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M. Zhao, H. Liu, C. Destache, G. L. Zhan, S. E. Ohia, C. A. Opere; Regulation of Endogenous Glutamate Levels by 8-isoPGF2 in Rabbit Retinae and Vitreous Humor, in vivo. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4193.
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There is evidence that isoprostanes (IsoPs) can regulate the release of exogenously applied radiolabeled excitatory amino acid neurotransmitter in isolated bovine retinae (Opere et al., Neurochem. Res. 30: 2005). However, the effect of IsoPs on endogenous glutamate concentrations in mammalian retinae remains unknown. In this study, we examined the effect of intravitreally injected 8-isoprostaglandin (8-isoPGF2α) on the level of endogenous glutamate and its metabolite, glutamine in rabbit retinae and vitreous humor, in vivo.
Albino rabbits (New Zealand strain) were anaesthetized by an intravenous injection of ketamine 50mg/kg and xylazine 5mg/kg and intravitreally injected with 8-isoPGF2α. Control eyes were injected with an equal volume of vehicle. After 4 hours, animals were sacrificed with overdose phentobarbital. Retinae and vitreous humor were isolated for measurement of glutamate and its metabolite glutamine by HPLC-EC. Samples were derivatised by o-phthaldialdehyde (OPA)/ 2-mercaptoethanol (ß ME) pre-column for detection. Amino acids were detected using homoserine as the internal standard and Shimadzu chromatographic software for peak area integration.
Intravitreally injected 8-isoPGF2α (1nM - 10µM) attenuated the level of glutamate and its metabolite, glutamine in rabbit retinae. For instance, 8-isoPGF2α (1nM and 10µM) decreased retinal glutamate levels by 25% (p<0.05) and 35% (P<0.05), respectively. Similarly, 8-isoPGF2α (1nM, 0.1µM and 10µM) significantly (p<0.05) reduced glutamine level in retina by 25%, 41% and 35%, respectively. A similar inhibitory effect was observed in the vitreous humor, where 8-isoPGF2α (0.1µM and 10µM) significantly (p<0.05) decreased glutamate levels by 55% and 34%, respectively. Interestingly, glutamine was not detected in rabbit vitreous humor.
We conclude that 8-isoPGF2α can regulate the levels of glutamate and its metabolite, glutamine in rabbit retinal tissues, in vivo. The mechanisms underlying the observed changes in neurotransmitter level due to this IsoP merits further investigation.
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