ET(A)-receptor blockade and ET(B)-receptor stimulation in experimental congenital diaphragmatic hernia

The aim of this study was to assess the role of nitric oxide (NO) and endothelin (ET)-1 in the pathophysiology of persistent pulmonary hypertension of the newborn in fetal lambs with a surgically created congenital diaphragmatic hernia (CDH). The pulmonary vascular response to various agonists and antagonists was assessed in vivo between 128 and 132 days gestation. Age-matched fetal lambs served as control animals. Control and CDH lambs had similar pulmonary vasodilator responses to acetylcholine, sodium nitroprusside, zaprinast, and dipyridamole. The ET(A)-receptor antagonist BQ-123 caused a significantly greater pulmonary vasodilatation in CDH than in control animals. The ET(B)-receptor agonist sarafotoxin 6c induced a biphasic response, with a sustained pulmonary vasoconstriction after a transient pulmonary vasodilatation that was not seen in CDH animals. We conclude that the NO signaling pathway in vivo is intact in experimental CDH. In contrast, ET(A)-receptor blockade and ET(B)-receptor stimulation significantly differed in CDH animals compared with control animals. Imbalance of ET-1-receptor activation favoring pulmonary vasoconstriction rather than altered NO-mediated pulmonary vasodilatation is likely to account for persistent pulmonary hypertension of the newborn in fetal lambs with a surgically created CDH.