Endothelin-1 receptors on the human placenta and fetal membranes: Evidence for different binding properties in pre-eclamptic pregnancies

Densities and affinities of tissue protein receptor sites for endothelin-1 in placental and fetal membranes of six preeclamptic and 16 normotensive women in the 36-41th week of gestation were determined by the use of a binding assay with [¹²⁵I]endothelin-1. The mean maximal density of receptor sites (B_max) was significantly higher in the placentas of the pre-eclamptic than of the normotensive women (905 ± 107 us. 539 ± 140fmollmg protein, p < 0.0001). No differences were found between the two groups with respect to the mean affinity (K_d) of placental receptors, or the mean B_max and the mean K_d of fetal chorionic samples. In the normotensive group, there were no differences in mean placental B_max values or in mean K_d values between women who went into spontaneous labor (whether delivered vaginally or abdominally) and those who were electively operated on prior to labor onset. No binding sites were detected in the fetal amniotic membranes of any of the women. Our results suggest that an increase in the maximal density of receptor sites to endothelin-1 in the placenta may play a role in the pathophysiology of pre-eclampsia by contributing to the placental insufficiency that characterizes this disorder.