Nitric oxide is involved in the etiology of ischemic damage in the rat retina

Purpose: Nitric oxide (NO) has been involved in the etiology of neurotoxicity, particularly that mediated by excitatory amino acids. The purpose of the present study was to investigate whether NO has a major role in the etiology of ischemic damage in the rat retina, a well established model of neuronal tissue. Methods: Retinal ischemia was induced in albino Lewis rats by increasing the intraocular pressure to 140 cm H₂O for 75 minutes. Two regimens of treatment with nitric oxide synthase (NOS) inhibitors (N^W nitro L-arginine and aminoguanidine) were examined: (1) prophylactic treatment in which NOS inhibitors were administered one hour before ischemia and (2) post-ischemic treatment, in which NOS inhibitors were administered one hour after reperfusion. Injury was evaluated morphologically and morphometrically by measuring the thickness of the inner retinal layers and by counting the retinal ganglion cells on flat retinal preparations. Results: According to morphometric and morphologic criteria, a significant protection of the inner retinal layers was noted in both study groups. Conclusion: This protective effect of NOS inhibitors suggests that NOS, and therefore NO, may be implicated in the mechanism of ischemic injury to the retina.