Physiologic Responses of Cross-Linked Hemoglobin in Endotoxin-Treated Rats

Abstract

Purified human cross-linked hemoglobin (ααHb) as well as recombinant human hemoglobin is undergoing clinical trials in the setting of acute blood loss and perioperative hemodilution. We have previously demonstrated that in rabbits with circulating plasma Hb, such as ααHb, infusion of endotoxin (LPS) impairs myocardial contractility which results in hypotension, tissue hypoperfusion and increased mortality. The untoward cardiovascular effects occurring after the combined infusion of LPS and ααHb in this model are similar to those reported for other agents that inhibit nitric oxide (NO) availability. To determine if the deleterious effects of ααHb and LPS were species specific, we performed similar studies in rats. Anesthetized Sprague-Dawley rats received LPS (4 mg/kg or 40 mg/kg) alone or in combination with ααHb (0.7 g/kg). Mean arterial blood pressures (MAP) increased in the group that received ααHb alone (105±8 to 120±7 mm Hg, p=0.2) and a decrease was noted in the groups that received low dose LPS (4 mg/kg, p=0.5) and high dose LPS (40 mg/kg, p=0.016). MAP in rats treated with the LPS at either dose combined with ααHb remained unchanged. Levels of urine nitrite, which was measured as a surrogate marker for plasma NO, were significantly decreased at 2 hr in groups that received the combination of ααHb and LPS at 4 mg/kg (p=0.022) and 40 mg/kg (p=0.003). No significant decrease was observed in animals treated only with ααHb (p=0.21) or LPS (4 mg/kg; p=0.78 and 40 mg/kg; p=0.65). Survival was evaluated during 72 hr in animals that were infused with high dose LPS (40 mg/kg) alone or in combination with ααHb and then allowed to recover. The survival of rats treated with LPS alone or the combination was 29% at the end of 24 hr and was 100% for rats receiving only aaHb. The data suggest that the toxicity of ααHb appears to be a species specific phenomenon.