“In endothelium-denuded guinea-… basilar artery preparations, hydroxocobalamin (30, 100 and 300 …) concentration-dependently inhibited the vasodilator responses to exogenous nitric oxide (NO), whereas the vasodilator responses to nitrergic nerve stimulation were slightly reduced … high (100 and 300 microM) but not by the low (30 microM) concentration of hydroxocobalamin.”