Biochemical Evidence of Ageing in the Placenta 137 



presence of any substance which is readily metabolized to 

 glueose-6-phosphate. Glucose is isolated from the medium at 

 the end of the incubation period, and its radioactivity is 

 measured. In this way the production of glucose can be 

 demonstrated directly and its rate of formation from the given 

 precursor can be estimated. By all three methods it was shown 

 that the placenta can secrete glucose early in pregnancy. 

 However, it gradually loses this ability, presumably by a loss 

 of the enzyme glucose-6-phosphatase (Table I). 



Table I 



The Metabolism of Glucose by Placental Slices 



* mean ± standard error of the mean. 



These experiments demonstrate that the placenta early in 

 gestation has the biochemical mechanism necessary for the 

 storage of glycogen and the secretion of glucose. It could 

 function to regulate the glucose content of the foetal blood 

 stream. Claude Bernard demonstrated the presence of gly- 

 cogen in the sheep placenta and in 1858 made the suggestion 

 that the placenta may act as an "accessory liver". 



The Metabolism of Pyruvic and Lactic Acids 



The net utilization of pyruvate, calculated simply from the 

 difference in the content of pyruvate in the medium before 

 and after incubation, by placentas at successive stages of 



