Gonadotropin-releasing hormone (GnRH) and cyclic amp positively regulate inhibin subunit messenger RNA levels in human placental cells

Abstract

Bioactive and immunodetectable levels of both inhibin and activin are present in the placenta, raising questions as to the regulatory control of their synthesis. This study was designed to determine the effect of cyclic AMP (cAMP) and gonadotropin-releasing hormone (GnRH) on inhibin subunit gene expression in short-term incubations of placental cells. A semi-quantitative polymerase chain reaction (PCR) technique was used after isolation of total RNA and first strand cDNA synthesis from mechanically dispersed trophoblast-enriched cells obtained from human placentae at term. The level of gene expression of inhibin subunits was higher for βA and α-subunits mRNA compared to the βB-subunit mRNA as determined by PCR in combination with Southern blotting or Northern hybridization. Steady-state levels of β-actin mRNA did not change throughout the 6-h incubation period and was used as a control of PCR amplification of the respective inhibin subunit gene transcripts following treatments with 8-bromo cAMP or GnRH. 8-bromo cAMP dose-dependently increased all three inhibin subunit gene transcripts with maximal responses seen at 150 μM (α-subunit mRNA 2.3-fold, βA-subunit mRNA 1.8-fold and βB-subunit mRNA 2.8-fold over control). GnRH (100 nM) significantly increased inhibin α and βB-subunit mRNA levels 2.9-fold and 2.0-fold, respectively ( P<0.01), but not βA-subunit mRNA. Collectively, the present findings demonstrate that in human term placental cells, gene expression of all inhibin subunits is under the direct influence of cAMP and further support a modulatory role of local GnRH in placental trophoblasts during late pregnancy.