ABSTRACT
<p><b>OBJECTIVE</b>To explore the expression of vascular endothelial growth factor (VEGF) and its receptors (flt-1 and flk-1) in the retina of retinopathy of prematurity (ROP), and its relation to the alteration of retinal blood vessels.</p><p><b>METHODS</b>Eighty-six newborn Sprague-Dawley rats were randomly divided into hyperoxia and air groups, then each group was further divided into 1, 3, 7 and 14 days subgroups. The rats in hyperoxia group inhaled 75% oxygen and ROP model was thus set up. These animals were sacrificed respectively after 1, 3, 7 and 14 days, then the retinal endothelial cells were marked by CD34 to observe the change of retinal blood vessels. The expression of VEGF, flt-1 and flk-1 in the retina was measured by immunohistochemistry.</p><p><b>RESULTS</b>The retinal capillary density index (RCDI) in control group increased as days went on (F = 21.589, P < 0.01, but it was the least on the 7th day in hyperoxia group, after the rats had been returned to air for 7 days, RCDI increased significantly (F = 67.885, P < 0.01); In the control group, the expression of VEGF and flk-1 was the strongest in the retina on the 7th day, the result had significant difference as compared with the 1st and 14th day (P < 0.05). The expression of VEGF and flk-1 on the 7th day in hyperoxia group was weaker than that of control group (P < 0.05). But on the 14th day in hyperoxia group, they were stronger than that of control (P < 0.05). The localization of the expression of flt-1 was changed when blood vessels altered, but there was no significant difference in expression intensity as a whole (P > 0.05).</p><p><b>CONCLUSION</b>When the premature retina was exposed to hyperoxia, the expression of VEGF and flk-1 was reduced, and retinal blood vessels were also decreased; but the expression of VEGF and flk-1 was stronger in retina when premature rats were exposed to relative hypoxia, and the retinal blood vessels also increased significantly. It is concluded that VEGF and flk-1 may play important roles in the development of retinal blood vessels and its change in ROP. However, flt-1 has less effect compared with flk-1.</p>