INSULIN-RESPONSE AFTER TREATMENT DEPENDS ON FASTING PLASMA-GLUCOSE LEVEL IN NIDDM

We investigated the relationship between the improvement in insulin se cretion and glycemic control in non-insulin-dependent diabetes mellitu s (NIDDM). Fifty-two patients were classified into three groups accord ing to their pretreatment fasting plasma glucose (FPG) level: Group A, FPG < 7.8 mM, n = 20; Group B, 7.8 mM less than or equal to FPG < 11. 1 mM, n = 17; and Group C, 11.1 mM less than or equal to FPG, n = 15. A 75-g oral glucose tolerance test (OGTT) and a glucagon loading test were performed to evaluate insulin secretion before and after treatmen t. Plasma glucose levels during a 75-g OGTT were decreased significant ly after treatment in all groups (P < 0.01). In Group A, there was no significant change in insulin secretion before and after treatment (14 66 +/- 213 pM to 1565 +/- 191 pM, P = 0.35). In contrast, in Groups B and C, insulin secretion was poor and suppressed initially, but increa sed significantly when good glycemic control was obtained after treatm ent (respectively, 587 +/- 70 pM to 863 +/- 79 pM, P < 0.01, and 621 /- 94 pM to 1236 +/- 232 pM, P < 0.01). The degree of improvement in i nsulin secretion in 75-g OGTT correlated positively with the degree of improvement in FPG level after treatment (r = 0.5, P < 0.001). Howeve r, the C-peptide response to glucagon did not change before and after treatment. In conclusion, impaired insulin secretion recovered by the good glycemic control in NIDDM with FPG levels above 7.8 mM. Therefore , strict glycemic control (FPG below 7.8 mM) seems important for maint aining good insulin secretion.