Effect of glipizide treatment on response to an infused glucose load in patients with NIDDM.

OBJECTIVE: This study was initiated to compare the effect of sulfonylurea treatment on the response to an infused glucose load of patients with non-insulin-dependent diabetes mellitus (NIDDM) at a basal insulin concentration and in response to physiological hyperinsulinemia. RESEARCH DESIGN AND METHODS: We used the insulin suppression test, in which subjects were infused for 180 min with somatostatin, exogenous insulin, and glucose. Since similar steady-state plasma insulin (SSPI) concentrations are reached in all subjects, the resultant steady-state plasma glucose (SSPG) concentration permits comparison of the ability of a given individual to maintain glucose homeostasis in response to the infused glucose load. RESULTS: We studied 15 nonobese patients at two different SSPI concentrations, before and after glipizide treatment, at basal (68 +/- 4 pmol/l) and high (470 +/- 31 pmol/l) levels. Values for SSPG concentrations were lower after treatment at both the basal (15.3 +/- 0.5 vs. 18.5 +/- 0.6 mmol/l; P < 0.001) and the high (10.6 +/- 0.7 vs. 14.2 +/- 0.7 mmol/l; P < 0.001) SSPI concentrations. To compare the responses of each patient before and after treatment, we calculated the fractional glucose metabolic rate, i.e., (glucose infusion rate--urinary glucose loss) divided by SSPG. To provide an alternative method of comparing the effect of sulfonylurea treatment, we divided the incremental increase in fractional metabolic glucose rate between the studies done at the low and high SSPI by the incremental increase in SSPI between the two studies (insulin sensitivity index [SI]). CONCLUSIONS: The results of these calculations indicated that glipizide treatment was associated with a significant increase in fractional glucose metabolic rate at a basal insulin concentration (29 +/- 3 to 42 +/- 2 ml.m-2.min-1, P < 0.001), and in response to the incremental change in SSPI (14 +/- 4 to 23 +/- 3 ml.m-2.min-1, P < 0.02). Finally, SI also increased in association with sulfonylurea (0.24 +/- 0.06 to 0.43 +/- 0.07 ml.m-2.min-1/microU.ml-1, P < 0.001).