KDR and pulmonary arterial hypertension: Rats injected with the Flk-1 receptor tyrosine kinase (also known as Vegfr2) inhibitor, SU5416 (Sugen), followed by housing in 10% oxygen develop PH that most recapitulates human PAH, with medial hyperplasia and neointima formation, luminal narrowing of small precapillary pulmonary arteries, and the development of plexiform lesions [22].