Regional differences in adrenergic function within the left ventricle

Since ischemic heart disease (IHD) is inhomogeneous, the adrenergic response of the heart to ischemia or infarction could depend on the level of adrenergic supply within specific regions of the myocardium. Therefore we quantified myocardial norepinephrine (NE) content of tissue samples from 54 different sites in the left ventricle (LV) of four normal dogs using high-pressure liquid chromatography with electrochemical detection. Up to 10-fold differences in NE content occurred within a single LV. The NE distribution followed a consistent pattern, demonstrating a gradient from apex (avg minimum value of 162 ng/g of tissue) to base (avg maximum value 844 ng/g). No epicardial-to-endocardial gradient was present. In six other dogs a similar pattern was found in myocardial uptake of radioactively labeled NE and epinephrine assessed 2 min after intravenous injection. These results suggest that areas of high tissue NE represent regions rich in adrenergic supply and high in adrenergic activity, not merely NE stored in inactive pools. Samples from a human autopsy specimen suggest that these findings can be extrapolated to humans.