Epinephrine release from the heart during left stellate ganglion stimulation in dogs

Plasma epinephrine (E) and norepinephrine (NE) concentrations were measured (radioenzymatic assay) in blood samples simultaneously withdrawn from the aorta (Ao) and coronary sinus (CS) on 10 anesthetized dogs immediately before and during a 1-min period of electrical stimulation of the left stellate ganglion (4 V, 4 ms, 10 Hz). Heart rate and systolic blood pressure significantly increased in response to electrical stimulation (152 +/- 8 to 180 +/- 15 beats/min and 128 +/- 12 to 149 +/- 12 mmHg, mean +/- SE; P less than 0.05). Plasma NE concentrations were not significantly different in the Ao and the CS (432 +/- 110 and 319 +/- 67 pg/ml) before the stimulation, whereas a net removal of E was present across the myocardium (Ao, 172 +/- 61; CS, 71 +/- 22 pg/ml). A large NE spillover in the CS was observed during the stimulation (Ao, 1,555 +/- 513; CS, 10,583 +/- 3,753 pg/ml). A significant output of E from the myocardium was also present (Ao, 165 +/- 42; CS, 291 +/- 74 pg/ml) during the stimulation. Determination of NE and E concentrations by high-performance liquid chromatography in five of the dogs confirmed the observation made with the radioenzymatic assay, i.e., a significant uptake (66%) of blood-borne E was present across the myocardium in the control situation (Ao, 320 +/- 97; CS, 110 +/- 23 pg/ml), whereas plasma E concentrations in the CS (280 +/- 61 pg/ml) were 1.5 times the values found in Ao (184 +/- 56 pg/ml) under electrical stimulation. These observations give further support to the hypothesis that endogenous tissue E can act as a cotransmitter of sympathetic fibers.