Résumé :
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We have analysed the effect of physiological doses of androgens administrated after orchidectomy on the skeletal muscle of male rats, as well as the relationships between muscle performance, hypertrophy as well as the Akt/mTOR signalling pathway which is involved in the control of anabolic and catabolic muscle metabolism. We studied the soleus muscles from intact adult rats (SHAM), orchidectomized rats treated during 3 months with vehicle (ORX), nandrolone (NAN) or dehydrotestosterone (DHT). Our results indicate that NAN and DHT treatments maintained highly androgen dependent tissues (levator ani muscle, seminal vesicle, prostate, bone) in a normal state after orchidectomy. We found that there is a trend for absolute and relative (normalized to muscle weight) maximal tetanic isometric forces and fatigue resistance to be reduced by orchidectomy. Whereas absolute and relative maximal tetanic isometric forces (respectively + 69% and + 49%) and fatigue resistance (+35%) in NAN rats were increased when compared to ORX rats. In contrast, DHT treatment did not improve muscle function. Interestingly, muscle weights, cross sectional area of muscle fibres, relative number of muscle fibres expressing slow myosin heavy chain and citrate synthase activity were identical in NAN, DHT, ORX and SHAM rats. Furthermore, phosphorylation levels of downstream targets of the Akt/mTOR signalling pathway, Akt, ribosomal protein S6 and eukaryotic initiation factor 4E-binding protein 1 were also similar in NAN, DHT, ORX and SHAM rats. In conclusion, physiological doses of androgens are sufficient to prevent virtually all the effects of orchidectomy in rats. Interestingly, their beneficial effects on muscle performance are not related to muscle fibre growth or activation of Akt/mTOR signalling pathway in the context of androgen deprivation.
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