STUDIES ON THE INSULIN RELEASE MECHANISM BY ARGININE

Abstract

The insulin release induced by arginine was studied in mormal subjects and hyperthyroid patients. Arginine hydrochloride (0.5g/kg) dissolved in 200ml of physiological saline was administered by intravenous infusion from a cubital vein over 30 minutes to normal subjects and hyperthyroid patients after overnight fasting. Blood samples were taken before and 2, 4, 6, 8, 10, 15, 30, 45, and 60 minutes after the start of the infusion. 2-deoxy-D-glucose (50 mg/kg) was administered over 45 minutes to normal subjects, and after 15 minutes of the start of its infusion, arginine was administered over 30 minutes. Plasma insulin was determined by the double antibody radioimmunoassay and the blood glucose was determined by autoanalyzer. The biphasic insulin release by arginine infusion was observed in normal subjects. The ΔIRI of the first peak at 4 minutes was 23.6±7.4μU/ml, and the second peak at 30 minutes was 40.9± 10.6μU/ml. Whereas, the monophasic insulin release by arginine infusion was observed in hyperthyroid patients.The ΔIRI of the first peak at 2 minutes was 13.6±2.71μU/ml, but the second peak was very low. The correlation coefficient between ΔIRI and ΔBS was-0.08 (not significant) in the first phase of insulin release and 0.72 (p<0.01) in the second phase of insulin release. This suggests that the second phase of insulin release is influenced by elevated blood glucose by arginine infusion. The correlation coefficient between ΔIRI and RSU was 0.22 (not significant) in the first phase of insulin release and -0.71 (p<0.01) in the second phase of insulin release. The ΔIRI of the first peak of arginine infusion was not reduced following 2-deoxy-D-glucose as compared to control studies, but the second peak was significantly (p<0.05) reduced from 47.3±7.7μU/ml to 21.8±4.6 μU /ml. We observed the differrent character of the first and the second phases of insulin release at correlation between ΔIRI and ΔBS, ΔIRI and RSU, and at the effect of 2-deoxy-D-glucose. We concluded that the first and the second phases of insulin release by arginine infusion seem to occur from the different mechanisms of insulin release.