Effects of testosterone propionate on hindlimb-immobilized rats.

Forty albino male rats were randomly divided into 4 groups of 10. Group I served as the nonimmobilized control and received daily placebo injections of sesame oil. The rats in group II were castrated, their hindlimbs were immobilized using a plaster cast, and they received daily injections of sesame oil. The group III rats were also castrated and casted but received a daily injection of 5 mg testosterone propionate. The animals in group IV were not castrated but were casted and received daily testosterone propionate injections. The duration of each treatment was 15 days for each rat. The gastrocnemius, quadriceps, soleus, and cardiac muscles were weighed after treatment. O2 consumption capacity (QO2), citrate synthase activities, and percentages of water were measured in the gastrocnemius, quadriceps, and cardiac tissues. Along with the atrophy of muscle and reduction in body size, the immobilization significantly reduced the aerobic capacity of affected muscle groups and cardiac tissue. The greatest reductions in body weight, muscle size, heart size, and QO2 were seen in the castrated group that received only placebo injections of sesame oil. The anticatabolic effects of the anabolic steroid were evident in groups III and IV. The results indicate that hindlimb immobilization not only causes severe atrophy in those muscles immobilized but has an overall catabolic effect on the animal. Testosterone, or the lack of it, can significantly affect the amount of muscle atrophy.