Patricia M. Norton

The Plasma Aminogram. I. Influence of the Level of Protein Intake and a Comparison of Whole Protein and Amino Acid Diets

Extract: The changes in plasma aminogram produced by variations in level of protein intake provided either as whole protein or a mixture of amino acids were studied. Controls were 29 normal infants, one to three months of age, fed a standard evaporated milk formula providing 3 to 3.5 g/kg/day of protein (fig. 1 and table II). Results obtained with the lowest protein intake (1.1 g/kg/day) are illustrated in figure 2 and presented in table III. Alterations in the plasma aminogram are noted as early as two days after the reduction in intake and become more pronounced as the feeding is prolonged. The most striking changes are depression of the branched chain amino acids (leucine, isoleucine and valine) and of lysine and tyrosine. Glycine and serine are elevated with glycine showing the greater elevation. Less striking changes are decreased concentrations of threonine, phenylalanine, ornithine, butyrine, cystine and proline.The aminograms obtained with feedings of 1.3 and 1.5 g/kg/day are very similar to those obtained with the more extreme degree of protein reduction (fig. 3 and table IV). The aminogram after feeding 1.7 g/kg/day remains within the range of average ±1 standard deviation except for the elevation of glycine.A high intake of milk protein, 9 g/kg/day, results in an increase in the levels of a majority of the amino acids (fig. 5 and table V). The sole exception is glycine, which tends to be low. Marked increases occur in the branched chain amino acids, valine being the most affected; there is also a large increase in the level of proline. The greatest elevations occur in the levels of methionine, which also show the most marked individual variation, elevations ranging from 2 to 35 times normal average value. An apparent tendency of the methionine level to return towards normal with prolonged feeding of the high protein diet is evident on the graph. The significance of this finding must be questioned, however, since the subjects who were maintained the longest on this diet were those who originally did not have the very high levels of methionine.There are some differences in the aminogram when infants are fed the equivalent of 3.5 g/kg/day in the form of amino acids instead of intact protein (fig. 6 and table VI). On the amino acid diets, lower average plasma values are seen for the branched chain amino acids, alanine, proline, asparagine and citrulline; higher values are observed for threonine and serine. The markedly elevated levels of plasma amino acid observed after feeding 9 g/kg/day of whole protein are not seen after feeding the equivalent amount of nitrogen as an amino acid mixture (fig. 7 and table VII). There is elevation only of valine and serine. When individual subjects were shifted from the high protein to the high amino acid diet, the pattern shifted within 24 hours.Speculation: A more precise and sensitive indicator of the state of protein nutrition is needed. While the level of the plasma amino acids changes rapidly with alterations in protein intake, much more work is necessary before it can be used to evaluate protein adequacy.

Observations on the urinary amino acid excretion in man : the influence of age and diet.

Abstract Using the Dowex 50 column chromatographic technique of Moore and Stein, studies have been made of free amino acid excretion in 12 infants and two older children in order to evaluate the influence of age and of diet. Consideration has been given to various stand ards of reference for evaluating amino acid excretion, and it is concluded that it is best expressed in terms of creatinine excretion. In terms of creatinine excretion it was found that premature infants excrete roughly ten times as much free amino acid as do subjects ten or more years old, and that full-term infants excrete roughly three times as much as the older subjects. Our data on 10-year-olds reveal values virtually identical with those reported for adults. The pattern of individual amino acid excretion was found to differ in early life from that seen in older children and adults. A number of amino acids are present in greater amount and several are found only at that time of life. Hydroxyproline has been identified in the urine of premature and newborn infants. An unidentified ninhydrin reactant, designated as peak No. 9 is described which has not been observed in subjects more than 5 months old. The anomalous behavior of taurine is described, being present in large quantities in the neonatal period, virtually disappearing thereafter, and reappearing again in quantity by the tenth year. Certain late effects of prematurity are described. The effects of diet on amino aciduria are considered, the indications being that the amino acid output in the urine is influenced to some extent by the diet. Comparisons were made of free amino aciduria on a diet of whole protein (milk) and on a synthetic diet supplying nitrogen as a mixture of natural amino acids. Certain differences were encountered the significance of which is discussed. The disappearance of peak No. 9 on the amino acid diet was particularly striking. Some preliminary attempts to identify it are reported.

