EFFECTS OF HYPOPHYSECTOMY AND THYROXINE ON THE EXPRESSION OF HEPATIC ESTROGEN, HYDROXYSTEROID AND PHENOL SULFOTRANSFERASES

Sulphation in rats, and other mammals, is carried out by a family of s ulphotransferase isoenzymes, which can be further subdivided into oest rogen, hydroxysteroid and phenol sulphotransferases. We have examined the effects of hypophysectomy on the activity and expression of repres entative members of the three major sulphotransferase sub-families in male Wistar rat liver cytosols, and have found that the different sub- families are subject to differential regulation by pituitary hormones. Our data show that in male rat liver hydroxysteroid sulphotransferase s activity was increased, oestrogen sulphotransferases activity was no t altered and phenol sulphotransferases activity was reduced. Further, we have studied the effect on sulphotransferase expression of adminis tration of thyroxine and dexamethasone to hypophysectomized rats. Trea tment of hypophysectomized rats with thyroxine virtually abolished oes trogen sulphotransferase activity in male rat liver but had no effect on hydroxysteroid sulphotransferase or phenol sulphotransferase activi ty. Treatment of hypophysectomized rats with dexamethasone had no effe ct on sulphotransferase activities. Quantitative immunoblot analysis o f liver cytosols showed that these changes in enzyme activity were rel ated to changes in levels of the respective enzyme proteins.