Lordosis response of senile female rats.

The lordosis response of 27 ovariectomized senile female rats (20 to 32 months old) primed with either estrogen-progestrone (E/P) or estrogen (E) alone was studied and compared with that of ovariectomized young adult rats (3 to 5 months old). As compared with the young rats, out of the 27 senile rats, only 11 showed decreased response with E/P priming and 6 with E priming only. When senile rats are classified into 4 groups according to their vaginal smear pictures and ovarian findings, i.e., prolonged vaginal cornification (PVC) with polyfollicular ovaries, anestrus (ANE) with atrophic ovaries, prolonged diestrus with hyperluteinized ovaries, and still preserved cycle, there is no significant difference in the incidence of decreased lordosis response among groups. In the 11 senile rats showing decreased response, the responsiveness of the system for sexual behavior to P seems to be decreased in 5 rats without changes in the responsiveness to E and that to E decreased in 6 rats. The lordosis response did not improve after adaptation in the rats which showed decreased response. The dysfunction of gonadotropin (Gn) secretion in senile female rats seems to occur earlier than aging of the system for behavioral estrus.