624 



PHYSIOLOGY OF GONADS 



Fig. 10.18. Surface view of contracted alveoli (of goat) showing myoepithelial cells. 

 (Courtesy of K. C. Richardson.) 



Fig. 10.19. Recording of pressure changes witliin 

 a galactophore of a forcibly restrained lactating 

 rabbit. The litter was allowed to suckle the non- 

 cannulated mammary glands but obtained only 

 8 gm. milk, there being only a slight rise in the 

 milk pressure probably associated with a slight 

 contraction of the myoepithelium in response to 

 mechanical stimulation. When 5 mU. oxytocin were 

 injected (5P) there was a rapid milk ejection 

 response which could be inhibited by injecting 1 

 yug. adrenaline (lA) just before the oxytocin. After 

 a few minutes 5 mU. oxytocin were again effective 

 and the litter obtained 44 gm. milk when they were 

 allowed to suckle. A more complete milk ejection 

 respon.so was obtained with 50 mU. oxytocin (50P) 

 and the young obtained a further 59 gm. milk. 

 Anesthesia did not enhance the milk-ejection re- 

 sponse to 50 mU. oxytocin. During emotional in- 

 hibition of milk ejection the mammary gland thus 

 remains responsive to oxytocin. (From B. A. Cross, 

 J. Endocrinol., 12, 29-37, 1955.) 



(19ooi who studied the local effects of 

 liighly purified oxytocin and vasopressin 

 and a number of other drugs on the mam- 

 mnry gland, and confirmed that oxytocin 

 and vasopressin produced alveolar contrac- 

 tion and widening of the ducts. Although in 

 these experiments the myoepithelial cells 

 themselves could not be visualized, never- 

 theless the effects observed leave little 

 doubt that the effector mechanism was the 

 niyoei)ithelium. 



The myoepithelium is responsive to stim- 

 uli other than those arising from the pres- 

 ence of neurohypophyseal hormones in the 

 blood inasmuch as partial milk ejection 

 may occur in response to local mechanical 

 stimulation of the mammary gland (Cross, 

 1954; Yokoyama, 1956; see also Fig. 10.191. 

 These observations may explain the recent 

 reports by Tverskoi (1958) and Denamui- 

 and Martinet (1959a, b) that milk yields 

 can be maintained in goats in the absence of 

 the milk-ejection reflex. 



E. INHIBITION OF MILK EJECTION 



(laines (1915) stressed that the conduc- 

 tion in the milk-ejection reflex pathway was 

 dei)endent on the psychic condition of the 



