Analysis of ultrashort feedback regulation in human placenta: Synthesis and secretion of GnRH by human trophoblastic cells

Background: Gonadotropin-releasing hormone (GnRH) presumably controls place ntal growth and functions by autocrine/paracrine mechanisms, and is therefo re an important part of the neuroendocrine network in human placenta. Aim: Our earlier work had indicated that GnRH was expressed in human placenta; i n extension to these findings, we wanted to analyse synthesis and release o f GnRH by trophoblastic cells. GnRH-associated peptide, co-linearily synthe sised with GnRH, was used as indicator of actual peptide synthesis. Method: First, we immunised rabbits with lipopeptides containing partial sequences of GnRH-associated peptide (GAP) and developed antibodies for immunohistoc hemical staining. Second, we set up a competitive enzyme immunoassay to mea sure GnRH: Non-biotinylated GnRH, GnRH analogues or trophoblastic cell cult ure supernatants were used to inhibit binding of biotinylated des-pGlu(1)-G nRH to a monoclonal anti-GnRH antibody. Results: a) Placental sections stai ned positive for GAP in the layers of trophoblastic cells. b) GnRH could be detect by a competitive EIA in supernatants of placental cultures in conce ntrations between 200 and 5 nM. Conclusions: GnRH is synthesised and releas ed by trophoblastic cells.