940 



SPERM, OVA, AND PREGNANCY 



in the course of gestation as cytoplasmic 

 basophilia decreases. In the human tropho- 

 blastic syncytium, alkaline phosphatase 

 first appears in the outer eosinophilic (alka- 

 line) zone and seems to advance into the 

 syncytium as the basophilia recedes. In the 

 placentas of other animals listed above al- 

 kaline phosphatase is also usually localized 

 in regions which are acidophilic. Wimsatt 

 (1949) reported an exception to this inverse 

 relationship of basophilia and phosphatase, 

 because in the bat both substances are 

 plentiful during the first half of gestation, 

 whereas, in the second half, phosphatase 

 activity declines while basophilia persists. 

 Wislocki and Dempsey (1945) observed 

 from study of the placentas of various ani- 

 mals that a layer of phosphatase intervenes 

 between the maternal blood stream and re- 

 gions where glycogen accumulates. Hard 

 (1946) observed a similar spatial relation- 

 ship in the placenta of the guinea pig be- 

 tween alkaline phosphatase, on the one 

 hand, and accumulation of glycogen and 

 lipid on the other. Wimsatt (1948, 1949) re- 

 ported similar relations between the two 

 substances in the placenta of the bat. 

 Whether or not these two phenomena are 

 related has been debated (Wimsatt, 1949; 

 Pritchard, 1947). In this connection it is of 

 interest, as more has been learned about the 

 localization of glycogen by the use of the 

 PAS reaction, that the cellular elements of 

 the secondary and tertiary villi of the hu- 

 man placenta up to 6 weeks of gestation are 

 moderately rich in glycogen, at a time when 

 extremely little alkaline phosphatase has 

 made its appearance in the placental bar- 



rier. And later, as alkaline phosphatase in- 

 creases tremendously in amount, stainable 

 glycogen disappears completely from the 

 chorionic villi. 



Wimsatt (1949) observed that the troph- 

 oblastic cells of the membranous chorion 

 of the bat "contain heavy deposits of neu- 

 tral fat, phospholipids, and cholesterids" 

 and concluded that phosphatases, abun- 

 dantly present in the adjacent decidua, 

 "may be involved in the lipid metabolism 

 and transport in this portion of the placental 

 barrier." Regarding this he called attention 

 to the i:)ossibility that phosphatases in the 

 placental barrier provide a mechanism 

 whereby ciruclating fats are phosphoryl- 

 ated, thereby facilitating the absorption 

 and transmission of lipids. In this connec- 

 tion, it is interesting to note that Green and 

 Meyerhof (1952) have shown that these 

 enzymes can phosphorylate some com- 

 pounds under certain circumstances. 



C. ALKALINE PHO.SPH.\TASE AND 



THE PERIODIC ACID-SCHIFF 



(PAS) REACTION 



Moog and Wenger (1952) reported that 

 neutral mucopolysaccharide, as demonstra- 

 ble by the PAS reaction, occurs at sites of 

 high alkaline phosphatase activity and they 

 cite examples in various tissues and organs. 

 They suggested that the mucopolysaccharide 

 may serve as a cytoskeleton for the enzyme. 

 They described the placental labyrinth of 

 the mouse as an illustration of this relation- 

 ship, stating that the trophoblastic syncy- 

 tium is rich in both substances. However, 

 in the similarly constructed placental 



Plate 15.XVIII 



Visceral endoderm of the rat yolk sac 



Figs. 15.78 and 15.79. Cytologic distribution of lipids in the visceral ondoderm. Frozen 

 section, sudan black B. In Figure 15.78 the large clear nuclei have tiny clinlcslciol containing 

 droplets which are truly intranuclear. The infranuclear cytoplasm is packed uitli lar^irr diop- 

 lets which are also rich in cholesterol. At the surface of these cells note I he ddicalc sudano- 

 philia of the brush border and also the narrow sudanophobic band immediately beneath this 

 border. The supranuclear cytoplasm contains many unstained vacuoles (Fig. 15.78) and also 

 clusters of tiny lipid droplets (Fig. 15.79). In Figure 15.79 the plane of section runs obliquely 

 through the apical cytoplasm. Three large lipid clusters are shown. X 1950. 



Fig. 15.80. Electron micrograph of a visceral endodermal cell at 12 days of gestation. A 

 large homogeneous cholesterol rich droplet is located in the cytoplasm near the polymorphic 

 nucleus. Two minute droplets (d), which are also rich in cholesterol, occur within the nucleus. 

 The apical cytoplasm contains vacuoles which are heterogeneous with respect to size and 

 content. The limiting membrane of these vacuoles is usually incomplete. The free surface 

 of this cell is formed of numerous microvilli. Beneath the surface, many small canaliculi with 

 dense walls can be seen. X 7600. 



