The pheromonal restoration of cyclic activity in young estrogenized persistent estrus female rats is a vomeronasal effect.

Eight sham-operated (SO) and six vomeronasalectomized (VMNX) young adult female rats were used to demonstrate the participation of the vomeronasal organ (VNO) in the pheromonal restoration of cyclic activity (PRCA). All rats were normal four-day cycling before and after surgery and they received a single subcutaneous injection of 2 mg of estradiol benzoate (EB) to induce an anovulatory persistent vaginal estrus. Fifteen days after EB injection, they were treated by spraying in the nostrils, every 10 min for one hour on only one day, 50 muL of urine from young fertile males. SO rats showed PRCA in the following days, while VMNX did not. These results support the VNO as the receptor of the male urinary pheromone (or pheromones) responsible for PRCA, demonstrating that it is possible to improve the function of aging ovaries acting with an exteroceptive stimulus.