ACTIVITY OF PROGESTERONE AND ANTI PROGESTINS IN A RAT MAMMARY PRIMARY-CELL CULTURE SYSTEM

A primary culture system of virgin rat mammary epithelial cells, grown in a serum-free medium, was developed as a means of assaying the effi cacy of compounds with known anti-progestational properties. Cells wer e grown in 24-well plates on hydrated collagen gels and could be cultu red for at least seven days. Experiments were routinely stopped three days after overnight attachment of cells using fibronectin (4 mu g/ml) . DNA synthesis, measured by thymidine incorporation, was significantl y increased by the addition of ovine prolactin (43 nM; P < 0.01) or pr ogesterone (0.15 mu M; P < 0.05) or both (P < 0.01) to the basal mediu m. When added to medium containing progesterone plus prolactin (comple te medium), RU486 (mifepristone) and ZK98734 (lilopristone) significan tly depressed DNA synthesis in a dose-dependent manner using doses ran ging from 0.015 mu M to 15 mu M. Maximum inhibition was achieved at 15 mu M for both compounds. DNA synthesis was 24.5 +/- 2.6% (mean +/- SE M, n = 4) and 32.0 +/- 2.2% (n = 3) of that in complete medium for RU4 86 and ZK98734, respectively (both P < 0.001). There was no inhibitory effect of either compound in basal medium or basal medium plus prolac tin, indicating the absence of toxicity and that the inhibitory effect is specific for a progesterone-mediated process. Copyright (C) 1996 E lsevier Science Ltd.