D-Alanine Is Reduced by Ocular Hypertension in the Rat Retina

<b>Purpose</b>: The purpose of this study was to investigate the physiological changes of amino acids in the rat retina caused by ocular hypertension. <b>Methods</b>: Adult Wistar rats were used as an experimental model of ocular hypertension. Retinas were hydrolyzed with HCl at 108°C to isolate amino acids. Residual amino acids were measured by reverse-phase high-performance liquid chromatography and the total volume of residual amino acids and the ratio of D- and L-amino acids were analyzed. Free D- and L-alanine levels were also measured using two-dimensional HPLC. <b>Results</b>: The amount of retinal alanine decreased in ocular hypertension compared with the control (<i>p</i> &lt; .05, Student’s <i>t</i>-test); the amounts of other amino acids did not differ between the two conditions. The D/L ratio of alanine was higher than that of other amino acids. Ocular hypertension reduced the D/L ratio of retinal alanine, while that of other amino acids was unchanged. Ocular hypertension increased the D/L ratio of free alanine. <b>Conclusions</b>: Ocular hypertension reduced the D/L ratio of retinal alanine, presumably due in large part to alanine peptides.