THE ENDOMETRIAL CUPS AND ALLANTOCHORIONIC POUCHES IN THE MARE WITH EMPHASIS ON THE SOURCE OF EQUINE GONADOTROPHIN

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Abstract
Pregnant mares (108) with fetuses ranging from 2.2 to 81.3 cm (crown-rump length) were used in these studies. The gross appearance of the endometrial cups and allantochor ionic pouches was observed in all animals. Histological study was made on sections from cups in 22 mares distributed over the period when cups are present. The gonadotropic potency was determined for the cups and the secretion separately in 34 mares. In 64 mares, the combined gonadotropic activity of the cups plus secretion was evaluated. In 47 cases, assays were made on the blood serum. The cups begin to form in the endometrium at a fetal crown-rump (C. R.) length of 2.0 cm , reach full development at approximately 4.0 cm and undergo little change until approximately 10.0 cm. Desquamation of the cups begins at approximately 10.0 cm and is complete at a C. R. length of 30.0 cm. The most marked histological changes occurring are the enlargement of the uterine glands and the hypertrophy of the stomal cells. Gonadotropic activity of the endometrial cups was found in the earliest stages at which the cups could be detected and reached a maximum at approximately 15.0 to 20.9 cm. The pressure of the accumulating endometrial cup secretion pushes in the allantochorion until a sac-like structure, which is referred to as the allantochorionic pouch, is formed. These pouches are not always found even though desquamating cups and large amounts of secretion are present. The pouches diminish in size and have disappeared in most stages beyond 30 cm. C. R. length. Further evidence that the endometrial cups secrete gonadotropin is presented. The hormone appears in the blood coincident with the initial development of the cup. When stained histochemically for glycoprotein, the endometrial cup secretion, the uterine epithelium and the glandular epithelium are stained while the large "decidual" cells give little evidence of any reaction, indicating that the epithelial cells in the cup area are the source of gonadotropin.