Dynamics of LHRH binding to human term placental cells from normal and anencephalic gestations

In order to improve our knowledge on human placental hCG production, we studied the binding of an LHRH agonist (N-Ac-Pro1,D-Leu6)-LHRH to third trimester intact placental cells from normal and anencephalic fetuses. In normal pregnancies, specific and saturable binding was found for both LHRH and its analogs with two classes of binding sites. Association constants were 4.7 +/- 2.2 (mean +/- SEM) X 10(5) M-1 for the low affinity sites and 1.7 +/- 0.8 X 10(8) M-1 for the higher affinity sites (P less than 0.01), and the estimated number of sites was 1.71 +/- 0.52 nmol/mg of cell protein and 2.79 +/- 0.54 pmol/mg of cell protein, respectively. Preincubation with increasing concentrations of LHRH agonist induced a progressive decrease in specific binding sites and manifested by a reduction in hCG production which paralleled the concentration of the agonist in preincubation buffer. Studies with placental cells from three anencephalic fetuses showed a decreased binding capacity for LHRH and its agonist, when compared to normal trophoblastic cells, as well as a reduced capacity to produce hCG. Our results suggest that mechanisms dependent upon LHRH binding to its receptor are required for placental hCG production in normal pregnancies. Furthermore our investigation suggests a role for the endocrine feto-placental milieu in the manifestation of these placental LHRH binding sites.