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 mug/kg body weig ht), which resulted in no changes in circulating insulin in the time interv al studied, induced a decrease in the incorporation of C-14-leucine to C-14 -skeletal muscle protein. No changes were observed in relation to muscle pr otein degradation (either measured in vivo following isotope preloading or in vitro as tyrosine released into the incubation medium) and gene expressi on associated with the different proteolytic systems (cathepsin B, m-calpai n and ubiquitin-proteasome system). The effects of leptin on amino acid inc orporation into muscle protein do not seem to be direct because incubation of isolated EDL muscles in the presence of 10 mug/ml of leptin did not modi fy either the protein incorporation or the oxidation of C-14-leucine. It ma y, therefore, be suggested that leptin is able to influence protein synthes is in skeletal muscle through the action of an unknown mediator. (J. Nutr. Biochem. 11:431-435, 2000) (C) Elsevier Science Inc. 2000 All rights reserv ed.