Nitric oxide is the endogenous neurotransmitter of bronchodilator nerves in humans.

In human airways, there is a prominent neural bronchodilator mechanism which is non-adrenergic. In human tracheal segments, we have demonstrated that this response is mediated entirely by nitric oxide (NO), since an inhibitor of NO synthesis, L-NG-nitroarginine methyl ester (L-NAME) (10(-4) M) abolishes this neural response. Identification of the neurotransmitter of this bronchodilator pathway may now make it possible to study its role in physiological control of airway calibre and in airway disease.