Elevations in free fatty acids (FFAs) impair glucose uptake in skeletal muscle. However, there is no information pertaining to the effect of elevated lipids on either basal protein synthesis or the anabolic effects of leucine and insulin-like growth factor (IGF)-I. In chronically catheterized conscious rats, the short-term elevation of plasma FFAs by the 5-h infusion of heparin + intralipid decreased muscle protein synthesis by 25% under basal conditions. Lipid infusion was associated with a redistribution of eukaryotic initiation factor (eIF)-4E from the active eIF4E-eIF4G complex to the inactive eIF4E-4EBP1 complex. This shift was associated with a decreased phosphorylation of eIF4G but not 4EBP1. Lipid infusion did not alter either the total amount or phosphorylation state of mTOR, TSC2, S6K1 or the ribosomal protein S6 under basal conditions. In control rats, oral leucine increased muscle protein synthesis. This anabolic response was not impaired by lipid infusion and no defects in signal transduction pathways regulating translation initiation were detected. In rats receiving IGF-I, lipid infusion attenuated the normal redistribution of eIF4E from the active to inactive complex, and largely prevented the increased phosphorylation of 4EBP1, eIF4G, S6K1 and S6. This IGF-I resistance was associated with enhanced Ser307 phosphorylation of insulin receptor substate (IRS)-1. These data indicate that short-term elevation of plasma FFAs impairs basal protein synthesis in muscle by altering eIF4E availability and this defect may be related to impaired phosphorylation of eIF4G, not 4E-BP1. Moreover, hyperlipidemia impairs IGF-I action but does not produce a leucine resistance in skeletal muscle.