Evidence for peroxidative damage by nitric oxide in experimental chronic cerebral vasospasm

Recent data has suggested a role for the nitric oxide metabolite peroxynitrite in peroxidative injury to endothelium associated with atherosclerosis. The present experiments were designed to elucidate whether such a mechanism might be involved in the morphological changes observed during chronic vasospasm after subarachnoid hemorrhage. For this purpose, chronic vasospasm was induced in male Wistar rats by an injection of autologous blood (100 microliters) in the cisterna magna followed by a second injection 24 hours later. Vasospasm was verified by pressure controlled internal carotid angiography after retrograde cannulation of the external carotid artery 7 days after the second injection. Animals were then perfusion fixed and the brains removed for immunohistochemical assessment of nitrotyrosine, the peroxidation product of peroxynitrite with tyrosine contained in tissue proteins. Staining for nitrotyrosine was quantified by microscopy in 40 microns coronal floating sections. The brains of rats with angiographic vasospasm revealed nitrotyrosine predominantly located with a perivascular distribution and in the pia. We conclude that peroxidation of membrane proteins by the nitric oxide metabolite peroxynitrite may contribute to the morphological damage evident in chronic vasospasm.