Background: Since there is considerable evidence that leukocytes contribute to tissue injury during ischemia and reperfusion, the present study was designed to: (1) determine whether reperfusion in vivo with leukopenic blood affords protection in a model of reversible hypothermic ischemia, (2) determine the duration of any protection, (3) characterize the relation between protection and duration of leukopenic perfusion, and (4) assess the effect of leukopenic reperfusion on myocardial glutathione content.
Methods and results: Rat hearts (n = 12 per group) were excised, immediately arrested with an infusion (2 minutes at 4 degrees C) of St Thomas' cardioplegic solution, and subjected to 4 hours of global ischemia (4 degrees C). The hearts were then transplanted (1 hour additional ischemic time) into the abdomen of saline-treated or leukopenic recipients. Leukopenia was induced by intraperitoneal administration of mustine hydrochloride (2 mg/kg) 3 days before study. Hearts were then reperfused in situ for 1, 4, or 24 hours, after which they were excised and either processed for histological examination (n = 4 per group) or perfused aerobically with bicarbonate buffer for 20 minutes, and contractile function was assessed (n = 8 per group); at the end of this period, some hearts (n = 5 per group) were taken for metabolite analysis. After 1 hour of reperfusion, contractile function in the saline-treated control group was significantly reduced compared with aerobic controls that had not been subjected to ischemia (left ventricular developed pressure [LVDP], 108 +/- 5 vs 126 +/- 3 mm Hg at an end-diastolic pressure of 12 mm Hg; P < .05). However, in the hearts with leukopenic reperfusion, LVDP (119 +/- 2 mm Hg) was similar to that of aerobic controls. This benefit, however, was lost after 4 and 24 hours of reperfusion. Cardiac compliance was not influenced by leukopenia. Coronary flow recovered significantly better in the leukopenic hearts during the first 4 hours of reperfusion (11.8 +/- 0.5 vs 9.3 +/- 0.4 mL/min at 1 hour and 10.0 +/- 0.5 vs 8.0 +/- 0.4 mL/min at 4 hours, P < .05), but again this benefit was lost after 24 hours of reperfusion. The myocardial contents of reduced and oxidized glutathione after 1, 4, and 24 hours of reperfusion were similar in saline-treated and leukocyte-depleted animals. In additional studies, the period of ischemia was extended to 8 hours, and similar results were obtained, with improved recovery of contractile function and coronary flow but not cardiac compliance in the leukopenic group after 1 hour of reperfusion. In further studies with the isolated blood-perfused rat heart, ischemia was induced for 8 hours; this was followed first by reperfusion for 0, 2, 10, 30, or 60 minutes with leukopenic blood and then by perfusion with blood from saline-treated animals for 60, 58, 50, 30, or 0 minutes, respectively. Reperfusion with leukopenic blood for 2 minutes did not improve the recovery of LVDP (106 +/- 7 vs 96 +/- 10 mm Hg in controls; NS) but when continued for 10, 30, or 60 minutes resulted in significant improvements (137 +/- 5, 138 +/- 3, and 150 +/- 10 mm Hg, respectively). Although coronary flow tended to be greater in all leukopenic groups, by the end of 60 minutes of reperfusion, only those hearts reperfused with leukopenic blood for the entire reperfusion period showed a significant improvement (3.4 +/- 0.3 vs 2.5 +/- 0.2 mL/min in controls; P < .05). Histological studies revealed no intravascular aggregation of leukocytes or features of myocyte necrosis.
Conclusions: Reperfusion with leukopenic blood accelerated the rate of recovery of cardiac function after reversible myocardial injury but did not lead to a sustained increase in the eventual extent of recovery. Reperfusion with leukopenic blood for the first 10 minutes of reflow is sufficient to obtain this benefit.