Argininemia treated from birth

pregnancy and a normal spontaneous delivery. Apgar scores were 9 and 10 at 1 and 5 minutes. Birth weight was 3.8 kg and physical examination was completely normal. At three hours of age the plasm a arginine level was .4.0 mg/dl (normal average 1.3) and arginase activity was not detectable in the erythrocytes. Repeated /tssays of erythrocyte arginase activity all revealed less than 5% of normal activity. Red blood cell arginine level determined just before the initiation of therapy was 4.22 mg/dl (normal 0.4). The infant was given glucose water until the essential amino acid mixture was started at 18 hours of age; a milk formula was never offered. The mixture was fed in an amount to provid? the equivalent of 2 gm of protein per kg of body weight. It was supplemented with Mead Johnson product 80056* to furnish a total caloric intake of 125 calories/kg. This was the only feeding for the first four months of life. After this, fruits, low protein vegetables and rice cereal were introduced. The diet was later supplemented with various protein-free products such as special bread, cookies, pasta, etc. The natural protein intake has never exceeded 5 grams/day, which provides an estimated 250 to 300 rag/day of arginine.

The Essential Amino Acid Requirements of Infants IX. Isoleucine

Acurate knowledge of essential nutrients is a sine qua non of good nutrition. Such information is needed for the prevention and repair of dietary deficiencies arising from food shortages and also in situations where the capacity to handle food is limited by disease states. Evaluation of the requirements for essential amino acids has been peculiarly difficult, since this involves the construction of a diet in which the quantity of a single amino acid can be varied at will. The problem has been approached in several ways: 1. Use has been made of natural proteins deficient in one or another amino acid. This method has very limited applicability, for nature has been singularly unobliging in providing a variety of such proteins. 2. Chemically degraded proteins or protein hydrolysates have been used. A number of procedures can be used to destroy one or more amino acids, which can then be replaced in any quantity desired. Diets constructed from such preparations have the advantage that the amino acids are present for the most part as the natural isomers and that unessential as well as essential amino acids are present. There is, however, the disadvantage that the na

The Relationship between the Branched Chain Amino Acids and Their |[alpha]|-Ketoacids in Maple Syrup Urine Disease

Summary: Plasma branched chain amino acid levels and their respective ketoacid analogues were determined in seven maple syrup urine disease patients ranging in age from 12 h to 12 years. One hundred one pairs were analyzed. There was a high degree of correlation between the amino acid and its ketoacid analogue at every amino acid level. The coefficient of correlation (0.84) was highest for leucine-α-ketoisocaproic acid. The ratio of ketoacid analogue to amino acid, (0.87), was also the greatest for leucine. The close correlation implies that adequate monitoring for therapy can be accomplished by the use of the technically simpler and more rapid determination of the plasma branched chain amino acids.

The nutritional therapy of histidinemia

Control of the plasma histidine level in histidinemia is possible with the use of an amino acid mixture free of histidine and a carefully monitored intake of histidine. This regimen is compatible with good physical growth and normal mental development. If further clinical experience demonstrates that widespread nutritional intervention in this disease is warranted, it should be possible to obtain good biochemical control.

Plasma and cerebrospinal fluid amino acid concentrations in phenylketonuria during the newborn period

Plasma and cerebrospinal fluid amino acid values were determined in 29 infants 9 to 30 days of age with a confirmed diagnosis of phenylketonuria. Phenylalanine concentrations in plasma and cerebrospinal fluid were markedly elevated; the degree of elevation in the cerebrospinal fluid had a significant relationship to that of the plasma. The only other significant deviations in the plasma were reductions in the threonine and tyrosine values. Cerebrospinal fluid threonine, alanine, and arginine concentrations were reduced, whereas those of serine, isoleucine, and histidine were elevated. This combined deficiency and excess of amino acids in the central nervous system may have a significant effect on protein synthesis at a time in life when this synthesis and turnover is most active.

Amino Acid Interrelationships: The Effect of a Load of Leucine on the Metabolism of Isoleucine

Summary The effect of a load of leucine on the metabolism of isoleucine was studied. Rats were fed L-isoleucine-(U)-14C and were given a load of leucine in gel form 12 hr later when the rate of 14CO2 expired had become constant. This resulted in a significant increase in 14CO2 expired, in every instance. This stimulation of the metabolism of isoleucine by a load of leucine offers an explanation for the previously observed depression of plasma isoleucine level after a load of leucine in human infants.