MAMMARY GLAND AND LACTATION 





Fig. 10.20. Sections from abdominal mammary gland of rats from wliuli Ur- pups were 

 removed on the fourth day of lactation and which received thereafter for 9 daj^s: A. LO 

 I.U. synthetic oxytocin three times daily. B. Saline daily. Note the maintenance of gland 

 structure in A. (Courtesy of Dr. G. K. Benson.) 



galactopoietic complex from the anterior 

 lobe. It was hoped to gain further evidence 

 on this point by studies on hypophysecto- 

 mized rats bearing pituitary homografts 

 under the kidney capsule (see Benson, 

 Cowie, Folley and Tindal, 1959) . As already 

 noted, such grafts secrete prolactin and will 

 give a slight maintenance of milk secretion, 

 but these grafts will not maintain normal 

 milk secretion even when such animals are 

 injected with oxytocin and ADH (Cowie, 

 Tindal and Benson, 1960). It must, there- 

 fore, be assumed that if these posterior 

 pituitary hormones are responsible for the 

 release of the galactopoietic complex, some 

 other hypothalamic factor is also necessary 

 to maintain the anterior lobe in a responsive 

 condition. Everett (1956) suggested that 

 the hypothalamus by way of its neurovas- 

 cular connections with the anterior lobe, 

 normally exerts a partial inhibitory effect on 

 prolactin secretion. It may thus be that 

 when the anterior lobe is removed from 

 hypothalamic influence, the synthetic ac- 

 tivities of its cells are centered on prolactin 



production to the detriment of the other 

 components of the galactopoietic complex, 

 so that these are no longer available for re- 

 lease in response to neurohypophyseal hor- 

 mones. There is need, however, for experi- 

 mentation in other species. 



The theory that the release of the galac- 

 topoietic complex is effected by the hor- 

 mones of the posterior lobe secreted in re- 

 sponse to the suckling stimulus is attractive 

 in that it appears to afford a simple explana- 

 tion of the hormonal integration of mam- 

 mary function, but it must be pointed out 

 that the observations on the maintenance of 

 mammary structure after weaning by injec- 

 tions of oxytocin do not prove that prolactin 

 or the galactopoietic complex is released in 

 response to oxytocin under normal condi- 

 tions of milking or suckling, and more re- 

 search, particularly in species other than the 

 rat, is necessary. Grosvenor and Turner 

 (1958a) injected oxytocin into anesthetized 

 lactating rats and, on the basis of assays of 

 the pituitary content of prolactin, considered 

 that oxytocin caused no significant release of 



