Biochemical Evidence of Ageing in the Placenta 135 



The Metabolism of Glucose 



The ability of the placenta to utilize or produce glucose was 

 calculated from the difference in glucose content of the incuba- 

 tion medium before and after incubation. Some of the earliest 

 placentas tested showed a net production of glucose during 

 the incubation (Fig. 5). From 15 weeks until term, however, 



+ 10 



T 5 



- 5 



-15 



% —- 



10 15 20 25 30 



WEEKS OF PREGNANCY 



35 



40 



Fig. 5. The metabolism of glucose by the placenta as a 

 function of age. Positive values indicate net glucose 

 production; negative values indicate net glucose utiliza- 

 tion. The values are expressed as ^tmoles per g. of wet 

 tissue per hour. The arrow at 40 weeks indicates the range 

 of values for term placenta. 



the average net rate of glucose utilization proved to be about 

 —7 micromoles of glucose per g. wet tissue per hour. From 

 the difference in the specific activity (c.p.m. per millimole 

 glucose) of the glucose in the incubation medium before and 

 after incubation, one can estimate the amount of glucose 

 produced by the placenta and secreted into the medium and 

 the true amount of glucose utilized. These calculations showed 

 that the placenta at 10 weeks has a glucose production of 

 about -{-12 micromoles per g. per hour and a true glucose 

 utilization of about —17 micromoles per g. per hour. The net 



