Anabolic effect of testosterone on the levator ani muscle of the rat.

Abstract

1. The effect of testosterone on the weight and on the contractile, histochemical and electrophysiological properties of the levator ani (LA) muscle and other skeletal muscles of non-castrated rats was studied. 2. Administration of testosterone for 12 days resulted in a more than two-fold increase of the weight of LA muscle and in increased muscle fibre diameter. Contraction time and other parameters of the twitch were markedly shortened. Twitch tension as well as maximum tetanic tension increased, in the latter case up to 250% of the control values. A similar, but less pronounced anabolic effect on the LA muscle was also observed after 30 days of testosterone administration. 3. No change in the muscle fibre pattern of ATP-ase activity was found in the LA muscle after long-term testosterone treatment. 4. Resting membrane potential of LA muscle fibres increased after 30 days of testosterone administration from 74–83 mV. Increase of resting potential was blocked only partially by 2×10−5 M ouabain in vitro. 5. LA muscle fibres from testosterone treated rats showed a 60% increase of input membrane resistance and a lower rate of sodium permeability activation during action potential generation. 6. Frequency of miniature end-plate potentials in LA muscles of rats treated for 12 and 30 days decreased to about one third of control values. 7. No similar changes of weight, contraction and electrophysiological properties were found in the soleus, extensor digitorum longus and diaphragm muscles of rats treated with testosterone for 12 and 30 days respectively.