Bile, prolactin, and the maternal pheromone.

When bile from females that had been lactating for 21 days was injected into the cecum of male rats it induced release of a maternal pheromone. Males injected with bile drawn from females in which prolactin had been inhibited, or from females that had been lactating for only 5 days, did not emit the pheromone. These data suggest a sex difference in the way prolactin alters the composition of bile so that the female can emit the maternal pheromone while the male normally cannot.