Impaired pituitary response to bromocriptine suppression: reversal after bromocriptine plus tamoxifen
Abstract. This study was designed to clarify whether previously resistant cases of adenomatous hyperprolactinaemia to bromocriptine might be improved by additive tamoxifen therapy. Ten hyperprolactinaemic women under bromocriptine (2.5–10 mg) with hypophyseal tumours of different extent were treated with a combined therapy of bromocriptine and tamoxifen (10–20 mg). Two of them had undergone incomplete resection of chromophobe adenomata. The others refused surgery or irradiation. Two other women without basal therapy because of side effects from bromocriptine, received the combined therapy from the beginning of the study. In 6 out of 10 women the addition of tamoxifen resulted in a marked suppression of prolactin serum values. Amenorrhoea and glactorrhoea ceased in 4 of them. One woman conceived. One reported a marked improvement of libido. One stated that side effects under bromocriptine disappeared through the addition of tamoxifen. The 2 women who previously were suffering from side effects were able to take bromocriptine when tamoxifen was added. Four patients were non-responders. Serum prolactin remained unchanged as well as the clinical follow-up. The effectiveness of the combined therapy was not related to the extent of the tumour or to the clinical or biochemical baseline date. We conclude that the suppressive effect of bromocriptine on prolactin secretion is enhanced by the addition of tamoxifen in most cases of adenomatous hyperprolactinaemia. Side effects of bromocriptine are considerably reduced. Anti-oestrogens are competitive inhibitors of the binding of oestradiol to the receptor. Oestrogen play an important role in the development of prolactin secreting adenomata. Our finding of responders and non-responders to tamoxifen suggests that the anti-oestrogen competes for greater or lesser concentrations of receptor sites in prolactinomata.