PITUITARY SEX STEROID-RECEPTORS - LOCALIZATION AND FUNCTION

The pituitary contains estrogen receptor (ER), progesterone receptor ( PR), and androgen receptor (AR). In accordance with immunocytochemistr y, it is agreed that sex hormone receptors reside into the nucleus. Al l three receptors are found predominantly in gonadotrophs and lactotro phs, and less frequently in other cell types. ER plays a major role in prolactin (PRL) production and lactotroph proliferation, and protract ed estrogen administration induces lactotroph hyperplasia and adenoma in rodents. Most research on PR and AR is focused on their role in the fine-tuning of gonadotropin secretion during estrous cycle. Contrary to the effect in nontumorous pituitary, estrogens can inhibit the prol iferation of transplantable rat pituitary tumors and of cell lines der ived from them. In humans, despite the presence of EW in all types of adenohypophysial tumors, the role of estrogen in tumor cell proliferat ion is still unclear. Few results indicate that tumor growth is stimul ated by estrogen, and inhibited by progesterone and androgen. Novel da ta reveal that steroid hormones can act directly on plasma membrane or via other receptors, and interact with growth factors, oncogenes, and other transcription factors. The mechanisms by which steroid hormones control cell proliferation remain a major challenge for future resear ch.