Epinephrine transiently increases amino acid disappearance to lower amino acid levels in humans

Background: Infusion of epinephrine decreases plasma amino acid concentrati ons. However, the mechanism by which this decrement occurs is not well char acterized. Methods: Epinephrine was infused (40 ng/kg/min) for 2 hours into eight normal healthy adults. The essential amino acid tracers L-[1-C-13]le ucine and L-[phenyl-H-2(5)] phenylalanine were infused before and during th e epinephrine infusion and blood samples obtained to determine amino acid r ates of appearance and disappearance from the time course of change in amin o acid concentration and tracer enrichments. Results: Epinephrine infusion decreased plasma leucine and phenylalanine concentrations over a period of 30 to 90 minutes after the start of the epinephrine infusion. Epinephrine i nfusion induced an immediate decrement in tracer enrichments. These changes defined sharp increases in both rate of appearance and rate of disappearan ce. By 30 minutes of epinephrine infusion, the rate of amino acid appearanc e from proteolysis had returned to baseline, but the rate of amino acid dis appearance remained elevated for 90 minutes before returning to baseline. I t was the protracted increase in amino acid disappearance that was responsi ble for the lowering of plasma amino acid concentrations. After this acute response, rates of amino acid appearance and disappearance returned to norm al whereas plasma amino acid levels remained suppressed. Conclusions: Epine phrine transiently affects both rates of amino acid appearance and disappea rance, with the net effect being increased in amino acid disappearance. How ever, epinephrine lowers amino acid concentrations beyond the period that i t affects kinetics. These results suggest that the effect of epinephrine on amino acid metabolism is not detrimental and that epinephrine allows amino acid metabolism to proceed normally but at lower concentrations of amino a cids.