[Possible role of nitric oxide in NANC relaxation of the airway and in airway hyperreactivity in airway disease].

In the lung, there is increasing evidence that endogenous nitric oxide (NO) plays multiple roles in physiological control of airway functions, immune responses and host defense against infection, and it is also implicated in inflammatory disease of the airways. As elsewhere, it is generally accepted that NO derived from constitutive NO synthase (cNOS) is involved in physiological regulation of airway function, whereas NO derived from inducible NO synthase (iNOS) is involved in immune responses and inflammatory diseases of the airway. In this mini review, first we describe evidence showing the possible roles of NO and NO-related compounds in nonadrenergic noncholinergic (NANC) relaxation and inhibitory action on excitatory neuro-effector transmission, thereby indicating that NO derived from neuronal cNOS plays a role to provide "double braking" in bronchoconstrictions. Secondly, we will discuss the possible involvement of epithelial damage due to excessive NO production through iNOS in the genesis of airway hyperreactivity and airway inflammation.