Plasma glucagon in insulinoma.

Nine patients with insulinoma were studied in order to investigate glucagon levels in the fasting state and the response of plasma glucagon to tolbutamide and arginine. Fasting plasma glucagon levels were within the normal range in all patients except two cases with malignant insulinoma. Although there was no correlation between blood glucose and plasma glucagon, a significant correlation between plasma glucagon and plasma insulin was observed. No detectable changes were found in glucagon levels during tolbutamide injection. In almost all patients except one an exaggerated response of plasma glucagon was demonstrated during arginine infusion test.