The Mating-induced Release of Prolactin: A Unique Neuroendrocine Response*

I. Introduction IN THE RAT, the corpus luteum is formed on the morning of estrus in response to the surge of luteinizing hormone released on the previous day, proestrus. However, unlike other mammals whose corpora lutea secrete increasing amounts of progesterone for several days (1), the newly formed corpora lutea of the rat secrete progesterone for only 2 days after formation (2, 3). In the absence of all other input, the corpora lutea subsequently fail and progesterone secretion wanes (3). It has long been appreciated that rodent corpora lutea could be maintained by either coital stimulation (4) or injection of pituitary extracts containing prolactin (PRL) activity (5, 6). An overwhelming literature now indicates that the mating stimulus induces the release of PRL which in turn “rescues” the corpora lutea of the cycle and prolongs the ability of these structures to secrete progesterone (3, 7–11). The mating stimulus or copulomimetic stimuli applied to the uterine cervix with a glass rod or appropriately...