Altered regulation of the ET-1 cascade in lambs with increased pulmonary blood flow and pulmonary hypertension

Plasma concentrations of endothelin-1 (ET-1) are increased in children with congenital heart disease associated with increased pulmonary blood flow. H owever, the role of ET-1 in the pathophysiology of pulmonary hypertension r emains unclear. Pre-proendothelin-1 gene expression is increased in adults with advanced pulmonary hypertension. To characterize potential early molec ular alterations in the ET-1 cascade induced by increased pulmonary blood f low and pulmonary hypertension, fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt). RNase protection assays and West ern blot analysis were performed on lung tissue prepared from 4-wk-old shun t lambs and age-matched controls. Endothelin-converting enzyme-1 [the enzym e responsible for the production of active ET-1 from big ET-1, mRNA (411%, p < 0.05)] and protein (170%, p < 0.05) were increased in lung tissue prepa red from shunt lambs, compared with age-matched controls. Endothelin type A receptor (the receptor that mediates vasoconstriction), mRNA (246%, p < 0. 05), and protein (176%, p < 0.05) also were increased in lung tissue prepar ed from shunt lambs compared with age-matched controls. Conversely, endothe lin type B receptor (the receptor that mediates vasodilation), mRNA (46%, p < 0.05), and protein (65%, p < 0.05) were decreased in shunt lambs. Both t he mRNA and protein levels for preproendothelin-1 were unchanged. Thus we c onclude that increased pulmonary blood flow and pulmonary hypertension indu ce early alterations in the ET-1 cascade that result in increased ET-1 prod uction, increased ET-1-mediated vasoconstriction, and decreased vasodilatio n. These early alterations in gene expression may contribute to the develop ment of pulmonary hypertension and its associated enhanced pulmonary vascul ar reactivity.