PHEROMONAL MALE-INDUCED DIESTRUS AND CYCLICITY IN AGING INTACT AND YOUNG ESTROGENIZED FEMALE RATS

Reproductive aging in female rats is characterized by irregular estrou s cycles, repeated pseudopregnancies, persistent estrus, and a decline in fertility. The persistently estrous rats do not ovulate or show cy clic increases of LH despite continued ovarian follicular development. These rats ovulate after mating with fertile males. On the other hand , a single injection of estradiol to young female cyclic rats causes p ersistent anovulatory estrus similar to that of aging rats, which has suggested that young cyclic estrogen-primed females may be a model for the study of reproductive senescence. We attempted to determine wheth er the male factor that elicits ovulation in aging females is pheromon al in nature. The effect of such a pheromonal factor on the persistent estrus of young estrogenized females was also tested. We observed the estrous cycle of aging (7-13-mo-old) and young estrogenized female ra ts daily. Nasal spraying of urine obtained from young adult male rats induced diestrus and regular cyclicity in both aging intact and young estrogenized female rats, probably because of due to pheromones contai ned in male urine. This fact suggests an important role of chemosensor y communication in prolongation of the period with normal estrous cycl es in the female's reproductive life.