Quantitative Studies on the Uptake and Metabolism of Estrogens and Progesterone by Human Endometrium

Rates of entry of estrone ( E1, estradiol (E2), progesterone (P), 20αdihydroprogesterone (20αDHP), estrone sulfate (E1S) and estradiol-3-sulfate (E2S) from buffer solutions into slices of human endometrium were measured in multiple-tracer continuous-flow incubations of the tissue. The fraction of perfused P entering the cells was found to be similar to that of E1 and E2. Increases in the concentrations of E2 in the medium to 5 μg/ml did not alter the fraction of perfused E1 and E2 going into cells. Estrone sulfate and E2S entered readily into endometrial cells and were completely converted to E1 and E2. Rates of interconversion between ElS-E2S, E1-E2 and P-20αDHP were measured. The conversion of E1 to E2 was relatively increased by the addition of E2 to the medium. A large fraction of E1 and P entering the tissue was released to the medium while E2 and 20αDHP left the cells only after being converted to the corresponding ketonic steroids. Consequently, the net uptake of E2 and 20αDHP was larger than the net uptake of E1 and P. The intracellular concentration of E1 was found to be proportional to the amount of the hormone appearing de novo in the tissue (production rate). The ratio of the production rate of the hormone per gram of tissue to its intracellular concentration was defined as the intracellular clearance of the hormone. Tissue concentrations of labeled and unlabeled steroids could be expressed in terms of intracellular clearances, production rates and rates of interconversion. (Endocrinology90: 390, 1972)