KDR and cyclic hematopoiesis: Given the inhibitory effects of SU5416 on MCEC VEGFR-2 activation, ERK phosphorylation, proliferation, and receptor transcription observed in vitro, we hypothesized that SU5416 might attenuate CH-PH induced RV angiogenesis through similar inhibition of RV EC VEGFR-2 activity in vivo.