End-systolic pressure-volume and MV̇O₂-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 (MV̇O₂-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 (V(o)) values. Linear regression analysis of the ESPVRs provided a mean slope (E(es)) of 419 ± 186 mmHg·g·ml^-1 and V(o) of 0 ± 0.12 ml, respectively (n = 6). The MV̇O₂-PVA relations were linear with a slope and MV̇O₂ 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 MV̇O₂-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 MV̇O₂-PVA intercept (0.52 ± 0.26 vs. 0.34 ± 0.20 x 10^-3 ml O₂·beat^-1·g^-1, P < 0.01), and no significant change in the MV̇O₂-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.