Glipizide does not affect absorption of glucose and xylose in diabetics without residual beta-cell function

We have previously demonstrated that oral glipizide suppresses the absorption of xylose in diabetics treated with diet alone. We suggested that glipizide might influence postprandial glucose levels by interfering with absorptive mechanisms. In the present study we have extended our observations to insulin-dependent diabetics (IDDM). Nine non-obese diabetics without residual beta-cell function and with normal respiratory sinus arrhythmia and Valsalva ratio were studied on two occasions. Their ordinary insulin treatment was discontinued 24 hours before the study and glucose control was maintained by i.v. insulin infusion. The experiments began at 8 a.m. after an overnight fast. Insulin was given as a continuous i.v. infusion of 0.01 U/kg/h at 8-11 a.m. and 0.005 U/kg/h at 11 a.m. -2 p.m. At 8 a.m. the patients ingested 25 g of xylose and 15 g of glucose in 300 ml of water. Glipizide (5 mg) or placebo were given 30 min prior to the glucose-xylose load in random order, each patient serving as his own control. Blood samples were taken every 60 min for analysis of glucose, xylose, C-peptide and glipizide. The rise in blood glucose in the control experiment was similar to that previously seen in non-insulin-dependent diabetics (NIDDM) given the same xylose-glucose load. Glipizide did not exert any effects on either blood C-peptide, glucose or xylose levels. We conclude that oral glipizide administered in a therapeutic dose does not reduce xylose absorption in IDDM, in contrast to its previously demonstrated effect in NIDDM.