932-87 Non-Mechanical Energy Expenditure is Preserved During the Transition from Compensatory Hypertrophy to Failure of the Left Ventricle in Dahl Salt-Sensitive Rats

Dahl salt-sensitive rats fed with a high-salt diet (8% NaCI) progressively develop concentric LV hypertrophy (LVH, 11 weeks), which is followed by LV dilatation with pulmonary congestion (CHF, 18 weeks). To clarify modulation in cardiac energetics during the transition from LVH to CHF, we measured LV pressure-volume area (PVA) and myocardial oxygen consumption (MVO2) in isolated, isovolumically contracting hearts from this animal model. Hearts were coronary-perfused with Tyrode's solution at 37°C and were paced at 3.33 Hz (perfusate Ca2+: 1 mM or 2 mM). The perfusion pressure was kept constant at 140 mmHg throughout the experiment. PO2in the perfusate and in the coronary effluent were continuously monitored with oxygen electrodes. The end-systolic pressure-volume relation (ESPVR) determined during the stepwise changes of the LV volume were fit by a binomial regression analysis, which provided a slope (Ees) and a volume intercept (V0). Linear regression analysis of the MVO2-PVA relation determined a slope (A) and a MVO2intercept (B).Ca2+EesV0ABmMmmHg.g.ml–1mlxl0–2mlO2.mmHg–1·ml–1x 10–2mlO2.beat–1.g–1LVH11352±l251.97±1.233.27±1.451.80±0.14In=5)21853±110*1.59±0.982.10±0.872.27±0.20*CHF1458±98†7.33±2.00†4.05±1151.18±0.06†(n=4)2649±148*,†5.60±1.56†3.47±0.861.52±0.l5*,†mean±SEM.*p<0.05 vs. Ca2+ 1 mM, paired t-test†p<0.05 vs. LVH, unpaired t-testDuring the transition from LVH to CHF, Ees was decreased and VO was increased These changes in inotropic state and in ventricular shape were associated with a decrease in the MVO2intercept, while the slope of MVO2-PVA relation was not altered. In conclusion, we confirm that the myocardial contractility and the ventricular remodeling occur during the transition from LVH to CHF in this animal model. Despite these changes, the oxygen cost of contractility does not change and the total energy cost of the remodeling myocardium might be preserved by reducing the expenditure for the non-mechanical process which includes the E-C couplin