HISTOCHEMISTRY OF PLACENTA 



937 



chrouiophobic cells are postulated as being 

 the precursors of the chromoi:)hilic elements. 

 Little is known about the site of placental 

 gonadotrophin production in infrahuman 

 mammals. The PAS reaction provides little 

 information about possible sites of forma- 

 tion of the hormone in various animals, be- 

 cause the reaction occurs in many placental 

 components. This undoubtedly reflects the 

 presence of other carbohydrate-containing 

 substances besides the gonadotrophic hor- 

 mone. Several reports on the mare (Cole and 

 Goss, 1943; Rowlands, 1947; Amoroso, 1952; 

 and Clegg, Boda and Cole, 1954) indicate 

 that the equine gonadotrophin is produced 

 by special parts of the endometrium of the 

 maternal placenta called endometrial cups. 

 Observations of Clegg, Boda and Cole 

 (1954) suggest that the glandular epithe- 

 lium is the site of gonadotrophic hormone 

 production. A recent detailed discussion of 

 the comparative aspects of hormonal func- 

 tions was presented by Amoroso (1960). 



IX. Significance and Relationships of 

 Some Placental Constituents 



A. RIBONUCLEOPROTEIN 



Most of the cytoplasmic basophilia en- 

 countered in the trophoblast, uterine sur- 

 face epithelium, and cells of the endometrial 

 glands is due to the presence of ribonucleo- 

 protein. Because most embryonic or rapidly 

 growing cells are rich in this nucleoprotein, 

 it has been difficult to separate the ribo- 

 nucleoprotein associated with grow^th from 

 that related to the synthesis of specific 

 proteins by placental cells. Intense cyto- 

 plasmic basophilia occurs in the trophoblast 

 of the pig (Wislocki and Dempsey, 1946b), 

 cat (Wislocki and Dempsey, 1946a), ro- 

 dents (Wislocki, Bunting and Dempsey, 

 1947), and man. Basophilia is extremely 

 intense in the early part of gestation and 

 diminishes in the second half of pregnancy, 

 except in the pig in which it remains con- 

 stant and in the bat in which, according to 

 Wimsatt (1949), it becomes more pro- 

 nounced. In the human, it has been pro- 

 posed (Wislocki, Dempsey and Fawcett, 

 1948) that one of the functions of the ribo- 

 nucleoprotein of the syncytium is to synthe- 

 size the proteins of the fetal blood plasma 



before the fetal liver becomes sufficiently 

 differentiated to assume that activity, 

 whereas the ribonucleoprotein in the periph- 

 eral trophoblasts might conceivably be re- 

 lated to the formation there of gonado- 

 trophic hormone. Consonant with the former 

 thought is the gradual decline in cytoplas- 

 mic basophilia as pregnancy progresses. 



Ribonucleoprotein is closely associated 

 with the secretory activities of uterine 

 glands. The surface epithelium and glands 

 of the uterus, just before and during gesta- 

 tion, are rich in basophilic substance, great- 

 est in amount in the pregnant sow, interme- 

 diate in carnivores, and least in rodents and 

 in pregnant women (Wislocki and Dempsey, 

 1945). In the epitheliochorial placenta of 

 the sow, all of the nutritive substances ob- 

 tained by the fetus must either traverse or 

 be secreted by the uterine surface epithelium 

 or the uterine glands. The glands which are 

 rich in ribonucleoprotein release a copious 

 secretion which reacts intensely with PAS 

 reagents (mucopolysaccharide), but is not 

 metachromatic. It gives a strong reaction 

 for acid phosphatase. This secretion, desig- 

 nated as uterine milk, seems to be absorbed 

 mainly by the cells of the chorionic fossae 

 and areolae. In the cat, the markedly baso- 

 philic paraplacental uterine glands release 

 a secretion w^hich is rich in mucopolysac- 

 charide, glycogen, and phosphatases and is 

 absorbed l)y the columnar cells of the brown 

 border of the chorion. The subplacental 

 glands of the cat are strongly basophilic, 

 but react only faintly with PAS reagents. 

 In rodents, the uterine glands and surface 

 epithelium also seem to secrete nutriment 

 which is absorbed through the yolk sac pla- 

 centa. These secretory cells are basophilic, 

 and their distal cytoplasm and secretion 

 react intensely for mucopolysaccharide with 

 PAS reagents. In the human, at the time of 

 implantation and for a considerable period 

 thereafter, the paraplacental and subpla- 

 cental glands are moderately basophilic and 

 contain glycogen, PAS-reactive mucopoly- 

 saccharide, lipids, and phosphatases. More- 

 over, unlike the uterine glands of various 

 animals, their secretion contains some meta- 

 chromatic mucin (Wislocki and Dempsey, 

 1948). The secretion of the glands located 

 in the basal decidua may supply the growing 



