THE HORMONES IN HUMAN REPRODUCTION 



This experiment works with some species of animals and not 

 with others ; we do not know surely about the human uterus in 

 this respect. In cats, strangely enough, progesterone sup- 

 presses the action of adrenalin on the uterus (something that 

 never happens in the rabbit) but does not suppress the action 

 of pituitrin. These differences present a remarkable and prob- 

 ably very subtle problem in the physiology of muscle. When 

 it is answered we shall know much more than we do now about 

 involuntary muscle and also about hormones. Details aside, 

 however, the experiment of Knaus shows us that progesterone 

 can act in a striking way on involuntary muscle. We owe to 

 S. R. M. Reynolds a very ingenious method of studying uterine 

 contractions in living rabbits. By a simple plastic operation, 

 done in a few minutes under complete anesthesia, the twin 

 cervices of the uterus are stitched to the belly wall and thus 

 made accessible. A rabbit so prepared suffers no inconven- 

 ience if properly cared for, and like any other healthy un- 

 frightened rabbit will lie quietly on her back for hours if 

 gently tied down. A tiny rubber balloon is carefully inserted 

 inside the uterus. From this a tube leads to a little bellows 

 which actuates a lever writing upon a revolving smoked drum. 

 Whenever the uterus contracts, the balloon is squeezed, the 

 bellows is inflated, and the lever goes up. With this apparatus 

 Reynolds found that the normal uterus of an adult female 

 rabbit undergoes more or less regular contractions. Castra- 

 tion suppresses the contractions, for the uterus which is 

 enfeebled by castrate atrophy (see page 79) becomes inactive. 

 Administration of estrogenic hormone, however, restores the 

 contractions. Progesterone promptly and effectively quiets 

 the uterus. The graph shown herewith (Fig. 18) illustrates 

 the effect of an injection of progesterone. At 10:20 a.m. the 

 uterus was contracting regularly. The hormone was given a 

 few minuteis later. In one hour (see third line of the graph) 

 the contractions became definitely smaller and less frequent. 



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