Sheng, Lavonne, Weilin Zhou, Alison A. Hislop, Basil O. Ibe, Lawrence D. Longo, and J. Usha Raj. Role of epidermal growth factor receptor in ovine fetal pulmonary vascular remodeling following exposure to high altitude long-term hypoxia. High Alt. Med. Biol. 10:365–372, 2009.—High altitude long-term hypoxia (LTH) in the fetus may result in pulmonary vascular smooth muscle cell (PVSMC) proliferation and pulmonary vascular remodeling. Our objective was to determine if epidermal growth factor receptor (EGFR) is involved in hypoxia-induced PVSMC proliferation or in pulmonary vascular remodeling in ovine fetuses exposed to high altitude LTH. Fetuses of pregnant ewes that were held at 3820-m altitude from ∼30 to 140 days (LTH) gestation and sea-level control pregnant ewes were delivered near term. Morphometric analyses and immunohistochemistry were done on fetal lung sections. Pulmonary arteries of LTH fetuses exhibited medial wall thickening and distal muscularization. Western blot analyses done on protein isolated from pulmonary arteries demonstrated an upregulation of EGFR. This upregulation was attributed in part to PVSMC in the medial wall by immunohistochemistry. Proliferation of fetal ovine PVSMC after 24 h of hypoxia (2% O₂) was attenuated by inhibition of EGFR with 250 nmol tyrphostin 4-(3-chloroanilino)-6,7-dimethoxyquinazoline (AG1478), a specific EGFR protein tyrosine kinase inhibitor, when measured by [³H]-thymidine incorporation. Our data indicate that EGFR plays a role in fetal ovine pulmonary vascular remodeling following long-term fetal hypoxia and that inhibition of EGFR signaling may ameliorate hypoxia-induced pulmonary vascular remodeling.