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 µg/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.