Aldose Reductase Inhibition Fails to Prevent Retinopathy in Diabetic and Galactosemic Dogs

To investigate a possible role of excessive polyol production in the pathogenesis of diabetic retinopathy, 16 ALX-induced diabetic dogs and 20 experimentally galactosemic dogs were randomly assigned to 5 yr of treatment with either sorbinil, an aldose reductase inhibitor, or a placebo. The severity of hyperglycemia in sorbinil-treated and placebo groups was monitored throughout the 5-yr study by assay of glycosuria and nonenzymatically glycated plasma protein and HbA₁ needed in an effort to avoid confounding possible group differences in hyperglycemia severity with possible drug effects. Inhibition of polyol production by sorbinil was monitored in erythrocytes throughout the study and also in retina and other tissue obtained at autopsy. Trypsin digests of retinal vessels were compared after 60 mo of diabetes and after 42 and 60 mo of galactosemia. In diabetic dogs, development of retinopathy was not significantly influenced by a sorbinil dose (20 mg · kg⁻¹ · day⁻¹) sufficient to prevent elevation of sorbitol levels in retina and other tissue. Likewise, in dogs made experimentally galactosemic for 42–60 mo, administration of sorbinil (60–80 mg · kg⁻¹ day⁻¹) had no significant effect on the development of retinopathy notwithstanding prevention of 93–96% of the polyol elevation in retina and other tissue. Retinal capillary basement membrane was significantly thicker than normal in diabetic and in galactosemic dogs and was not significantly influenced by administration of sorbinil in either dog model. Thus, no evidence was found that the development of retinopathy is critically dependent on excessive polyol production or accumulation.