Comparison of the biological effectiveness of injected testosterone propionate and testosterone released from silastic capsules.

The in vitro release and biological effectiveness of silicone rubber implants containing testosterone in orchidectomized male rats was investigated over a period of 20 weeks. A marked reduction in release in 0.9% saline solution could be observed in vitro relative to the incubation time in the medium. The reduction in release was greatest during the first few weeks of the experiment. Rat seminal vesicles and prostates, which were greatly stimulated at the start of the experiment, lost weight corresponding to the release rate in vitro. The implants containing testosterone used here were 4 to 26 times more effective than testosterone propionate injected s.c.