Effects of postnatal progesterone treatment on ovarian function in adult rats.

Long-lasting postnatal progesterone administration in female rats induced an early or delayed ovulatory failure with persistent vaginal estrus. Short-term treatment was ineffective. The beginning and incidence of ovulatory failure appeared to depend on the beginning and duration of progresterone treatment. The necessary duration of progesterone administration exceeds the critical postnatal steroid sensitive period of sexual differentiation of the hypothalamus. Moreover, long-lasting progesterone treatment results in ovulatory failure even if started after termination of this period.