Epinephrine Transiently Increases Amino Acid Disappearance to Lower Amino Acid Levels in Humans

Abstract

Background: Infusion of epinephrine decreases plasma amino acid concentrations. However, the mechanism by which this decrement occurs is not well characterized. Methods: Epinephrine was infused (40 ng/kg/min) for 2 hours into eight normal healthy adults. The essential amino acid tracers L-[1-¹³C]leucine and L-[phenyl-²H₅]phenylalanine were infused before and during the epinephrine infusion and blood samples obtained to determine amino acid rates of appearance and disappearance from the time course of change in amino 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 infusion induced an immediate decrement in tracer enrichments. These changes defined sharp increases in both rate of appearance and rate of disappearance. By 30 minutes of epinephrine infusion, the rate of amino acid appearance from proteolysis had returned to baseline, but the rate of amino acid disappearance remained elevated for 90 minutes before returning to baseline. It was the protracted increase in amino acid disappearance that was responsible for the lowering of plasma amino acid concentrations. After this acute response, rates of amino acid appearance and disappearance returned to normal whereas plasma amino acid levels remained suppressed. Conclusions: Epinephrine transiently affects both rates of amino acid appearance and disappearance, with the net effect being increased in amino acid disappearance. However, epinephrine lowers amino acid concentrations beyond the period that it 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 acids. ( Journal of Parenteral and Enteral Nutrition 23:279-287, 1999)