Molecular Parameters Involved in the Estrogenicity of Mestranol and Ethynylestradiol

Abstract

Summary

Two molecular parameters of estrogenicity, binding to estrogen receptors and induction of uterine RNA synthesis, were used to compare the estrogenicity of mestranol and ethynylestradiol. Following iv injection of tritiated mestranol, both mestranol and ethynylestradiol accumulated in the uterus with a predominance of the latter. Unlabeled estradiol-17β depressed uptake of both drugs by the uterus in vivo, and both compounds bound in vitro to a component of high speed uterine supernatant believed to be the estrogen receptor. Ethynylestradiol has a greater binding affinity for its receptor than does mestranol. At a dose of 0.1 μg/animal only ethynylestradiol induced significant RNA synthesis. However, at a markedly elevated dose, mestranol generated equivalent and identical RNA synthesis.