SEPARATION BETWEEN ISCHEMIC AND REPERFUSION INJURY BY SITE-SPECIFIC ENTRAPMENT OF ENDOGENOUS ADENOSINE AND INOSINE USING NBMPR AND EHNA

Background. Although myocardial ATP is essential for myocardial viabil ity and ventricular function, it is a major source of free radical sub strates for endothelial xanthine oxidase. Correlation between myocardi al ATP and ventricular function has been hindered by the impact of ATP catabolites on ventricular function during reperfusion. Objectives: T his work results from four separate experiments assessing the role of nucleoside efflux in reperfusion mediated injury to determine the dual role of myocardial ATP in postischemic ventricular dysfunction. An ad enosine deaminase inhibitor, erythro-9-(2-hydroxy-3-nonyl)adenine (EHN A), and an adenine nucleoside transport blocker, p-nitrobenzylthioinos ine (NBMPR), were used to specifically inhibit adenosine deamination a nd block nucleoside release, respectively. This pharmacological interv ention results in site-specific entrapment of intramyocardial adenosin e and inosine, generated during ischemia, and blocks degradation to fr ee radical substrates during reperfusion, thereby limiting the impact of reperfusion mediated injury. Methods: Forty-three anesthetized dogs were instrumented to monitor left ventricular performance from the sl ope of the relationship between stroke work and end-diastolic length ( SW/EDL). Hearts were subjected to varying periods (30,60, or 90 min) o f global ischemia and 60 or 120 minutes of reperfusion. Two control gr oups for 30 and 60 minutes of ischemia (16 dogs) received only saline solution. Four treated groups (27 dogs) received saline containing 100 muM EHNA and 25 mM NBMPR prior to ischemia or only during reperfusion (n = 7). Myocardial biopsies were analyzed for ATP catabolites and NA D+. Results: Myocardial ATP and left ventricular function were severel y depressed by 50% and 80% in the untreated controls, following 30 and 60 minutes of ischemia (37-degrees-C), respectively. Ventricular dysf unction was inversely related to inosine levels in the myocardium at t he end of the ischemic period. Administration of EHNA/NBMPR before isc hemia or only during reperfusion resulted in significant accumulation of mainly adenosine or inosine, respectively. Entrapment of nucleoside s was associated with complete recovery of ventricular function after 30 or 60 minutes of ischemia. Hearts subjected to 90 minutes of ischem ia developed contracture. Conclusions: Despite severely reduced ATP le vels, ventricular function significantly recovered to preischemic valu es only in the EHNA/NBMPR-treated groups. Selective blockade of purine release during reperfusion is cardioprotective against postischemic r eperfusion mediated injury. ft is concluded that nucleoside transport plays an important role in regulation of endogenous adenosine and inos ine affecting the degree of myocardial injury or protection from reper fusion mediated injury.