Glucagon-induced insulin secretion in normal diabetic subjects

Eight normal subjects and ten diabetic patients were studied to compare the response of plasma insulin to glucagon with that to glucose and tolbutamide. Oral glucose tolerance test, glucagon test and tolbutamide-glucagon test were performed at intervals of several days. In glucose tolerance test, insulin response was reduced in the patients with severe diabetes. Plasma insulin increased and reached the peak 3 min after glucagon injection (glucagon I) in the normal controls, while plasma insulin response was reduced in diabetic patients, especially in the severe diabetics. In the normal controls plasma insulin rose and reached the peak 6 min after the tolbutamide injection and thereafter fell to the initial level. Glucagon injection following tolbutamide (glucagon II) caused the rise in insulin in the control subjects. In diabetics insulin response to either tolbutamide or glucagon I was reduced. Tolbutamide or glucagon II caused a significant difference in plasma insulin response in all the diabetic groups compared with the normal subjects, while glucose or glucagon I showed a significant increment of plasma insulin between the normal subjects and the severe diabetics. These results suggest that injection of tolbutamide as well as glucagon II provides a definite discrimination of insulin response in diabetics from the normal controls. The usefulness of the tolbutamide-glucagon test in the diagnosis of diabetes mellitus was discussed. -- glucose tolerance test; glucagon test; tolbutamide-glucagon test; plasma insulin.