Olfactory environment and coitus-induced ovulation and/or luteinization in the cyclic female rat

The role of pheromones in the process of ovulation and/or luteinization induced by coitus was studied in female rats primed with estradiol benzoate (EB) and early mated during 4-day cycles. The effects of coitus were evaluated by using 1) the proportion of females displaying postovulatory corpora lutea (POCL) and/or luteinized unruptured follicles (LUF), and 2) the ovulation coefficient (OC) computed in each female by dividing the number of POCL by the total number of POCL and LUF. A greater proportion of females displayed ovulation and/or luteinization following coitus than those given EB only. This proportion was slightly but significantly increased when females were exposed to bedding soiled with 5 ml of male urine prior to mating, an effect prevented by complete olfactory bulbectomy. However, in the females given EB only, the pheromonal stimulus remained inefficient. Weak ovulatory effects of coitus, as assessed by low OC values, were noted whether the females were exposed or not to male urine. An increase in the frequency of lordosis occurred after olfactory bulbectomy, but no significant changes in OC values were observed in this experimental group. It was concluded that pheromones, act as a primer on the neuroendocrine mechanisms governing ovulation in the cyclic female rat, as in other species of rodents.