Abstract
The aim of the present study was to compare the oxygen (O2) cost of left ventricular (LV) contractility (equivalent maximal elastance; eEmax, an index for contractility) for dobutamine (a β-receptor stimulant) with that for calcium (Ca2+) in normal rat hearts and to assess the O2 cost of LV eEmax for dobutamine in Ca2+ overload-induced failing rat hearts. The mean O2 cost of LV eEmax (×10−4 μl O2·beat−1·mmHg−1·ml·g−2) for Ca2+ was 1.30±0.37 in 12 normal hearts, and for dobutamine it was 1.26±0.30 in eight different normal hearts. In the same five normal hearts, the mean O2 cost of LV eEmax for dobutamine was 1.15±0.27, and for Ca2+ it was 0.81±0.36. These mean values showed no significant differences between Ca2+ and dobutamine. In five Ca2+ overload-induced failing hearts, the mean O2 cost of LV eEmax for Ca2+ could not be assessed, but the mean O2 cost of LV eEmax for dobutamine was 1.04±0.40. This mean value for dobutamine did not differ significantly from those (see above 1.26±0.30 or 1.15±0.27) in the normal hearts. The present results indicate, in terms of the coupling of mechanical work and energetics of the heart, that the total Ca2+ handling VO2 in excitation-contraction coupling against unit LV contractility change for dobutamine in the contractile failing hearts does not differ from that in the normal hearts. This suggests that in the Ca2+ overload-induced contractile failing hearts, there were no changes in the sensitivity of the contractile machinery for Ca2+, in the Ca2+/ATP in the total Ca2+ handling, and in the ATP/VO2 in the mitochondria.
