Cardiac norepinephrine and intrinsic properties of isolated hypertrophied hearts from DOCA hypertensive rats

Alterations in cardiac norepinephrine (NE) levels often accompany cardiac hypertrophy. The present study addresses the question of whether such differences in endogenous NE might be responsible for hypertrophy-dependent differences in acutely measured mechanical and metabolic properties of isolated rat heart preparations. Hypertrophied hearts (H) of deoxycorticosterone acetate-hypertensive rats and normal hearts (N) of sham-treated rats were perfused in Langendorff fashion with atrial tissue removed. Assessment of ventricular NE after 3 to 5 min indicated that the concentration was lower in H than N but total content of the left ventricle was not significantly different. Assessment of ventricular NE after three hours suggested that some washout or depletion of NE occurred in H but not N. Mechanical and metabolic characteristics of the isovolumic preparation were determined. When compared to N, H had greater spontaneous ventricular beating rates and, when paced with field stimuli, higher systolic pressures, longer relaxation times and mechanical refractory periods, and greater oxygen consumption. When the latter was normalized for ventricular mass and systolic pressure, H utilized less oxygen/g/100 mmHg pressure than N. Elimination of the acute effects of endogenous NE by either blockade (propranolol) or depletion (reserpine) eliminated the difference in ventricular automaticity between H and N, but did not influence the other differences (or similarities) between H and N. We conclude that aside from changes in ventricular automaticity, hypertrophy-dependent alterations in cardiac mechanical and metabolic properties are not likely to be a result of differing acute influences of endogenous norepinephrine.