Acute effect of PMSG on ovarian androgen-binding sites in the intact immature female rat

Abstract

Androgen-binding activity in ovaries containing only immature follicles is compared with that in ovaries stimulated with pregnant mare serum gonadotrophin to induce development of large preovulatory follicles. The androgen-binding sites present in cytosols prepared from unstimulated ovaries exhibited kinetics, affinity and a range of specificities for natural and synthetic androgens consistent with those exhibited by the androgen receptor isolated from androgen-sensitive tissues. Studies of sedimentation and DNA binding suggest that the receptor-like androgen-binding site present in unstimulated ovaries exists as the 'non-activated' form which is able to undergo transformation and bind to nuclear DNA. Properties of the androgen-binding sites isolated from ovaries stimulated with gonadotrophin were very different from those of the androgen receptor present in unstimulated ovaries. Specificity for androgens was reduced, capacity for dihydrotestosterone (DHT) and methyltrienolone (R1881) increased and androgen-binding activity was associated exclusively with the 4.5S form which was not able to bind to nuclear DNA. These data confirm that a shift from a receptor-like to a nonfunctional androgen-binding site is associated with the development of ovulatory follicles and suggest that shifts in androgen-binding populations will determine the response of developing ovarian follicles to androgens.