Estriol: A Review

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Abstract
Newly developed methods for the quantitative determination of estriol, estrone and estradiol in blood and urine show different concentrations of each in a variety of conditions, and suggest the quantitative importance of estriol. This suggestion is confirmed by studies of the relative potencies of the various estrogens in different actions which show that estriol itself is a potent estrogen, contrary to the usual conception of its being just a metabolite of the more potent estrone and estradiol. Although ordinarily less effective than estrone and estradiol in promoting vaginal cornification, estriol, under optimum conditions, approaches their effectiveness for this purpose. Estriol is more potent than estrone or estradiol in causing establishment and opening of the vaginal orifice, in promoting imbibition of uterine fluid, in increasing lactic dehydrogenase activity in the uterus, and in stimulating mitotic activity in the epidermis of the mouse ear. The activity of estriol is of the same order of magnitude as that of estrone and estradiol in other estrogenic actions, such as to promote uterine growth at low concentrations (although less effective at high doses), to increase [beta]-glucuronidase and reduced diphosphopyridine nucleotide oxidase activity in the uterus, to reduce motility of the uterus in vivo, and to stimulate ovarian growth, body weight, phagocytosis of carbon by reticuloendothelial cells, ciliary movements of the buccopharyngeal mucosa of the frog, and new bone formation. The fibromatogenic activity of estriol in the guinea pig is much less than that of estrone or estradiol. Recent experiments suggest and partly vertify the hypothesis that estriol stimulates the cervix, vagina and vulva more effectively than estrone or estradiol, whereas the latter are much more effective on the corpus uteri. These findings, together with the observation that the synthetic estriol now available did not cause endometrial proliferation and bleeding even when high doses were given, led to its successful use in the treatment of disorders due to estrogen deficiency, such as menopausal complaints, dysmenorrhea and sterility involving an insufficiently developed cervix, dyspareunia due to a narrow vagina, vaginitis, cervicitis, vaginal ulcers, and pruritus of the vulva involving kraurosis and leukoplakia.
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