HISTOCHEMISTRY OF PLACENTA 



923 



1946; Bridgman, 1948a, b; Wislocki and 

 Padykula, 1953; Davies, 1956; Padykiila, 

 1958). The Ashbel-Seligman reaction for 

 carbonyl groups has been briefly described 

 in the placentas of various mammals (Ash- 

 bel and Seligman, 1949; Wislocki, 1952), as 

 has also the PAS reaction (Wislocki, 1950) . 

 Many histochemical observations on a va- 

 riety of placentas were summarized by 

 Starck (1945-50). 



Present information on the histochemical 

 localization of lipids in various placentas is 

 fragmentary. The main effort has been di- 

 rected toward localizing within the placenta 

 the type of lipid droplets which occur in the 

 steroid-producing cells of the adrenal cor- 

 tex and gonads. These droplets are acetone 

 soluble, birefringent, exhibit greenish fluo- 

 rescence, and give positive Ashbel-Seligman 

 and Schif! reactions for carbonyl groups. 

 As has been discussed in the section on 

 methods, these nonspecific reactions actu- 

 ally reflect the degree of unsaturation in 

 the compounds comprising the fixed lipid 

 droplets. Certainly further work is needed 

 to characterize more fully the various lipids 

 of placentas, especially in relation to the 

 storage of cholesterol and triglycerides. 



In the following descriptions it will be 

 seen that the lipid reactions characteristic 

 of steroid-producing cells usually occur in 

 some part of the trophoblast. In the human 

 placenta, only the syncytium contains the 

 lipid droplets characteristic of steroid-pro- 

 ducing cells. The cat possesses a so-called 

 endotheliochorial type of placenta, consist- 

 ing of sinusoidal maternal capillaries and 

 "decidual" giant cells arranged in sheets 

 alternating with lamellae of trophoblast, 

 the latter enclosing the fetal stroma and 

 capillaries. The trophoblast consists of an 

 outer syncytial and an inner cellular layer. 

 The cellular layer contains abundant lipid 

 droplets of variable, but relatively large 

 size. They are sudanophilic and birefrin- 

 gent (Fig. 15.59), exhibit greenish fluores- 

 cence, give an Ashbel-Seligman reaction for 

 carbonyl groups (Fig. 15.20) and stain in- 

 tensely with Schiff's reagent. The syncy- 

 tium is negative in these respects, except for 

 a mild diffuse coloration bv the Ashbel- 



Seligman carbonyl method (Fig. 15.20) and 

 a greyish tint with sudan black B which is 

 attributable probably to mitochondria. The 

 "decidual" giant cells, generally regarded as 

 of maternal origin, and the maternal endo- 

 thelium give no lipid reactions beyond a 

 delicate sudanophilia associated with the 

 presence of mitochondria. 



In rodents two types of placentas, a cho- 

 rio-allantois of the hemochorial type and a 

 yolk sac placenta, function concurrently 

 throughout gestation. Lipids occur in many 

 placental constituents of the rat: labyrinth- 

 ine trophoblast, giant cells, parietal endo- 

 derm, visceral endoderm, decidua capsularis, 

 and mesothelium lining the exocoelom. 

 Bridgman (1948) pointed out that in the rat 

 the labyrinthine trophoblast contains lipid 

 from the 12th day onward and that it di- 

 minishes shortly before term. This lipid in 

 rats and mice is birefringent and gives an in- 

 tense carbonyl reaction (Figs. 15.16, 15.17, 

 and 15.21) (Wislocki, Deane, and Dempsey, 

 1946; Ashbel and Seligman, 1949; Wislocki, 

 1952). This cellular layer is a logical sus- 

 pect as the site of steroid hormonal synthe- 

 sis. However, these reactions are present 

 also in the visceral endoderm of the yolk 

 sac where lipid droplets occur in great abun- 

 dance from 9 to 17 days (Figs. 15.74-15.77) . 

 These lipids which occur principally as 

 large infranuclear droplets (Figs. 15.78 and 

 15.83) are birefringent, strongly fluorescent, 

 and give a strong carbonyl reaction with the 

 Schiff reagents (Wislocki, Deane and 

 Dempsey, 1946). Further work has con- 

 firmed these observations and has also 

 shown this acetone-soluble lipid gives a 

 strong Ashbel-Seligman reaction and con- 

 tains cholesterol. It immediately turns a 

 brilliant blue-green in the Schultz test 

 (Padykula, unpublished observations) . One 

 difference between the labyrinthine and 

 endodermal lipids is the color response in 

 the Schultz test. The labyrinthine lipid 

 turns red-brown but never the blue-green 

 which indicates the presence of cholesterol. 

 Lehner (1914) reported that intranuclear 

 lipid droplets are abundant in the visceral 

 endoderm of the mouse. This finding is con- 

 firmed in the rat by electron microscopy 

 (see Figs. 15.78 and 15.80). The significance 

 of this lipid in the yolk sac is not clear, al- 



