Nitric oxide and hemoglobin interactions in the vasculature

As an endothelium-derived relaxing factor, nitric oxide (NO) maintains bloo d flow and O-2 transport to tissues. Under normal conditions a delicate bal ance exists in the vascular system between endothelium-derived NO, an antio xidant, and the pro-oxidant elements of the vascular system, O-2(-), and pe roxynitrite (a by-product of the reaction of NO and superoxide); in additio n there is a balance between neurogenic tonic contraction and NO-mediated r elaxation. The former balance can be disrupted in favor of peroxynitrite an d hydrogen peroxide under the conditions of ischemia/reperfusion. This revi ew suggests that NO may be beneficial, not only in terms of its new potenti al in improving O-2 transport without accompanying significant increase in tissue blood flow, but also in its ability to suppress the prooxidative rea gents of the vascular systems. These include NO-mediated inhibition of tran sendothelial migration by leukocyte and the antioxidative effects of NO wit h regard to ischemia/reperfusion; the relevance of these hypotheses to syst emic administration of NO donors is discussed. (C) 1999 Elsevier Science B. V. All rights reserved.