Early secretion of chorionic gonadotrophin by marmoset embryos in vivo and in vitro.

The control mechanisms of early pregnancy in primates differ from those in non-primate species in the early secretion of chorionic gonadotrophin (CG) by the embryo and in the support of the corpus luteum. This study describes the initiation of secretion of CG by the embryo of the marmoset monkey examined in vivo and in vitro. A bioassay for gonadotrophin, which did not distinguish between CG and LH, was adapted and validated for the marmoset. A system of embryo culture was developed whereby embryos were grown from morula/blastocyst stages until at least the differentiation of the trophoblast and yolk sac, facilitated by the embryo attaching to a monolayer of marmoset fibroblast cells. Gonadotrophin concentrations were measured in the peripheral circulation of marmosets during precisely timed stages during the first 84 days of the 144-day gestation period, providing a profile of secretion that was maintained at high levels for longer than the profile seen in Old World primates, including man. A clear increase above baseline levels was seen by day 17 after ovulation, implantation commencing in the marmoset on days 11-13. Gonadotrophin was secreted by embryos in culture from the time of attachment in vitro, but there was no clear evidence of secretion before attachment. Levels of gonadotrophin secreted by embryos in vitro increased rapidly, reaching a maximum mean production rate of 90 mIU/24 h within 4 days after attachment. The experimental systems developed here will allow the examination of the local function of CG at the implantation site, intra-embryonic control of its secretion and its possible involvement in embryonic development.