Effect of VEGF on retinal microvascular endothelial hydraulic conductivity: The role of NO

PURPOSE. Vascular endothelial growth factor (VEGF) increases microvascular permeability in vivo and has been hypothesized to play a role in plasma lea kage in diabetic retinopathy. Few controlled studies have been conducted to determine the mechanism underlying the effect of VEGF on transport propert ies (e.g., hydraulic conductivity [Lp]). This study Nas conducted to determ ine the effect of VEGF on bovine retinal microvascular endothelial LP and t he role of nitric oxide (NO) and the guanylate cyclase/guanosine 3',5'-cycl ic monophosphate/protein kinase G (GC/cCMP/PKG) pathway downstream of NO in mediating the VEGF response. METHODS. Bovine retinal microvascular endothelial cells (BRECs) were grown on porous polycarbonate filters, and water flux across BREC monolayers in r esponse to a pressure differential was measured to determine endothelial Lp . RESULTs. VEGF (100 ng/ml) increased endothelial LP within 30 minutes of add ition and by 13.8-fold at the end of 3 hours of exposure. VEGF stimulated e ndothelial monolayers to release NO and incubation of the BRECs with the ni tric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA; 100 muM) si gnificantly attenuated the VEGF-induced LP increase. It was observed that i ncubation of the monolayers with the GC inhibitor LY-83583 (10 muM) did not alter the VEGF mediated Lp response. Addition of the cGMP analogue 8-brcGM P (1 mM) did not change the baseline LP over 4 hours. Also, the PKG inhibit or KT5823 (1 muM) did not inhibit the response of BREC Lp to VEGF. CONCLUSIONS. These experiments indicate that VEGF elevates hydraulic conduc tivity in BRECs through a signaling mechanism that involves NO but not the GC/cGMP/PKG pathway.