Developmental changes in localization of steroid synthesis enzymes in camelid placenta.

The uninucleate trophoblast of epitheliochorial camelid placenta produces multinucleate giant cells starting between day 30 and day 35 of pregnancy. The giant cells are found scattered along the trophoblast at similar frequency throughout gestation. Light microscope immunocytochemistry indicates that the four steroid synthesis enzymes (cholesterol side chain cleavage, 3beta-hydroxysteroid de-hydrogenase, 17alpha-hydroxylase and aromatase) are present in all uninucleate trophoblast cells between day 14 and day 30 of pregnancy, but are found only in the giant cells once they are established, and that this localization persists until term. The giant cells show massive amounts of smooth endoplasmic reticulum and numerous small mitochondria, again as has been shown in other steroid-producing cells. As progesterone from the corpus luteum is necessary throughout gestation in camels, the capacity for oestrogen production by the trophoblast presumably has an important role, but one limited mostly to the immediate vicinity of the fetomaternal interface.