To examine the regulation of aldose reductase (AR) activity by nitric oxide (NO) in human lens epithelial cells (HLEC), cultured rat lens, and normal and diabetic rat lens, we have incubated HLEC or cultured rat lenses with 1 mm of the NO donors S-nitroso-N-acetylpenicillamine (SNAP) or S-nitrosoglutathione (GSNO), and the AR activity and sorbitol content were measured. Non-diabetic and diabetic (treated with streptozotocin 65 mg kg(-1) body wt, i.p.) rats were injected with the nitric oxide synthase (NOS) inhibitor, L-NAME (50 mg kg(-1) body wt day(-1), x 10 days i.p.) or NOS substrate, L-arginine (200 mg kg(-1) body wt day(-1), x 10 days i.p.). In a separate group of rats, a nitroglycerin (NG)-patch that releases 200 ng min(-1) NO was applied to the dorsal neck region. After 10 days of treatment, the lenses were removed and their AR activity and sorbitol content were measured. Incubation of HLEC with SNAP or GSNO reduced AR activity. A similar reduction in AR activity and sorbitol accumulation was observed when diabetic and non-diabetic rat lenses were cultured in the presence of SNAP and GSNO. Total protein-SSG in diabetic lens was lower compared to normal lens. Treatment of diabetic and non-diabetic rats with L-NAME enhanced AR activity and sorbitol accumulation, whereas NG patch and L-arginine significantly decreased AR activity and sorbitol accumulation in diabetic lenses compared to non-diabetic. Increased S-glutathiolation of AR was observed in the presence of SNAP. These results suggest that decreased glutathiolation of cellular proteins in diabetic rat lens compared to non-diabetic lens is related to decreased NO availability in diabetic rats which would decrease GSNO. Restoring the NO levels in diabetic animals increases glutathiolation of cellular proteins, inhibits AR activity and prevents sorbitol accumulation. Exogenous delivery of NO may represent a potentially useful strategy for preventing or delaying diabetic cataractogenesis and the development of other diabetic complications.