Differential effects of hydroxocobalamin on NO-mediated relaxations in rat aorta and anococcygeus muscle

In rat aortic rings, hydroxocobalamin (10-30 microM) produced concentration-dependent reductions of the relaxant action of nitric oxide (NO) and the endothelium-dependent, NO-mediated, relaxant action of acetylcholine. In anococcygeus muscles, hydroxocobalamin (10-30 microM) reduced but also prolonged, NO-induced relaxations, but had no effect on non-adrenergic, non-cholinergic-mediated relaxations. Hydroxocobalamin had no effect on the NO-independent relaxant action of papaverine in either tissue. It is suggested that hydroxocobalamin sequesters NO by forming nitrosocobalamin. Nitrosocobalamin did not relax aortic rings, but produced a slowly developing and prolonged relaxation of anococcygeus muscles.