Contrasting effects of epinephrine on forearm hemodynamics and arterial plasma norepinephrine

Circulating catecholamines are widely considered to cause vasoconstriction. However, in the present study an intravenous infusion of 0.01 micrograms/kg/min epinephrine for 10 min in healthy men (n = 40, 20 to 40 years of age), which raised arterial plasma epinephrine from 100 +/- 13 to 231 +/- 22 pg/mL (mean +/- SE), increased forearm blood flow (FBF) from 2.79 +/- 0.17 to 3.45 +/- 0.25 mL/100 forearm tissue/min (P < .001), and decreased forearm vascular resistance (FVR) from 37.0 +/- 2.4 to 31.1 +/- 2.1 (arbitrary units). Further stepwise increase in epinephrine infusion rate progressively raised FBF (to a maximum 6.91 +/- 0.46) and decreased FVR (to minimum 16.7 +/- 2.0), and increased arterial plasma norepinephrine by more than 60% (P < .001). Thus, circulating epinephrine in concentrations that can be produced by mental stress has, despite its ability to increase sympathetic drive, a regional vasodilating effect in the human forearm.