Platelet serotonin 5‐HT_2A receptor binding in patients with carcinoid tumor

Abstract

Background: As carcinoid tumors produce and secrete serotonin, various serotonin markers in blood, plasma and urine have been used as diagnostic tools, and quantification of the urinary excretion of the serotonin metabolite 5‐hydroxyindoleacetic acid (5‐HIAA) is the method most frequently used. Methods: [³H]lysergic acid diethylamide ([³H]LSD) binding to the platelet serotonin 5‐HT_2A receptor was investigated in nine patients with carcinoid tumors. The possible effect of serotonin‐rich food on the receptor binding was also investigated. Results: B_max for [³H]LSD binding was significantly lower in the carcinoid group than in the control group (mean±SD: 17.6±1.3 vs. 23.9±5.2 fmol/mg protein; p=0.007). K_d for [³H]LSD binding was significantly higher in the carcinoid group than in the control group (median: 1.14 vs. 0.71 nmol/L; p=0.03). B_max was inversely related to the urinary 5‐HIAA excretion, but the correlation did not reach statistical significance (r_s=−0.57; p=0.14). Intake of five bananas per day for one week had no effect on B_max or K_d in healthy volunteers. Conclusions: The results are consistent with a down‐regulation of the 5‐HT_2A receptor as a response to the high serotonin levels found in patients with carcinoid tumors. Intake of serotonin‐rich food does not affect the receptor characteristics. Further studies are needed to determine whether the platelet 5‐HT_2A receptor status can be used as a supplement to urinary 5‐HIAA and other biochemical variables in carcinoid tumors.

• Carcinoid
• 5‐hydroxyindoleacetic acid
• lysergic acid diethylamide
• platelet
• serotonin
• tumor markers