INDUCTION OF HEPATIC ESTROGEN SULFOTRANSFERASE EXPRESSION BY HYPOPHYSECTOMY IN FEMALE RATS

We have examined the effects of hypophysectomy and treatment with thyr oxine (T-4) on enzyme activity and expression (as determined by immuno blot analysis) of members of the three principal sulfotransferase (ST) sub-families (phenol STs, PST; estrogen STs, EST; hydroxysteroid STs, HST) in cytosols prepared from female Wistar rat livers. The results demonstrate that in female rat liver cytosol, EST activity was decreas ed by treatment with T-4, increased following hypophysectomy and that treatment of hypophysectomized animals with T-4 also greatly reduced E ST activity. T-4 had no significant effect on PST or HST activity in n ormal animals, but it decreased HST activity in hypophysectomized rat liver cytosol. Immunoblot analysis of these cytosols with antibodies r ecognising HST and PST indicated that where changes in enzyme activity occurred they mirrored changes in enzyme protein expression. In norma l adult female rat livers, EST protein is not expressed, and the small residual activity results predominantly from the action of HST. Hypop hysectomy induced EST activity and the expression of EST enzyme protei n in female rat liver cytosol, and T, treatment of hypophysectomized a nimals reduced the activity to below normal levels without reducing th e corresponding enzyme protein levels, indicating that T-4 regulation of EST in females is via a post-translational mechanism.