Short-term effects of leptin on skeletal muscle protein metabolism in the rat

We have examined the short-term effects of leptin on protein metabolism in the rat. Indeed, an intravenous leptin administration (100 μg/kg body weight), which resulted in no changes in circulating insulin in the time interval studied, induced a decrease in the incorporation of 14C-leucine to 14C-skeletal muscle protein. No changes were observed in relation to muscle protein degradation (either measured in vivo following isotope preloading or in vitro as tyrosine released into the incubation medium) and gene expression associated with the different proteolytic systems (cathepsin B, m-calpain and ubiquitin-proteasome system). The effects of leptin on amino acid incorporation into muscle protein do not seem to be direct because incubation of isolated EDL muscles in the presence of 10 μg/ml of leptin did not modify either the protein incorporation or the oxidation of 14C-leucine. It may, therefore, be suggested that leptin is able to influence protein synthesis in skeletal muscle through the action of an unknown mediator.