RESUMO
In this study, the influence of steroid and thyroid hormones and epidermal growth factor on the productin of SHBG by placenta tissue explants was investigated. Explants of trophoblastic tissue obtained from normal term placentas were cultured for 48 h in serum free culture medium, and then for an additional 24 h period in the presence or absence of various concentrations of either estradiol (0.25 - 5 nM), testoterone (0.5 - 500 nM), triiodothyronine (0.01 - 100 nM) or EGF (2-40 µM), respectively. Human SHBG concentration in culture media was estimated on each day by specific two-site time-resolved fluoroimmunometric assay and the results expressed as pmol/mg tissue protein. Binding characteristics and molecular structure of secreted SHBG were determined by [3H]5a-DHT binding assays and Western blot analysis, espectively. Estradiol and triidothyronine but not testoterone increased significantly (p<0.05 vs. control) the secretion of SHBG into the culture media. Addition of EGF did not significantly change the production of SHBG at the various concentrations studied. [3H]5a-DHT binding assays and Western blot analysis of placental SHBG resulted in identical binding affinities (Kd 2.0 ñ 0.16 x 10-9M= and molecular structure to those obtained in serum from normal pregnant women. These findings support and extend previous observations by our laboratory indicating that SHBG gene is expressed in the placenta and provide further evidence on the hormonal regulatory characteristics of this steroid-binding protein in cultured placenta