EVIDENCE OF LACK OF PASSAGE OF HUMAN-PROLACTIN THROUGH HUMAN PLACENTAL MEMBRANES

Human prolactin (hPRL) derived from either amniotic fluid (AF) or pituitary was rested for its passage capability through amniotic and chorionic membranes placed in an in vitro perfusion chamber. The passage of both 'cold' and labelled prolactin were investigated using intact monomeric iodinated hPRL isolated from amniotic fluid which also served as a tracer in a homologous double antibody radioimmunoassay used for prolactin determinations. Throughout 4 h incubation period at 37°C, there was no passage of 'cold' hPRL from either of the sources across either direction. Also, in contrast to free iodine ions, there was no passage of intact labelled prolactin in either direction. Decomposition of labelled prolactin occurred only in the chorionic side, and only decomposed labelled prolactin molecules passed into the amniotic side. These became detectable 1 h after commencement of incubation. These results may explain the long half-life and the high concentration of hPRL in amniotic fluid, and also suggest that the source of AF hPRL is not maternal.