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Nitric oxide (NO) is a relative newcomer to pharmacology, as the paper which initiated the field was published only 25 years ago. Nevertheless its impact is such that to date more than 31,000 papers have been published with NO in the title and more than 65,000 refer to it in some way. The identification of NO with endothelium-derived relaxing factor and the discovery of its synthesis from L-arginine led to the realisation that the L-arginine: NO pathway is widespread and plays a variety of physiological roles. These include the maintenance of vascular tone, neurotransmitter function in both the central and peripheral nervous systems, and mediation of cellular defence. In addition, NO interacts with mitochondrial systems to regulate cell respiration and to augment the generation of reactive oxygen species, thus triggering mechanisms of cell survival or death. This review will focus on the role of NO in the cardiovascular system where, in addition to maintaining a vasodilator tone, it inhibits platelet aggregation and adhesion and modulates smooth muscle cell proliferation. NO has been implicated in a number of cardiovascular diseases and virtually every risk factor for these appears to be associated with a reduction in endothelial generation of NO. Reduced basal NO synthesis or action leads to vasoconstriction, elevated blood pressure and thrombus formation. By contrast, overproduction of NO leads to vasodilatation, hypotension, vascular leakage, and disruption of cell metabolism. Appropriate pharmacological or molecular biological manipulation of the generation of NO will doubtless prove beneficial in such conditions.

The formation of nitric oxide (NO) from L-arginine is now recognized as a ubiquitous biochemical pathway involved in the regulation of the cardiovascular, central, and peripheral nervous systems, as well as in other homeostatic mechanisms. The L-arginine:NO pathway comprises a substrate, L-arginine, a family of enzymes, the NO synthases, and at least one physiological effector system, the soluble guanylate cyclase. NO also inhibits enzymes in target cells and can interact with oxygen-derived radicals to produce other toxic substances. Thus, NO also plays a role in immunological host defense and in the pathophysiology of certain clinical conditions. Several steps in the L-arginine:NO pathway are amenable to manipulation. Some substances will change the concentration and/or actions of NO with consequences that, in certain cases, may be therapeutic. In addition, other agents themselves generate NO and thus mimic the actions of the endogenous mediator. This brief overview will discuss some possible interventions in the pathway and the potential benefits as well as undesirable side effects that might arise from them.

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