Cardiac microdialysis in isolated rat hearts: interstitial purine metabolites during ischemia

Cardiac microdialysis is a recently developed technique that allows intramyocardial interstitial fluid (ISF) to be sampled via the implantation and perfusion of a small, hollow dialysis fiber within the myocardium. The purpose of this paper is to describe initial studies using cardiac microdialysis in the isolated perfused heart. Microdialysis probes, constructed in the laboratory, were implanted in the left ventricular myocardium of isolated perfused rat hearts and perfused at 0.5 microliter/min with Krebs-Henseleit buffer. The effluent dialysate, assayed for adenosine, inosine, hypoxanthine, xanthine, and uric acid, was used as an index of intramyocardial levels of these purine metabolites. All metabolites were elevated initially after implantation, declined rapidly in the first 45 min, and were then stable for the next 90 min. Based on in vitro percent recovery data, baseline dialysate concentrations were extrapolated to yield estimates of intramyocardial ISF (in microM) 0.47 adenosine, 0.85 inosine, 0.29 hypoxanthine, 0.49 xanthine, and 8.6 uric acid. During global zero-flow ischemia (37 degrees C), dialysate levels of all purine metabolites were elevated, with inosine being the predominant compound. Pretreatment of the hearts with 50 microM erythro-9-(2-hydroxy-3-nonyl)adenine, an adenosine deaminase inhibitor, markedly enhanced ISF adenosine accumulation and attenuated the accumulation of inosine, hypoxanthine, and xanthine. The simplicity and versatility of cardiac microdialysis in the isolated perfused heart suggest that this technique may be a valuable adjunct to the many studies performed using this preparation.