Studies on Patients With Islet-Cell Tumor, Including the Phenomenon of Leucine-Induced Accentuation of Hypoglycemia*

Three patients with islet-cell tumor of the pancreas are presented. All had severe fasting hypoglycemia relieved by the administration of glucose. However, 1 had a normal intravenous tolerance curve and 2 did not show any sensitivity to intravenous glucagon-free insulin. The effects of leucine and glycine on the blood sugar level were studied. Administration of leucine consistently caused accentuation of the tumor-induced hypoglycemia—the fall ranging from 21 to 76 per cent below the fasting level—accompanied by clinical symptoms, whereas administration of glycine caused no appreciable changes. Following extirpation of the tumors, leucine provoked no significant degree of hypoglycemia. In 2 normal subjects and in 5 patients with functional hypoglycemia, administration of leucine caused no changes in the blood sugar levels. The data favor the view that, in cases of islet-cell tumor, leucine acts by potentiating the peripheral action of insulin.