Cardiac uptake and secretion of catecholamines during adrenergic stimulation in vivo

Cardiac uptake and secretion of epinephrine (Epi) and norepinephrine (NE) were studied at rest and during the response to systemic vasodilation with dipyridamole in conscious dogs. Chronically implanted catheters in the left atrium and anterior great coronary vein allowed simultaneous measurement of arterial and venous levels of NE and Epi across the segment of myocardium perfused by the left anterior descending coronary artery. Arterial Epi was greater than coronary venous Epi both at rest and during vasodilation. Arterial and venous NE levels were similar at rest. However, arterial NE rose more than venous NE during dipyridamole. Thus, there was net cardiac uptake of NE as well as Epi when systemic plasma catecholamine levels increased in response to vasodilation. Fractional extraction [(A-V)/A X 100)] of Epi by the heart was 50% and was not affected over a sevenfold range of coronary artery flow. Fractional extraction of NE (5-15%) was significantly lower than that of Epi, most likely due to cardiac secretion of NE. Cardiac NE secretion was estimated to increase fourfold during dipyridamole. Thus, cardiac tissue of trained dogs avidly takes up circulating catecholamines. Despite an apparent increase of NE secretion by the heart during the systemic adrenergic response to dipyridamole, the heart remained an organ of net NE uptake and therefore did not contribute to the observed increase of systemic NE levels.