Glutamate elevation in rabbit vitreous during transient ischemia-reperfusion.

PURPOSE To investigate the response of the retina to an ischemic insult, we measured the levels of glutamate in the vitreous of rabbit eyes. METHODS Ocular ischemia was induced in the vitreous of rabbit eyes by simultaneous ligature of the optic nerve, ciliary arteries, and extraocular muscles for 45 minutes. Contralateral eyes were subjected to a conjunctival peritomy to serve as sham-operated controls. Reperfusion was achieved by releasing the ligature. Eyes were enucleated at the end of the ischemic period or 15, 45, or 75 minutes after reperfusion. RESULTS Analysis of the vitreous free amino acids showed a significant increase in glutamate levels in the operated eyes at the end of the ischemic period (P <.001) and after 15 minutes of reperfusion (P <.05) as compared with the contralateral, sham-operated eyes. Glutamine levels in the vitreous were unchanged throughout the study. CONCLUSIONS These results show that glutamate, which is considered to be derived from synaptic release of the retinal neurons or accumulation due to a deterioration of glutamate uptake or a degradation system in the retina, was transiently elevated in the vitreous.