Pheromonal male-induced diestrus and cyclicity in aging intact and young estrogenized female rats

Reproductive aging in female rats is characterized by irregular estrous cycles, repeated pseudopregnancies, persistent estrus, and a decline in fertility. The persistently estrous rats do not ovulate or show cyclic 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 persistent 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 whether the male factor that elicits ovulation in aging females is pheromonal 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 rats 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 contained in male urine. This fact suggests an important role of chemosensory communication in prolongation of the period with normal estrous cycles in the female's reproductive life.