Early abundance of nerves containing NO synthase in the airways of newborn pigs and subsequent decrease with age

We have localized by immunocytochemistry, and quantified by intercept counting, NO-synthase-containing nerves in newborn pig intrapulmonary airways and maturational changes in their density in juvenile and adult lung. NO-synthase-containing nerves supplying airway smooth muscle and epithelium were evident at all ages (<2 h, 1-2 days, 3-5 days, 6-10 days, 10 and 16 weeks). They were most abundant in neonates, and their density decreased with age (intercepts/mm(2) +/- SEM: newborn, 94 +/- 3.3; 16 weeks, 7 +/- 0.3; P < 0.001), as did their percentage of the total nerves defined by the general neuronal marker PGP 9.5 (newborn, 38 +/- 2.7%; 16 weeks, 18 +/- 2.3%; P < 0.01). Neural-derived NO may be important in pulmonary adaptation to extra-uterine life.