Local epinephrine release in the rabbit myocardial interstitium in vivo

Although several investigations have suggested cardiac epinephrine (Epi) release, local Epi release in the myocardial interstitium in vivo has not been measured. Using cardiac microdialysis in the rabbit, we measured dialysate Epi and norepinephrine (NE) concentrations as indices of myocardial interstitial Epi and NE levels, respectively. Exocytotic release induced by local administration of KCl (100 mM) through the dialysis probe increased Epi to 24.2 +/- 13.2 pg/ml from a control value of 3.2 +/- 3.6 pg/ml (P < 0.01, n = 6). Non-exocytotic release induced by the local administration of tyramine (10 microg/ml) also increased Epi to 34.6 +/- 15.3 pg/ml (p < 0.05 from control, n = 6). We conclude that Epi can be released via both exocytotic and non-exocytotic release mechanisms from the heart.