Are the differences between estradiol and other estrogens, naturally occurring or synthetic, merely semantical?

Abstract

I n 1923, Allen and Doisy' described a bioassay that de- tected estrogenic activity in extracts of biological materials.This test also enabled the determination of relative estrogenic potencies of many compounds and of inhomogeneous materials of natural origin.During the intervening 70 years this bioassay, or modifications of it, has been used to identify and characterize synthetic estrogens and those obtained from natural sources, e.g.mammalian tissues, excreta, and plants, and from chemical syntheses.The numerous chemical compounds and biological materials that have been labeled as estrogens because they responded positively in the above bioassay differ enormously from each other with respect to their chemical structures.The following abbreviated list will illustrate the point: estradiol, estriol, equilin, 17-ethynylestradiol, stilbesterol, xenoestrogens (DDT etc), phytoestrogens (coumestrol), clinically-useful extracts of horse urine (premarin), etc.Thus under one rubric a potpourri of chemical entities have been designated estrogens.Frequently investigators give no recognition to the differences that undoubtedly exist among members of the class.Focusing on only this one characteristic, i.e. a positive response in a bioassay and neglecting the many differences in biological activities that undoubtedly exist among these materials, cannot help but cause unnecessary confusion.In a subject as complex as reproductive endocrinology this lack of concern for the dissimilarities among various estrogens promotes neither understanding nor progress.To provide a common starting point for the view presented in this comment several propositions are presented below.These statements concentrate, in a simplistic way, upon the knowledge that is needed to address the question posed in the title.Ordinarily these theorems are taught early in the education of reproductive biologists but, as evidenced by many flawed publications, their reiteration here may have value.1.A definition: estrogens are materials that, when administered (usually by injection im as solutions in some oil) into sexually immature or castrated female rodents, cause cornification of epithelial cells of the vagina.2. Estradiol, the estrogenic hormone in mammals, is a member of this class of biologically active chemicals.