Abstract

Nitric oxide (NO) plays a key role as a vasodilator, neurotransmitter, and inflammatory mediator in the airways and is produced in increased amounts in asthma. It may have beneficial effects on airways function as a bronchodilator and is the neurotransmitter of bronchodilator nerves in human airways. On the other hand, NO may have deleterious effects on the airways as a vasodilator by increasing plasma exudation, and may also amplify the asthmatic inflammatory response. Proinflammatory cytokines and oxidants increase the expression of an inducible form of NO synthase (NOS) in airway epithelial cells in asthma, and this may underlie the increased levels of NO found in exhaled air of asthmatic patients. Inducible NOS is inhibited by glucocorticoids, but selective inhibitors of this enzyme may have therapeutic potential in asthma.