o-raffinose cross-linked hemoglobin improves the hemostatic defect associated with anemia and thrombocytopenia in rabbits

Several different preparations of crosslinked hemoglobin (CLHb) are being e valuated for their efficacy and safety as red cell substitutes in a variety of preclinical and clinical settings. Because CLHb is known to sequester n itric oxide (NO) and inhibit NO-mediated processes, we hypothesized that CL Hb would have a hemostatic effect by enhancing platelet reactivity, inducin g vasoconstriction, or both. Infusion of o-raffinose CLHb shortened the pro longed microvascular bleeding time and decreased blood loss from ear incisi ons in rabbits rendered anemic and thrombocytopenic, Moreover, this hemosta tic effect persisted for at least 24 hours after infusion. Phenylephrine in duced a degree of vasoconstriction similar to that induced by CLHb but did not shorten the bleeding time or decrease blood loss, suggesting that vasoc onstriction alone cannot account for the hemostatic effect of CLHb, There w as no evidence of CLHb-induced activation of coagulation in vivo, since inf usion of CLHb did not increase circulating levels of thrombin-antithrombin complex. In vitro, CLHb abolished the inhibitory effect of the NO donor 3-m orpholinosydnonimine on platelet aggregation and enhanced the aggregation o f stimulated but not resting platelets, This potentiating effect was not at tenuated by the addition of superoxide dismutase or catalase. To evaluate t he potential arterial thrombogenicity of CLHb, a model of carotid artery th rombosis was developed in rabbits without thrombocytopenia or anemia. Compa red with albumin infusion, CLHb infusion shortened the time to complete car otid occlusion, These data suggest that CLHb may shift the thromboregulator y balance toward clot formation, resulting in decreased bleeding in anemic and thrombocytopenic rabbits and possibly increasing arterial thrombogenici ty in normal rabbits. (C) 2000 by The American Society of Hematology.