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 viability and ventricular function, it is a major source of free radical substrates for endothelial xanthine oxidase. Correlation between myocardial ATP and ventricular function has been hindered by the impact of ATP catabolites on ventricular function during reperfusion.

OBJECTIVES

This 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 adenosine deaminase inhibitor, erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), and an adenine nucleoside transport blocker, p-nitrobenzylthioinosine (NBMPR), were used to specifically inhibit adenosine deamination and block nucleoside release, respectively. This pharmacological intervention results in site-specific entrapment of intramyocardial adenosine and inosine, generated during ischemia, and blocks degradation to free 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 slope of the relationship between stroke work and end-diastolic length (SW/EDL). Hearts were subjected to varying periods (30, 60, or 90 min) of global ischemia and 60 or 120 minutes of reperfusion. Two control groups for 30 and 60 minutes of ischemia (16 dogs) received only saline solution. Four treated groups (27 dogs) received saline containing 100 microM EHNA and 25 mM NBMPR prior to ischemia or only during reperfusion (n = 7). Myocardial biopsies were analyzed for ATP catabolites and NAD+.

RESULTS

Myocardial ATP and left ventricular function were severely depressed by 50% and 80% in the untreated controls, following 30 and 60 minutes of ischemia (37 degrees C), respectively. Ventricular dysfunction was inversely related to inosine levels in the myocardium at the end of the ischemic period. Administration of EHNA/NBMPR before ischemia or only during reperfusion resulted in significant accumulation of mainly adenosine or inosine, respectively. Entrapment of nucleosides was associated with complete recovery of ventricular function after 30 or 60 minutes of ischemia. Hearts subjected to 90 minutes of ischemia developed contracture.

CONCLUSIONS

Despite severely reduced ATP levels, ventricular function significantly recovered to preischemic values only in the EHNA/NBMPR-treated groups. Selective blockade of purine release during reperfusion is cardioprotective against post-ischemic reperfusion mediated injury. It is concluded that nucleoside transport plays an important role in regulation of endogenous adenosine and inosine affecting the degree of myocardial injury or protection from reperfusion mediated injury.