The differential cardioprotective effects of nucleoside transport inhibitor on moderate and deep hypothermic ischemia with cold cardioplegia

The differences in the cardioprotective effects of nucleoside transport inh ibitor (NTI) which is known to accumulate endogenous adenosine, on moderate and deep hypothermic ischemia, were examined. Using the Langendorff model, isolated, perfused rat hearts were arrested with cold cardioplegia and sub jected to 90 min of global ischemia followed by 40 min of reperfusion. The temperature during ischemia was maintained at either 10 degrees C (groups 1 and 2) or 25 degrees C (groups 3 and 4). In groups 2 and 4, NTI in the for m of R75231, 1 mg/l, was added to the cardioplegic solution. The intramyoca rdial adenosine triphosphate content at the end of ischemia was significant ly lower in the moderate hypothermia groups than in the deep hypothermia gr oups. In the moderate hypothermia groups, NTI significantly enhanced the ad enosine accumulation at the end of ischemia. Moreover. the recovery of both the contractile function and coronary flow rate in group 4 was superior to that in group 3, and was similar to those in groups 1 and 2. The addition of NTI to the cardioplegic solution generated a sufficient cardioprotective effect in moderate hypothermic ischemia, but not in deep hypothermic ische mia. The mechanism of this discrepancy is attributed to the differences in the levels of endogenous adenosine accumulated during ischemia.