Susceptibility of equine erythrocytes to oxidant-induced theologic alterations

Objective-To evaluate the theologic responses of equine versus human RBC to oxidant stress induced by superoxide anions. Sample Population-Equine blood samples were obtained from 8 healthy, 3- to B-year-old various breed horses of either sex; human blood samples were obt ained from 8 healthy adults. Procedure-Washed RBC were exposed to superoxide anions generated by the xan thine oxidase (XO)hypoxanthine system (XO activity of 0 to 0.1 U/ml). Defor mability of RBC was assessed by ektacytometry, and RBC aggregation was meas ured in autologous plasma or 3% solution of dextran 70 via a defined-shear photometric technique. Results-Equine RBC had XO dose-dependent increases in methemoglobin concent ration that were greater by 60 to 110% than in human RBC and an enhanced te ndency for echinocyte formation (ie, 40% echinocyte formation at highest ac tivity of XO). Oxidant stress reduced deformability (ie, increased rigidity ) for equine and human RBC with the effect more prominent for equine RBC. E quine RBC aggregation had a biphasic response with a significant increase i n plasma and dextran 70 at low XO activities and inhibition at high activit ies; echinocytes were incorporated into equine, but not human, RBC aggregat es. Conclusions and Clinical Relevance-Compared with human RBC, equine RBC are more sensitive to oxidant damage as judged by the extent of methemoglobin f ormation, alteration of aggregation, and reduction of cellular deformabilit y. The high susceptibility of equine RBC to oxidant damage, and the resulti ng hemorheologic alterations, may have important consequences for tissue pe rfusion and cardiovascular adequacy in horses; they may be of particular re levance in physiologic or pathophysiologic changes associated with increase d oxidant stress.