Physiological Hypercortisolemia Increases Proteolysis, Glutamine, and Alanine Production

Physiological elevations of plasma cortisol levels, as are encountered in stress and severe trauma, were produced in six normal subjects by infusing them with 140 micrograms.kg-1.h-1 of hydrocortisone for 64 h. Amino acid kinetics were measured in the postabsorptive state using three 4-h infusions of L-[1-13C]leucine, L-[phenyl-2H5]-phenylalanine, L-[2-15N]glutamine, and L-[1-13C]alanine tracers 1) before, 2) at 12 h, and 3) at 60 h of cortisol infusion. Before and throughout the study, the subjects ate a normal diet of adequate protein (0.8 g.kg-1.day-1) and energy intake. The cortisol infusion raised plasma cortisol levels significantly from 10 +/- 1 to 32 +/- 4 micrograms/dl, leucine flux from 83 +/- 3 to 97 +/- 3 mumol.kg-1.h-1, and phenylalanine flux from 34 +/- 1 to 39 +/- 1 (SE) mumol.kg-1.h-1 after 12 h of cortisol infusion. These increases were maintained until the cortisol infusion was terminated (64 h). These nearly identical 15% increases in two different essential amino acid appearance rates are reflective of increased whole body protein breakdown. Glutamine flux rose from 325 +/- 28 to 453 +/- 28 mumol.kg-1.h-1 by 12 h of cortisol infusion and remained elevated at the same level at 64 h. The increase in flux was primarily due to a 55% increase in glutamine de novo synthesis. Alanine flux increased from 207 +/- 13 to 285 +/- 23 mumol.kg-1.h-1 with acute hypercortisolemia and increased further to 475 +/- 59 mumol.kg-1.h-1 at 60 h of cortisol infusion, a result primarily of increased alanine de novo synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)