Vascular Endothelial Growth Factor Improves Pulmonary Vascular Reactivity and Structure in an Experimental Model of Chronic Pulmonary Hypertension in Fetal Sheep

Abstract

Persistent pulmonary hypertension of the newborn (PPHN) is characterized by elevated pulmonary vascular resistance, impaired vasodilation, and muscularization of small pulmonary arteries. Past studies have shown that lung vascular endothelial growth factor (VEGF) surges just prior to birth but is markedly decreased in a fetal lamb model of PPHN. In addition, treatment of fetal lambs with an inhibitor of VEGF-165 caused pulmonary hypertension, impaired vasodilation, and increased pulmonary artery muscularization. We hypothesized that treatment with recombinant human VEGF-165 would reduce the severity of pulmonary vascular remodeling and improve endothelial-dependent vasodilation in an experimental model of PPHN. We studied the effects of daily intrapulmonary infusions of recombinant human VEGF in fetal lambs after partial ligation of the ductus arteriosus. We performed surgery in 23 late-gestation fetal lambs (125 to 128 days gestation; term, 147 days), with catheters placed in the main pulmonary artery, left atrium, and aorta for pressure measurements. A catheter was placed in the left pulmonary artery for drug infusions, and a ligature was placed around the ductus arteriosus. Recombinant human VEGF-165 (50 μg/d; n = 11) or its vehicle (n = 12) were infused for 7 or 14 days. In the first group, acetylcholine (15 μg) or 8-bromo-guanosine monophosphate (1.5 mg) were infused on days 2 and 13 to assess endothelium-dependent and endothelium-independent vasodilation, respectively. Animals in the second group had morphometric analysis of small pulmonary arteries performed. We found that although pulmonary vasodilation to 8-bromo-guanosine monophosphate remained intact, acetylcholine-induced vasodilation was reduced in PPHN control lambs after 14 days (change in pulmonary blood flow from baseline, 106% vs 11%; p < 0.05). In contrast, the response to acetylcholine was preserved in lambs treated with recombinant human VEGF (change in pulmonary blood flow, 94% vs 90%; p = not significant). At autopsy, recombinant human VEGF treatment decreased pulmonary artery wall thickness by 34% vs PPHN lambs (p < 0.001 vs ligation). We conclude that VEGF-165 improves endothelium-dependent vasodilation and reduces the severity of pulmonary vascular remodeling in experimental PPHN. We speculate that impaired VEGF signaling contributes to endothelial dysfunction and altered vascular structure in experimental PPHN.