PARS GLANDULARIS AND LACTATION 



stimulation of the release of lactogenic hormone from the 

 pars glandularis is prevented by section of the spinal cord. 

 The author severed the spinal cord between the last thoracic 

 and first lumbar segments in lactating rats and covered the 

 6 upper nipples, which were still sensitive, with tape. Despite 

 vigorous suckling of the insensitive nipples, the young died 

 within 48 hours. However, if only two sensitive nipples were 

 left exposed or if a hemisection of the spinal cord was per- 

 formed, lactation continued in the breasts of the anesthetized 

 and paralyzed abdomen. Reece and Turner (1936) investi- 

 gated the effect of suckling and removal of the secreted milk 

 on the amount of lactogenic hormone in the pituitary of 

 lactating rats. In terms of pigeon-units, the results obtained 

 in one set of observations are given in Table 4. Thus, it ap- 



TABLE 4 



Units per Gland 



I. Normal suckling 7.7 



1. Accumulation of milk without suckling tor 15 hours. 9.2 



3. No suckling for 12 hours followed by suckling tor 



3 hours 31 



4. Suckling (as in 3) but without removal ot milk due 



to ligation of main galactophores 5.2 



pears that suckling causes a marked release of stored lacto- 

 genic hormone and that the removal of accumulated milk 

 may be an additional factor. 



Lactogenic hormone as a factor in promoting the secretion of 

 milk in hypophysectomized a?iimals. — It is well known that 

 lactation promptly ceases after the pituitary body has been 

 removed from lactating animals. For the restoration of lac- 

 tation in such animals the lactogenic hormone is necessary 

 but not sufficient. Several authors have pointed out that 

 crude anterior pituitary extracts will again initiate lacta- 

 tion in hypophysectomized mammals, whereas refined lacto- 

 genic extracts will not (Gomez and Turner, 1936; Nelson and 

 Gaunt, 1936). 



[159] 



