Myocardial release of lactate, inosine and hypoxanthine during atrial pacing and exercise-induced angina.

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 less than 0.0005) and increased (24 +/- 13%) during exercise (p less than 0.05). The arterial values at rest (850 +/- 330 mumol/1) were unchanged during pacing and increased five-fold during exercise (4380 +/- 1860 mumol/1). The mean myocardial inosine extraction at rest (33 +/- 10%) was transformed to release values (-41 +/- 30%) during pacing (p less than 0.0005) as well as during exercise (-20 +/- 27%) (p less than 0.0005). The hypoxanthine extraction at rest (25 +/- 11%) decreased during pacing (-7.8 +/- 29%) (p less than 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.