Hyperglycemia mediates endothelial cell dysfunction through a number of potential mechanisms that could result in the decrease of retinal blood flow early in diabetes. The aim of this study was to explore the role of endothelin receptor A (ET(A)) in the early decrease of retinal blood flow in diabetic mice. Diabetes was induced by streptozotocin, then ∼1 wk later the mice were administered drinking water with or without the ET(A) receptor antagonist atrasentan (7.5mg/kg/day) for the following 3 weeks. Non-diabetic age-matched mice with or without atrasentan were included as controls. For each mouse, measurements of retinal vascular diameters and red blood cell (RBC) velocities were obtained via intravital microscopy for the 5-7 feed arterioles (and draining venules) extending out of (and into) the optic disk, and from these values, flow rates and wall shear rates were calculated. Additionally, the number of retinal capillaries was counted by fluorescent immunostaining of platelet-endothelial cell adhesion molecule-1 (PECAM-1). Diabetes induced statistically significant decreases in RBC velocity, flow rate, and wall shear rate, with these alterations partially inhibited by atrasentan. No changes were observed in PECAM-1 expression among groups. The changes induced by diabetes, and the attenuation provided by atrasentan, were greater in the smaller retinal arterioles. In summary, ET(A) appears to play a role in the early decreases in retinal blood flow in a mouse model of diabetes.
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