[Placental glycoproteins in the mammals]

Placental tissue exhibits a typical glycosylation pattern, which differs from that observed in the pituitary gland. Depending to the species and pregnancy period, the placenta synthesizes diverse glycoproteins, some of which have significant hormonal activity, others being detected in maternal circulation. Thus, these molecules are of interest both from a fundamental and clinical point of view. Among the mammalian placental glycoproteins currently recognized, chorionic gonadotrophins from primates and Equidae, placental lactogen from bovines and the pregnancy-associated glycoproteins from ruminant species are particularly noteworthy. The diversity of saccharidic structures leads to multiple forms of placental glycoproteins exhibiting distinct structural and biological properties. For instance, concerning the chorionic gonadotrophins, the association of both alpha and beta subunits is essential for the binding of the hormone to specific receptors. Moreover, the N-linked oligossacharides are required for the activation of effectors systems. Bovine placental lactogen is a glycosylated hormone, exhibiting somatotropin- and prolactin-like activities. Several N-glycosylation sites confer to pregnancy-associated glycoproteins a long half-life (8-10 days) in maternal circulation. Assay of these molecules can be used for routine early pregnancy diagnosis and the follow-up of embryonic and fetal mortalities.