GONADOTROPIN-RELEASING-HORMONE (GNRH) AND CYCLIC-AMP POSITIVELY REGULATE INHIBIN SUBUNIT MESSENGER-RNA LEVELS IN HUMAN PLACENTAL CELLS

Bioactive and immunodetectable levels of both inhibin and activin are present in the placenta, raising questions as to the regulatory contro l of their synthesis. This study was designed to determine the effect of cyclic AMP (cAMP) and gonadotropin-releasing hormone (GnRH) on inhi bin subunit gene expression in short-term incubations of placental cel ls. 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 w as higher for beta A and alpha-subunits mRNA compared to the beta B-su bunit mRNA as determined by PCR in combination with Southern blotting or Northern hybridization. Steady-state levels of beta-actin mRNA did not change throughout the 6-h incubation period and was used as a cont rol of PCR amplification of the respective inhibin subunit gene transc ripts following treatments with g-bromo cAMP or GnRH. 8-bromo cAMP dos e-dependently increased all three inhibin subunit gene transcripts wit h maximal responses seen at 150 mu M (alpha-subunit mRNA 2.3-fold, bet a A-subunit mRNA 1.8-fold and beta B-subunit mRNA 2.8-fold over contro l). GnRH (100 nM) significantly increased inhibin alpha and beta B-sub unit mRNA levels 2.9-fold and 2.0-fold, respectively (P<0.01), but not beta A-subunit mRNA. Collectively, the present findings demonstrate t hat in human term placental cells, gene expression of all inhibin subu nits is under the direct influence of cAMP and further support a modul atory role of local GnRH in placental trophoblasts during late pregnan cy.