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 binding of nitric oxide (NO). We postulated that binding of NO by cross-linked hemoglobin (alpha alpha Hb) could also increase platelet deposition at sites of subintimal injury. METHODS AND RESULTS: Male Sprague-Dawley 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. 111In-labeled platelets were infused after endarterectomy, and platelet deposition was measured 20 minutes later. In control endarterectomized rats (n = 8), mean platelet deposition was 7.7 +/- 0.7 x 10(6)/mm2. Platelet deposition was significantly increased above controls in rats that received alpha alpha Hb (13.2 +/- 0.9 x 10(6)/mm2, P = .0004) and in rats infused with L-NMMA (13.9 +/- 1.0 x 10(6)/mm2, P = .0002). The increase was prevented by infusion of L-arginine (150 mg/kg) immediately after alpha alpha Hb or L-NMMA. To determine whether aspirin (ASA) blocked the increased deposition induced by alpha alpha Hb, rats received oral ASA (10 mg/kg) 18 hours before endarterectomy. Platelet deposition in animals receiving ASA alone was 6.4 +/- 0.9 x 10(6)/mm2 (n = 8). This was significantly increased to 10.8 +/- 0.8 x 10(6)/mm2 (P = .002) for the ASA-treated group that received alpha alpha Hb at the time of endarterectomy (n = 8). The prolonged bleeding times induced by ASA were unaffected by the infusion 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 induced by alpha alpha Hb can be prevented by administration of L-arginine but not by pretreatment with aspirin.