Abstract
In the present study, we examined the suppressive effect of exogenous insulin on endogenous insulin and glucagon secretion by measuring the plasma C-peptide (CPR) and glucagon (IRG) levels in NIDDM during insulin infusion using the glucose clamp technique. Moreover plasma Gut GLI levels, elevation of which has been reported in the diabetic state, were also measured to study the effect of insulin. Steady-state plasma IRI was achieved at an insulin infusion rate of 40mU/m2/min, and plasma glucose concentration was maintained at the fasting level during the two-hour glucose clamp study. The MCR of glucose in NIDDM was markedly lower at 4.9±0.4ml/kg/min than the 8.8±0.2ml/kg/min in normal subjects. Under these conditions, plasma CPR, IRG, and Gut GLI levels fell significantly from the basal levels in both normal and diabetic subjects. However, the mean maximal percentages of suppression of basal CPR, IRG and Gut GLI levels in diabetic subjects were noticeably lower Compared with those in normal subjects. These findings could also be observed in diabetic subjects with normal fasting glucose levels under good control.
In conclusion, insulin inhibits the secretion of not only insulin and glucagon but also enteroglucagon. However, in NIDDM, as well as the decrement in the MCR of glucose during insulin infusion, the suppressive effect of insulin on the secretion of these hormones diminished in comparison with that in normal subjects.
