PARS GLANDULARIS AND LACTATION 



normal secretory activity of the ovaries; ovarian secretions 

 (or placental secretions, or both in pregnant animals) bring 

 about the elaboration of a new anterior pituitary secretion 

 which causes growth and development of the mammary 

 glands. 



Provided that prelactation development has occurred in 

 the breasts, another anterior pituitary hormone — the lacto- 

 genic hormone — brings about lactation. However, this hor- 

 mone alone cannot initiate lactation in hypophysectomized 

 animals. Perhaps because of its effects on salt metabolism, 

 adrenal cortical hormone must also be available to the 

 organism. In hypophysectomized animals lactation from 

 adequately developed breasts can be initiated by the injec- 

 tion of lactogenic hormone in combination with adrenal cor- 

 tical hormone from the adrenals or adrenal cortical stimu- 

 lating hormone from the pituitary. It is probable that the 

 maintenance of lactation depends upon additional hormones, 

 including those responsible for the continued development 

 of the breasts. 



The greater part of the attention of investigators has been 

 focused on the lactogenic hormone. This substance appar- 

 ently has been isolated as a crystalline substance, which is 

 either a protein or is closely related to proteins. It is con- 

 veniently assayed by its stimulating effect on the growth of 

 the crop-glands in the pigeon. In the rat, at least, its libera- 

 tion from the pars glandularis largely depends upon centripe- 

 tal nervous impulses due to suckling. The amount of hor- 

 mone secreted during lactation may exceed the needs of the 

 mammary glands, so that the unused portion is excreted in 

 the urine. Other data concerning the physiology of the lac- 

 togenic hormone are discussed not only in this chapter but 

 also in the two which precede it. 



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