Different effects on oestrogen binding sites and anti-oestrogenic action of danazol and progesterone

Danazol decreases transcription of estrogen receptor gene in human monocytes

1. Administration of danazol for over one month reduced the levels of estrogen receptor (ER) and its mRNA to approximately 50 and 20%, respectively in monocytes. 2. Danazol did not alter the degradation rate of ER mRNA in monocytes. 3. Danazol decreased the transcription rate of ER gene to approximately 50% in monocytes in a run-on assay. 4. Danazol may release estrogen predominance via the reduction of transcription for ER gene, which leads to the reduction of ER mRNA and ER expressions in monocytes.

Effects of danazol and medroxyprogesterone acetate on estrogen-(estradiol and estriol) specific binding sites in rabbit uterus

In rabbit uterus, the presence of separate specific binding sites for not only estradiol but also estriol has been proposed. These sites may be correlated with an antiestradiol effect. Therefore, this study was designed to investigate the effect of antiestrogenic agents such as danazol and medroxyprogesterone acetate (MPA), especially on the estriol binding sites. Danazol and MPA in combination with estradiol were administered subcutaneously to immature female rabbits daily for 10 days, and resulted in a significant (p < 0.05) decrease in uterine weight and estradiol binding sites in the uterus. Treatment with MPA significantly (p < 0.05) decreased the level of estriol binding sites, but treatment with danazol resulted in this to a minimal extent in the uterus primed by estradiol. MPA did not bind to estradiol and estriol binding sites, while danazol at a high concentration bound to estriol binding sites with some affinity, but not to estradiol binding sites in the uterine cytosol of estrogen-primed rabbits. These results suggest that within the antiproliferative effect of danazol and MPA (an antiestrogenic action on estrogen-stimulated uterine growth) there are likely to be specific differences between some of the possible mechanisms of danazol and MPA in their action at the estriol binding site.

Estrogen binding sites in peripheral blood monocytes and effects of danazol on their sites in vitro

1. This study was designed to investigate the presence of estrogen type I (high affinity, low capacity) and type II (low affinity, high capacity) binding sites in human peripheral blood monocytes and the effects of danazol on these sites. 2. These two types of estrogen binding sites existed in human peripheral blood monocytes. 3. Danazol bound to these sites in high concentration (10(-6) M, clinical serum concentration during danazol therapy) and decreased the number of both sites. 4. It is suggested that danazol has an anti-estrogenic action to the monocytes through the competition and suppression of estrogen binding sites as seen in the estrogen target organ.