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Nowadays the problem of muscle recovery from disuse atrophy (caused by gravitational unloading or hypokinesia) is urgent for rehabilitation and space medicine. Therefore the aim of the study was to analyse intracellular signaling pathways which are responsible for protein synthesis (anabolic markers - ribosomal kinases p-p70s6K and p-p90RSK) and protein breakdown (markers of proteolysis - E3 ubiquitin ligases MuRF-1 and MAFbx/atrogin-1) in rat soleus muscle. The experiment was carried out in accordance with the rules of biomedical ethics certified by the Russian Academy of Sciences Committee on Bioethics. Thirty-five male Wistar rats weighing 190-210 g were randomly assigned to the 5 groups (n=7 for each group): ground control (C), hindlimb suspension for 14 days (14HS), hindlimb suspension for 14 days followed by 3-day recovery (14HS+3R), 7-day recovery (14HS+7R) and 14-day recovery (14HS+14R). Gravitational unloading was simulated by hindlimb suspension of rats (Morey-Holton, Globus, 2002). Animals were anaesthetised with 10% avertin (8ml/kg). Ribosomal kinases content was established by gel electrophoreses with immunoblotting. Expression of mRNA of E3 ligases was assessed by RT PCR. Values were expressed as means ± S.E., compared by 2-way ANOVA. The unloading resulted in 30% decrease of p-p70s6K content but increase of expression of E3 ligases (p<0.05) vs. (C). At the same time content of p-p90RSK was 50% higher compared to (C). Content of E3 ligases mRNA was increased after 3 days of recovery (p<0.05). The content of p-p90RSK and p-p70s6K was reduced by the 7-th day of recovery vs. 14HS group. Expression of MuRF-1 and MAFbx/atrogin-1 returned to control level after 7 days of recovery. By the 14-th day of recovery period content of both ribosomal kinases retuned to control levels. Thus, activity of anabolic signaling pathways demonstrated irregular dynamics during recovery period following gravitational unloading. At the same time increased activity of the ubiquitin-proteaosome pathway contributes to degradation of structural and functional proteins in rat soleus. These data can explain low rates of protein restoration in soleus muscle at early stages of recovery from disuse atrophy. [ABSTRACT FROM AUTHOR]