Anti-estrogenic suppression of the lordosis response in female rats.

The anti-estrogen, Cl 628, was used to suppress the lordosis response induced by sequential injections of estrogen and progesterone in ovariectomired (OVX) female rats. Appropriate doses of Cl 628 completely abolished sexual receptivity in females administered estradiol benzoate (EB) in sesame oil. This behavioral effect could be attenuated by providing increased quantities of EB or decreased quantities of CI 628. Antiestrogenic effects on lordosis induced by free estradiol in saline (E) were assessed after first establishing behaviorally equivalent doses of EB and E. This was accomplished by determining thresholds for E-induced lordosis. OVX females were approximately seven times less sensitive to E than to EB. CI 628 had no significant effects on E-induced lordosis, in contrast to the complete abolition of lordosis in females treated with behaviorally equivalent EB doses. A possible mechanism to explain this differential responsiveness of EBand E-treated females is discussed.