Glycine and alanine concentrations of body fluids; experimental modification.

The determination of individual amino acids in body fluids under pathological and experimental conditions should permit extension of information farther than is possible wit.h procedures that measure amino acids collectively. We are reporting some observations upon experimentally produced changes in the concentrations of glycine and alanine, as measured by chemical methods (1, 2) which are specific to the uncombined forms of t,hese amino acids. The ingestion of 25 to 32 gm. of glycine by human subjects resulted in rises of the plasma concentration of glycine nitrogen from the normal of 0.28 to 0.37 mg. per cent to values of 2.9 to 7.7 mg. per cent, the maximum being attained in about an hour. Glycine entered the erythrocytes slowly, the concentration remaining below that of plasma for more than 4 hours (Table I). After the glycine nitrogen of plasma had been held at levels of 3 to 5 mg. per cent for 4 to 5 hours by the ingestion of several portions of glycine totaling 30 and 35 gm., the glycine nitrogen concentrations of the spinal fluid were 0.065 and 0.07 mg. per cent, compared with five normal values of 0.022 to 0.042 mg. per cent, averaging 0.031 mg. per cent. The ingestion of 25 gm. of glycine increased the conjugated a-amino nitrogen of tungstic acid filtrates of plasma, only a small part of the increase being due to glycine. The bound glycine extractable by ethyl acetate from acidified tungstic acid filtrates of plasma (which would include hippuric acid) was not significantly increased. The ingestion of 5 and 6 gm. of sodium benzoate led to a decrease of the free plasma glycine, a greater reduction of the plasma a-amino acids, and an increase of 0.4 to 0.7 mg. per cent in the conjugated diffusible glycine nitrogen of plasma, presumably due to hippuric acid. Table II illustrates one of these experiments. The ethyl acetate-extractable, conjugated amino acid nitrogen of urine was taken by Henriques and S@rensen (3) as a measure of hippuric acid excretion. In human urine they found about half of the conjugated amino nitrogen to be extractable. We have partitioned the conjugates by the extraction of acidified urine, employing three extractions of 1 volume each, which was sufficient to extract 99 per cent of the hippuric acid from the aqueous solution. Whereas glycine made up only 6 to 17 per cent of the