Corpora lutea formed after post-partum ovulation in the rat become functionally active under the influence of prolactin released as a result of suckling. During this period of luteal activity (lactational pseudopregnancy) ovulations do not occur. Despite continued suckling plasma prolactin declines gradually during lactation but this gradual decrease was not observed when adrenalectomy was performed on day 2 of lactation. The prolongation of lactational pseudopregnancy after adrenalectomy is probably associated with this observation. Daily treatment of adrenalectomized lactating rats with 5 mg corticosterone acetate, but not with 1·5 mg, reduced the duration of lactational pseudopregnancy to that of controls.
Removal of litters of five pups on day 13 of lactation was followed by resumption of ovulation 3 days later in control animals. However, in adrenalectomized rats the interval between removal of the five-pup litter and the next ovulation was prolonged to 10 or more days because of the persistence of luteal activity. This prolonged interval in adrenalectomized rats was not caused by an acute effect of the absence of adrenal hormones since it was not observed in rats which had been adrenalectomized 3 days before removal of the litter. Furthermore, the increase in the interval between removal of the five-pup litter and resumption of ovulation was also not due to the absence of the main glucocorticoid in the rat, since daily treatment with corticosterone from the day of adrenalectomy failed to prevent the occurrence of the long delay. Adrenal transplants could, however, prevent the effect induced by adrenalectomy. Since the medulla of these transplants had become necrotic, it seems that factors of adrenocortical, but not of adrenal medullary origin, are important in preventing the occurrence of the prolonged interval.
It is concluded that the adrenal glands affect the regulation of prolactin secretion during lactation and, as a consequence, are important in establishing the duration of the anovulatory state during lactation.
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