134 



Claude A. Villee 



after incubation, the net change in glycogen content was cal- 

 culated and expressed as micromoles of glucose units per g. 

 of wet tissue per hour. The placenta early in gestation has a 

 marked ability to synthesize glycogen in vitro (Fig. 4). This 

 ability begins to decrease after 10 to 12 weeks of pregnancy 

 and decreases steadily to term. The average rate of glycogen 

 utilization of the thirty term placentas was —1-92 micro- 

 moles per g. per hour, and only one of the thirty showed a 



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5 10 15 20 25 30 35 40 



WEEKS OF PREGNANCY 



Fig. 4. The metabolism of glycogen by the placenta as a 

 function of age. Positive values indicate net glycogen 

 synthesis; negative values indicate net glycogen utiliza- 

 tion. The values are expressed as /nmoles of glucose units 

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

 indicates the range of values for term placenta. 



net production of glycogen (-f-0-22 micromoles per g. per 

 hour). Corroborative evidence was obtained from the radio- 

 activity measurements of the glucosazones derived from the 

 tissue glycogen after incubation. These showed that term 

 placentas have a just barely detectable ability to incorporate 

 [ 14 C]glucose into glycogen in vitro. In contrast, 8 to 14 week 

 placentas have a marked ability to incorporate 14 C from both 

 glucose and pyruvate into glycogen in vitro. This ability 

 decreases with gestation and was absent from two of the three 

 placentas aged 22 to 24 weeks. 



