ABSTRACT
OBJECTIVE: Our previous study demonstrated that the placental GnRH and GnRH mRNA did not parallel the time course of hCG secretion, though it is thought to be one of the potential paracrine regulators of hCG secretion from the trophoblasts. The present study was designed to examine the potential variation in GnRH-receptor mRNA expression in the placenta, which may account for the GnRH-mediated action of hCG secretion during pregnancy. METHODS: Human placentas in firt, second, and third trimester of normal pregnancy were obtained. These placentas were fixed with 4% paraformaldehyde and embedded in OCT compound, and sectioned by cryostat. For in situ hybridization, S labeled RNA probes were used and followed by autoradiography. RESULTS: The GnRH-receptor mRNA signals were present in both cytotrophoblast and syncytiotrophoblast cell layers. Signal intensities varied with gestational ages and were abundant at 6-7 weeks, peaked at 9-12weeks, declined at 14 and 24 weeks, and were barely detectable at term. The present study demonstrates that GnRH-receptor mRNA exhibits changes paralleling the time course of hCG secretion during pregnancy CONCLUSION: These data provide mechanistic understanding that the paracrine/autocrine regulation of hCG secretion by placental GnRH is mediated through an increase followed by a decline in GnRH-receptor mRNA expression from the first trimester to term placenta.