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 the optic nerve. MATERIALS AND METHODS: Endothelin-1, 0.1 microg/d (5 rabbits), or balanced salt solution (4 rabbits) was delivered to the perineural region of the anterior optic nerve by osmotically driven minipumps for 2 weeks. Vitreous specimens were obtained, and their amino acid contents were determined by high-performance liquid chromatography. RESULTS: There was a statistically significant elevation in the mean +/- SEM vitreous concentrations of glutamate (264% +/-41%; P = .04), aspartate (269% +/-31%; P = .04), and glycine (232% +/-26%; P = .04) in the eyes subjected to endothelin-1 when compared with the fellow control eyes. CONCLUSION: Administration of endothelin-1 to the microvasculature of the optic nerve leads to elevation of glutamate, aspartate, and glycine concentrations 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, including glaucomatous optic neuropathy, and may play a role in the neuronal damage that is seen in these diseases.