Ovulation and mating behavior in female rats under various environmental stresses or androgen treatment

In the normal female rat the peak in sexual receptivity occurs during the proestrus-estrus stage of the estrus cycle. In the androgen sterilized female rat (10µg Testosterone propionate (TP) at 5 days of age) copulation did not induce ovulation. Progesterone (2.0 mg) enhanced mating behavior in these rats with no ovulation, but the additional administration of TP 0.2 mg suppressed the ability of progesterone to increase mating behavior. In normal ovariectomized rats which otherwise do not copulate, mating behavior was induced by daily treatment of 0.2 mg TP and three injections of 2.0 mg progesterone. However, if the amount of TP was increased to 2.0 mg this action of progesterone was suppressed. Environmental stresses such as light, sound, or odor caused persistent and prolonged vaginal cornification or prolonged diestrus. The degree of sexual receptivity was reduced; however, copulation did induce ovulation. A possible inference is that small amounts of TP suppress the ovulating center of the hypothalamus, apparently without inhibiting the mating center in the female rat. The mating center is responsive to progesterone, which enhances mating behavior. On the other hand, large amounts of TP appear to inhibit both the ovulating and mating centers, thus rendering the mating center less responsive to progesterone. The mating and ovulating centers are not always synchronized. Provocation of the mating center enhances activity of the ovulating center which has been rendered refractory by stressful conditions.