114 Source o£ Equine Gonadotrophin 



hormone, the endometrium between the cups might be expected to contain 

 more hormone than the endometrium in the cup area because of the close 

 apposition of maternal and fetal tissues and consequently the better oppor- 

 tunity for exchange (pi. i, fig. i). On the contrary, however, the cups contain 

 twenty times or more hormone per gram and the total hormone in the cup is 

 at least three times greater, even though the total weight of the cup tissue is 

 much less than that of the intervening endometrium (tables i and 2). 



To what cells of the endometrium should one ascribe the secretion of 

 gonadotrophin? Presumably both the glands and the interglandular tissue 

 contribute to the endometrial-cup secretion. Also both tissues differ markedly 

 histologically from the endometrium between the cups. A number of cases 

 sacrificed just prior to and after the appearance of hormone in the blood 

 should provide additional evidence on this point. 



Summary and Conclusions 



Quantitative studies on the gonadotrophic concentration in the tissues of four 

 mares, sacrificed between the 62d and 105th days of pregnancy, were made, 

 coincident with histological studies of the endometrium and chorion, in order 

 to elucidate the source of equine gonadotrophin. Distributed over a part of 

 the endometrium in apposition to the chorion, specialized structures are found 

 which we have referred to as endometrial cups. These cups contain 4 to 12 

 I.U. of gonadotrophin per milligram of fresh tissue and furthermore they 

 elaborate a secretion into the uterine space containing 50 to 314 I.U. per milli- 

 gram of secretion in the fresh state. The histological character of both the 

 glands and the interglandular tissue of these cups differs conspicuously from 

 the endometrium in other areas. We conclude that these endometrial cups are 

 the chief source of equine gonadotrophin. 



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