Dynamics of Insulin Secretion in Myotonic Dystrophy

Abstract

Excessive insulin responses to oral and intravenous glucose have been observed in patients with myotonic dystrophy. This report describes the effects of 5 other modifiers of insulin secretion in 8 patients with myotonic dystrophy. Marked hypersecretion of insulin occurred after intravenous tolbutamide, comparable to that seen in islet cell adenoma patients. Intravenous glucagon produced immediate marked hyperinsulinemia and a normal rise in glucose. The insulin response to oral leucine was also increased, but not to the degree seen in insulinoma patients. Normal suppression of insulin release occurred with epinephrine. Plasma insulin was moderately suppressed on prolonged fasting, and the blood sugar fell only slightly. The data show that insulin secretion in myotonic dystrophy patients is markedly exaggerated in response to glucose, glucagon and tolbutamide. Normal control mechanisms are still operative in that epinephrine and fasting inhibited insulin secretion. The blood glucose responses to the exaggerated insulin secretion seem to be inappropriate.