Nitric oxide (NO) synthesis in vascular endothelium of patients with hypertension is altered. Calcium antagonists have been shown to improve endothelial function in hypertensive patients. Here we report that pranidipine, one of the latest long-acting calcium antagonists in the dihydropyridine group, enhances the actions of NO released from endothelial cells (ECs). Pranidipine significantly enhanced cGMP accumulation in vascular smooth muscle cells cocultured with ECs, whereas amlodipine and nifedipine had no significant effects. In addition, pranidipine also suppressed basal and thrombin-stimulated endothelin-1 production from ECs. Pranidipine also enhanced cGMP accumulation in rat aortic segments with endothelium but not in endothelium-denuded vessels. In contrast, pranidipine had no effect in the presence of N(G)-monomethyl-L-arginine, an inhibitor of NO synthesis. Pranidipine did not affect the basal expression of endothelial NO synthase in ECs. However, pranidipine upregulated the activity of superoxide dismutase in ECs. These findings suggest that pranidipine enhances NO action through inhibition of superoxide-induced NO decomposition in the vessel wall. Thus, pranidipine may be useful in the treatment of impaired endothelial function in patients with hypertension.