Oestrogen production by blastocyst and early embryonic tissue of various species.

Oestrogen synthesis by the early embryo in vitro was studied with tissue from pigs, sheep, cows, roe deer, ferrets, cats, rabbits and a plains viscacha. Definitive evidence for aromatase activity and oestrogen synthesis in preimplantation trophoblast was obtained for the pig with the formation of oestrone, oestradiol-17 beta and oestradiol-17 alpha from 3H-labelled androstenedione and dehydroepiandrosterone. Aromatase activity was appreciably lower in all other species studied, and labelled oestrogens were recovered only from incubations of allantochorionic tissue of roe deer, recovered shortly after implantation, and from pooled samples of early embryonic tissue of cows. High aromatase activity in preimplantation trophoblast of pigs was associated with the maternal recognition of pregnancy and the occurrence of superficial implantation in this species.