Influence of danazol on cytoplasmic and nuclear estrogen binding capacity in the uterus

Sprague-Dawley rats with estrous cycles were exposed to danazol (Danocrine) at a single dose of 10 mg/kg for either 6 or 24 hours, or daily until a pattern of no cycles (6 days) was noted on vaginal smears. The animals were individually housed and exposed to a 14-hour light/10-hour dark environment. Prior to drug administration, daily vaginal smears were obtained to ensure cycle normalcy. After the appropriate exposure to medication, the animals were killed, the uterine horns were removed, and determination was made of cytoplasmic and nuclear estrogen receptors. The animals in the control group (6 and 24 hours, and daily injected) received vehicle only (mineral oil). The influence of danazol on sex-steroid receptor levels appeared to be related to the phase of the estrous cycle at the time of sacrifice. At both 6 and 24 hours of exposure to danazol, there was a slight decrease in specific estrogen binding capacity of cytosols, with no alteration in the levels of nuclear receptors in the uteri of rats with cycles. In the groups with no cycles, there was an increase in cytosolic estrogen binding capacity at 1 and 6 days of danazol treatment, with a slight decrease in nuclear receptor binding when compared with treated rats with cycles. Statistical evaluation revealed a significant difference in cytosolic estrogen binding capacity between the series with cycles and the series without cycles (p less than 0.01). This study provides further information in regard to danazol action on cytosol and nuclear receptors correlated with phase of the estrous cycle.