Nitric oxide and asthma

Nitric oxide (NO) is a universal signalling molecule, involved in many physiological and pathophysiological processes, including asthmatic airway inflammation. Nitric oxide synthases (NOS) are newly identified enzyme systems active in airway epithelial cells, macrophages, neutrophils, mast cells, non-adrenergic non-cholinergic neurons, smooth muscle cells and endothelial cells. Two functional classes of NOS can be identified: the inducible form temporarily leading to large amounts of NO, and the constitutive form continuously leading to small amounts of NO. Large amounts of NO contribute to airway inflammation and killing of micro-organism, whereas small amounts of NO lead to smooth muscle relaxation. Asthmatic airway obstruction is induced by various bronchoconstricting factors (like allergens, pharmacological spasmogens, physical stimuli, infectious disease state) and is inhibited by NO. The development of specific inhibitors for the inducible form of NOS might open up a new era of antiasthmatic drugs.