[Studies on optimal reperfusate temperature following hypothermic ischemic arrest in the isolated rat hearts]

This study was undertaken to evaluate the optimal reperfusate temperature during early reperfusion period for 10 min of non-working mode followed by 20 min of normothermic working mode in the isolated hypothermic ischemic (20 degrees C, 60 min) rat hearts. The reperfusate temperature was selected 20 degrees C (group A) and 30 degrees C (group B) as a hypothermic reperfusion, and 37 degrees C (group C) for normothermia. Functional recovery of aortic flow rate (AFR), heart rate (HR), peak systolic pressure (PSP), coronary flow (CF), and rate pressure product was compared among three groups as well as myocardial biochemical (adenosine triphosphate (ATP), creatine phosphate (CP)) and ultrastructural change. During non-working reperfusion, HR and CF showed significant positive correlation to reperfusate temperature. At the end of 10 min of non-working reperfusion, myocardial creatine phosphate (CP) significantly increased in all groups beyond the pre-ischemic level, however CP in the group A and B was significantly better compared to that in the group C. And myocardial ATP was better recovered near to the pre-ischemic level in the hypothermic groups compared to the group C without significant recovery, being significantly different between group A and C. The integrity of mitochondrial ultrastructure was also well maintained in group A compared to group C. At the end of normothermic reperfusion in the working mode for 20 min, percent recovery of AFR was 85.1% (B), 73.3% (A) and 70.3% (C), and percent recovery of rate pressure product was 92.5% (A), 89.1% (B) and 78.6% (C) with significant difference between the hypothermic and the normothermic groups. PSP, CF and HR recovered without significant difference among three groups. Myocardial ATP and CP declined significantly during 20 min of working reperfusion to the same level as those of three groups. CP only in group C was significantly lower than pre-ischemic level, although ATP in all groups at the end of reperfusion was significantly lower than the pre-ischemic level. These data suggest that hypothermic (20 degrees C, 30 degrees C) reperfusion seemed to provide better functional and metabolic recovery in association with better preservation of ultrastructure through improving energy production-utilization balance in early reperfusion period. And rapid warming in the reperfusion period may deteriorate or delay the myocardial recovery from ischemic isult.