Effects of leucine supplementation and resistance exercise on dexamethasone-induced muscle atrophy and insulin resistance in rats

Abstract

ObjectiveWe aimed to evaluate the effects of resistance exercise (RE) and leucine (LEU) supplementation on dexamethasone (DEXA)-induced muscle atrophy and insulin resistance. MethodsMale Wistar rats were randomly divided into DEXA (DEX), DEXA + RE (DEX-RE), DEXA + LEU (DEX-LEU), and DEXA + RE + LEU (DEX-RE-LEU) groups. Each group received DEXA 5 mg · kg−1 · d−1 for 7 d from drinking water and were pair-fed to the DEX group; LEU-supplemented groups received 0.135 g · kg−1 · d−1 through gavage for 7 d; the RE protocol was based on three sessions of squat-type exercise composed by three sets of 10 repetitions at 70% of maximal voluntary strength capacity. ResultsThe plantaris mass was significantly greater in both trained groups compared with the non-trained groups. Muscle cross-sectional area and fiber areas did not differ between groups. Both trained groups displayed significant increases in the number of intermediated fibers (IIa/IIx), a decreased number of fast-twitch fibers (IIb), an increased ratio of the proteins phosphoSer2448/total mammalian target of rapamycin and phosphoThr389/total 70-kDa ribosomal protein S6 kinase, and a decreased ratio of phosphoSer253/total Forkhead box protein-3a. Plasma glucose was significantly increased in the DEX-LEU group compared with the DEX group and RE significantly decreased hyperglycemia. The DEX-LEU group displayed decreased glucose transporter-4 translocation compared with the DEX group and RE restored this response. LEU supplementation worsened insulin sensitivity and did not attenuate muscle wasting in rats treated with DEXA. Conversely, RE modulated glucose homeostasis and fiber type transition in the plantaris muscle. ConclusionResistance exercise but not LEU supplementation promoted fiber type transition and improved glucose homeostasis in DEXA-treated rats.