Effects of thyroxine on oestrogen receptor concentrations in anterior pituitary and hypothalamus of hypothyroid rats

Abstract

ABSTRACT The effects of thyroxine (T4) were studied on the concentration of oestrogen receptors in the anterior pituitary gland and hypothalamus of ovariectomized euthyroid and hypothyroid rats. A group of rats was made hypothyroid by the administration of I. Seven days after ovariectomy, animals were separated into five groups: I, euthyroid controls; II, hypothyroid controls; III, hypothyroid and injected with oestradiol benzoate (10 μg/day for 10 days); IV, hypothyroid and injected with T4 (4 μg/day for 10 days) and V, hypothyroid and injected with both oestradiol and T4 as described above. In group I, oestrogen receptor levels in pituitary cytosol were 44·4 ± 3·4 (s.d.) fmol/mg protein and in the nucleus 47·7 ± 4·0 fmol/mg DNA. In group II the respective values were 12·8 ± 1·7 fmol/mg protein (P <0·01) and 12·7 ± 1·7 fmol/mg DNA (P <0·01 compared with group I). In group III, cytosolic receptor concentrations decreased when compared with those in group II (P <0·05), whereas nuclear receptor concentrations rose significantly (P <0·01). Group IV had both pituitary cytosolic and nuclear receptors increased (P <0·01 compared with group II). In group V there were no changes in cytosolic receptor concentrations but a significant (P <0·01) rise in nuclear receptors as compared with group II. Hypothalamic oestrogen receptors in untreated hypothyroid rats (group II) were unchanged in the cytosol and diminished (P <0·01) in the nucleus in relation to euthyroid controls (group I). Thyroxine, but not oestrogen, was effective in increasing the concentration of cytosolic receptors (P <0·05). Neither hormone caused changes in nuclei. The results show that there is a pronounced decrease in pituitary and hypothalamic (nuclei) oestrogen receptors in untreated hypothyroid rats and that this decrease can be reversed by T4 treatment. J. Endocr. (1988) 119, 383–387