Measurement of Estradiol-17β Dehydrogenase Activity in Rat Endometrium during the Estrous Cycle and the First Half of Pregnancy

Abstract

Estradiol-17β dehydrogenase (E₂DH) activity was measured in the endometrium of immature and of mature rat uteri at different times of the estrous cycle and during the first 10 days of pregnancy. E₂DH activity is not detected in immature or castrated mature rats. During the estrous cycle, E₂DH activity is 565 ± 103 pmol/mg protein/h (mean ± SEM, n = 7) at proestrus; 479 ± 80 (n = 6) at estrus; 94 ± 18 (n = 6) at metestrus; and 73 ± 12 (n = 6) at diestrus. During pregnancy E₂DH activity is 605 ± 97 (n = 6) at P1 (corresponding to the day of estrus). It decreases to 347 ± 76 (n = 6) on P2; 66 ± 10 (n = 6) on P3; 78 ± 17 (n = 14) on P4; and 137 ± 27 (n = 10) on P5. It then increases again to 2246 ± 340 (n = 6) on P6 and stays high until at least P10. Decidualization and the presence of the blastocysts are not necessary for the development of the enzyme activity during pregnancy. Therefore, the interconversion of estradiol-17β and estrone in rat endometrium is a function of the maturity of the animal, of the stage of the estrous cycle and of the stage of pregnancy.