Serotonin, catecholamines, and spontaneous midgut carcinoid flush: Plasma studies from flushing and nonflushing sites

Abstract

$\text{Background/Aims}\text{:}$ Serotonin is the diagnostic hallmark of midgut carcinoids, but the pathophysiology of spontaneous flushing is unknown. The aim of this study was to assess to what extent serotonin and catecholamine blood levels are related in time with spontaneous midgut carcinoid flush. $\text{Methods}\text{:}$ Using specific radioenzymatic assays, we measured prospectively before, during, and after spontaneous flushing platelet-poor plasma and whole blood serotonin and plasma catecholamines and their metabolites in 10 patients with primary midgut carcinoids. Blood was drawn simultaneously from a forearm vein and an external jugular vein draining the flushing area. $\text{Results}\text{:}$ During flushing, plasma serotonin and norepinephrine levels increased (P < 0.001) over preflush levels at both sampling sites. Intraflush serotonin and norepinephrine were twice as high (P < 0.01) in external jugular (9.57 ± 1.40 ng/mL and 857 ± 33 pg/mL, respectively) than in antecubital plasma (4.59 ± 0.73 ng/mL and 471 ± 26 pg/mL). Preflush and postflush levels were similar at both venous sites. $\text{Conclusions}\text{:}$ Vein plasma serotonin and norepinephrine levels do increase during midgut carcinoid flush, especially in the flushing area. This may reflect a local release secondary to flush but also suggests a role for these bioamines in the pathogenesis of flushing.