Effect of Hypophysectomy upon Pregnancy and Lactation in Mice

Abstract

In the rat, hypophysectomy during lactation leads promptly to cessation of milk secretion; 1 hypophysectomy during the second half of pregnancy does not usually prevent the birth of living young nor the development of the mammary glands, in fact milk secretion begins normally at parturition but ceases within 26 hours. 2 Caesarian section shortly before term regularly induces lactation, but fails to do so if the pituitary is removed. 3 Mammary development in virgin rats under the influence of ovarian hormone secretion stimulated by the anterior-pituitary-like hormone leads to milk secretion when the luteinized ovaries are removed, but this reaction also does not occur in the absence of the pituitary. 4 These findings are in accord with the view of Riddle, 5 Turner, 6 and others that a specific hormone of the anterior pituitary is responsible for the actual initiation of lactation, and that a sudden decrease in the amount of ovarian hormones in the circulation is a stimulus for the production of this hormone (Nelson and Smelser 7 ), but they also indicate that the contents of the pregnant uterus may take the place of the anterior pituitary in this reaction.

We have recently succeeded in hypophysectomizing albino mice by a parapharyngeal operation, almost identical with the modified Smith procedure used by us in rats and described elsewhere. 8 In the mouse the pituitary is situated somewhat more caudally, relative to the spheno-occipital synchondrosis; the bone is therefore drilled exactly over this synchondrosis. We have experienced no trouble from hemorrhage, no mice have been lost during the operation, and the post-operative mortality has been somewhat lower than in rats.

Six mice, 3 months of age, were hypophysectomized on the second or fourth day of lactation. All recovered from the operation and attempted to rear their litters, but milk secretion failed and within 24 hours the stomachs of the young were empty.