Inhibitory nerve distribution and mediation of NANC relaxation by nitric oxide in horse airways

Inhibitory nerve distribution and mediation of NANC relax-ation by nitric oxide in horse airways. J. Appl. Physiol. 76(l): 339-344, 1994.-The distribution of inhibitory nerves and the mediator of the inhibitory nonadrenergic noncholinergic (iN-ANC) nervous system were investigated in smooth muscle prep-arations from seven regions of equine airways. In tissues incu-bated with atropine and precontracted with histamine, electri-cal field stimulation produced frequency-dependent relaxation, and the magnitude of the relaxation decreased from trachea to central bronchi and was absent in peripheral airways. The de-gree of relaxation in bronchi was not simply a function of bron-chial size or generation. Propranolol inhibited part of the relax-ation only in the cranial trachealis. After propranolol, NG-nitro-L-arginine, a nitric oxide (NO) synthase inhibitor, eliminated the remaining relaxation in all preparations. Thi