Effects of the antiestrogen, RU 58668, on female sexual behavior in rats.

RU 58668 is a steroidal antiestrogen believed to be devoid of any partial agonist activity. Most of the work with RU 58668 has focused on its potential as an antineoplastic agent in the treatment of breast cancer, but it has not been tested for its effects on the brain and behavior. Other antiestrogens are problematic because most are either partial agonists or do not cross the blood-brain barrier. The purpose of this study was to test if RU 58668 blocks two classic estrogen-dependent behaviors: female sexual behavior and feeding behavior. We used a repeated measures design to examine if RU 58668 reversibly blocked female sexual behavior. RU 58668 significantly reduced both the level of sexual receptivity and the level of proceptivity in a reversible manner. Changes in body and food weight were also measured. Our results show that RU 58668 blocked estrogen's suppressive effects on feeding behavior and body weight. Therefore, RU 58668 is the first antiestrogen that blocks estradiol's effects on female sexual behavior while also inhibiting estradiol's effects on feeding behavior and body weight.