Abstract
In order to investigatet he responses of plasma glucose (PG), insulin (IRI) and C-peptide (CPR) to varying glucose loads in elderly, 50g and 75g glucose tolerance test (GTT) were performed in 52 subjects who were aged 60 years or more. Thirty-five of them revealed diabetic glucose tolerance (Group I) during 50g GTT (1-hour PG value≥185mg/dl and 2-hour PG value≥150mg/dl) and the others revealed either slightly impaired or normal glucose tolernace (Group II).
In Group I, the 2-hour and 3-hour values during 75g GTT were significantly higher than those during 50g GTT (p<0.01 and p<0.001, respectively). In Group II, only the 3-hour value was higher in 75g GTT than in 50g GTT (p<0.05). The ratios of increment of insulin to that of plasma sugar (ΔIRI/ΔPG) at 30 minutes after glucose loading were not different between 50g and 75g GTT in both groups, but the sum of the insulin values (ΣIRI) during the GTT was significantly higher in 75g GTT than in 50g GTT in both groups (p<0.01 and p<0.001, respectively). The sum of CPR (ΣCPR) during GTT was significantly higher in 75g GTT than in 50g GTT in Group I (p<0.01), but not in Group II. The slope of the regression line between ΣIRI and ΣCPR in 50g GTT was identical to that in 75g GTT. The result may indicate that the kinetics of insulin secretion was not changed by increasing glucose loading from 50g to 75g in the aged subjects.
Furthermore, highly significant correlation between plasma glucose levels after 50g glucose load and those after 75g glucose load was observed. Plasma glucose levels at 1 hour after 75 glucose load correspond to the same levels of those at 1 hour after 50g glucose load. Plasma glucose levels of 200, 140 and 120mg/dl at 2 hours after 75g glucose load correspond to those of 180, 130 and 110mg/dl, repectively, at 2 hours after 50g glucose load.
