138 



Claude A. Villee 



gestation is given in Fig. 6. There is a considerable amount of 

 variation between placentas of the same age. A slight de- 

 crease in the net utilization is evident after 10 weeks of 

 development. The amount of pyruvate produced during the 

 incubation period can be calculated from the dilution of 

 the radio-pyruvate in the medium by unlabelled pyruvate 

 produced by the cells. The true utilization, i.e., the net 



10 



25 



20 



25 



30 



35 



40 



WEEKS OF PREGNANCY 



Fig. 6. The utilization of pyruvate by the placenta as a 



function of age. The values are expressed as /xmoles per g. 



of wet tissue per hour. The arrow at 40 weeks indicates 



the range of values for term placenta. 



utilization corrected for the amount produced, can then be 

 estimated. Both production and true utilization of pyruvate 

 increase from 7 weeks to 24 weeks and then decrease at term 

 (Table II). The net utilization based on these calculations 

 (column 5 of Table II) is maximum at 10 to 12 weeks and then 

 gradually decreases to term. The rate at which pyruvate is 

 produced from glucose remains essentially constant from 7 

 weeks to term (column 6 of Table II). The fact that labelled 

 carbon from pyruvate can be incorporated into glycogen 

 indicates that the glycolytic cycle can operate in reverse, 



