THE HORMONES IN HUMAN REPRODUCTION 



dometrium breaks down. Ovulatory menstruation is thus a 

 special case of estrin-deprivation bleeding. 



This explanation of the normal cycle is, of course, simply 

 a hypothesis which has been formulated to explain our ob- 

 servations. Whether things happen this way in the normal 

 monkey or in woman remains to be proved. It is at least not 

 contradicted by any of the known facts, and it has the merit 

 of simplicity, because it calls for a cyclic variation in only 

 one hormone, namely progesterone. Its one unproved as- 

 sumption, that progesterone somehow cuts down the action 

 of estrogen on the uterus, is supported by various other 

 evidences of a sort of antagonism between the two hormones 

 in some of their other activities. It has been suggested that 

 progesterone has the property of speeding the elimination 

 of estrogens from the body. If this proves correct it is all 

 we need to complete our hypothesis. 



This scheme does not explain anovulatory menstruation, 

 for in cycles without ovulation there is, of course, no coming 

 and going of the corpus luteum. Anovulatory menstruation 

 is therefore probably due to estrin-deprivation alone. We 

 can imitate it perfectly in castrate animals by simply giving 

 a course of estrogen injections interrupted or sharply 

 reduced at suitable intervals. What is actually happening 

 in the female organism remains to be worked out. We are not 

 yet sure that there is an actual up-and-down of estrogen 

 in the body sufficient to produce deprivation bleeding. The 

 daily assay of estrogens in the blood is very expensive and 

 at present not reliable enough for our purpose. Zuckerman 

 has shown that when a castrate monkey is kept on a rela- 

 tively small but constant daily dose of estrogen, there is a 

 tendency to occasional uterine bleeding which may become 

 fairly regular. We may conjecture, on this basis, that per- 

 haps some sort of give-and-take relation exists between 

 estrogen and some other hormone, just as between estrogen 

 and progesterone when the corpus luteum is present, so that 



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