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E Budzynski, ND Wangs-Wirawan, RA Linsenmeier, L Padnick-Silver; Intraretinal pH Distribution in Diabetic Cats . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1329.
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Purpose: The intraretinal distribution of H+ in cats with long-standing diabetes was examined in order to understand changes in pH during diabetic retinopathy. Methods: H+-selective microelectrodes were used to measure intraretinal extracellular H+ concentration ([H+]O) in the retina of anesthetized cats. The four animals had varied stages of diabetic retinopathy based upon fundoscopic evaluation. The profiles of [H+]O as a function of retinal depth were fitted with a three-layer diffusion model to extract values for H+ production in the outer retina. Profiles were recorded in "normal" and damaged areas of the retina and were compared to profiles recorded in the retina of normal cats. Results: In normal animals the pH in the middle of the retina is lower than in the vitreous, and the profile shape indicated that there was clearance of H+ by both the retinal and choroidal circulations. Profiles in diabetic animals were classified as "normal" or damaged, based upon the H+ clearance in the inner retina. Profiles with a pH difference of less than 0.02 pH units between mid-retina and vitreous were considered damaged. "Normal" diabetic areas had an H+-clearance that was significantly greater than that seen in normal retinas. Damaged diabetic areas had an H+-clearance that was significantly lower than both normal retinas and "normal" diabetic areas. The average inner retinal [H+]O was significantly increased in diabetic cats (7.86 ± 1.9 x 10-8 M) compared to normal animals (7.04 ± 1.4 x 10-8M). The average production of H+ in the outer retina was greater in the "normal" areas (4.0 ± 3.1 x 10-9 mol/L/sec) than in the damaged areas (1.9± 1.4 x 10-9 mol/L/sec) of the diabetic retina. Conclusions: H+ distribution in the diabetic retina varies from "normal" to damaged areas. It appears that diabetes leads to acidification of the inner retina. In areas of capillary occlusion, H+ production by photoreceptors is also impaired.
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