ENHANCEMENT OF PLATELET DEPOSITION BY CROSS-LINKED HEMOGLOBIN IN A RAT CAROTID ENDARTERECTOMY MODEL

Background Purified human cross-linked hemoglobin, which is now being used in clinical trials, increases mean arterial pressure through bind ing of nitric oxide (NO). We postulated that binding of NO by cross-li nked hemoglobin (alpha alpha Hb) could also increase platelet depositi on at sites of subintimal injury. Methods and Results Male Sprague-Daw ley rats were infused with alpha alpha Hb (0.88 g/kg, n=8) or with the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 30 mg/kg, n=7 ) before undergoing microsurgical carotid endarterectomy. In-111-label ed platelets were infused after endarterectomy, and platelet depositio n was measured 20 minutes later. In control endarterectomized rats (n= 8), mean platelet deposition was 7.7+/-0.7x10(6)/mm(2). Platelet depos ition was significantly increased above controls in rats that received alpha alpha Hb (13.2+/-0.9x10(6)/mm(2), P=.0004) and in rats infused with L-NMMA (13.9+/-1.0x10(6)/mm(2), P=.0002). The increase was preven ted by infusion of L-arginine (150 mg/kg) immediately after alpha alph a Hb or L-NMMA. To determine whether aspirin (ASA) blocked the increas ed deposition induced by alpha alpha Hb, rats received oral ASA (10 mg /kg) 18 hours before endarterectomy. Platelet deposition in animals re ceiving ASA alone was 6.4+/-0.9x10(6)/mm(2) (n=8). This was significan tly increased to 10.8+/-0.8x10(6)/mm(2) (P=.002) for the ASA-treated g roup that received alpha alpha Hb at the time of endarterectomy (n=8). The prolonged bleeding times induced by ASA were unaffected by the in fusion of alpha alpha Hb. Conclusions These data suggest that in a rat endarterectomy model, alpha alpha Hb increases platelet deposition at sites of subintimal injury by binding NO. Increased deposition induce d by alpha alpha Hb can be prevented by administration of L-aginine bu t not by pretreatment with aspirin.