THE SOURCE OF EQUINE GONADOTROPHIN 



THE BLOOD and tissues of a mare at the 70th day of pregnancy contain 1 to 4 

 million I.U. of gonadotrophin. This paper relates to the source of this 

 hormone. Catchpole and Lyons^ considered this question and concluded that 

 the chorion produced the hormone on the basis of their findings: 



1. The mare pituitary gives very little histological or physiological evidence 

 of increased secretory activity at the time when the hormone level is increasing 

 rapidly. 



2. Large amounts of hormone are stored in the endometrium. To accept 

 the view of hypophysial origin one must assume that the hormone is selectively 

 accumulated in the fertile horn of the uterus. 



3. One case of early pregnancy was found in which hormone was present in 

 the chorion but not in the blood or endometrium. This, they felt, gave evi- 

 dence that hormone was first formed in the chorion from which it later passed 

 to the endometrium and maternal blood. 



4. The endometrium in contact with the chorion is much richer in gonado- 

 trophin than is the endometrium of the infertile horn, though marked proges- 

 tational proliferation occurs in both. 



In 1937 we had occasion to test the potency of the endometrium of several 

 mares and were struck by the cup-shaped structures distributed over that part 

 of the endometrium in contact with the chorion. Testing of these cups re- 

 vealed an extremely high potency as compared to the intervening endo- 

 metrium. As we did not take samples of these organs for histological study 

 or attempt to make quantitative studies on the amount of hormone in vari- 

 ous tissues, publication was withheld until more complete data were available. 

 In 1941 we had an opportunity to obtain material from four grade Welsh pony 

 mares at known stages of pregnancy, and this material forms the basis of the 

 present report. The high concentration of gonadotrophin in these cups led 

 us to suspect that they might be the source of the hormone. The present studies 

 were initiated to determine the validity of this view. 



We shall first describe these structures briefly and then present the data 

 comparing the potency of these cups with other tissues of the mare. 



Description of the Endometrial Cups 



Most of the early workers studying the changes in the endometrium of the 

 pregnant mare failed to observe these structures because of lack of material 

 during the stages in which they are present. Schauder^ has described them, 

 however, in considerable detail and we shall only attempt to add to his de- 

 scription. He expressed the view that the hippomanes of the horse are derived 

 from these cups— an opinion which we can confirm, in part at least, for in 

 mare 4, sacrificed at the 105th day of pregnancy, the cups appear as pendulous 

 structures from the allanto-chorion extending into the allantoic cavity, 



1:107] 



