Vitreous body glutamate concentration in dogs with glaucoma

Abstract

OBJECTIVE: To analyze the vitreal amino acid concentrations in dogs with breed-related primary glaucoma to determine whether excitotoxic amino acids associated with retinal genglion cell death in other species were present in affected dogs. SAMPLES: 11 normal control and 10 glaucomatous canine eyes. PROCEDURE: Amino acid analyses were performed by high-pressure liquid chromatography in masked manner. RESULTS: Eyes from dogs with primary glaucoma had significantly high vitreal glutamate concentration, compared with values for eyes of clinically normal control dogs. Mean (+/-SD) glutamate concentrations were 31.7 +/- 12.4 and 6.9 +/- 6.3 microM in glaucomatous and normal eyes, respectively (P < 0.0001). Eyes from dogs with glaucoma also had lower vitreal glycine (37.0 +/- 17.0 vs 59.4 +/- 28.2 microM; P < 0.043) and higher of vitreal tryptophan (39.0 +/- 22.8 vs 17.5 +/- 11.2 microM; P < 0.012) concentrations, compared with values for normal eyes. CONCLUSION: Glutamate concentration potentially toxic to retinal ganglion cells is associated with the pathogenesis of primary glaucoma in dogs. Increased glutamate concentration provides evidence of an ischemic mechanism for retinal ganglion cell death and optic nerve atrophy in dogs with glaucoma. CLINICAL RELEVANCE: The emphasis on reduction and normalization of high intraocular pressure as the primary focus of treatment for glaucoma in dogs should be augmented by other therapeutic approaches.