Muscle protein synthesis and balance responsiveness to essential amino acids ingestion in the presence of elevated plasma free fatty acid concentrations

Context: Elevated plasma free fatty acid (FFA) concentrations are observed under various clinical circumstances and are associated with impaired glucose disposal in skeletal muscle. Objective: The aim of the study was to determine the effects of elevated plasma FFA concentrations onthe response of protein synthesisandbalance in muscle after essentialaminoacids (EAAs) ingestion. Design: Leg protein kinetics were determined in young healthy individuals before and after the ingestion of EAAs at 10 h after the initiation of either lipid (Liposyn/heparin+EAA) or saline (saline+EAA) infusions. Results: Plasma insulin responses where higher (P <0.05) in the Liposyn/heparin+EAA group than the saline+EAA group both before (14 ± 4 vs. 6 ± 1 μIU · ml^-1) and after (1038 ± 257 vs. 280 ± 87 μIU · ml^-1 · 210 min^-1) the EAA ingestion. After the EAA ingestion, the rates of both leg phenylalanine disappearance (Rd; nmol · min^-1 · kg lean leg mass^-1) and muscle proteins fractional synthesis (FSR;% · h^-1) increased (P<0.05) in both the Liposyn/heparin+EAAand saline+EAAgroups, but these changes were not different between the two groups (Rd, 102 ± 32 vs. 118 ± 34; FSR, 0.014 ± 0.005 vs. 0.018 ± 0.007; P > 0.05). Although the leg phenylalanine rate of appearance (Ra; nmol · min ^-1 · kg lean leg mass^-1) was lower (381 · 47 vs. 518 ± 40) and the balance was greater (-109±20 vs.-172±17) in the Liposyn/heparin+EAAgroup compared to the saline+EAA group before the EAA ingestion (P <0.05), the changes in both of these parameters were not different between groups after the EAA ingestion (P > 0.05). Conclusions: Elevated plasma FFA concentrations do not interfere with the response of muscle protein synthesis and balance to a bolus ingestion of EAAs.