Pathophysiology of congenital diaphragmatic hernia. X: Localization of nitric oxide synthase in the intima of pulmonary artery trunks of lambs with surgically created congenital diaphragmatic hernia.

The pathophysiology of congenital diaphragmatic hernia (CDH) results from a combination of pulmonary hypoplasia, pulmonary hypertension, and surfactant deficiency. Previously we demonstrated that inhaled nitric oxide (NO), a known vasodilator, only improves oxygenation and decreases pulmonary artery pressures when the lamb model of CDH is pretreated with exogenous surfactant. Nitric oxide synthase (NOS) in endothelial cells is responsible for the production of NO, a mediator of smooth muscle cell relaxation. Pulmonary hypertension in CDH may result from a defect in the endogenous production of NO. Our aim was to determine whether the main pulmonary artery trunks in CDH lambs have NOS immunoreactivity. Cryostat sections of paraformaldehyde-fixed specimens of pulmonary artery and aortic rings from 10 CDH lambs and five control lambs were processed for NADPH-diaphorase activity. Immunolocalization of NOS was studied in paraformaldehyde-fixed sections and compared with serially cut specimens from identical rings that were tested for NADPH-diaphorase activity. Intense NADPH-diaphorase staining was present in the intimal layer (endothelial lining) of the pulmonary artery and aortic rings of both the CDH and control lambs. This activity colocalized with NOS immunoreactivity in all specimens. Both NOS immunoreactivity and NADPH-diaphorase staining were lacking in cartilage, which were used as negative controls. NOS is present in the main pulmonary artery trunks of CDH lambs. To our knowledge, this is the first report of NOS immunoreactivity in CDH. We can only speculate whether this activity is preserved in other areas of the vascular tree in CDH, ie, pulmonary capillaries and veins. Perhaps the pulmonary hypertension in CDH is not caused by an NOS deficiency.