Hypothesis: placental membranes produce prolactin.

Orthodox views for the origin of the high concentration of prolactin (PRL) present in amniotic fluid suggest it is derived from maternal or fetal serum. However, the data on which these conclusions are based can also be interpreted to indicate that this hormone may be a product of placental or periplacental tissues. Trophoblast or amnion do not appear to produce PRL, while PRL synthesis by decidua-chorion is suggested from experiments in the rhesus monkey and by in vitro incubation of human tissue. Production of PRL by an extrapituitary cell is not without precedent and would be a simple explanation for high amniotic fluid PRL concentrations. Moreover, decidual-chorionic PRL would be strategically placed to mediate local functions of this hormone such as osmoregulation and myometrial inhibition.