Morphological effects of oestradiol-17beta, and selective oestrogen receptor alpha and beta agonists on luteinising hormone-secreting cells in tamoxifen-treated ovariectomised rats

To investigate the role played by the different rat gonadotroph oestrogen receptor (ER) pools in the effects of oestradiol-17beta (E2) on gonadectomy cells, two-week ovariectomised (OVX) rats were used. The basic experimental group of rats was injected with 3 mg of the selective ER modulator tamoxifen (TX) on days 15-20 after OVX. Groups of TX-treated OVX rats were additionally injected on days 18-20 after OVX with 10 microg oestradiol benzoate (EB), 1 mg of the selective ERalpha agonist propylpyrazole triol (PPT), or 1 mg of the selective ERbeta diarylpropionitrile (DPN). Negative and positive control groups were OVX rats injected over six days after OVX with 0.2 ml oil and EB, respectively. On day 21 after OVX, anterior pituitary glands were dissected out and divided into halves. One hemipituitary was processed for light microscopy and immunocytochemistry for betaLH subunit and progesterone receptor (PR), and the other hemipituitary for ultrastructural evaluation. Results showed that: gonadotrophs were the only pituitary cell type expressing PR; treatment with TX alone shrunk gonadectomy cells and induced both reorganization of membrane-enclosed intracellular organelles and PR expression, and treatment with DPN or EB, but not PPT, reduced the agonistic morphological effects of TX. Considering that TX activates nuclear ERalpha, the results indicate that activation of nuclear ERalpha is determinant for the reversal effects of E2 on gonadotrope morphology and PR expression, and the simultaneous activation of ERbeta modulates the action of ERalpha in an inhibitory fashion.