The finding of the MRS 2578 present study that mTOR activity was reduced in the SDR muscles compared to the muscles of GH-administered SDR is consistent with those of previous reports. Sharp etal. reported that the phosphorylation of p70S6K is decreased in Ames dwarf mice with hypopituitarism due to Prop1 mutation. mTOR activity has been reported to be lower in other GH-deficient or GH receptor knockout mice than in normal mice. Also, from a point of view of Dex-induced mRNA expressions, mTOR activity appeared to increase in SDR muscles after the GH administration. BCAA has been reported to stimulate mTOR activity to attenuate the Dex-induced increases in Bnip3, atrogin-1 and MuRF1 mRNAs. In the present study, BCAA reduced Bnip3 and atrogin-1 mRNAs in SDR muscles after GH administration, not without GH administration. These findings suggest that mTOR might be a target of GH and that SDRs might exhibit some abnormalities in mTOR function. To exclude the possibility that themTORC1 dysfunction was due to the reduced amount of mTOR, we Pridinol Methanesulfonate measured mTOR protein levels in SDR and SD rats; however, we found that the mTOR contents were not different between the SDR and SD rat muscles. Moreover, the amounts of Raptor and G��L, both of which are componentsofmTORC1, were increased in the SDRs compared to SD rats in the present study. These results suggested that the reduced mTORC1 activity was not due to reductions in the quantities of these subunits. The protein levels of PI3Kand Akt, which are upstream of mTORC1, were not different between the SD and SDR muscles. The levels of p70S6K and 4E-BP1, which are downstream of mTORC1, in the SDR muscles were not reduced compared to the SD rat muscles. These results indicated that GH affected the function of mTORC1 but not the amounts of mTORC1 or the molecules upstream and downstream of mTORC1. In contrast to our hypothesis, BCAA did not exert a marked effect on muscle mass in GH-deficient rats, and GH was required for the BCAA��s action on muscle mass.Sancak etal. recently reported that amino acids stimulated the interaction of Rag proteins with mTORC1 and that this was necessary for the activation of the mTORC1 pathway by amino acids.