IDENTIFICATION, CHARACTERIZATION AND LOCALIZATION OF CORTICOTROPIN-RELEASING HORMONE RECEPTORS IN HUMAN PLACENTA

The purpose of this work was to identify, characterise, and localise s pecific CRH binding sites in whole vaginally delivered term human plac ental membranes as well as in dispersed and purified trophoblastic mem branes. We have found that whole placenta membranes contained specific and saturable CRH-binding sites. Maximum specific binding was obtaine d at pH 7.2-7.4, 22 C, for 2 h. The order of potency of CRH analogs wa s h/rCRH>alpha-helCRH>oCRH. Scatchard analysis revealed a single popul ation of high affinity binding sites with a dissociation constant of 1 .25 nM and maximum binding capacity of 119 fmol/mg of protein. Purifie d syncytiotrophoblast membranes contained high affinity CRH binding si tes exhibiting the same dissociation constant and maximum binding capa city as whole placental membranes, suggesting that the CRH binding sit es are expressed almost exclusively by the syncytiotrophoblast. Our fi ndings indicate that CRH binding sites in the human placenta are exhib it similar characteristics to that described for anterior pituitary, b rain and adrenals.