THE LACTOGENIC HORMONE 



and growth-promoting hormones of the pars glandularis and 

 from prolan. They concluded that the lactogenic hormone 

 could be found only in the pars glandularis of the pituitary. 

 Methods of preparing lactogenic extracts have been described 

 by Gardner and Turner (1933), Lyons and Catchpole (1933), 

 and by Riddle and his colleagues (1933). 



According to Gardner and Turner (1933) and xAnselmino 

 and Hoffmann (1934), the lactogenic hormone is heat-labile, 

 being readily inactivated in solution at temperatures of 60°- 

 70° C. within 5-15 minutes. On the other hand, Riddle and 

 others (1933) reported that the potency of a lactogenic ex- 

 tract in aqueous solution at pH 7.5-8.5 was only slightly re- 

 duced after the solution had been boiled for i hour. At other 

 hydrogen-ion concentrations, higher or lower^ partial or com- 

 plete destruction was caused by this treatment. Bates, 

 Riddle, and Lahr (1934) found that tryptic digestion de- 

 stroyed the lactogenic properties of an extract. 



THE PARS NEURALIS AND LACTATION 



Nothing significant has been added to our knowledge of the 

 relationship between the hormone(s) of the pars neuralis and 

 the secretion of milk.^' Probably extracts of the pars neu- 

 ralis do not affect the activity of the secretory cells but simply 

 cause the contraction of smooth muscle, or of cells resembling 

 those of smooth muscle, so that nearly all the milk already 

 secreted can be removed from the alveoli, secondary ducts, 

 and galactophores.^" There is no evidence that the hormones 

 of the pars neuralis are of any physiological importance in 

 lactation. 



''See Gelling (1926); Sharpey-Schafer (1926); and Trendelenburg (1929) for 

 reviews of the literature. 



'" For recent experiments in the milch cow and in lactating women, see Turner 

 and Slaughter (1930), and Kulka (1933). 



245] 



