Feto-Placental Hypoxemia Regulates the Release of Fetal Activin A and Prostaglandin E2

The evaluation of the role of critical hypoxia in unexplained fetal death in utero has been hampered by the lack of a physiological marker. Here we report the novel observation that feto-placental hypoxemia is an acute trigger for increased activin secretion from the feto-placental unit in late pregnancy. Hypoxemia was induced in chronically cannulated late pregnant fetal sheep by restricting blood flow through the maternal uterine arteries. Using maternal and fetal blood samples and amniotic fluid obtained via chronically implanted catheters, fetal blood gas parameters, plasma and amniotic fluid concentrations of activin A, prostaglandin (PG) E(2) and PGFM, the circulating metabolite of PGF(2alpha), were determined before, during and after a ten hour period of fetal hypoxemia. Hypoxemia acutely increased activin A and PGE(2) levels in both amniotic fluid and the fetal circulation with values rapidly returning to baseline with normoxemia. PGFM also increased in both compartments with a relatively delayed time frame compared to that of activin A and PGE(2). The increase in activin A and PGE(2) induced by hypoxemia may be a mechanism to regulate feto-placental blood flow during fetal compromise and also offers the possibility that activin A represents a useful marker of feto-placental hypoxemia.