Steroidogenesis in Rabbit Preimplantation Embryos

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 72; no. 1; pp. 298 - 300
• Main Authors: Dickmann, Zeev, Dey, Sudhansu K., Gupta, Jayasree Sen
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 01.01.1975; National Acad Sciences
• Subjects: Animals; Blastocyst; Blastocyst - enzymology; Blastocyst - metabolism; Dehydrogenases; Embryo Implantation; Embryo, Mammalian - enzymology; Embryo, Mammalian - metabolism; Embryos; Enzymes; Estradiol - biosynthesis; Estrogens; Female; Hormones - biosynthesis; Hydroxysteroid Dehydrogenases - metabolism; Morula; Rabbits - embryology; Species Specificity; Steroid hormones; Steroidogenesis; Steroids; Steroids - biosynthesis; Zygotes
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.72.1.298

Rabbit preimplantation embryos were flushed from the reproductive tract at 24 hr (1- to 2-cell stage), 48 hr (morula), 72 hr (morula), 96 hr (blastocyst), 120 hr (blastocyst), and 144 hr (blastocyst) post coitum. At 168 hr (early postimplantation period), gestation sacs were excised, frozen, and sectioned in a cryostat. Δ5-3β -Hydroxysteroid dehydrogenase [3(or 17)β -hydroxysteroid:NAD(P) oxidoreductase, EC 1.1.1.51] activity was determined histochemically in whole preimplantation embryos and in sectioned postimplantation embryos. 3β -Hydroxysteroid dehydrogenase activity began at 48 hr and was sustained through the late blastocyst stage (144 hr), with the exception of a brief drop, possibly cessation, of activity at 72 hr. There was no activity at 168 hr. Since 3β -hydroxysteroid dehydrogenase is a key enzyme in the metabolism of steroid hormones, its presence is strong evidence for steroidogenesis. Only 144-hr preimplantation embryos were used to determine 17β -hydroxysteroid dehydrogenase (estradiol-17β :NAD 17-oxidoreductase, EC 1.1.1.62) activity, which was present, suggesting synthesis of estrogen. By means of radioimmunoassay, 144-hr preimplantation embryos were found to contain estradiol-17β . Other authors have shown that rabbit blastocysts contain progesterone and other steroids, and these embryos can synthesize steroids from non-steroid and steroid precursors. Therefore, our results plus those of others prove that rabbit pre-implantation embryos synthesize steroid hormones. Our present and previous results (with rats, hamsters, and mice) suggest that the steroid hormones synthesized by the embryo are critical for preimplantation embryogenesis and for implantation of the blastocyst.