Importance of elevated circulating hormones in modulating resistance exercise-induced protein kinase B signaling

Hormones and muscle contraction alter protein kinase B (Akt) signaling via distinct mechanisms. Therefore, the purpose of this study was to determine if physiologicallyelevated circulating hormones modulate resistance exercise (RE)-induced Akt signaling. Because RE invokes large increases in circulating growth hormone (GH), a known stimulus of translational efficiency, we hypothesized that high concentrations of circulating hormones would potentiate the signaling response. Seven healthy men (mean SD age: 27 ± 4 y; height: 177 ± 5 cm; body mass: 79.1 ± 13.6 kg; body fat: 16 ± 7%) performed two identical lower-body RE protocols (5 sets of 5 maximal repetitions of knee extensions) in a randomized order: one protocol was preceded by rest and the other was preceded by a bout of high-volume upper-body RE using short rest periods. Given the physiological and metabolic demands, one trial (lower-body exercise only) resulted in low circulating hormonal concentrations (LHC) and the other trial (lower-body and upper-body exercise) resulted in high circulating hormonal concentrations (HHC). Experimental trials were separated by 1–3 weeks. The HHC trial invoked significantly (p ≤ 0.05) greater GH and cortisol concentrations compared to the LHC trial. There were minimal differences between trials in insulin and insulin-like growth factor-I concentrations. Contrary to our hypothesis, 70-kDa ribosomal protein S6 kinase (p70 S6K) Thr 389 phosphorylation in the vastus lateralis was attenuated at 180 min post-RE during the HHC trial. RE did not affect Akt or glycogen synthase kinase-3β (GSK-3β) phosphorylation, nor were there differences between trials. Immediately post-RE, eukaryotic initiation factor 4E binding protein-1 (4E-BP1) phosphorylation declined and adenosine monophosphate-activated protein kinase (AMPK) phosphorylation increased; however, there were no differences between trials in these variables. In conclusion, p70 S6K Thr 389 phosphorylation was attenuated during the HHC trial despite dramatically greater (>2.5-fold) circulating GH concentrations; this was potentially due to cortisol-induced inhibition of p70 S6K Thr 389 phosphorylation.