Because of their extensive wounds, burn patients are chronically exposed to inflammatory mediators. Thus, burn patients, by definition, already have

Mixed muscle protein fractional synthesis rate (FSR) and fractional breakdown rate (FBR) were examined after an isolated bout of either concentric or eccentric resistance exercise. Subjects were eight untrained volunteers (4 males, 4 females). Mixed muscle protein FSR and FBR were determined using primed constant infusions of [2H5]phenylalanine and 15N-phenylalanine, respectively. Subjects were studied in the fasted state on four occasions: at rest and 3, 24, and 48 h after a resistance exercise bout. Exercise was eight sets of eight concentric or eccentric repetitions at 80% of each subject's concentric 1 repetition maximum. There was no significant difference between contraction types for either FSR, FBR, or net balance (FSR minus FBR). Exercise resulted in significant increases above rest in muscle FSR at all times: 3 h = 112%, 24 h = 65%, 48 h = 34% (P < 0.01). Muscle FBR was also increased by exercise at 3 h (31%; P < 0.05) and 24 h (18%; P < 0.05) postexercise but returned to resting levels by 48 h. Muscle net balance was significantly increased after exercise at all time points [(in %/h) rest = -0.0573 +/- 0.003 (SE), 3 h = -0.0298 +/- 0.003, 24 h = -0.0413 +/- 0.004, and 48 h = -0.0440 +/- 0.005], and was significantly different from zero at all time points (P < 0.05). There was also a significant correlation between FSR and FBR (r = 0.88, P < 0.001). We conclude that exercise resulted in an increase in muscle net protein balance that persisted for up to 48 h after the exercise bout and was unrelated to the type of muscle contraction performed.

The catecholamine-mediated hypermetabolic response to severe burns causes increased energy expenditure and muscle-protein catabolism. We hypothesized that blockade of β-adrenergic stimulation with propranolol would decrease resting energy expenditure and muscle catabolism in patients with severe burns. Twenty-five children with acute and severe burns (more than 40 percent of total body-surface area) were studied in a randomized trial. Thirteen received oral propranolol for at least two weeks, and 12 served as untreated controls. The dose of propranolol was adjusted to decrease the resting heart rate by 20 percent from each patient's base-line value. Resting energy expenditure and skeletal-muscle protein kinetics were measured before and after two weeks of beta-blockade (or no therapy, in controls). Body composition was measured serially throughout hospitalization. Patients in the control group and the propranolol group were similar with respect to age, weight, percentage of total body-surface area burned, percentage of body-surface area with third-degree burns, and length of time from injury to metabolic study. Beta-blockade decreased the heart rates and resting energy expenditure in the propranolol group, both as compared with the base-line values (P<0.001 and P=0.01, respectively) and as compared with the values in the control group (P=0.03 and P=0.001, respectively). The net muscle-protein balance increased by 82 percent over base-line values in the propranolol group (P=0.002), whereas it decreased by 27 percent in the control group (P not significant). The fat-free mass, as measured by whole-body potassium scanning, did not change substantially in the propranolol group, whereas it decreased by a mean (±SE) of 9±2 percent in the control group (P=0.003). In children with burns, treatment with propranolol during hospitalization attenuates hypermetabolism and reverses muscle-protein catabolism.

We recently demonstrated that muscle protein synthesis was stimulated to a similar extent in young and elderly subjects during a 3-h amino acid infusion. We sought to determine if a more practical bolus oral ingestion would also produce a similar response in young (34 ± 4 yr) and elderly (67 ± 2 yr) individuals. Arteriovenous blood samples and muscle biopsies were obtained during a primed (2.0 μmol/kg) constant infusion (0.05 μmol·kg^-1·min^-1) of l-[ ring-²H₅]phenylalanine. Muscle protein kinetics and mixed muscle fractional synthetic rate (FSR) were calculated before and after the bolus ingestion of 15 g of essential amino acids (EAA) in young ( n = 6) and elderly ( n = 7) subjects. After EAA ingestion, the rate of increase in femoral artery phenylalanine concentration was slower in elderly subjects but remained elevated for a longer period. EAA ingestion increased FSR in both age groups by ∼0.04%/h ( P < 0.05). However, muscle intracellular (IC) phenylalanine concentration remained significantly higher in elderly subjects at the completion of the study (young: 115.6 ± 5.4 nmol/ml; elderly: 150.2 ± 19.4 nmol/ml). Correction for the free phenylalanine retained in the muscle IC pool resulted in similar net phenylalanine uptake values in the young and elderly. EAA ingestion increased plasma insulin levels in young (6.1 ± 1.2 to 21.3 ± 3.1 μIU/ml) but not in elderly subjects (3.0 ± 0.6 to 4.3 ± 0.4 μIU/ml). Despite differences in the time course of plasma phenylalanine kinetics and a greater residual IC phenylalanine concentration, amino acid supplementation acutely stimulated muscle protein synthesis in both young and elderly individuals.

This study was designed to determine the response of muscle protein to the bolus ingestion of a drink containing essential amino acids and carbohydrate after resistance exercise. Six subjects (3 men, 3 women) randomly consumed a treatment drink (6 g essential amino acids, 35 g sucrose) or a flavored placebo drink 1 h or 3 h after a bout of resistance exercise on two separate occasions. We used a three-compartment model for determination of leg muscle protein kinetics. The model involves the infusion of ring-²H₅-phenylalanine, femoral arterial and venous blood sampling, and muscle biopsies. Phenylalanine net balance and muscle protein synthesis were significantly increased above the predrink and corresponding placebo value ( P < 0.05) when the drink was taken 1 or 3 h after exercise but not when the placebo was ingested at 1 or 3 h. The response to the amino acid-carbohydrate drink produced similar anabolic responses at 1 and 3 h. Muscle protein breakdown did not change in response to the drink. We conclude that essential amino acids with carbohydrates stimulate muscle protein anabolism by increasing muscle protein synthesis when ingested 1 or 3 h after resistance exercise.