Endogenous regulation of the GnRH receptor by GnRH in the human placenta

Gonadotrophin releasing hormone (GnRH) plays an important regulatory role i n the function and growth of human placenta, but its placental expression s ites and co-localization with GnRH receptor (GnRH-R) are not well known, Gn RH and GnRH-R expression has been found in both placenta and cultured troph oblasts; however, cultured trophoblastic cells very quickly lose GnRH-R mes sage and subsequently receptor protein. Speculating that endogenously relea sed GnRH induced this down-regulation, we determined GnRH-R in cultures of trophoblastic cells in the presence of a neutralizing anti-GnRH antibody, C ells incubated with this antibody showed a strong signal for the GnRH-R, wh ile those cultured without did not las analysed by immunofluorescence, reve rse transcription-polymerase chain reaction, protein 'dot blot' and Western blotting), Furthermore, addition of the GnRH agonist buserelin led to a re duction of the receptor protein. We have therefore shown that GnRH released from trophoblastic cells down-regulates GnRH-R in these trophoblastic cell s. Having previously shown that trophoblast layers were synchronously posit ive for GnRH and GnRH-R, these new findings support the hypothesis of an ul trashort feedback regulation of trophoblasts by GnRH involving autocrine re gulation of GnRH-R.