Elevated glutamate levels in the vitreous body of an in vivo model of optic nerve ischemia

Objective: To explore the possibility that an elevation of glutamate levels in the vitreous might be associated with the microvascular compromise of t he optic nerve. Materials and Methods: Endothelin-l, 0.1 mu g/d (5 rabbits), or balanced sa lt solution (4 rabbits) was delivered to the perineural region of the anter ior optic nerve by osmotically driven minipumps for 2 weeks. Vitreous speci mens were obtained, and their amino acid contents were determined by high-p erformance liquid chromatography. Results: There was a statistically significant elevation in the mean +/- SE M vitreous concentrations of glutamate (264% +/- 41%; P = .04), aspartate ( 269% +/- 31%; P = .04), and glycine (232% +/- 26%; P = .04) in the eyes sub jected to endothelin-l when compared with the fellow control eyes. Conclusion: Administration of endothelin-l to the microvasculature of the o ptic nerve leads to elevation of glutamate, aspartate, and glycine concentr ations in the vitreous. Clinical Relevance: The increase of excitatory amino acids in the vitreous might be associated with various ischemic processes of the optic nerve, inc luding glaucomatous optic neuropathy, and may play a role in the neuronal d amage that is seen in these diseases.