Cole and Goss 1 1 ^ 



fact that practically no hormone is present in fetal tissues (Catchpole and 

 Lyons^) makes the alternative supposition untenable. 



Endometrium. It is our belief that equine gonadotrophin is produced in 

 the endometrium and for the most part by the endometrial cups. Catchpole 

 and Lyons^ were the first to draw attention to the high concentration of hor- 

 mone in the fertile endometrium. Against the view that the endometrium 

 secretes the hormone, however, they cited the fact that the fertile endometrium 

 is high in hormone, whereas the infertile horn is low, even though both horns 

 undergo progestational proliferation. The finding of specialized structures, 

 the endometrial cups, confined solely to the fertile endometrium and very 

 rich in hormone, removes this objection. Another point which they raised 

 against the secretion of the hormone by the endometrium was that in one 

 early pregnancy case gonadotrophin was found in the chorion but not in the 

 endometrium or blood plasma. In this case, they reasoned, the hormone had 

 been produced in the chorion but had not as yet passed in recognizable 

 amounts to the other tissues. As previously pointed out, this case may be ex- 

 plained by assuming that the gluelike endometrial-cup secretion had adhered 

 to the chorion rather than to the endometrium. As this secretion is extremely 

 potent, a few milligrams of it would account for the total activity manifested 

 by the chorion. Even though the assumption of adherence of endometrial-cup 

 secretion to the chorion were false, the finding of hormone in the chorion 

 while it is absent in the endometrium of this mare (K5) is nullified as an argu- 

 ment for chorionic source of the hormone by the fact that in two other cases of 

 early pregnancy which they studied (D31 and D23) relatively large amounts of 

 hormone were present in the endometrium while the chorion contained none. 



Now that we have considered the objections raised to the secretion of 

 gonadotrophin by the endometrium, what is the positive evidence in favor of 

 this vicAV? 



1. The endometrial cups contain more hormone per gram than any other 

 tissue. The relatively minute amount of hormone in the chorion, in fact, 

 almost precludes it as a possible source (tables 1 and 2). 



2. The waxy material in the endometrial cups contains more hormone than 

 any tissue of the mare (in mare 3 up to 300 1.U. per milligram of fresh secretion 

 or 600 I.U. per milligram of total solids) and a major part of this material 

 which we have referred to as endometrial-cup secretion certainly is derived 

 from the endometrium. 



3. One can account for the coincident high concentration of the hormone 

 in the endometrial-cup secretion and in the blood most easily by assuming an 

 endometrial source. 



4. The endometrial cups are specialized structures to which one can at- 

 tribute special secretory activity. 



5. Considerable hormone is present in the endometrium between the cups 

 (table 2). This strongly suggests that the hormone is not formed exclusively 

 by the endometrial cups. If one were to assume chorionic production of the 



