THE LACTOGENIC HORMONE 



growth of the mammary glands and lactation, comparable 

 to that following normal pregnancy, by injecting an extract 

 of the whole pituitary body of the sheep into adult, virgin, 

 spayed rabbits. Inasmuch as the rabbit does not ordinarily 

 ovulate except after copulation, it was reasonable for Corner 

 to conclude that the lactogenic hormone can cause the secre- 

 tion of milk in the absence of any previous conditioning of 

 the mammary gland by corpus luteum hormone. Similar 

 results in the rabbit were obtained by Lyons and Catchpole 



(1933)- 



Instead of favoring the action of the lactogenic hormone, 

 once growth of the breasts has occurred, the ovary and its 

 internal secretions seem rather to antagonize it. Lyons and 

 Catchpole (1933) reported that merely the removal of the 

 ovaries from the adult, virgin rabbit may be followed by 

 lactation for as long as a month (apparently maintained by 

 the lactogenic hormone of the animal's own pituitary). Nel- 

 son (1935) transplanted the ovary into the male guinea pig; 

 if the ovarian graft was removed, lactation set in and was 

 often pronounced. He also found that ovariectomy alone 

 might be followed by lactation in the guinea pig. According 

 to Selye and his colleagues (1933), lactation promptly ap- 

 pears in the mature or immature rat after the removal of the 

 ovaries if pronounced luteinization has been produced in the 

 latter by injections of prolan." Likewise, the removal of the 

 ovaries of the pregnant rat is followed by lactation within 24 

 hours (Collip, Selye, and Thomson, 1933). From studies in 

 the mouse, Bradbury (1932) concluded that ovariectomy 

 (and/or hysterectomy) was followed by lactation provided 

 that an anterior-lobe extract had been administered to cause 

 a development of the alveoli of the mammary gland. The 

 anterior-lobe extract caused considerable luteinization of the 



7 Lactation does not appear if the pituitary has been removed before ovariec- 

 tomy. 



[239] 



