Serotonin (5-hydroxytryptamine) in medullary thyroid carcinoma with or without pheochromocytoma.

An increased synthesis of serotonin by medullary thyroid carcinoma (MTC) has been postulated because an increased concentration of serotonin in the MTC cells and an increased urinary excretion of 5-hydroxyindoleacetic acid have been observed in some patients with MTC. Ten patients with sporadic MTC and 18 patients with familial MTC of either the MEN-IIa or MEN-IIb types were investigated. Three of the patients with MEN-IIa and the patient with MEN-IIb had concomitant pheochromocytomas. The concentrations of serotonin in serum were measured in order to investigate the contributions of the MTC and pheochromocytoma to the overall synthesis of serotonin. The concentrations of serotonin in sera from patients with MTC or MEN-IIa without pheochromocytomas were not different from the concentrations measured in healthy subjects (P greater than 0.10). The four patients with MEN-II syndromes with pheochromocytomas had increased concentrations of serotonin in sera (P less than 0.01), and decreases in the concentrations occurred following adrenalectomy in all four patients. The results show that the MTC made only little if any contribution to the overall synthesis of serotonin in the 28 patients studied; and serotonin was produced in pheochromocytoma tissue from four patients with MEN-II syndromes with pheochromocytoma.