Constitutive nitric oxide synthase is associated with retinal vascular permeability in early diabetic rats

Aims/hypothesis. We investigated the association between vascular permeability and constitutive nitric oxide synthase in rats with diabetes for a short duration (2 weeks). Methods. Retinal vascular permeability was evaluated in rats with diabetes induced by streptozotocin using vitreous fluorophotometry and a small animal adapter. We carried out in situ hybridization and semi-quantitative reverse transcription-polymerase chain reaction to study the expression of endogenous constitutive nitric oxide synthase mRNA in diabetic retinas. We also examined changes in the protein expression of constitutive nitric oxide synthase in diabetic retinas using immunohistochemistry and Western blotting. Results. Retinal vascular permeability was significantly higher in diabetic rats (median, 1.09 arbitrary unit) compared with control rats (median, 0.69 arbitrary unit) (p < 0.05). The expression of both neuronal nitric oxide synthase (NOS) and endothelial nitric oxide synthase mRNA was higher in diabetic retinas than in the retinas of control rats as determined by in situ hybridization and reverse transcription-polymerase chain reaction. Immunohistochemistry and Western blotting also showed that neuronal nitric oxide synthase increased in diabetic retinas. The immunohistochemistry of endothelial nitric oxide synthase indicated that non-vessel tissues increased in diabetic retinas while retinal vessels weakened. Western blotting showed that the amount of endothelial nitric oxide synthase increased. Conclusion/interpretation. These results suggest that increases in both constitutive NOSs (nNOS and eNOS) could be associated with retinal vascular permeability and that NOS is associated with clinical vascular dysfunction in the early stages of diabetes.