Baseline blood flow and bradykinin-induced vasodilator responses in the human forearm are insensitive to the cytochrome P4502C9 (CYP2C9) inhibitor sulphaphenazole

A substantial portion of the vasoclilator response elicited by bradykinin in the human forearm is unaffected by the combined inhibition of nitric oxide (NO) synthases and cyclo-oxygenases. The cytochrome P450 (CYP) 2C9 inhibitor sulphaphenazole was recently identified as a potent inhibitor of NO- and prostacyclin (PGI(2))-independent relaxation in porcine coronary arteries. The aim of the present study was to determine the effect of sulphaphenazole on basal and bradykinin-induced NO/PGI(2)-independent changes in the forearm blood flow (FBF) of healthy subjects. Eleven healthy male volunteers participated in this placebo-controlled study. Test agents were infused into the brachial artery and FBF was measured by bilateral venous occlusion plethysmography. Sulphaphenazole (0.02-2 mg/min) alone did not affect basal blood flow. Inhibition of the NO synthases by N-G-monomethyl-L-arginine (L-NMMA; 4 mumol/min) and cyclo-oxygenases by ibuprofen (1200 mg, orally) reduced FBF to 48 +/- 7% in the absence and 50 +/- 8% in the presence of sulphaphenazole (2 mg/min; P = not significant). After pretreatment with L-NMMA (16 mumol/min) and ibuprofen (1200 mg, orally), sulphaphenazole (6 mg/min) did not substantially inhibit bradykinin-induced vasodilation. We conclude that CYP2C9-derived metabolites (i) are not involved in the regulation of baseline blood flow, and (ii) do not mediate bradykinin-induced NO/PGI(2)-independent vasorelaxation in the human forearm. However, determining the contribution of this enzyme to regulation of blood flow in pathological conditions associated with endothelial dysfunction requires further studies.