Changes in sensitivity of uteri of ovariectomized rats to estrogen in relation to age

Abstract

Groups of female rats, ovariectomized at 21 days of age, were injected with 0.5 µg estradiol-17ß at 22, 26, 46, 66, 96, 156 or 186 days of age. They were autopsied at the end of the 24th hour after initial estrogen treatment. The sensitivity of the uteri to estrogen increased with advancing age and a peak was reached at about 46 days of age when the animals, if intact, would have reached puberty. The uterine sensitivity to estrogen decreased markedly with further increase in age. Similar results were shown when 1.0 µg or 2.0 µg estradiol-17ß per 100 gm body wt. was administered. The duration of postovariectomy period of adult rats did not influence the sensitivity of the uteri to estrogen. It was suggested that under normal conditions the change in uterine sensitivity is as important as the hormonal factor in bringing the female rat to a stage of puberty.