Specific cells of human amnion selectively localize prolactin.

The presence of PRL in high concentration in human amniotic fluid has been related to changes in water transport across amnion but not chorion leave. The cellular composition of human amniotic epithelium has been reported to include at least two structurally distinct cell types, known as light cells and dark cells, that differ in their ability to transport large molecules. In the present study, human amnion obtained from term cesarean section was evaluated through the use of autoradiography as to its ability to localize hormones of similar and variant molecular sizes. Amniotic epithelium exposed to [125I]human PRL, [125I]human Gh, [125I]human beta-endorphin, [125I]bovine FSH, and sodium 125I alone was found to display a selectivity in its ability to localize [125I]human PRL only. Furthermore, the selective localization of [125I]human PRL was found to be specific to the light cells, because dark cells failed to localize any of the other tracers used. These data provide additional evidence in support of the recently proposed concept that term human amniotic epithelium consists of at least two functionally distinct cell types. Furthermore, the high levels of PRL in amniotic fluid may have a specific physiologic role in the amniotic membrane during human gestation.