No abstract

The effects of oestrogen are mediated by two specific intracellular receptors, oestrogen receptors (ER) and , which function as ligand-activated transcriptional regulators. Ovariectomized macaques (Macaca fascicularis) were used to study the regulation of ER and ER in the endometrium by immunohistochemistry and in situ hybridization after long-term hormone treatment. Animals were treated continuously for 35 months with either conjugated equine oestrogen (CEE), medroxyprogesterone acetate (MPA), combined CEE/MPA, or tamoxifen (TAM). Treatment with CEE/MPA down-regulated ER in the superficial glands. In the superficial stroma the ER level was lower in the CEE/MPA group than in the CEE and MPA groups. ER immunostaining was faint with minor variation in response to treatment, but increased in the superficial stroma after MPA treatment. The ratio of ER /ER increased in superficial stroma and gland after CEE/MPA treatment, and also in stroma after MPA and TAM. Cystic endometrial hyperplasia was observed in TAM-treated animals, in combination with a high level of ER protein expression. The present data show that long-term hormone treatment affects the ER and ER protein levels in the endometrium. The balance between ER and ER seems to be important for the proliferative response to oestrogen.