Hydrogen peroxide acts as an EDHF in the piglet pial vasculature in response to bradykinin

We investigated the mechanism of EDHF-mediated dilation to bradykinin (BK) in piglet pial arteries. Topically applied BK (3 mumol/l) induced vasodilation (62 +/- 12%) after the administration of N-omega-nitro-L-arginine methyl ester (L-NAME) and indomethacin, which was inhibited by endothelial impairment or by the BK2 receptor antagonist HOE-140 (0.3 mumol/l). Western blotting showed the presence of BK2 receptors in brain cortex and pial vascular tissue samples. The cytochrome P-450 antagonist miconazole (20 mumol/l) and the lipoxygenase inhibitors baicalein (10 mumol/l) and cinnamyl-3,4-dyhydroxy-alpha-cyanocinnamate (1 mumol/l) failed to reduce the BK-induced dilation. However, the H2O2 scavenger catalase (400 U/ml) abolished the response (from 54 +/- 11 to 0 +/- 2 mum; P < 0.01). The ATP-dependent K+ (K-ATP) channel inhibitor glibenclamide (10 mu mol/l) had a similar effect as well (from 54 +/- 11 to 16 +/- 5 mu m; P < 0.05). Coapplication of the Ca2+-dependent K+ channel inhibitors charybdotoxin (0.1 mumol/l) and apamin (0.5 mumol/l) failed to reduce the response. We conclude that H2O2 mediates the non-nitric oxide-, non-prostanoid-dependent vasorelaxation to BK in the piglet pial vasculature. The response is mediated via BK2 receptors and the opening of K-ATP channels.