BULLETIN OF THE NEW ENGLAND MEDICAL CENTER 



nitrogen retention may be expected. Severe growth inhibition 

 has been observed in diets containing gelatin supplemented 

 with essential amino acids, and in diets containing abnormal 

 amounts of glycine, proline, methionine and other amino acids. 

 If a person is fed glycine it will be found that his plasma 

 alanine goes up; if fed alanine, his plasma glycine rises. 



Such an agent as sulfadiazine can be given to a patient ac- 

 cording to a variety of dosage schedules. But if his nitrogen 

 nutrition is to be helped, he cannot be given a midday meal 

 that is deficient in methionine and then be given five grams 

 of methionine at two o'clock without doing him anything 

 but harm. Nor can he be given twenty grams of methionine, 

 even with his lunch, on the theory that if a little is good 

 a lot is better. 



This question of imbalance is undoubtedly a great deal more 

 delicate when the amino acids are injected intravenously, so that 

 intense changes can be produced quickly in the medium bathing 

 the cell. 



Feeding glutamic acid actually reduced the plasma amino 

 acids, both in the guinea pig and in the dog. Tissue analyses 

 indicated that this amino acid increases the extent to which 

 cells concentrate amino acids. This is a clue to the nature of 

 the concentrating process. 



Now if growth were accelerated by shifting the equilibrium 

 to the right for reactions 1 and 2, the cellular amino acids 

 should be decreased. A good example is the precipitous fall in 

 the glycine of liver that is producea by its conjugation to form 

 hippuric acid when stimulated by the feeding of sodium ben- 

 zoate. In two instances of very rapid growth we have ob- 

 served, irijstead, elevated amino acids. 



Fetal muscle cells of the guinea pig show concentrations of 

 both glycine and residual amino acids three times as high as 

 the maternal muscle cells. Similar relations were observed in 

 the rabbit for both skeletal and cardiac muscle. There are two 

 factors acting to produce these higher concentrations: 



1. The placenta concentrates amino acids. This undoubtedly 

 has a large effect on the partitioning of amino acids between the 

 fetus and the mother. 



2. The fetal muscle, despite its very rapid growth, con- 

 centrates amino acids to a greater extent than does the maternal 

 muscle. 



The concentrating activity of the placenta for amino acids 



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