Relaxation to bradykinin in bovine pulmonary supernumerary arteries can be mediated by both a nitric oxide-dependent and -independent mechanism.

1. The aim of the present study was to determine the relative contribution of prostanoids, nitric oxide and K(+) channels in the bradykinin-induced relaxation of bovine pulmonary supernumerary arteries. 2. In endothelium-intact, but not denuded rings, bradykinin produced a concentration-dependent relaxation (pEC(50), 9.6+/-0.1), which was unaffected by the cyclo-oxygenase inhibitor indomethacin. The nitric oxide scavenger hydroxocobalamin (200 micro M, pEC(50), 8.5+/-0.2) and the nitric oxide synthase inhibitor L-NAME (100 micro M, pEC(50), 8.9+/-0.1) and the combination of L-NAME and hydroxocobalamin (pEC(50), 8.1+/-0.2) produced rightward shifts in the bradykinin concentration response curve. 3. The guanylyl cyclase inhibitor ODQ (10 micro M, pEC(50), 9.6+/-0.4) did not affect the response to bradykinin. 4. Elevating the extracellular [K(+)] to 30 mM did not affect the response to bradykinin but abolished the response when ODQ or L-NAME was present. 5. The K(+) channel blocker apamin (100 nM), combined with charybdotoxin (100 nM), produced a small reduction in the maximum response to bradykinin but they abolished the response to bradykinin when ODQ, L-NAME or hydroxocobalamin were present. Apamin (100 nM) combined with iberiotoxin (100 nM) also reduced the response to bradykinin in the presence of hydroxocobalamin or L-NAME. 6. The concentration response curve for sodium nitroprusside-induced relaxation was abolished by ODQ (10 micro M) and shifted to the right by apamin and charybdotoxin. 7. These studies suggest that in bovine pulmonary supernumerary arteries bradykinin can stimulate the formation of nitric oxide and activate an EDHF-like mechanism and that either of these pathways alone can mediate the bradykinin-induced relaxation. In addition nitric oxide, acting through guanylyl cyclase, can activate an apamin/charbydotoxin-sensitive K(+) channel in this tissue.