Glucose Metabolism and Insulin Secretion in the Carcinoid Syndrome1

Abstract

ABSTRACT To evaluate the effect of serotonin on carbohydrate tolerance and insulin secretion, serial intravenous glucose tolerance tests were carried out on two patients with the carcinoid syndrome. One patient had impaired glucose tolerance (glucose disposal constant = 0.60) with subnormal insulin secretion, while the other had borderline glucose tolerance (glucose disposal constant = 1.11) with a normal insulin secretion pattern. Following therapy with streptozotocin, an anti-tumor antibiotic, both patients experienced clinical improvement with a decrease in urinary 5-hydroxyindoleacetic acid (S-HIAA) excretion. The patient with the impaired glucose tolerance had a 58% reduction in S-HIAA, accompanied by a 44% increase in glucose-stimulated insulin secretion; the other patient had a 46% reduction in S-HIAA excretion accompanied by a 60% increase in glucose-stimulated insulin secretion. There was a significant improvement in glucose disposal constants in both patients. Thus increased serotonin production...