Testosterone esters are less polar than free testosterone. Testosterone esters in oil Injected intramuscularly are absorbed slowly from the lipid phase; thus, testosterone cypionate can be given at intervals of two to four weeks.
Testosterone in plasma is 98 percent bound to a specific testosterone-estradiol binding globulin, and about 2 percent is free. Generally, the amount of this sex-hormone binding globulin in the plasma will determine the distribution of testosterone between free and bound forms, and the free testosterone concentration will determine its half-life.
About 90 of a dose of testosterone is excreted in the urine as glucuronic and sulfuric acid conjugates of tesrtosterone and its metabolites; about 6 percent of a dose is excreted in the feces, mostly in the unconjugated form. Inactivation of testosterone occurs primarily in the liver. Testosterone is metabolized to various 17-keto steroids through two different pathways.
The half-life of testosterone cypionate when Injected intramuscularly is approximately eight days.
In many tissues the activity of testosterone appears to depend on reduction to dihydrotestost-
erone, which binds to cytosol receptor proteins. The steroid-receptor complex is transported to the nucleus where it initiates transcription events and cellular changes related to androgen action.