Alterations of glutamate, glutamine, and related amino acids in the anterior eye secondary to ischaemia and reperfusion.

PURPOSE: To assess the amino acid levels of the ciliary epithelium, aqueous and lens under normal conditions and secondary to ischaemia and reperfusion.

METHODS

We assessed the amino acids glutamate, glutamine, aspartate, alanine, gamma-amino butyric acid, glycine, arginine and taurine in albino Sprague-Dawley rats. Acute ischaemia was created in the eye and the different anterior eye components were assessed for amino acid levels. Quantitative immunocytochemistry was used to compare amino acid profiles within the ciliary processes immediately after ischaemia and after 4 days of reperfusion. Liquid chromatography was used to determine amino acid levels in the aqueous humour and quantitative immunocytochemistry to determine the location and alterations of amino acids in the lens 4 days after ischaemia/reperfusion.

RESULTS

Elevated amino acid levels were evident in the ciliary epithelium immediately after ischaemia. After 4 days of reperfusion, decreased levels of glutamine, gamma-aminobutyric acid, glycine and arginine were evident in the ciliary epithelium, in particular the nonpigmented epithelial cells. The amino acid levels in the aqueous humour remained unchanged after ischaemia/reperfusion and thus showed considerable resilience to this kind of injury. However, significant reductions of glutamate, glutamine, alanine, glycine, arginine and taurine were observed in the lens 4 days after ischaemia/reperfusion.

CONCLUSIONS

We propose a model to explain the maintenance of amino acid homeostasis in the aqueous humour despite altered levels in both the ciliary processes and lens.