PARS GLANDULARIS AND LACTATION 



spite the injection of progestin or progesterone to term. 

 Gomez and Turner (1938) suggest that a pituitary "mam- 

 mogenic" hormone is secreted in response to an oestrogen or 

 to an oestrogen and progesterone and that this hormone, per- 

 haps made up of two components, brings about the growth of 

 the mammary ducts and the development of the lobules and 

 their alveoli. The authors injected simple preparations of the 

 anterior pituitary of pregnant or non-pregnant heifers into 

 a small number of rats and rabbits which had been spayed 

 when immature. The administration of anterior pituitary 

 from non-pregnant heifers — although lactogenic hormone was 

 present in the injected anterior pituitary — did not affect the 

 mammary gland. On the other hand, if anterior pituitary of 

 pregnant heifers was injected for several weeks, mammary 

 development corresponding to advanced pseudopregnancy 

 or pregnancy could be produced both in rabbits and rats. 



These results indicate that the growth and development 

 of the breasts are as dependent upon the pars glandularis as 

 lactation itself. A complex interplay of the hormones of the 

 anterior pituitary and the ovary may take place normally. 

 Gonadotropic hormone secreted by the anterior pituitary 

 maintains ovarian function, whence arises the secretion of 

 oestrogen and progesterone. In non-pregnant animals oestro- 

 gen chiefly causes the formation and liberation of a substance 

 from the anterior pituitary, so that partial growth and de- 

 velopment of the breasts occur. In pregnant animals the 

 production of "mammogenic" hormone(s) is increased further 

 not only by the increased quantities of oestrogen produced in 

 the ovaries and placenta but also by the added stimulation 

 afforded by the prolonged secretion of corpus luteum hor- 

 mone. As a result, full development of the breasts prepara- 

 tory to lactation occurs. The lactogenic hormone of the 

 anterior pituitary then initiates the secretion of milk. 



Progesterone as a factor in the development of the mammary 

 glands. — Progesterone, the secretion of the corpus luteum, is 



