HISTOCHEMISTRY OF PLACENTA 



931 



of assay in the placenta of the sow, being 

 excreted between the 20th and 30th days of 

 gestation and thereafter diminishing, to in- 

 crease again around the 10th or 12th week 

 and continuing to do so until term (Cowie, 

 1948). As a possible source of estrogens, 

 the sudanophihc lipid droplets, present in 

 the columnar cells of the sow's chorionic 

 fossae in the latter half of gestation (Wis- 

 locki and Dempsey, 1946b), should be in- 

 vestigated further. 



An histochemical method for visualizing 

 steroid-3/3-ol-dehydrogenase activity by 

 tetrazolium salts has proved useful in iden- 

 tifying steroid-producing cells in the rat ad- 

 renal, ovary, and testis (Levy, Deane, and 

 Rubin, 1959) . Application of this technique 

 to the rat placenta (Deane, Lobel, Driks, 

 and Rubin, I960) has localized steroid-3/?- 

 ol-dehydrogenase activity in the tropho- 

 blastic giant cells. This activity is greatest 

 between the 8th and 15th day, becomes low 

 by 18 days, and is nearly absent by the 21st 

 day of gestation. Further application of this 

 technique to other placental types should be 

 fruitful. 



VIII. Evidence of the Possible Site 



of Production of Placental 



Gonadotrophic Hormones 



A. HUMAN PLACENTA 



Friedheim (1929), Sengupta (1935), Gey, 

 Jones and Hellman (1938), Jones, Gey and 

 Gey (1943), and Stewart, Sano and Mont- 

 gomery (1948) have grown human placental 

 trophoblast in tissue cultures. It has been 

 observed that the cytotrophoblast rather 

 than the syncytium proliferates and that 

 the latter, in so far as it arises, seems to be 

 derived from the cellular form, and is small 

 in amount and atypical in appearance. 

 Friedheim observed no conversion of cyto- 

 trophoblast into syncytium in actively grow- 

 ing cultures. Furthermore, Gey, Jones and 

 Hellman (1938), Jones, Gey and Gey 

 (1943) , and Stewart, Sano and Montgomery 

 (1948) demonstrated that tissue cultures 

 ■containing actively growing cytotropho- 

 blast produce appreciable quantities of 

 chorionic gonadrotrophic hormone, even 

 after repeated transplantation over several 

 months. These observations indicate that 



the trophoblast, and more particularly the 

 cytotrophoblast, is the Sburce of the hor- 

 mone. 



Stewart, Sano and Montgomery reported 

 their inability to grow trophoblast from 

 mature placentas of the 8th and 9th months. 

 Inasmuch as the syncytium does not divide 

 mitotically and the Langhans cells are nu- 

 merically much decreased at this period, 

 the result is not surprising. However, if they 

 had cultured tissue containing peripheral 

 trophoblasts, obtained specifically from the 

 placental septa or basal plate, growth might 

 have been anticipated. 



Chorionic gonadotrophic hormone is, as a 

 rule, al)undantly present in the urine of 

 women suffering from hydatidiform moles 

 or chorion epitheliomas (Tenney and Parker 

 1939, 1940; Rubin, 1941), and disappears 

 promptly after the successful surgical re- 

 moval of these tumors. Tenney and Parker 

 noted that the amount of hormone corre- 

 sponds roughly to the number of tropho- 

 blastic cells in a mole or chorion epitheli- 

 oma and that a mole with cystic villi and 

 slight trophoblastic proliferation gives a low 

 titer. These findings also indicate that pro- 

 liferating cytotrophoblast is the source of 

 the hormone and that the syncytium is of 

 less or of no importance. 



Wislocki and Bennett (1943) emphasized 

 that the curve of excretion of chorionic gon- 

 adotrophic hormone corresponds very well 

 with the period of active proliferation of the 

 trophoblastic shell. Nevertheless, a discrep- 

 ancy seemed to exist in that the cytotropho- 

 blast has generally been believed to degen- 

 erate and disappear in the last trimester, 

 whereas the excretion of chorionic gonado- 

 trophin continues throughout gestation 

 (Venning, 1948). This apparent discrepancy 

 is now understandable in the light of obser- 

 vations reported here which demonstrate 

 that, although the Langhans cells which are 

 chromophobic diminish greatly in number, 

 the peripheral cytotrophoblasts which are 

 chromophilic survive until full term in large 

 numbers in the septa placentas and basal 

 plate as viable, functional cells (Wislocki, 

 1951). 



Baker, Hook and Severinghaus (1944) 

 described blue granules in both the cyto- 

 trophoblast and the syncytium of the hu- 



