BULLETIN OF THE NEW ENGLAND MEDICAL CENTER 



shows much the same characteristics shown by liver or muscle 

 cells: 



1. After glycine was fed it appeared at higher concentra- 

 tions in the fetal than in the maternal plasma. 



2. When enough L-proline, L-histidine or DL-methionine 

 was fed to produce high plasma levels, the difference between 

 the glycine in the fetal and maternal plasmas was largely 

 abolished. (Again competition between amino acids is shown.) 



3. L-glutamic acid feeding produced extremely high fetal 

 plasma concentrations without affecting the glycine distribution. 



Human fetal plasma showed 1.7 to 1.8 times as high con- 

 centrations of glycine and residual amino acids as the maternal 

 plasma, whether obtained at normal deliveries or deliveries by 

 cesarian section. We are indebted to Dr. Clement Smith and 

 his colleagues for these samples. 



A second instance where elevated amino acid concentrations 

 were associated with very rapid growth was during hepatic re- 

 generation after surgical removal of two-thirds of the liver of 

 the rat. As is known, restoration is very rapid, with mitosis 

 beginning about twenty-four hours after the operation, and the 

 liver remnant doubling its weight during the second and third 

 day. In coincidence with this growth, after a twenty to twenty- 

 six hour latency the residual amino acids of the liver rose about 

 50 per cent with an accompanying increase in glutathione. The 

 concentrations and growth rate then subsided together. 



Our observations upon fetal muscle and upon regenerating 

 liver support the view that growth acceleration may occur by 

 effects upon the equilibrium reaction 3 and 4 rather than by 

 direct effects upon reactions 1 or 2. We are extending these 

 observations to other instances of rapid growth. Probably we 

 are dealing here with two questions: 



1. Is growth a mass action effect resulting when the various 

 amino acids are at adequate concentrations in the cell? 



2. Are changes in the quantitative relation between protein 

 synthesis and catabolism produced by changes in the extent to 

 which the cells concerned concentrate amino acids? The first 

 question concerns the nature of growth, the second the control 

 of growth. 



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