Biology of Reproduction, Vol 12, 431-437, Copyright © 1975 by Society for the Study of Reproduction

A Developmental Comparison of Steroid-Induced and Male-Induced Ovulation in Young Mice

¹ Department of Zoology, University of Texas at Austin. Austin, Texas 78712

Exposure of immature female mice of a particular body weight to an adult male results sequentially in a rapid subovulating release of LH, a dramatic surge in circulating estradiol, and two days later, an ovulating release of LH. The development of this response, using indirect measures such as uterine growth and/or ovulation itself, was the subject of the present research. Preliminary experiments evaluated the ovulatory efficacy of a range of doses of injected estrogen and documented the importance of progesterone in steroid-induced ovulation in young mice. In the primary experiments, immature females were male-exposed, injected with an estradiol-progesterone sequence, or left undisturbed, all treatments lasting for three days and being initiated at all one gram ranges in body weight during the relevant stages of development. As adjudged by uterine growth, the ability to release estrogen in response to a male matures early in the life of a female mouse. The capacity to ovulate in response to three days of male exposure, however, develops much later and simultaneously with the establishment of ovulatory responsiveness to steroid injection. In a related experiment, continuous cohabitation with an adult male from an early age also yielded ovulation concurrently with maturation of ovulatory responsiveness to exogenous steroid. Regardless then of the enhanced secretion of estrogen among female mice cohabiting with males, it may be concluded that their pubertal ovulation is delayed until the independent development of a steroid-sensitive, positive feedback system.