The catabolic effects of prolonged inactivity and acute hypercortisolemia are offset by dietary supplementation

We compared the anabolic stimulus provided by an essential amino acid and carbohydrate (AA/CHO) supplement to a mixed clinical meal during bed rest (BR) and episodic hypercortisolemia (∼24 μg·dl^-1). In the experimental (EXP; n = 7) and control (CON; n = 6) groups, femoral arteriovenous blood samples and vastus lateralis biopsy samples were obtained during a primed constant infusion of L-[ring-²H₅]phenylalanine and a 14-h infusion of hydrocortisone sodium succinate (60 μg·kg·h ^-1) before (pre-BR) and after (post-BR) 28 d of BR. Muscle protein kinetics were calculated during the postabsorptive state, for 2.5 h after ingestion of a meal and for 2.5 h after ingestion of an AA/CHO supplement (EXP) or placebo (CON). Postabsorptive net phenylalanine balance values were as follows: EXP, -35.14 ± 2.93, and CON, -32.60 ± 6.65 (pre-BR); and EXP, -32.91 ± 5.67, and CON, -30.43 ± 6.28 nmol phe·ml ^-1·100 ml leg volume^-1 (post-BR). After AA/CHO supplementation, net phenylalanine balance improved to 33.51 ± 8.06 (pre-BR) and 24.15 ± 11.4 nmol phe·ml^-1·100 ml leg volume^-1 (post-BR), but remained negative after the meal. Cumulative 5.5-h mixed muscle fractional synthetic rate was greater in the EXP group pre-BR (EXP, 0.108 ± 0.01, and CON, 0.073 ± 0.04%·h^-1) and post-BR (EXP, 0.111 ± 0.015, and CON, 0.05 ± 0.002%·h^-1). Unlike a typical clinical meal, AA/ CHO supplementation stimulated net muscle protein synthesis despite acute hypercortisolemia and prolonged inactivity.