Effects of sympathectomy on heart size and function in aortic-constricted rats

Effects of chemical sympathectomy with 6-hydroxydopamine on left ventricular mass, norepinephrine content, and performance in aortic-constricted and sham-constricted rats were examined. Sympathectomy did not affect mean arterial pressure but it led to lower final body weights in aortic-constricted rats. Of the hypertensive aortic-constricted rats, those that had also been sympathectomized showed greater increases in left ventricular weight-to-body weight, right ventricular weight-to-body weight, and lung weight-to-body weight ratios. Left ventricular norepinephrine content was depressed by either sympathectomy or aortic constriction and was severely depleted by their combination. Sympathectomy had no effect on maximal cardiac output or left ventricular stroke work during rapid saline infusion. In aortic-constricted rats, however, it lowered heart rate during the infusion and increased left ventricular end-diastolic pressure at peak stroke work. This evidence suggests that elimination of the adrenergic nervous system's chronotropic influence promotes greater left ventricular filling, and the resultant increase in preload may importantly contribute to the stimulation of cardiac hypertrophy.