Endothelin B Receptor Deficiency Predisposes to Pulmonary Edema Formation via Increased Lung Vascular Endothelial Cell Growth Factor Expression

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Abstract
Endothelin (ET) may contribute to pulmonary edema formation, particularly under hypoxic conditions, and decreases in ET-B receptor expression can lead to reduced ET clearance. ET increases vascular endothelial cell growth factor (VEGF) production in vitro, and VEGF overexpression in the lung causes pulmonary edema in vivo. We hypothesized that pulmonary vascular ET-B receptor deficiency leads to increased lung ET, that excess ET increases lung VEGF levels, promoting pulmonary edema formation, and that hypoxia exaggerates these effects. We studied these hypotheses in ET-B receptor–deficient rats. In normoxia, homozygous ET-B–deficient animals had significantly more lung vascular leak than heterozygous or control animals. Hypoxia increased vascular leak regardless of genotype, and hypoxic ET-B–deficient animals leaked more than hypoxic control animals. ET-B–deficient animals had higher lung ET levels in both normoxia and hypoxia. Lung HIF-1α and VEGF content was greater in the ET-B–deficient animals in both normoxia and hypoxia, and both HIF-1α and VEGF levels were reduced by ET-A receptor antagonism. Both ET-A receptor blockade and VEGF antagonism reduced vascular leak in hypoxic ET-B–deficient animals. We conclude that ET-B receptor–deficient animals display an exaggerated lung vascular protein leak in normoxia, that hypoxia exacerbates that leak, and that this effect is in part attributable to an ET-mediated increase in lung VEGF content.