Progesterone receptors in the prostate.

The lateral prostate of the castrate rat has low levels of specific cytosol progesterone binding which can be increased by treatment of the animals with estradiol. Although progesterone alone is a relatively ineffective agonist in either the ventral prostate or the lateral prostate, treatment of animals with a combination of progesterone and estradiol caused selective growth of the lateral prostate. This response did not occur in the ventral prostate which had a very low or undetectable level of specific cytosol progesterone binding which did not respond to treatment with estradiol. The effects of progesterone in the lateral prostate were not mediated via the androgen receptor suggesting that the cytosol progesterone receptor is capable of mediating a growth response to an agonist in the lateral prostate. An endogenous agonist for the cytosol progesterone receptor in the prostate remains to be identified, and its relevance to BPH remains to be defined.