Effects of VEGF and nitric oxide synthase inhibition on blood-brain barrier disruption in the ischemic and non-ischemic cerebral cortex.

OBJECTIVES: This study was performed to compare the effects of exogenous vascular endothelial growth factor (VEGF) and nitric oxide synthase (NOS) inhibition on blood-brain barrier (BBB) disruption in the ischemic cortex (IC) and non-ischemic contralateral cortex (CC) during the early stage of focal cerebral ischemia in rats.

METHODS: A middle cerebral artery (MCA) was occluded after a craniotomy in each rat under isoflurane anesthesia. Two more craniotomies were performed over the contralateral non-ischemic hemisphere to expose cerebral cortex. For the control rats, the normal saline patches were applied to all three craniotomy holes (control group). To inhibit NOS, NG-nitro-L-arginine-methyl ester (L-NAME) (10 mg/kg) was administered i.v. 20 minutes after MCA occlusion (L-NAME group). In another group, VEGF (10(-10) M) was topically applied 30 minutes after MCA occlusion on the IC as well as one of the holes of the contralateral cortex (VEGF group). To investigate the effects of the combination of VEGF and L-NAME, both L-NAME and VEGF were administered as described above (L-NAME+ VEGF group). The transfer coefficient (Ki) of 14C-alpha-aminoisobutyric acid and the volume of 3H-dextran (70 000 Da) distribution were determined to measure the degree of BBB disruption at 1 hour after MCA occlusion.

RESULTS: In the control group, Ki of the IC was significantly higher than the contralateral cortex (CC) (p<0.005). VEGF application increased the Ki of the IC further when compared with the control group (+51%, p<0.05%). L-NAME administration produced no significant decrease in the Ki of the IC when compared with the control group. With L-NAME+ VEGF administration, the Ki of the IC became significantly lower than that of the VEGF alone (-38%, p<0.005). Thus, L-NAME produced a much greater decrease in the Ki of the IC in the VEGF treated than the control animals (p<0.05). In the non-IC, VEGF, L-NAME, or their combination did not affect BBB disruption. The volume of dextran distribution followed a similar pattern to Ki.

DISCUSSION: Our data suggest that even in the early stage of focal cerebral ischemia, the degree of BBB disruption in response to the exogenous VEGF is much greater in the ischemic than in the non-IC and that the mechanism of the increase of BBB disruption by VEGF in the IC involves the NOS pathway.