OBJECTIVETo examine the expression of mRNA of vascular endothelial growth factor (VEGF) in a rat model of hyperoxia-induced retinopathy and to investigate the role of VEGF in the process of neovascularization in retinopathy.

METHODSOne hundred fifty one-day-old neonatal Sprague-Dawley rats were randomly divided into hyperoxia-induced retinopathy and normal control groups. The rats in the retinopathy group were exposed to (80 +/- 2)% oxygen for 7 days and then replaced by room air. The rats in the control group were exposed to room air all the time of the experiment. The morphologic changes of retinal vessels were estimated by observing the vascular pattern in adenosine diphosphate ase (ADPase) stained retina flat mounts. The newborn vessels were quantified by haematoxylin and eosin staining. Reversal transcription-polymerase chain reaction (RT-PCR) was used to detect the VEGF mRNA expression.

RESULTSIn the retinopathy group at 7 days of age, most of central radial vessels became constricted and blocked, and central perfusion decreased obviously. After switching to room air exposure for 7 days (14 days of age), noticeable retinal neovascularization appeared. The expression of VEGF mRNA in the retinopathy group at 7 days of hyperoxia exposure was noticeably lower than in the control group, and increased gradually after switching to room air exposure. At 9 and 14 days of age, the expression of VEGF mRNA in the retinopathy group was noticeably higher than in the control group. The expression of retinal VEGF mRNA in the retinopathy group increased before neovascularization occurred, and decreased with regression of new vessels.

CONCLUSIONSHyperoxia exposure may decrease the transcription of VEGF mRNA and the growth of retinal blood vessels. The relative hypoxia after hyperxia withdrawal can up-regulate the transcription of VEGF mRNA, resulting in a significant retinal neovascularization. The abnormal expression of VEGF in the retina may play an important role in the development of neovascularization in retinopathy.