Observations on the Reproductive Pheromones of Mice

Summary. Ovo-implantation is blocked in over 80% of newly mated female mice by exposing the females to fresh urine of alien (CBA) males. The same effect is also produced by topical application of male urine to the females three times a day. Pseudopregnancy induced by sterile mating is also blocked by exposure of the females to the fresh urine of alien males. Urine of alien males collected in a mixture of antibiotics and an antioxidant and stored for 1 to 7 days retains the pregnancy-blocking capacity to a large extent. The percentage of pregnancy failures in untreated controls is close to the percentage of spontaneous failure of pregnancy in undisturbed females. Hence it is concluded that urine is the immediate source of the pheromones produced by male mice which cause the failure of ovo-implantation in newly mated females.