Susceptibility of equine erythrocytes to oxidant-induced rheologic alterations

To evaluate the rheologic responses of equine versus human RBC to oxidant stress induced by superoxide anions.

Equine blood samples were obtained from 8 healthy, 3- to 6-year-old various breed horses of either sex; human blood samples were obtained from 8 healthy adults.

Washed RBC were exposed to superoxide anions generated by the xanthine oxidase (XO)-hypoxanthine system (XO activity of 0 to 0.1 U/ml). Deformability of RBC was assessed by ektacytometry, and RBC aggregation was measured in autologous plasma or 3% solution of dextran 70 via a defined-shear photometric technique.

Equine RBC had XO dose-dependent increases in methemoglobin concentration that were greater by 60 to 110% than in human RBC and an enhanced tendency for echinocyte formation (ie, 40% echinocyte formation at highest activity of XO). Oxidant stress reduced deformability (ie, increased rigidity) for equine and human RBC with the effect more prominent for equine RBC. Equine RBC aggregation had a biphasic response with a significant increase in plasma and dextran 70 at low XO activities and inhibition at high activities; echinocytes were incorporated into equine, but not human, RBC aggregates.

Compared with human RBC, equine RBC are more sensitive to oxidant damage as judged by the extent of methemoglobin formation, alteration of aggregation, and reduction of cellular deformability. The high susceptibility of equine RBC to oxidant damage, and the resulting hemorheologic alterations, may have important consequences for tissue perfusion and cardiovascular adequacy in horses; they may be of particular relevance in physiologic or pathophysiologic changes associated with increased oxidant stress.