Reduction of oxygen delivery during post-ischemic reperfusion protects the isolated guinea pig heart.

Objective: To further characterise the influence of oxygen delivery during early reperfusion (first 5 min) in the isolated guinea pig heart, three modes of coronary reperfusion were chosen, differing with respect to reperfusion flow and arterial PO2.

Methods: Isolated working guinea pig hearts underwent ischemia and reperfusion (15 min each). Reperfusion was at constant pressure (Group 1, 60 mmHg, n = 7) or at constant flow (Group 2, 5 ml/min, n = 7) with a PO2 of 600 mmHg. Group 3 (n = 8) was reperfused at 5 ml/min with a PO2 of 300 mmHg for 5 min and a PO2 of 600 mmHg thereafter. Lactate release and oxygen consumption were determined during reperfusion. Glutathione release served to assess myocardial oxidative stress.

Results: After ischemia, hearts in Group 1 (mean coronary flow 14.4 +/- 1.1 ml/min during the first 5 min of reperfusion) performed external heart work at 31 +/- 2% of the pre-ischemic level. Performance in Group 2 recovered to 50 +/- 3% and in Group 3 to 68 +/- 3%. Myocardial oxygen consumption during early reperfusion (2nd min) was lowest in Group 3 (1.9 micromol/min) and highest in Group 1 (8.3 micromol/min). No difference in lactate release was observed. Release of glutathione during the first 5 min of reperfusion was 43.8 +/- 7.9 nmol in Group 1, but only 3.6 +/- 0.7 in Group 2 (p < 0.05).

Conclusions: In isolated guinea pig hearts, controlled oxygen delivery during post-ischemic reperfusion by both, reduction of coronary flow and PO2, improves recovery of pump function. The effect is accompanied by less oxidative stress, as indicated by lowered rates of glutathione release.