Permeability-surface-area products (PA) for sucrose at the blood-retinal barrier (BRB) were determined with quantitative in vivo techniques and compared in control rats, rats fed a 50% galactosemic diet, and rats fed a diet containing both galactose and the aldose reductase inhibitor sorbinil. The mean PA ± SE for controls was 0.656 × 10−5 ± 0.13 ml · g1 · s1 and increased by ∼500% in galactose-fed animals to 3.13 × 10−8 ± 0.32 ml · g1 · s1 . Animals fed both galactose and sorbinil showed no significant difference from control animals (P > .05), with a PA of 0.91 × 10−5 ± 0.22 ml · g1 · s1. No breach in the BRB to horseradish peroxidase was detected in any of the groups. These results demonstrate an increased permeability at the BRB to small molecules in galactosemic rats that is prevented by an aldose reductase inhibitor. This suggests that the retinal capillary basement membrane thickening seen in galactosemic rats is associated with an increased permeability of the BRB and that aldose reductase is implicated in its pathogenesis.

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