NITRIC-OXIDE SYNTHASE-IMMUNOREACTIVE NEURONS IN HUMAN AND PORCINE RESPIRATORY-TRACT

The presence of nitric oxide synthase (NO-synthase), the enzyme respon sible for the production of nitric oxide (NO) from L-arginine, is show n immunocytochemically in the intrinsic neurons of the human and porci ne respiratory tract. NO-synthase immunoreactivity is demonstrated in a subpopulation of neurons of the microganglia present in the wall of the extra- and intrapulmonary bronchi as well as in the hilar region o f the lung in relation to blood vessels. The immunostaining was also f ound in some nerve fibers of the respiratory nervous system. Human and porcine lung gave similar results. The possible involvement of NO in the nonadrenergic noncholinergic (NANC) nervous regulation of the lung is discussed.