INFLUENCE OF INGESTION OF SINGLE AMINO ACIDS ON THE BLOOD LEVEL OF FREE AMINO ACIDS

Abstract

Our studies of normal and abnormal subjects have demonstrated that the postabsorptive levels of the free amino acids of the plasma remain within rather narrow normal limits except in very extreme terminal conditions.This investigation was made to determine whether the levels of all of the amino acids in the plasma are maintained by the same mechanism and whether there are any cross-relationships between the various amino acids.By feeding a large dose of a single amino acid, the plasma level of that amino acid is raised much above normal.This disturbance of the normal blood pattern gives some indication of the interrelationships existing between the free amino acids of the plasma.Earlier workers have made similar studies of the effect of single amino acids on the blood amino nitrogen level, but no studies have been made of the effect of ingestion of one amino acid on the level of the other individual amino acids in the blood.Seth and Luck (1) fed by gavage various amino acids in water to rabbits in amounts equivalent to 560 mg. of amino nitrogen per kilo.They found that glycine, alanine, and histidine caused marked increases in amino nitrogen, whereas leucine, tryptophan, glutamic acid, aspartic acid, and cystine caused very slight if any increases.In a later study with rats Luck (2) found that when glycine or alanine was given to rats there was a marked increase in amino nitrogen, whereas the dicarboxylic acid fraction, the hexone base fraction, and the monoamino acid fraction from casein caused no increase in amino nitrogen.Bang (3) found no increase in the blood amino nitrogen level of rats fed leucine by mouth.Johnston and Lewis (4) working with rabbits found increased blood amino nitrogen levels following glycine, nn-alanine, and glutamic acid feeding but no change following aspartic acid, arginine, and lysine feeding.Shambaugh, Lewis, and Tourtellotte (5) gave 1 gm. of tyrosine and 0.91 gm. of phenylalanine per kilo to rabbits and found no rise in the amino acid nitrogen of the blood at any period, although an increase in phenol content was noted.King and Rappaport (6) injected tyrosine intravenously and found that 95 to 98 per