Determination of Secretory Rates of Estrogens in Pregnant and Nonpregnant Women from the Specific Activities of Urinary Metabolites

Abstract

Estradiol-17β-6,7-H³ has been administered intravenously to 2 women at the time of ovulation, and to 6 pregnant women. Estrone (E₁), estradiol-17β (E₂) and estriol (E₃), isolated from urine after enzymatic hydrolysis of their glucuronosides, were purified to constant specific activity. In the 2 nonpregnant females, the specific activities of these urinary products were essentially identical and the secretory rates of estradiol calculated from them were 0.2 and 0.5 mg/day. By contrast, in all pregnant women the specific activities of urinary estriol were much lower than those of estrone and estradiol, which were nearly equal. A 2-compartment model representing the situation that prevails in pregnancy has been analyzed mathematically. The fate of the injected and endogenous hormone has been evaluated in relation to the rates of transfer of the hormone between the maternal and fetal compartments and the metabolism in each of these compartments. It has been concluded that in pregnancy the secretory rate of estradiol cannot be determined with certainty from the specific activities of any of its urinary metabolites. Furthermore, the relatively low specific activity of estriol may result from the fact that estradiol is metabolized differently in the maternal and fetal compartments. It is possible that the situation prevailing in pregnancy is such that the secretory rate of estradiol as calculated from the specific activities of urinary estrone or estradiol would measure the secretion of the hormone into the maternal compartment rather than the total endogenous production.