EVIDENCE THAT HUMAN PLACENTA IS A SITE OF SEX HORMONE-BINDING GLOBULIN GENE-EXPRESSION

The presence of an androgen-binding component in placenta was investig ated in vitro using a tissue culture system of human placental explant s. Explants of trophoblastic tissue from normal term placentas were ke pt in culture under appropriate conditions for at least 48 h in a seru m-free medium. The existence of an androgen-binding protein was explor ed by binding assays, immunohistochemistry studies and Northern blot a nalyses of placental mRNA. Steady-state polyacrylamide gel electrophor esis and Scatchard plot analyses revealed the presence of a high affin ity specific binding component for 5alpha-dihydrotestosterone in cultu red placenta. Immunohistochemical studies performed on intact placenta and on Percoll-gradient purified trophoblastic cells demonstrated the presence of specific immunoreactivity in the cytoplasm of syncytial c ells. Northern blot analyses of placental mRNA showed a single hybridi zable P-32-labeled human sex hormone-binding globulin (SHBG) cDNA band of approx. 1.6 kb which was identical in size to that obtained with l iver mRNA. The results strongly suggest the placenta as an origin of S HBG and point out this tissue as an additional site of SHBG synthesis during pregnancy.