Possible function of 17β-hydroxysteroid dehydrogenase in preimplantation hamster embryos

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Abstract
17β-Hydroxysteroid dehydrogenase (17β-HSD) catalyzes the interconversion of estradiol-17β (E2) and estrone (E1). The present study is designed to investigate the following: (1) the developmental stage of hamster embryos at which 17β-HSD activity first becomes detectable, and (2) the E1 → E2 and E2 → E1 conversion rate in the preimplantation hamster embryo. Embryos obtained from superovulated hamsters on days 1–4 were cultured in medium containing 107 ng [3H]E1 or – E2/ml and the respective conversion product, [3H]E2 or – E1, was isolated and assayed. The results show that (1) E1 → E2 conversion was active in all embryos at the rate of 0.57, 0.66, 0.54 and 0.48 fmol/embryo/hr for day 1 (one-cell), 2 (two-cell), 3 (eight-cell) and 4 (blastocyst), respectively, and (2) E2 → E1 conversion was not detectable in hamster embryos. In long-term blastocyst culture, E2 → E1 conversion becomes detectable at 25 hours and increases sharply from 25 to 47 hours. These results suggest that (1) 17β-HSD may function mainly to convert E1 into E2 in preimplantation hamster embryos and (2) E2 → E1 conversion may become active only during and after implantation.