Peripheral antiglucocorticoid action of RU 486 in man

In order to evaluate the peripheral antiglucocorticoid activity of RU 486 in man we examined its ability to antagonize the effects of acutely administered glucocorticoids on blood leukocyte counts. The study was performed on eight normal male subjects. They were given 400 mg RU 486 (or placebo) orally at 0730 h and 1 mg dexamethasone (or placebo) orally at 0830 h, using a double-blind, cross-over, latin-square design with a one week interval between each of the four different treatments. Circulating eosinophils, lymphocytes, and neutrophils were counted at 0730 h and 1330 h, and their variations (1330 h counts/0730 h counts x 100) were compared under each treatment. For each cell type, dexamethasone induced variations (eosinophil and lymphocyte drop, neutrophil rise) which were significantly (P less than 0.05) different from those under the three other treatments; these latter treatments (placebo, RU 486, and RU 486 + dexamethasone) were equivalent to each other, inducing no variations of leucocyte counts. These data show that RU 486 inhibits dexamethasone induced leukocyte changes; this simple test provides a useful means to further analyse the peripheral antiglucocorticoid activity of RU 486 in man.