Effect of Tempol on Diabetes-Induced Decreases in Retinal Blood Flow in the Mouse

Purpose: The purpose was to investigate the effect of the superoxide dismutase mimetic tempol on decreases in retinal blood flow that are found in diabetic mice. Materials and Methods: Streptozotocin (STZ) was injected into male C57BL/6 mice to induce hyperglycemia. One week following the STZ injection, subsets of the mice were given drinking water with or without 1 mM tempol for an additional three weeks. At the end of the four-week protocol, microvascular parameters were quantified via intravital microscopy, and included measurements of retinal diameters, red blood cell (RBC) velocities, blood flow rates, and wall shear rates. Results: Diabetes induced similar to 40-45% decreases in retinal blood flow rate (p < 0.001) four weeks following injection of STZ. The decrease in blood flow rate occurred with decreases in microvascular diameters (D) and RBC velocities (V). The average percentage decrease in velocity was greater than the percentage decrease in diameter and, therefore, wall shear rates (= 8 V/D) were similar to 25% lower in the diabetics than in the non-diabetics (p < 0.05). A three-week administration of tempol in the STZ mice allowed significantly higher blood flow rates than in the untreated STZ mice, with RBC velocities improved by the antioxidant (p < 0.05 on the venular side). However, tempol provided only moderate (and not statistically significant) improvements in wall shear rates. Conclusions: The antioxidant tempol provides partial improvements in retinal microvascular hemodynamics early in the progression of STZ-induced diabetes in mice.