Inhibition of estrogen-induced sexual receptivity by androgens: Role of the androgen receptor

Both naturally occurring and synthetic androgens have been shown to inhibit estrogen-induced sexual receptivity when administered to ovariectomized (O VX) rats. The mechanisms by which androgens exert these effects, however, r emain unclear. Experiments were conducted to determine the role of the andr ogen receptor in the inhibition of estrogen-induced sexual receptivity in O VX rats by using flutamide, an androgen receptor antagonist. In each experi ment, OVX Long-Evans rats received 6 consecutive days of estradiol benzoate (EB; 2.0 mu g/day) followed by 15 days of EB concurrent with flutamide (10 .0 mg/kg; twice daily) or the vehicle and one of the following androgens or the vehicle: dihydrotestosterone propionate (7.5 mg/kg), 3 alpha-androstan ediol (3.75 mg/kg), 17 alpha-methyltestosterone (7.5 mg/kg), stanozolol (7. 5 mg/kg), or nandrolone decanoate (7.5 mg/kg). On Day 15, all female rats r eceived progesterone (P; 1.0 mg/rat) 4 h before testing. Tests for sexual r eceptivity were conducted on Days 3, 6, 14, and 15 of androgen/flutamide tr eatment. Each androgen inhibited sexual receptivity as expected, and concur rent treatment with flutamide reversed the inhibitory effects of all androg ens on sexual receptivity on all test days. High levels of sexual receptivi ty were displayed in response to P on Day 15, regardless of experimental tr eatment. These results suggest that naturally occurring and synthetic andro gens act at the androgen receptor to inhibit estrogen-induced sexual recept ivity in OVX rats. (C) 1998 Academic Press.