Responsiveness of vaginal cells to estradiol during postnatal development of rat.

Ontogeny of responsiveness to hormones is mainly regulated by the presence of receptors; their type, number, and location in the hormone target cells. Some of these parameters have been used to study the responsiveness of rat vagina to estradiol. The estrogen binding sites (EBS) in the cytosol of rat vagina are present immediately at birth, however the animal becomes responsive to the hormone only after 25 +/- 5 d of age. The authors demonstrate how the serum and tissue levels of estradiol affect the EBS in this tissue during the postnatal development of the rat. The various responses observed after a single i.p. injection of estradiol in the immature rats are explained based on the status of the binding sites for estrogen in this tissue.