Diabetes-induced vascular dysfunction in the retina: role of endothelins

Aims/hypothesis. Vasoactive factors like endothelins, by virtue of the microvascular regulation as well as by other effects, possibly play important parts in the pathogenesis of diabetic retinal microangiopathy. We investigated retinal vascular dysfunction in streptozotocin-induced diabetes and its relation with endothelins in short- and long-term diabetes. Methods. Diabetic rats with or without an endothelin receptor antagonist (bosentan) treatment were investigated after 1 month and 6 months of follow-up. Retinal blood flow was measured and compared with age- and sex-matched non-diabetic control animals. Retinal tissues were analysed for endothelin-l. endothelin-3, endothelin A and endotherin B mRNA. Distribution of endothelin-l and endothelin-3 was investigated by immunocytochemistry and that for endothelin receptors by ligand binding and autoradiography. Results. Diabetic animals showed hyperglycaemia, glycosuria, elevated glycated haemoglobin values and reduced body weight gain. Retinal blood flow showed an increased resistivity index, an indicator of vasoconstriction, after I month of diabetes which was prevented by treatment with bosentan. This functional change in diabetes was eliminated after 6 months of followup. The retina from the diabetic animals showed increased mRNA expression for endothelin-l, endothelin-3 and endothelin A after one month. In addition, endothelin B mRNA expression was increased after 6 months. Furthermore, endothelin-l and endothelin-3 immunoreactivity and endothelin receptor concentrations were increased in the retina of diabetic rats. Conclusion/interpretation. The results from this study indicate that the endothelin system is of importance in mediating retinal changes in diabetes although mechanisms of the endothelin system alteration as well as their effects might vary depending on the duration of diabetes.