The reduction of muscle mass associated with aging might be the result of an altered response of muscle protein anabolism to oral amino acid intake, possibly due to age-related differences in the utilization of alimentary amino acids. Thus, we studied 4 elderly (E, age 68±1 yrs, BMI 25±1 kg/m2) and 4 young (Y, age 31±3 yrs, BMI 24±1 kg/m2) healthy volunteers in the post-absorptive state (basal) and during the oral administration of an amino acid mixture (OAA, E 3.2±0.1, Y 3.1±0.1 mg·kg-1-min-1) given as small drinks every 10 minutes for 3 hours. We measured leg muscle protein kinetics by the means of a three compartment model which requires L-[ring-2H5]phenylalanine infusion, blood samples from femoral artery and vein blood samples, and leg muscle biopsies. In addition, first pass splanchnic phenylalanine extraction was measured by adding L-[ring-13C6]phenylalanine to the drink. The oral amino acid mixture increased (p<0.02 vs. basal) phenylalanine transport into the muscle (E: basal 78±14, OAA 133±35; Y: basal 79±21, OAA 207±47; nmol·min-1·100ml of leg-1), and protein synthesis (E: basal 33±12, OAA 61±14; Y: basal 43±16, OAA 62±15; nmol·min-1·100ml of leg-1) with no significant differences between the two groups. Phenylalanine net balance (nmol·min-1·100ml of leg-1) became positive to the same extent in E (basal -24±8, OAA 10±2) and in Y (basal -19±7, OAA 15±4). However, phenylalanine first pass splanchnic extraction was higher in the elderly (48±5% vs. 30±5%, E vs. Y, p<0.05). In conclusion, oral amino acids stimulate muscle protein synthesis and net muscle protein anabolism in the elderly as in the young despite an age-related increase in first pass splanchnic uptake.
|Original language||English (US)|
|State||Published - Mar 20 1998|
ASJC Scopus subject areas
- Molecular Biology