Comparative effects of diet or glibenclamide on insulin secretion and action in non-obese NIDDM

We compared the effects of dietary treatment (D) and diet plus glibenclamide (DPG), for 3 weeks, on glycemia, insulin secretion and action in 2 groups of non-obese patients with NIDDM matched for fasting plasma glucose level. Fasting glycemia decreased in both groups with greater reductions after DPG (n = 7, 10.0 +/- 0.6 to 6.3 + 0.3 mmol/l, M +/- SEM, P less than 0.02) than after D (n = 7, 10.1 +/- 0.8 to 8.7 +/- 0.7 mmol/l, M +/- SEM, P less than 0.02). The magnitude of day-time elevation of plasma glucose over the fasting level, however, was reduced only after DPG. DPG but not D improved the plasma insulin response to glucose ingestion and in vivo insulin action measured by insulin tolerance test with unaltered erythrocyte 125I-insulin binding. This might indicate potentiation of insulin action at post-receptor binding steps. Improvements in in vivo insulin action and in insulin secretion after DPG closely correlated with decrease in fasting glycemia and reduction in the day-time elevation of plasma glucose levels, respectively. In conclusion, diet improved glycemic control in non-obese patients with NIDDM mainly by reducing fasting glycemia, although the mechanism remains unknown. Glibenclamide added to the diet further decreased fasting glycemia by improving in vivo insulin action and reduced the magnitude of day-time elevation of plasma glucose by enhancing endogenous insulin secretion.