Properties of free and occupied androgen receptor in rat skeletal muscle cytosol: effect of testosterone.

Our aim was to investigate the effect of a single testosterone (T) injection on the androgen receptor (AR) in rat skeletal muscle (SM) cytosol. The properties of AR were studied in order to establish the protocol for differential determination of free and hormone-occupied AR in SM cytosols from non-hormone-deficient animals. Using the developed ligand-exchange protocol, we demonstrated that injection of T (1 mg/kg) caused alternating changes of the total AR binding. The binding minimum (23% of the control) was measured 1 h after the injection. It was followed by pronounced and lasting elevation of the AR binding. In the control cytosols, AR complexes constituted approximately 25% of the total receptor content. Changes of their relative content immediately after T administration were consistent with rapid nuclear translocation of the AR. Inhibition of protein synthesis by cycloheximide (CHI) injection demonstrated that delayed and lasting increase of the AR binding after T injection partially depended on the stimulated protein synthesis. Altogether, the obtained evidence supports the assumption that the AR mediates elevation of its own gene expression in SM upon administration of T.

Influence of physical exercise on polyamine synthesis in the rat skeletal muscle.

BACKGROUND: Physical exercise and testosterone administration result in a series of adaptive anabolic phenomena in the skeletal muscle. The role of polyamines in these processes has been poorly explored. DESIGN: We measured the activities of polyamine-synthesising enzymes, ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) and polyamine content in skeletal muscle of male rats exposed to endurance or resistance exercise, or a single testosterone treatment. Soleus muscle (consisting mainly of slow-twitching oxidative fibres-STO) and extensor digitorum longus (mainly fast-twitching glycolytic muscle fibres-FTG) were analysed for polyamine content by HPLC, and ODC and SAMDC activity. RESULTS: Both endurance and resistance exercise induced a threefold increase in endogenous testosterone production. Two hours after exercise, ODC was increased in STO fibres, returning to baseline after 24 h; in FTG fibres the increase was less prominent. An increase in SAMDC activity occurred in a more sustained manner, with its peak 8 h after exercise. Polyamines were subsequently accumulated in both skeletal muscle fibres, with a rise in putrescine concentration after 2 h, and a fall corresponding to conversion of putrescine to spermidine and spermine by SAMDC. Single dose of 17alpha-methyltestosterone resulted in a similar increase in polyamine-synthesising enzyme activities and polyamine concentrations in the skeletal muscle. CONCLUSION: Polyamine accumulation in the skeletal muscle after physical exercise is likely to occur secondary to testosterone production. Polyamines are apparently involved in the oxidative, but not in glycolytic processes related to muscle adaptation to exercise.