EFFECTS OF NUCLEOSIDE TRANSPORT INHIBITION ON LONG-TERM EXVIVO PRESERVATION OF CANINE HEARTS

The effect of nucleoside transport inhibition on 24-hour preservation of canine hearts was studied in 36 hearts arrested either with a cold hyperkalemic cardioplegic solution without (group I) or with supplementation of a specific nucleoside transport inhibitor (R75231, 1 mg/L) (groups II and III. Tle hearts were excised and stored for 24 hours at 0.5-degrees-C. Then they were reperfused for 3 hours with use of a closed perfusion system primed with normal blood (groups I and II) or with blood supplemented with the same nucleoside transport inhibitor (0.32 mg/L) (group III). Serial biopsy specimens for determination of myocardial purines were taken. Creatine kinase and heat-stable lactate dehydrogenase release from the myocardium were examined during reperfusion. Recovery of function was studied during reperfusion by measurement of isometric contraction in, a fluid-filled intraventricular balloon. After 24 hours of preservation, without the use of the drug, myocardial inosine and hypoxanthine accumulated to, respectively, 4.05 +/- 1.18 and 0.28 +/- 0.08 mumol/gm dry weight. In the drug-treated groups (II and III pooled), significantly less inosine and hypoxanthine accumulated (1.68 +/- 0.33 and 0.05 +/- 0.02 mumol/gm dry weight, respectively) (p < 0.05 versus group I). Upon reperfusion, intramyocardial adenosine was lost in the control hearts and maintained in the drug-treated hearts. Hypoxanthine accumulated significantly (p < 0.05) during reperfusion in group I (1.08 +/- 0.43 versus 0.16 +/- 0.13 in group II and 0.03 +/- 0.03 mumol/gm dry weight in group III). The rate of creatine kinase and heat-stable lactate dehydrogenase release was significantly lower (p < 0.05) in group III (that is, pretreatment and posttreatment with the drug) than in the control group. Functional recovery of hearts in group III was superior to that in group II (p < 0.05), while hearts in group I showed no recovery at all. We conclude that nucleoside transport inhibition improves long-term preservation of the heart and that the mechanism of this protection may be related to an increase in endogenous adenosine and reduction of myocardial hypoxanthine content.