Troglitazone, an insulin sensitizer, increases forearm blood flow in humans

To test whether troglitazone, a thiazolidinedione insulin sensitizer, increases the peripheral blood flow, the changes in forearm blood flow (FBF) were evaluated by venous occlusion plethysmography in 11 lean healthy male volunteers (age range, 24 to 39 years) after a single oral dose of 200 mg of troglitazone. Forearm vascular resistance (FVR) was calculated from FBF and blood pressure. Two hours after the dose, FBF increased from 3.66 ± 0.31 to 4.81 ± 0.57 mL/100 mL/min (P< .01), and FVR decreased from 24.7 ± 2.2 to 20.2 ± 2.2 units (P< .01), whereas both these values did not change during the control recordings obtained without troglitazone. Blood pressure, blood glucose levels, and serum immunoreactive insulin levels did not change significantly during the observation period. Serum concentrations of nitrate ions decreased from 27.0 ± 3.5 mmol/L to 23.1 ± 2.7 mmol/L (P< .01) after the administration. These results suggest that troglitazone increases muscular blood flow through vasodilation induced by a mechanism other than the correction of hyperinsulinemia or the increase in nitric oxide. The present study provides the first evidence that troglitazone dilates the vasculature in humans.