The effect of ethynyloestradiol and medroxyprogesterone acetate on the in vivo uptake and metabolism of 3H-oestradiol by breast tumour tissue in postmenopausal women.

The uptake and metabolism of 3H-oestradiol by breast tumour tissue was studied in three postmenopausal women before, after 1 week of treatment with ethynyl-oestradiol (EE, 10 micrograms/day) and again two weeks later after treatment with medroxyprogesterone acetate (MPA, 500mg/day, i.m.). Treatment with EE reduced the tissue: plasma gradients for both 3H-oestradiol and 3H-oestrone and little further change in these ratios occurred after MPA treatment. The proportion of oestrogen present as 3H-oestrone increased in tumours from 2/3 women after treatment with MPA but not EE, although no increase in the activity of oestradiol 17 beta-hydroxysteroid dehydrogenase (E2DH) was detected. Plasma and tissue concentrations of 5-androstenediol, dehydroepiandrosterone and dehydroepiandrosterone sulphate were all reduced after MPA treatment. The results from this study show that treatment with EE and MPA can reduce the uptake of oestradiol by breast tumours. No increase in E2DH activity was detected but it is possible that MPA influences other enzymes involved in oestradiol metabolism.