We tested the hypothesis that the activation of the androgen receptor (AR) is required for full expression of female goat sexual behavior. Once a week for 6 weeks, ovariectomized (OVX) females were given priming doses of progesterone 72 and 48 h before behavioral observation. Estradiol (E2; 100 μg), testosterone (T; 100 mg), or sesame oil was supplied 14 h before behavioral testing. Six goats received the AR antagonist flutamide (9 mg/kg sc) 8 h before and 4 h after steroid injection. Six goats received the carrier only. After 3 weeks, flutamide and carrier treatments were switched so that all females received all treatments. Treatments with E2 and T were equally effective in eliciting estrus-typical behaviors (sniffing, courting, leg kicks, mount attempts by males, bouts of thrusting by males, ejaculations, and flehman responses) compared to treatment with oil. Flutamide treatment enhanced proceptive behaviors in E2-treated females compared to other treatment groups; this was most likely via enhanced tail wagging. Moreover, compared to goats given T + carrier, T + flutamide significantly reduced receptivity in females. The results of this experiment implicate the AR as an important facilitator of some aspects of the female goat sexual behavior. However, the results of this experiment do not show whether androgens influence estrous behaviors alone or in some combination with estrogen.
In most ovariectomized (OVX) female mammals that are spontaneous ovulators, induction of estrus is accomplished by sequential administration of estradiol (E2) or progesterone (P4) in some combination. For example, although E2 alone elicits some components of estrus in OVX female rodents, only E2 plus P4 (24–48 h after E2) allows for the full complement of female sexual behavior (Auger, 2001). However, estrus in OVX goats may be induced by E2 alone or, outside the breeding season, by P4 treatment before E2 administration (Billings and Katz, 1997).
In addition to estrogens, androgens may be important modulators of female sexual behavior (see review by Dörner, 1976) either directly or following aromatization to estrogen. Work done using sheep and goats supports the notion that the androgen receptor (AR) may play a facilitative role in female sexual behavior. In the ovary-intact goat, both estrogens and androgens are produced concomitant with the regression of the corpus luteum (Homeida and Cooke, 1984). Plasma testosterone (T) and E2 concentrations continue to increase in the female, and when a threshold level is reached, estrus is observed. In sheep, the antiandrogen cyproterone acetate in conjunction with T administration blocked receptivity; however, this work is controversial as cyproterone acetate also functions as a progestin (Fabre-Nys and Signoret, 1980).
Preliminary data in our laboratory suggested that the aromatizable androgens T and androstenedione (A4) induce the expression of female goat sexual behavior (Lindia and Katz, 2000). These researchers attempted to induce estrus in OVX goats using E2, T, A4, or DHT. They found that E2, A4, and T all increased expression of estrous behavior. However, T and A4 tended to elicit higher attractivity and receptivity scores than E2 treatment. Dihydrotestosterone alone had no effect on sexual behavior. Increased doses of E2 did not enhance behavioral responses. Taken together, these observations suggest that female goat and sheep sexual behavior is not solely due to estrogens derived from aromatization, but may require, in addition, androgen action.
The biological effects of androgens are transduced via the AR (Roy et al., 2001). If androgens, in conjunction with estrogens, are necessary for full expression of female goat sexual behaviors, we hypothesize that blockade of the AR should reduce attractivity or receptivity scores. In the present report, we examined the effects of a highly specific, nonsteroidal AR antagonist flutamide on the sexual behavior of OVX female goats given E2, T, or sesame oil.
