Chronological Changes in Placental Function 123 



different functions, not only as a whole but in different parts 

 of the placenta and in different species. 



The peak of placental glycogen in the rat is at the 16th 

 day, after which it decreases. Some years ago my former 

 colleague, Professor J. J. Pritchard, and I investigated the 

 effect on the placenta of experimental foetal death in the rat 

 (Huggett and Pritchard, 1945; Pritchard and Huggett, 1947). 

 Oestrogens caused decidual necrosis and foetal death but 



DOSE :- 



0«4lmg./. day for 7 days 



2 • 8 mg. spread over 7 days 

 PROGESTERONE * 

 IMPLANTED "~ 



NORMAL CONTROLS 



IO II 12 i3 14 IS 16 17 18 19 20 21 22 



RAT FOETAL AGE DAYS 



Fig. 6. Daily averages of placental glycogen in the last 

 third of pregnancy in normal pregnant rats and rats im- 

 planted with progesterone during the previous 7 days. 

 Average absorption • 28 per day. 



progesterone had no such effect; rather the foetus thrived. 

 An extension of these experiments has demonstrated that the 

 implantation of progesterone during a period of 7 days in 

 the pregnant rat with an average absorption of • 41 mg. per 

 day per rat produces an accelerated decrease of the glycogen 

 in the period of placental glycogen decrease (Fig. 6). It also 

 causes a decrease of placental weight accompanied by an 

 increase of foetal weight (Figs. 7 and 8). 



In summary, therefore, the placenta changes composition 

 not in a regular sequence to old age but spasmodically, 

 suggesting that different functions are exercised at different 



