. A. H., Arlt, W., & Semple, R. K. (Eds.).

المصدر:  Oxford Textbook of Endocrinology and Diabetes

الجزء والصفحة:  3rd edition , p972

2026-08-20

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NETs normally produce and secrete several different amines like serotonin, kinins, kallikrein, and prostaglandins. However, when the primary site is within the gut, the secreted amines are degraded by the liver and symptoms do not generally occur. In the presence of hepatic metastases, metastatic lesions secrete amines mainly serotonin that will exceed and bypass the degradation capacity of the liver and then reach the systemic circulation. In these cases, carcinoid syndrome will develop. Exceptions for this pathway are ovary, testicular, retroperitoneal, bronchial primary NETs, or metastases because they can directly access the systemic circulation.

In healthy people, serotonin is inactivated and metabolized to 5- HIAA by the hepatic monoamine oxidase and which is cleared by the kidneys. In these people, approximately 99% of tryptophan is used for the synthesis of nicotinic acid and less than 1% is converted to serotonin. However, in patients with carcinoid tumours there is a shift toward the production of serotonin.