Effect of Hydrogen Peroxide on Glutamate and Glycine Concentrations in the Bovine Retina and Vitreous Humor

Abstract

Abstract: : Evidence from our laboratory indicates that hydrogen peroxide (H₂O₂) can inhibit potassium (K⁺)-depolarization evoked [³H]D-aspartate release from bovine isolated retinae (Exp. Eye Res. 71: abs. no. 386, 2000). Purpose: In the present study, we investigated the effect of exogenous H₂O₂ on glutamate and glycine concentrations in the bovine retina and vitreous humor in an ex vivo eye model. It was of interest to determine whether the observed action of H₂O₂ on K⁺-evoked [³H]D-aspartate release could be replicated in an ex vivo model. Methods: Whole eye organ cultures were incubated at 37^oC for 15 minutes. After incubation, H₂O₂ (1 – 100 µM) or sterile distilled water (vehicle) was injected intravitreally into each eye. Thirty minutes after injection, the retina and vitreous humor were removed for analysis of glutamate and glycine concentrations by HPLC with fluorescence detection. Results: H₂O₂ (1-100 µM) caused a concentration-related decrease in glutamate levels reaching a maximum inhibitory response of 63% at 100 µM. Likewise, low concentrations of H₂O₂ (1-10 µM) caused a decrease in glutamate levels in the vitreous humor. In contrast, a higher concentration of H₂O₂ (100 µM) caused a significant (p<0.001) increase in glutamate levels in the vitreous humor. H₂O₂ (1-100 µM) produced a concentration-dependent decrease in glycine levels in the retina reaching a maximum of 35% at 100 µM. H₂O₂ (1-10 µM) also caused a decrease in glcyine concentrations in the vitreous humor. Conclusion: We conclude that exogenously administered H₂O₂ can alter the integrity of endogenous pools of both glutamate and glycine in the posterior segment of the eye.

Keywords: pharmacology • retina: neurochemistry • neurotransmitters/neurotransmitter systems