Abstract des Autors

Changes in the number of androgen receptors in rat gastrocnemius muscle following muscle contraction caused by electrical stimulation were investigated. The gastrocnemius muscle of one leg, which was selected at random for each rat, was stimulated with needle type electrodes, for 2 s at 10 V and 100 Hz, with 5-s intervals. One set consisted of ten such stimuli, followed by 5-min rest. 3 sets every 2 d caused a statistically significant increase in muscle mass. Stimulation over 4 wks induced an increase in the area of the cross-section of the muscle fibres to about 30 more than that of control muscles, though the total muscle fibre numbers were slightly reduced. Electromechanical properties supported the development of the muscle by stimulation, because the maximal isometric tetanic force and peak twitch force markedly increased in the stimulated muscle. The androgen receptors in the muscle cytosol fraction were determined by means of a binding assay involving (3H)methyltrienolone, which is an analogue of testosterone, the number having rapidly increased in the stimulated leg, when compared with that in the control leg, about 25 after the 3rd d. The increase then slowed down, reaching a plateau after the 5th d of stimulation. The receptor dissociation constants for (3H)methyltrienolone remained unchanged, approximately 0.3 to 0.4 nmol throughout the experimental period. These findings suggested that a rapid increase in the number of androgen receptors occurred as an early event in the development of muscle hypertrophy.