Electrophysiological and contractile properties of the levator ani muscle after castration and testosterone administration.

Electrical and contractile properties of the levator ani muscle were studied in normal rats, in castrated rats and in castrated rats treated with testosterone. 2. No significant changes in the frequency of miniature end-plate potentials were found 6 months after castration. The frequency increased already 6 h after testosterone treatment; an increase of about 100% was observed after 7 days of testosterone treatment. 3. Castration led to a 2-fold increase of the input resistance of the muscle fibres. After 7 days of testosterone treatment the input resistance was only slightly higher than normal. 4. The weight of the muscle was decreased to 18% of the control value after 6 months castration. It increased to 46% after 7 days of testosterone treatment. 5. The muscles of castrated animals revealed a prolongation of contraction time and marked changes in maximal rate of tension development and half relaxation time. Partial recovery of these parameters was found after 7 days of testosterone treatment. 6. Long-term castration did not induce any denervation-like changes of action potential parameters, and no tetrodotoxin resistance was found in spite of marked muscle atrophy.