Testosterone-induced prostate growth is blocked by co-and preadministration of norethisterone enanthate in castrated cynomolgus monkeys.

Introduction: Prostate size and function are regulated by testosterone. However, the progesterone receptor is ex- pressed in the primate prostate. Progestins affect the pros- tate by endocrine suppression, but can also act directly. Ex- amining the role of progestins, we studied the effects of norethisterone (NET) on testosterone undecanoate (TU)-in- duced prostate growth in castrated macaques. Materials and Methods: Two groups (n = 6 for each group) received TU every 9 weeks. Using a crossover setting, group I received norethisterone enanthate (NETE) 3 times at 3-week intervals, while group II received placebo. After 9 weeks, placebo was administered to group I, and group II received NETE. Results: In group II, the prostate grew under TU and placebo over the first period. In group I, coadministered with NETE, the in- crease was lower. After the crossover, prostates of animals previously treated with NETE did not increase to normal val- ues under placebo. Prostates of animals treated with TU and placebo in the first period shrank following NETE administra- tion after the crossover. The long half-life of NET can explainthe lack of a TU effect on animals coadministered with NETE after the crossover. Conclusions: Pre- and coadministration of NET reduces testosterone-induced prostate growth with possible implications for the treatment of benign prostate hyperplasia and hormonal male contraception.