Hemoglobin and the Paracrine and Endocrine Functions of Nitric Oxide

Nitric oxide, a key factor in the maintenance of vascular tone, causes vascular smooth muscles to relax. Hemoglobin rapidly destroys nitric oxide, thereby limiting the activity of the gas to the local environment. Recent work suggests that nitric oxide reacts with hemoglobin at high oxygen tensions to form relatively long-lived products. At low oxygen tensions, these products release vasodilatory nitric oxide. This work is controversial, but it provides evidence of the potential of inhaled nitric oxide as a therapeutic agent.