Effects of epinephrine on human muscle glucose and protein metabolism

Systemic epinephrine infusion causes hypoaminoacidemia and inhibits whole body leucine flux (proteolysis) in humans. Its specific action on muscle protein is not known and is difficult to assess during systemic epinephrine infusions, which affect plasma insulin, amino acid, and free fatty acid concentrations. During a steady-state infusion of L-[ring-2,6-3H]phenylalanine, we examined the effect of locally infused epinephrine on the metabolism of protein and glucose in forearm muscle of 10 healthy human volunteers. During local epinephrine infusion, systemic concentrations of glucose, phenylalanine, insulin, and epinephrine were unchanged and lactate declined (P < 0.02). Compared with baseline, epinephrine induced significant increases in forearm blood flow (P < 0.01) and net lactate release (P < 0.001) and a decrease in glucose uptake (P < 0.01) at both 2 and 4 h. At 2 and 4 h phenylalanine release from muscle proteolysis was suppressed (P < 0.01), and at 4 h the net phenylalanine balance was less negative than baseline (P < 0.02), indicating an anticatabolic effect on muscle protein. We conclude that in human forearm muscle epinephrine, at physiological concentrations, has a catabolic effect on muscle glycogen but an anticatabolic action on muscle protein. The mechanism of this latter effect is not known.