Effect of glyburide in type II diabetes mellitus. Studies of monocyte membrane fluidity, lipid composition, and insulin binding.

Monocyte membrane lipid composition, fluidity, and insulin binding were studied in 10 previously untreated obese type II (non-insulin-dependent) diabetic subjects before and 2-7 days, 1 mo, and 3 mo after glyburide therapy. A significant reduction in fasting blood glucose levels occurred within 1 wk after initiation of therapy in all subjects. Serum insulin levels did not change significantly. After a transient increase at 2-7 days, insulin binding and receptor number decreased to less than pretreatment levels after 3 mo of therapy despite continued improved glycemic control. Molar cholesterol-phospholipid ratios increased significantly at 2-7 days and then reverted to pretreatment levels. A significant positive correlation between insulin binding and cholesterol-phospholipid ratios was seen at all durations of treatment. Membrane microviscosity as measured by fluorescence polarization of the probe diphenylhexatriene was significantly decreased after 3 mo of therapy. The results indicate that the glycemic effect of glyburide represents enhancement of insulin action and occurs independently of membrane insulin receptors.