HI8T0CHEMLSTRY OF PLACENTA 



897 



not represent the true location of the en- 

 zyme, because on localizing the enzyme 

 by both histochemical and biochemical 

 methods and comparing the results, Palade 

 ( 1951 ) found in the case of the hepatic cells 

 of the rat that the enzyme was confined al- 

 most entirely to the cytoplasm. Further- 

 more, recent biochemical evidence indicates 

 that this enzyme is located in a particular 

 cytoplasmic fraction, the lysosomes (De- 

 Duve, 1959). 



High esterase activity is demonstrable in 

 the troi)hoblast following the use of the 

 method of Barrnett and Seligman ( 1952) on 

 unfixed frozen sections ( Wislocki, 1953) . It 

 could not be determined with certainty 

 whether the intense but poorly localized 

 crystalline reaction product was entirely 

 in the syncytium or whether some was pres- 

 ent in the Langhans cells (Fig. 15.36). With 

 the method for esterase (Nachlas and Selig- 

 man, 1949) carried out on sections of ace- 

 tone-fixed, paraffin-embedded material, the 

 <trophoblast shows no reaction. Acetone 

 fixation destroys cholinesterases and some 

 aliesterase, as a consequence of which a 

 tissue poor in aliesterase would be negative. 

 The combination of the positive Barrnett 

 and Seligman reaction on unfixed frozen 

 sections and of the negative reaction by the 

 method of Nachlas and Seligman on ace- 

 tone-fixed sections indicates that cholines- 

 terases and possibly a small amount of 

 aliesterase are present in the trophoblast. 

 Cholinesterase has been found in high ac- 

 tivity in the human placenta by chemical 

 means (Torda, 1942; Ord and Thompson, 

 1950). Acetylcholine has been reported by 

 a histochemical method devised by Wen, 

 Chang and Wong (1936) as occurring in 

 large amounts in the border and on the 

 surface of the syncytium. 



The indophenol oxidase reaction was per- 

 formed with the nadi reagents on fresh, 

 unfixed, teased villi, and on unfixed, frozen 

 sections of human placenta of the 6th week 

 of gestation (Dempsey and Wislocki, 1944). 

 Indophenol blue appeared in the syncytium 

 (Fig. 15.5), where it was interpreted as re- 

 vealing the presence of the cytochrome oxi- 

 dase-cytochrome c system. In contrast to 

 the syncytium, the stroma of the villi did 

 not give the indophenol reaction. 



A series of reduction-oxidation indicators 



was similarly applied to placental villi. The 

 syncytium concentrated the dyes in their 

 oxidized form, whereas the stroma of the 

 villi reacted far less intensely. These results 

 indicate that the syncytium is maintained 

 in the air at a more positive reduction- oxi- 

 dation potential than the stroma and are in 

 keeping with the similar distribution of in- 

 dophenol l)lue. 



3. Stroma of the Chorionic Villi; Hofbauer 

 Cells 



The stroma of the villi consists of mes- 

 enchymal connective tissue composed of 

 cells, argyrophil reticular fibers, and fetal 

 blood vessels. The surface of the stroma 

 upon which the syncytium and Langhans 

 cells rest is condensed into a basement mem- 

 brane assumed to be composed of argyro- 

 philic reticular fibers and ground substance. 

 This membrane stains deeply with con- 

 nective tissue stains, such as Mallory's 

 and Heidenhain's azan (Fig. 15.9). It is 

 stained also with varying intensity by the 

 PAS reagents (Figs. 15.29, 15.32 and 15.54), 

 the reaction probably being attributable to 

 a ground substance consisting of mucopoly- 

 saccharide or glycoprotein which surrounds 

 the reticular collagenous fibers. The mem- 

 brane is quite variable in intensity of stain- 

 ing and definition, being best differentiated 

 at the distal ends of the growing secondary 

 villi (Fig. 15.32). In the latter region the 

 basement membrane also exhibits meta- 

 chromatic staining with toluidin blue (Wis- 

 locki and Dempsey, 1948), a response in- 

 terpreted as indicating the presence of acid 

 mucopolysaccharide. 



It is of interest that the basement mem- 

 brane described here, as being rich in muco- 

 polysaccharide, is also a site in which iron 

 (Fig. 15.8) (Hofbauer, 1905; Zancla, 1912; 

 Wislocki and Dempsey, 1946c), calcium 

 (Schimig, 1929; Wislocki and Dempsey, 

 1946c ) , and variable amounts of alka- 

 line phosphatase (Wislocki and Dempsey, 

 1946c) are concentrated. It should be noted 

 that in the early months of gestation these 

 substances are demonstrable principally to- 

 ward the growing tips of the villi, a finding 

 which suggests possible functional differ- 

 ences in various regions. 



The surface of contact between the Lang- 

 hans cells, the syncytium, and the stroma 



