Effect of increases in myocardial epinephrine content on epinephrine release from the dog heart

The effect of short-term (10 min) and prolonged (180 min) epinephrine (E) infusion (92.5 ng.kg-1.min-1) on E content of the myocardium and on the subsequent release of E from the heart during stimulation of the left stellate ganglion (4 and 10 Hz, 4 V, 2 ms, 1 min) was studied in anesthetized dogs. The E content in the free wall of the left ventricle significantly increased 1.7- and 4.2-fold following short-term and prolonged E infusion, respectively, compared with a control group infused with saline. Tissue norepinephrine (NE) content was not modified by E infusion. The plasma E concentration gradient across the heart indicated a significant release of E during electrical stimulation of the left stellate ganglion, which was related to the amount of E stored in the tissue (e.g., control, 126 +/- 60; 10-min infusion, 279 +/- 105; 180-min infusion, 1487 +/- 287 pg.mL-1; at 10 Hz). NE release from the heart also tended to increase with the amount of E stored in the myocardium and released upon electrical stimulation of the left stellate ganglion, although the difference did not reach statistical significance. These results provide further direct evidence that blood-borne E can be taken up and stored in sympathetic nerve endings and can be released as a cotransmitter with NE. Locally released E could favor NE release.