Attenuation of estrogenic effects by dihydrotestosterone in the pig uterus is associated with downregulation of the estrogen receptors.

Androgens are known to attenuate some effects of estradiol-17beta (E) in the uterus. The objectives of the present experiment were to determine effects of 5alpha-dihydrotestosterone (DHT) on estrogenic actions in the pig uterus and its associations with changes in expression of the estrogen receptor (ER) alpha and ERbeta. Postpubertal gilts (120-130 kg of body weight; n = 16) were ovariectomized, and 3-4 weeks later received once-a-day injections (i.m.) of one of the following treatments during four consecutive days: 1) vehicle (corn oil), 2) E (250 microg), 3) E (250 microg) plus 1 mg DHT, or 4) E (250 microg) plus 10 mg DHT. Uterine tissues were collected 24 h after the last treatment. Gilts receiving E or E plus 1 mg DHT had greater uterine wet weight, uterine horn diameter, luminal epithelium thickness, and endometrial gland diameter compared with gilts treated with vehicle or E plus 10 mg DHT. Gilts receiving E or E plus 1 mg DHT were not different in these characteristics. Relative amounts of mRNAs in the endometrium for the cell proliferation marker histone H2a and the E-inducible protein complement component C3 increased in gilts treated with E compared with gilts treated with vehicle. E-induced increases in histone H2a and C3 mRNAs were not altered by cotreatment with E plus 1 mg DHT but were inhibited by E plus 10 mg DHT. Androgen receptor (AR) mRNA in the endometrium increased by treatment with E. Cotreatment of gilts with E and DHT did not alter the E-induced AR mRNA increase. Gilts treated with E plus 10 mg DHT had lesser amounts of immunoreactive ERalpha in cell nuclei of the myometrium and endometrial stroma and a tendency for a decrease in luminal epithelium compared with gilts treated with E. Amounts of immunoreactive ERalpha in glandular epithelium were not influenced by the treatments. Relative amounts of ERalpha and ERbeta mRNAs decreased in the endometrium of gilts treated with E plus 10 mg DHT compared with gilts treated with E. Downregulation of the ERs, particularly ERalpha in the myometrium and endometrial stroma, might be a relevant mechanism in the antagonism of estrogenic effects by DHT in the pig uterus.