Luteolytic Action of Prolactin During Estrous Cycle of the Mouse

In the rat prolactin has been shown to exent a luteotropic action an newly formed corpora lutea and a lutmlytic effect on older corpora lutea (1). During each estrous cycle of the rat, luteolysis of corpora lutea from previous cycles occurs (2, 3). Recent work from our laboratory has shown that the proestrous surge of prolactin during the estrous cycle is responsible for luteolysis of the old corpora lutea (4). Billeter and Fluckiger (5) also reported a luteolytic action by prolactin when injected daily in cycling rats with an ergot drug (CB 154) for 21 days. In the mouse prolactin produces a luteotropic action on the corpora lutm (2), but a luteolytic action for prolactin has not been described. A brief report by Kwa and Verhofstad (6) states that during the estrous cycle of the mouse, blood prolactin rises beginning late in proestrus and reaches a peak early in estrus. It was of interest therefore to determine in the mouse whether inhibition of prolactin secretion by the drug ergocornine (EC) during proestrus and estrus could prevent luteolysis of the old corpora lutea, and whether concurrent administration of prolactin could induce luteolysis. EC previously was reported to decrease pituitary prolactin levels in the mouse (7) as well as in the rat (879).