Biology of Reproduction, Vol 3, 105-109, Copyright © 1970 by Society for the Study of Reproduction

Relative Potencies of 17and 17-Estradiol in the Rabbit

¹ Department of Anatomy and Brain Research institute, UCLA School of Medicine, Los Angeles, California 90024, and Veterans Administration Hospital, Long Beach, California 90801

The relative potencies of 17and 17-estradiol were compared as to their respective abilities to maintain luteal function in 25 mature, hypophysectomized rabbits and to promote uterine growth in 28 immature rabbits which had been ovariectomized between 8 and 10 weeks of age. Estradiol-17 was found to be 100 times more active in sustaining luteal function and at least 10 times more effective in promoting uterine growth than the isomer. Luteal function was sustained in adult hypophysectomized animals with either 1 or 2 µg estradiol-17 (0.25 or 0.5 µg/kg) administered twice daily sc, and uterine growth and water uptake were stimulated in immature ovariectomized rabbits after 4 days of treatment during which 0.1 µg/kg of this estrogen was administered twice daily. These results suggested that, although both the uterus and the ovary are estrogen target tissues, less estrogen is required to promote uterine growth than to maintain lutal weight and activity. It is concluded that 17-estradiol is not the principal estrogenic hormone of the rabbit.