PHYSIOLOGICAL-RESPONSES, ORGAN DISTRIBUTION, AND CIRCULATION KINETICS IN ANESTHETIZED RATS AFTER HYPOVOLEMIC EXCHANGE-TRANSFUSION WITH TC-99M-LABELED LIPOSOME-ENCAPSULATED HEMOGLOBIN

Physiological responses and circulation properties of liposome-encapsulated hemoglobin (LEH) labeled with technetium-99m Tc-99m) were measured in rats after a 10% (170 mg/kg hemoglobin, 430 mg/kg phospholipid) or a 50% (450 mg/kg hemoglobin, 2.3 g/kg phospholipid) hypovolemic exchange transfusion (n = 5 per exchange group). Mean arterial pressure returned to baseline values (105 +/- 8 mmHg) by 90 min post-infusion for both groups. By 20 h, mean arterial pressure remained at baseline values for the 10% group, but dropped to 30 +/- 14 mmHg for the 50% group. For both groups, bradycardia was seen after the exchange period, but heart rate recovered by 30 min for the 10% group and by 90 min for the 50% group. The (99m) Tc-99m-LEH remained in circulation longer for the 50% group (18.2 h half-life) than for the 10% group (2.4 h half-life). Removal of Tc-99m-LEK from the bloodstream was via the liver and spleen. At 20 h, Tc-99m-LEH accumulation in these organs was greater for the 10% group (liver, 36.2 +/- 1.7%; spleen, 37.5 +/- 2.5%) than for the 50% group (liver, 17.0 +/- 1.4%; spleen, 17.1 +/- 1.4%). The data show that there is less clearance of Tc-99m-LEH from the bloodstream by the reticuloendothelial system after a 50% hypovolemic exchange transfusion, thus supporting the possible use of LEH as an oxygen-carrying resuscitative fluid in situations of severe blood loss.