Androgen inhibition of sexual receptivity is modulated by estrogen

Abstract

Sexual receptivity induced in ovariectomized rats by the long-term administration of estradiol benzoate (EB) can be inhibited by concurrent administration of androgens. Experiment 1 examined the role of time course and dose of androgens in the inhibition of estrogen-induced sexual receptivity. Ovariectomized rats were treated with EB (2.0 microg per rat per day) for 6 days and tested for sexual receptivity (Test Day I). EB treatment continued for 15 days concomitant with daily administration of one of three doses of dihydrotestosterone propionate (DHTP; 7.5, 0.75, 0.075 mg/kg) or 3α-androstanediol (3α-Adiol; 3.75, 1.0, 0.375 mg/kg). Four tests for sexual receptivity were conducted on days 3, 6, 14, and 15 of the androgen/vehicle treatment period (Test Days II-V). On Day 15 (Test Day V), the rats received progesterone (1.0 mg per rat) 4 h before testing. Using the same experimental design, Experiment 2 examined the effect of increasing the dose of estrogen on the androgenic inhibition of sexual receptivity. Ovariectomized rats were treated with one of two doses of EB (2.0 or 10.0 microg per rat per day) concomitant with daily administration of DHTP (7.5 mg/kg) or 3α-Adiol (3.75 mg/kg). In Experiment 1, the highest doses of both DHTP and 3α-Adiol significantly inhibited estrogen-induced sexual receptivity. Data from Experiment 2 indicate that the inhibitory effects of DHTP but not 3α-Adiol can be moderated by an increased dose of EB.

Figure 1

Mean (±SEM) Lordosis quotients (LQs) were determined on sexual receptivity tests conducted after 6 days of estradiol benzoate (EB; 2.0 µg/day; Test Day I), and again following 3, 6, 14, and 15 days (Test Days II, III, IV, and V, respectively) of continued EB treatment concurrent with dihydrotestosterone propionate (DHTP; 7.5 mg/kg, 0.75 mg/kg or 0.075 mg/kg) or the oil vehicle or 5α-androstane-3-α, 17β-diol (3α-Adiol; 3.75 mg/kg, 1 mg/kg, or 0.375 mg/kg) or the propylene glycol (PG) vehicle. On Day 15 (Test Day V), all female rats received progesterone (1.0 mg/rat) 4 h before testing. N ≥ 9 per group. * P < 0.05 vs. all other groups on the same Test Day # P < 0.05 vs. 0.075 mg/kg DHTP or 0.375 mg/kg DHTP group on the same Test Day

Figure 2

Mean (±SEM) Lordosis quotients (LQs) were determined on sexual receptivity tests conducted after 6 days of estradiol benzoate (EB; 2.0 or 10.0 µg/day; Test Day I), and again following 3, 6, 14, and 15 days (Test Days II, III, IV, and V, respectively) of continued EB treatment concurrent with dihydrotestosterone propionate (DHTP; 7.5 mg/kg) or the oil vehicle or 5α-androstane-3-α, 17β-diol (3α-Adiol; 3.75 mg/kg) or the propylene glycol (PG) vehicle. On Day 15 (Test Day V), all female rats received progesterone (1.0 mg/rat) 4 h before testing. N ≥ 7 per group. * P < 0.05 vs. all other groups on the same Test Day # P < 0.05 vs. both EB + oil/PG treated groups on same Test Day