INTERACTIONS OF OESTRADIOL BENZOATE AND PROMEGESTONE UPON BASAL AND TRH-INDUCED PROLACTIN SECRETION IN POSTMENOPAUSAL WOMEN

The interactions of ovarian steroids with PRL secretion in women are still controversial. Ten healthy postmenopausal women, on no medication, received during the first period of 2 months later in a cross-over design study, i.m. injections of 0.625 mg of oestradiol benzoate (EB) alone for 10 d or in combination with 750 micrograms/d of a pure progestin promegestone for 10 d. A TRH (200 micrograms i.v.) stimulation test was performed before the start and at the completion of each treatment period. Basal plasma gonadotrophins, PRL and oestradiol were measured every day by radioimmunoassay. The EB-induced rise in oestradiol levels was similar during the two periods. In response to EB treatment serum PRL levels increased from 6.1 +/- 0.9 ng/ml to 22.9 +/- 3.4 ng/ml. With the addition of promegestone, the increase in PRL, from 6.7 +/- 1.3 ng/ml to 13.8 +/- 2.5 ng/ml, was significantly diminished (P less than 0.001). The PRL release induced by TRH was significantly greater with EB treatment than was the response with the combined treatment (P less than 0.05, Wilcoxon test to compare the areas under the curves). These data suggest that in postmenopausal women oestrogens act as stimulators of PRL release and promegestone is able to partially counteract the stimulatory effect of oestradiol benzoate upon basal and TRH-stimulated PRL secretion.