End-systolic pressure-volume and MVO2-pressure-volume area relations of isolated rat hearts

We tested the utility of a standard isolated, crystalloid-perfused, isovolumic rat heart preparation for studying ventricular metabolism in terms of the myocardial oxygen consumption-pressure-volume area (MVO2-PVA) relations. The end-systolic pressure-volume relations (ESPVRs) determined between volumes of 0.15 and 0.65 ml were fit equally well by linear and nonlinear regression analysis within the data range but predicted widely differing volume-intercept (Vo) values. Linear regression analysis of the ESPVRs provided a mean slope (Ees) of 419 +/- 186 mmHg.g.ml-1 and Vo of 0 +/- 0.12 ml, respectively (n = 6). The MVO2-PVA relations were linear with a slope and MVO2 intercept of 1.30 +/- 0.31 x 10(-5) ml O2.mmHg-1.ml-1 and 0.38 +/- 0.09 x 10(-3) ml O2-beat-1.g-1, respectively. These MVO2-PVA parameters were not significantly different from those obtained when nonlinear regression analysis was applied to the ESPVR. Decreasing perfusate calcium concentration ([Ca2+]) (n = 7) resulted in a downward shift in the ESPVR, a decrease in the MVO2-PVA intercept (0.52 +/- 0.26 vs. 0.34 +/- 0.20 x 10(-3) ml O2.beat-1.g-1, P less than 0.01), and no significant change in the MVO2-PVA slope (1.33 +/- 0.47 vs. 1.57 +/- 0.69 x 10(-5) ml O2.mmHg-1.ml-1, NS). We conclude that this preparation may be a useful alternative to more expensive preparations for selected experiments in cardiac energetics.