Norepinephrine Release and Left Ventricular Pressure in the Isolated Heart

In an isolated dog heart, perfused with blood from an anesthetized donor, left ventricular performance was observed during periods in which the left ventricle either contracted isovolumically or was allowed to eject saline. Heart rate and left ventricular end-diastolic pressure were comparable in both. Ventricular performance, as judged by peak systolic ventricular pressure, declined relatively rapidly during isovolumic loading when initial systolic pressures were higher. The efflux of norepinephrine (NE) from the heart was directly related to the systolic pressure of the left ventricle both when the NE concentration of the perfusing blood was normal and when it was reduced to undetectable levels by dialysis. Changes in heart rate did not affect NE efflux nor was NE efflux increased by isobaric loading when the ventricle was distended in diastole without developing pressure in systole. A pathway is described whereby ventricles developing a high systolic pressure may be depleted of NE.