BIOLOGICALLY-ACTIVE STEROID AND THYROID-HORMONES STIMULATE SECRETION OF SEX HORMONE-BINDING GLOBULIN BY HUMAN TERM PLACENTA IN CULTURE

In this study, the influence of steroid and thyroid hormones and epide rmal growth factor on the production of SHBG by placental tissue expla nts was investigated, Explants of trophoblastic tissue obtained from n ormal term placentas were cultured for 48 h in serum free culture medi um, and then for an additional 24 h period in the presence or absence of various concentrations of either estradiol (0.25 - 5 nM), testoster one (0.5 - 500 nM), triiodothyronine (0.01 - 100 nM) or EGF (2 - 40 mu M), respectively, Human SHBG concentration in culture media was estim ated on each day by specific two-site time-resolved fluoroimmunometric assay and the results expressed as pmol/mg tissue protein, Binding ch aracteristics and molecular structure of secreted SHBG were determined by [H-3]5 alpha-DHT binding assays and Western blot analysis, respect ively, Estradiol and triiodothyronine but not testosterone increased s ignificantly (p <0.05 vs, control) the secretion of SHBG into the cult ure media. Addition of EGF did not significantly change the production of SHBG at the various concentrations studied, [H-3]5 alpha-DHT bindi ng assays and Western blot analysis of placental SHBG resulted in iden tical binding affinities (Kd 2.0 +/- 0.16 x 10(-9)M) and molecular str ucture to those obtained in serum from normal pregnant women, These fi ndings support and extend previous observations by our laboratory indi cating that SHBG gene is expressed in the placenta and provide further evidence on the hormonal regulatory characteristics of this steroid-b inding protein in cultured placenta.