THE HORMONES IN HUMAN REPRODUCTION 



This question is now the key problem in the theory of 

 menstruation, and it remains unsolved. The attack upon it is 

 in the stage of skirmishing, in which all the possible explana- 

 tions are being put forward for discussion and trial ; but up 

 to the present no one of them has found support by experi- 

 ment. The reader may, however, be interested in the mental 

 processes of a group of puzzled investigators, and therefore 

 I list the conjectures for what they are worth. To merit 

 consideration at all, any explanation must fit the facts that 

 (a) hormone withdrawal causes uterine bleeding; (b) this 

 does not take place at once, but only after 3 to 8 days; 

 (c) the bleeding, once hormone deprivation is well under 

 way, cannot be postponed by renewed injections of estrogen 

 or progesterone; (d) it takes place in grafted bits of en- 

 dometrium (in the eye or elsewhere) which have no con- 

 nection with the nervous system. 



Since all of these conjectures involve the arteries, it may 

 be helpful to recall the fact that the walls of an artery 

 contain numerous cells of involuntary muscle, laid on in 

 circular fashion around the inner tube (endothelium) that 

 conducts the blood. When these muscle fibers contract, they 

 squeeze down upon the blood stream like a man's fingers 

 abput a rubber bulb. It is thus that the blood pressure is 

 raised by a dose of adrenin or by a strong emotional state, 

 both of which cause the arterial muscle cells to contract. 

 Such muscular cells exist in the coiled arteries of the uterus 

 as in all other arteries (Appendix II, note 13). 



Hypothesis 1. It may be that the coiled arteries are pe- 

 culiarly and directly dependent upon the ovarian hormones, 

 in some such way (for example) as the ovary is dependent 

 upon the pituitary. This means that withdrawal of the 

 ovarian hormones would let down the condition of the 

 coiled arteries, causing them to contract. This hypothesis is 

 the simplest, calling for no other hormones or special sub- 

 stances, but it is exceedingly difficult to try out, for the only 



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