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H Levkovitch-Verbin, KR G Martin, HA Quigley, LA Baumrind, M Pease, D Valenta; Measurement of Amino Acid Levels in the Vitreous Humor of Rats after Chronic Intraocular Pressure Elevation or Optic Nerve Transection . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4039.
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Purpose:To investigate whether the levels of free amino acids and protein in the vitreous of rat eyes are altered with chronic experimental glaucoma or after optic nerve transection. Methods:The amounts of 20 amino acids in excised vitreous humor were measured by high performance liquid chromatography in both eyes of 61 rats with unilateral intraocular pressure (IOP) elevation that was induced by translimbal photocoagulation. Eyes were studied 1 day and 1, 2, 4, and 9 weeks after initial IOP elevation. The same amino acids were measured in 55 rats, 1 day and 2, 4, and 9 weeks after unilateral transection of the orbital optic nerve. Intravitreal protein level was assayed in 22 rats with experimental glaucoma and 12 rats after nerve transection. The amount of optic nerve damage was evaluated by 2 masked observers, using a semiquantitative, light microscopic technique. Results:In rats with experimental glaucoma, amino acid concentrations were unchanged 1 day after treatment. At one week, 7 of 20 amino acids (glutamate, aspartate, proline, alanine, lysine, serine and glycine) were higher than in control eyes at p < 0.03 or less, but with Bonferroni correction, none achieved p < 0.0025. No amino acid was significantly different from control in the nerve transection group (all p≷ 0.05). Vitreous protein level was significantly higher in glaucomatous eyes than their paired controls at 1 day (p<0.0001), 1 week, (p < 0.002) and 4 weeks (p = 0.04). One day and 1 week after optic nerve transection, vitreal proteins were significantly elevated compared to control eyes from untreated animals (p<0.0020 and p<0.0022 respectively) though not compared to their fellow eyes (p = 0.25 and 0.10). Conclusion:Chronic experimental glaucoma and transection of the optic nerve increase the amount of protein in the rat vitreous over control levels. In the vitreous of rats with experimental glaucoma, a number of free amino acids, including glutamate, are transiently elevated to a modest degree, possibly due to proteolysis.
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