The effect of anterior pituitary extracts on established lactation in the cow

In 1928 Strieker and Grueter found that the administration of a crude anterior pituitary extract to rabbits, which had been ovariectomized during pseudopregnancy, resulted in the secretion of milk. This result was of fundamental importance as it suggested that the stimulus to the onset of lactation after parturition was the secretion of a substance by the pituitary gland, and not merely the removal of the stimuli which cause growth of the mammary gland during pregnancy. The results of Strieker and Grueter have been widely confirmed, and at the present time the theory is generally accepted that initiation and maintenance of lactation are controlled by the anterior pituitary gland. The chief evidence for this theory, which has been adequately reviewed recently by Nelson (1936), is, briefly, that normal lactation does not occur spontaneously in the absence of the pituitary gland, although the secretion of milk may, in suitable circumstances, follow the administration of anterior pituitary extracts to normal or hypophysectomized animals.