Cytoplasmic and nuclear estrogen binding capacity in the rat uterus during treatment with danazol and testosterone

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Danazol, testosterone and dihydrotestosterone (DHT) were tested as competitors for estrogen receptors on immature rat uterus cytosol. No competitive binding could be demonstrated for any of these steroids. After that, prepubertal Wistar rats were exposed to danazol, testosterone or propylene glycol (control) for 3 days or 17 days. After the appropriate exposure to medication, the animals were killed. Both danazol and testosterone appeared to be uterotropic after 3 days of treatment, although the increase in the uterine weight was significant only in the danazol-treated group ( p < 0.05). This effect was lost after 17 days of treatment. Estradiol receptor binding assays were done on the cytosolic and nuclear fractions of the homogenized uterine tissue of each group. The estrogen binding capacity of cytosols was increased in both the danazol ( p < 0.05) and the testosterone ( p < 0.01) groups after 3 days of treatment. A parallel increase was found in the nuclear fraction of both groups. After 17 days of treatment, the comparison between the 3 groups showed no differences in the cytosolic or nuclear estrogen binding capacity. The information provided by this study suggests that some effects of danazol may be due to an androgenic action and that may be associated to increases in the free fraction of testosterone.