In-vitro steroid synthesis by the placenta of cows in late gestation and at parturition

Placental tissues were collected during late gestation (Group I, N = 11), pre partum (Group II, N = 9) and post partum (N = 29): 15 of the post-partum cows released the fetal membranes normally (Group III) and 14 retained the fetal membranes (Group IV). Preparations of dispersed fetal placental cells, preparations enriched in binucleate cells (BNC) or in small principal cells as well as tissue minces were utilized. Maternal placental tissue (caruncle) and fetal placental principal cells made minimal conversion of prenenolone and androstenedione to other steroids (less than 15% conversion). Fetal placental tissue and enriched preparations of BNC were more active and were similar in their conversion of pregnenolone and androstenedione to other steroids. BNC converted pregnenolone primarily to progesterone during late gestation, but this was altered in the direction of oestrogens pre partum and post partum. BNC were capable of converting androstenedione to oestrogens, but this ability diminished greatly post partum if the fetal membranes were released normally. In-vitro treatment of fetal placental tissue minces with dexamethasone increased the conversion of pregnenolone to androstenedione and the oestrogens but did not alter the conversion the primary cell type involved in fetal placental steroidogenesis peripartum and that dexamethasone may alter this steroidogenesis by activating the C17,20-lyase enzyme complex.