Studies Concerning the Mechanism Controlling the Initiation of Lactation at Parturition I. Can Estrogen Suppress the Lactogenic Hormone of the Pituitary?1,2

THE MECHANISM RESPONSIBLE for the control of the initiation of lactation at parturition has long remained a mystery. No definite progress was made on this problem until 1928 and 1929 when Strieker and Grueter (1, 2) announced the discovery of a factor in the pituitary which was capable of initiating lactation in animals whose mammary glands had been suitably developed. This work was soon confirmed in this country by Corner (3), Nelson and Pfiffher (4), Asdell (5), and Turner and Gardner (6). Riddle and his coworkers (7, 8) suggested the use of the pigeon as a sensitive assay animal, which has proven invaluable in the study of the chemistry and physiology of this hormone. Excellent extraction methods for obtaining lactogen in relatively pure form were devised by Bates and Riddle (9), Lyons (10), and Bergman and Turner (11).