Epinephrine produces a prolonged elevation in metabolic rate in humans

Abstract

Background: Epinephrine increases the metabolic rate and contributes to the hypermetabolic state in severe illness. Objective: We sought to determine the effect of prolonged elevation of epinephrine on resting energy expenditure (REE). Design: Thirteen healthy men were placed on a well- defined diet for 5 d. Beginning on the morning of the second diet day, the subjects were infused for 24 h with saline, then for 23 h with epinephrine (0.18 nmol · kg-1 · min-1) to increase plasma epinephrine concentrations into the high physiologic range (4720 ± 340 pmol/L). REE and the respiratory quotient (RQ) were measured by indirect calorimetry in the postabsorptive state at the same time every morning. Results: Infusion of epinephrine significantly increased heart rate and systolic blood pressure, but the response was transient (values after 23 h of epinephrine infusion were not significantly different from those on the day saline was infused). Infusion of epinephrine significantly increased REE by 12% and increased the P(Q. These changes were apparent at the end of the 23-h infusion (REE: 97.5 ± 2.3 kJ · kg-1 · d-1 with saline infusion and 108.9 ± 2.3 kJ · kg-1 · d-1 with epinephrine infusion; RQ: 0.832 ± 0.012 with saline infusion and 0.879 ± 0.013 with epinephrine infusion). REE returned to baseline by 24 h after the epinephrine infusion ended, but the postabsorptive RQ remained modestly elevated. Infusion of epinephrine also produced a transient increase in urine flow and in urinary nitrogen excretion. This diuresis was compensated for by a drop in urine volume and nitrogen excretion after the epinephrine infusion was stopped. Conclusions: Epinephrine produced a prolonged increase in REE in healthy subjects. The fuel for this increase in REE, determined by the RQ, was from increased carbohydrate oxidation, not from that of fat or protein.