Effects of alcohol on the human placental GnRH receptor system

Isolation of human term placental membranes in the presence or absence of p rotease inhibitors indicated that protease inhibitors significantly reduced the amounts of [I-125]-labelled gonadotrophin-releasing hormone (GnRH) bin ding to membrane GnRH-receptors in vitro by similar to 20%. This decrease w as largely due to the ethanol used to dissolve the serine protease inhibito r, phenylmethylsulphonylfluoride (PMSF). Ethanol alone decreased the specif ic binding of [I-125]-labelled GnRH isoform (IC50, 7.9 +/- 0.8 mg/ml; n = 6 ) or agonist tracers (IC50, 10.0 +/- 1.4 mg/ml; n = 6) to human placental m embranes in a dose-dependent manner. Other alcohols also interfered with [I -125]-GnRH isoform or agonist binding: inhibition increased with increasing carbon chain length and was dependent on the isomeric position of the hydr oxyl group. Fractionation of term placental cytosol by gel chromatography d emonstrated the presence of a high molecular weight fraction (similar to 60 -70 kDa) which inhibited [I-125]-GnRH binding to human placental membranes. However, placental cytosol fractions did not cross-react significantly wit h a specific anti-GnRH antibody. Surprisingly, re-assay of cytosol fraction s in the presence of a cocktail of protease inhibitors generated a factor ( molecular weight similar to 40-50 kDa) which did cross-react strongly with the GnRH antibody. The generation of this factor was due to the ethanol sol vent rather than to the protease inhibitors per se, as treatment of pooled 'latent' cytosol fractions with ethanol alone generated GnRH-like immunoact ivity (irGnRH) which competed in parallel with GnRH standard. The amount of irGnRH generated depended on the concentration of ethanol added to the 'la tent' cytosol fractions. However, ethanol had no effect on the assay in the absence of cytosol fraction, or with inactive cytosol fractions. Thus, eth anol can perturb the human placental GnRH/GnRH-receptor system in vitro in two distinct ways: by inhibition of GnRH binding to receptor, and by dissoc iation of complexed endogenous GnRH-like factor(s) from a GnRH-binding prot ein. It is postulated that high alcohol consumption in vivo may interfere w ith placental GnRH secretion/action and affect placental secretion of facto rs important to the establishment and maintenance of pregnancy.