The coronary venous efflux of lactate, inosine and hypoxanthine during pacing-induced angina has been compared with myocardial extraction of the catabolites during exercise-induced angina. Inosine and hypoxanthine were analyzed by enzyme assay after separation by column chromatography.
Myocardial lactate extraction at rest (15 ± 9%, mean ± SD) was converted to production levels (-34 ± 26%) during pacing-induced angina (p lt; 0.0005) and increased (24 ± 13%) during exercise (p lt; 0.05). The arterial values at rest (850 ± 330 Amol/1) were unchanged during pacing and increased fivefold during exercise (4380 ± 1860μumol/l). The mean myocardial inosine extraction at rest (33 ± 10%) was transformed to release values (-41 ± 30%) during pacing (p lt; 0.0005) as well as during exercise (-20 + 27%) (p lt; 0.0005). The hypoxanthine extraction at rest (25 ± 11%) decreased during pacing (-7.8 29%) (p lt; 0.0025) and exercise (10 ± 25%) (NS). The slight increase of arterial inosine and hypoxanthine values was not significant. Myocardially produced lactate, a sensitive marker of pacing-induced ischemia, was obscured by elevated arterial concentrations during exercise. However, inosine significantly correlated with lactate during pacing, and was useful in detecting ischemic myocardial energy deficiency during exercise-induced angina.