Male-Induced Precocial Puberty in Female Mice: Confirmation of the Role of Estrogen

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Abstract
Previous work has shown that exposure of prepubertal female mice to an adult male results in an immediate, sequential release of LH and estrogen. An ovulating release of LH follows in a predictable 3-day period, providing that male-exposure occurs at a particular body weight. Using this three day system, the present objective was to determine how effectively exogenous estrogen would substitute for the male's presence. Control experiments established that neither social isolation nor exposure to a castrated male would yield ovulatory puberty within the 3-day experimental period. Immature females were then subjected to a variety of sequences of three daily treatments including male-exposure and/or steroid injection. Two days of male exposure and no treatment on the third day was as effective in eliciting ovulation on the third night as 3 full days of cohabitation. Furthermore, either or both of the first two days of male-exposure could be mimicked by single injections of estrogen if followed by male-exposure for the remainder of the experimental period. A single injection of estrogen on the first day was ineffective in eliciting ovulation unless followed by male-exposure for 2 days, by a second injection of estrogen on day 2, or by an injection of progesterone on the third day. It was concluded that, as far as the induction of puberty is concerned, the important action of the male's presence is to elicit estrogen secretion (via a subovulating release of LH), and that this process must continue for 2 days, even in immediately prepubertal females, if the pubertal ovulation is to occur during the third night.

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