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.