Capacity of Skeletal Muscle of Castrated Female Rats for Sustaining Work Output

Abstract

In a previous experiment, 1 I have made a comparison of normal and castrated male rats in respect to the capacity of the gastrocnemius muscle for performing work when made to contract by faradic stimulation. In the present experiment, normal and castrated female rats were studied in a similar manner.

Albino female rats were closely matched into 10 pairs on the basis of weight and one animal in each pair was castrated during the second month following birth. Each rat was prepared for the work test when it reached a weight ranging from 185 to 195 g.

The animal was anesthetized with phenobarbital sodium, its gastrocnemius muscle was weighted with 100 g and was stimulated directly to contract 3 times per second until the muscle became “fatigued,” or for 120 hours. The amount of work performed was recorded automatically. Each rat received 6 cc of a physiologic solution of saline by subcutaneous injection every 12 hours. A detailed description of the apparatus and procedure used has been presented. 2

The data on averages and ranges of work for 10 pairs of rats are summarized in Table I. Inferiority as regards the ability of castrated female rats to sustain work of the gastrocnemius muscle was not observed in this experiment.

The results of this experiment are similar to those of my previous study on castrated male rats. They do not agree with the results of Miley, 3 who found that castrated female rats were deficient in their capacity for work.

The daily values for work in this experiment were occasionally higher than on the preceding day although the stimulation was continuous. This is a frequent observation on performance of work when studied under the experimental conditions used in this investigation.