Elevation of plasma free fatty acids attenuates basal muscle protein synthesis but not the anabolic action of essential amino acids

Abstract

This study sought to determine whether elevation of plasma free fatty acids attenuates muscle protein synthesis in the basal state and following essential amino acids ingestion. Eight subjects (4F, 4M; 31 ± 2 yr; 70 ± 5 kg; mean ± SE) ingested ~ 7 g of essential amino acids (control group), while another five (2F, 3M; 30 ± 3 yr; 85 ± 8 kg) ingested the same amino acids during the course of Liposyn + heparin infusion to increase plasma free fatty acid concentrations (Liposyn group). Primed constant L-[ring-2H5]phenylalanine infusion and vastus lateralis muscle biopsies were used to determine fractional synthetic rate (FSR) of skeletal muscle protein synthesis. Basal FSR was determined during a 3-hour period after seven hours of Liposyn infusion, followed by the determination of FSR for the 3.5-hour period immediately after the amino acids ingestion. The control subjects underwent similar experimental procedures with the exception of the Liposyn + heparin infusion. Basal FSR was lower in the Liposyn group than the control group (Liposyn: 0.031 ± 0.005 %/h; control: 0.048 ± 0.005 %/h: P < 0.05). However, the change in the FSR following the amino acids ingestion was not different between the two groups (Liposyn: 0.017 ± 0.005 %/h; control: 0.015 ± 0.008 %/h: P > 0.05). These results suggest that the basal muscle protein synthesis is attenuated following elevation of plasma free fatty acids, but muscle protein synthesis still remains responsive to the anabolic action of ingested essential amino acids.