Postnatal changes of vascular endothelial growth factor (VEGF) expression in the retinae of normal and hypertensive rats

Vascular endothelial growth factor (VEGF) has been shown to have potent mitotic activity specific to vascular endothelial cells and has been related to vascular permeability, angiogenesis and cell proliferation in both normal and pathological situations. The present study aimed at elucidating the spatio-temporal changes in the postnatal expression pattern of VEGF in the retinae of both normal and hypertensive rats. In situ hybridization;with a riboprobe showed that in the pre-hypertensive stage (2 weeks postnatal, prior to the increase of the blood pressure of the hypertensive rat), VEGF expressed strongly in the retinal pigment epithelium (RPE) and inner nuclear layer (INL) but weakly in the ganglion cell layer and nerve fiber layer in both the normal and hypertensive rats. During the early hypertensive stage (6 weeks postnatal, initial increase of the blood pressure of the hypertensive rat), similar expression pattern was maintained but the INL of the hypertensive rat was found to have more positive cells in clusters than that of the normal rat. When a sustained high blood pressure was developed (12 weeks postnatal, sustained hypertensive stage) in the hypertensive rat, the VEGF expression was much reduced in all layers of the retina although weak expression was still observed in the RPE of the normal rat and RPE and INL of the hypertensive rat. Western blot analysis however showed that VEGF protein expression in the retina was much stronger in the hypertensive rat than in the normal rat at 2 and 6 weeks postnatal. At 12 weeks, the VEGF protein returned to a level comparable to that found in the normal rat. It is speculated that the change of the VEGF protein expression pattern during the early phase of the development of hypertension may be related to the subsequent changes in the retinal vasculature of the hypertensive rat.