Abstract

Atrial natriuretic peptide (ANP) has potent vasodilatory and natriuretic actions and may have therapeutic benefit in congestive heart failure (CHF). These benefits may be offset by a negative inotropic effect of ANP seen in isolated preparations. However, ANP’s integrated effect on left ventricular (LV) contraction and relaxation, independent of loading conditions, both under normal conditions and after CHF, is not known. We studied six conscious dogs, instrumented to measure LV and left atrial pressures and to determine LV volume from three dimensions. ANP produced significant (P < .05) decreases in LV end-systolic pressure (101.2 ± 11.8 versus 91.7 ± 11.2 mm Hg, P < .05) in normal dogs and in dogs with CHF (93.1 ± 6.4 versus 87.1 ± 4.4 mm Hg,P < .05). ANP also caused significant reductions of the slope of end-systolic pressure-end-systolic volume relation both before (7.0 ± 1.5 versus 6.3 ± 1.5 mm Hg/ml) and after CHF (4.8 ± 1.3 versus 4.4 ± 1.2 mm Hg/ml, P< .05). Both before and after CHF, ANP slowed LV relaxation at matched end-systolic pressure. Before CHF, steady-state stroke volume and peak LV filling rate (dV/dt_max) were reduced. However, after CHF, the fall in end-systolic pressure more than offset the load-independent LV depression, as stroke volume, the rate LV relaxation, and dV/dt_max were increased and minimum LV pressure reduced. ANP has negative effects on LV contractility and relaxation both before and after CHF. However, after CHF, afterload reduction with ANP overcomes its negative effects, resulting in net improvement of LV ejection and relaxation. Thus, the direct cardiodepressant effects of ANP should not limit its usefulness in CHF.