Biochemical Evidence of Ageing in the Placenta 139 



Table II 



Metabolism of Pyruvate by Placental Slices 



* mean ± standard error of the mean. 



presumably via glucose-6-phosphate. This is evidence that 

 the inability of the term placenta to secrete glucose is due 

 to the absence of the enzyme glucose-6-phosphatase and not 

 to the failure of some part of the glycolytic cycle. 



The production of lactic acid by placental slices was cal- 

 culated from its rate of appearance in the incubation medium. 

 As with pyruvate utilization, there was considerable variation 

 in the values obtained early in gestation, but there was a 

 gradual decrease in lactate production from 10 weeks to term 

 (Fig- 7). 



The source of the lactic acid was determined by experi- 

 ments in which slices of term placenta were incubated in 

 media containing different substrates (Table III). When no 

 substrate was present in the incubation medium, lactate was 

 produced at a rate of about 5 (jtmoles/g./hour. This lactate 

 is derived primarily from the breakdown of glycogen, for 

 glycogen disappearance occurred at the rate of 2 to 3 jxmoles/ 

 g./hour. Each micromole of glucose unit in glycogen yields 

 two micromoles of lactate. The presence of 10 jxmoles pyruvate 

 per ml. of incubation medium resulted in the production of an 

 additional 2 to 3 (xmoles of lactate per g. per hour. Glucose in 

 the medium at a level of 1 1 • 1 (jimoles per ml. increased the 

 production of lactate 6 to 7 (jimoles per g. per hour over that 



