Studies on the maternal control of pregnancy-stage specific function of the placenta

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The placenta plays an essential role in fetal growth/survival and the maintenance of maternal luteal function during pregnancy. The function of placenta expresses pregnancy-stage specific manner ; i.e.the secretory profiles of placental hormones including placental lactogens (PLs) show specific changes during the course of pregnancy. We succeeded to isolate a clone of the cDNA for a novel mid-pregnancy specific PL.This novel PL, PL-m, is expressed specifically on days 10 and 12, and has possible N-glycosylation sites. The mid-pregnancy-specific PLs including, PL-Im and PL-I, are secreted again during late pregnancy if the period of pregnancy is extended. This second secretion of PLs depends entirely on factors originating from the ovary, either by induction of a new set of corpora lutea by successive treatment with PMSG and hCG or implantation of progesterone. We also identified several placental glycoconjugates including glycoproteins and glycolipids which expresses pregnancy-stage specific manner. The glycoproteins also reappear in these prolonged pregnancy model. The results of our investigation indicate that the ovary is involved in the control mechanism of placental function, providing the concept that an information flow from the ovary to the placenta exists to control placental function.