Effects of copulation on reproductive function in aged female rats

Old female rats in persistent vaginal estrus (PVE) were exposed to varying degrees of copulatory stimulation. While limited mating experiences had no noticeable effects on reproductive function, cohabitation with sexually vigorous males or other forms of exposure to extended mating experiences disrupted the PVE state. Prolonged diestrus, irregular cycles, pseudopregnancy and pregnancy were observed subsequent to extensive copulatory experiences. Except for a tendency to be less receptive to initial mounts old females displayed sexual behavior comparable to that observed in younger, virgin animals. Ten or more intromissions disrupted the PVE. Induction of pregnancy or pseudopregnancy appears to require 30 or more intromissions in these animals. It is concluded that the PVE observed in aged female rats is at least partly due to the absence of coital stimulation. These observations are taken to suggest that age-related changes in the reproductive capacity of female rats may be attributable to alterations in the sensitivity of ovulatory and progestational mechanisms to hormonal and sensory influences.