Elevation of Plasma Epinephrine Concentrations Inhibits Proteolysis and Leucine Oxidation in Man via @i-Adrenergic Mechanisms

The role of elevated plasma epinephrine concentrations in the regulation of plasma leucine kinetics and the contribution of,8-receptors were assessed in man. Epinephrine (50 ng/kg per min) was infused either alone or combined with propranolol (f,-blockade) into groups of six subjects fasted overnight; leu-cine flux, oxidation, and net plasma leucine forearm balance were determined during 180 min. Constant plasma insulin and glucagon concentrations were maintained in all studies by in-fusing somatostatin combined with insulin and glucagon re-placements. Plasma leucine concentrations decreased from baseline during epinephrine infusion by 27±5 gmol/liter (P < 0.02) due to a 22±6 % decrease in leucine flux (P < 0.05 vs. controls receiving saline) and to an increase in the metabolic clearance rate of leucine (P < 0.02). Leucine oxidation de-creased by 36±8 % (P < 0.01 vs. controls). fl-Blockade abol-ished the effect of epinephrine on leucine flux and oxidation. Net forearm release of leucine increased during epinephrine (P < 0.01), suggesting increased muscle proteolysis; the fall of total body leucine flux was therefore due to diminished prote-olysis in nonmuscle tissues, such as splanchnic organs. Non-oxidative leucine disappearance as a parameter of protein syn-thesis was not significantly influenced by epinephrine. Plasma glucose and FFA concentrations increased via f,-adrenergic mechanisms (P < 0.001). The results suggest that elevation of plasma epinephrine concentrations similar to those observed in severe stress results in redistribution of body proteins and exerts a whole body protein-sparing effect; this may counteract catabolic effects of other hormones during severe stress