The Oral and Parenteral Phenylalanine Requirements for Nitrogen Equilibrium in Man 1

Abstract

From published data on the minimum quantity of whole protein (milk, soy flour, white flour, and egg) required (1) or estimated (2) to maintain nitrogen balance in adults, and from analytical data of the amino acid content of these proteins (3), Harte and Travers (4) have calculated the "minimum" requirements for man of the essential amino acids. For phenylalanine, 1.4 Gm. daily was considered to be sufficient. The observations reported here indicate that the daily phenylalanine requirement for man is greater when the daily protein intake (protein hydrolysate) is given intravenously than when given orally. These studies were made during the course of investigations employing as a sole source of nitrogen a 10 per cent solution of amino acids2 prepared by complete acid hydrolysis of casein, largely freed of glutamic and aspartic acids, and supplemented with dl-tryptophane, dl-methionine, and glycine (5, 6). MATERIALS AND METHODSIn Table I the composition of two lots of the solution of amino acids with respect to the 8 amino acids essential for man (7) and for arginine and histidine is shown and is compared to that of casein. The results are based on analyses by microbiological assay (8,9,10). Likewise the quantity of amino acids in 1,000 cc. of this 10 per cent solution (average of the two nearly identical lots) is compared with the "minimum" amino acid requirements calculated by Harte and Travers (4). It is apparent that from 2 to 15 times these "minimum" quantities of amino acids are supplied in 1,000 cc. of the solution with the exception of phenylalanine, which might therefore be expected to be the "limiting" amino acid in this solution. The low phenylalanine content of these particular lots (1.7 per cent and 1.9 per cent) enabled us to investigate the effect on the nitrogen bal-1 The expenses of this investigation were defrayed in part by a

Urinary Excretion of Amino Acids Following the Rapid Injection of a Solution of Amino Acids in Man 12

“…This value is identical with that observed to follow the oral ingestion of 50 gm. of whole casein (6).…”

“…of amino acids there is an average loss into the urine of from 1 to 16 per cent of the individual amino acids infused, of 4.3 per cent of the 10 "essential" amino acids injected, and of 9.5 per cent of the alpha amino nitrogen administered." The excretion of 6 Because neither food nor glucose was supplied with the amino acid infusions, our values probably represent maximum urinary losses since optimum sparing of nitrogen (and presumably amino nitrogen) occurs only if adequate carbohydrate and protein are simultaneously provided (16). both alpha amino nitrogen and individual amino acids was completed within four hours after the infusion by which time the elevated blood amino nitrogen had returned to within normal limits.…”

“…The renal loss of amino nitrogen following parenteral administration may be as great as 28 times the loss from the administration of an equivalent amount of nitrogen as whole protein orally (6). If, in addition to such urinary losses, one or more of the essential amino acids were present in "limiting" amounts or were preferentially excreted, the amount of a protein just capable of maintaining nitrogen equilibrium when given orally might be insufficient when given intravenously as a hydrolysate (6).…”

Vitamin C Therapy in Geriatric Practice

“…Eckhardt and Davidson (18) stated that vitamin C may act through the adrenals on the protein metabolic processes. With appropriate techniques, the cells of the adrenal cortex can be shown to contain considerable amounts of vitamin C. The adrenocorticotropic hormone (ACTH), if given in sufficient amounts, rapidly depletes these cells of their stores of cholesterol and vitamin C.…”

Improvement of Active Liver Cirrhosis in Patients Maintained With Amino Acids Intravenously as the Source of Protein and Lipotropic Substances 12

“…The provision of 50 grams of amino acids to this patient of large stature only represented approximately 0.5 gram of protein per kilogram of body weight which borders on the minimum oral requirement (30). Furthermore, the quantitative requirement of hydrolyzed protein administered intravenously is likely greater than that of an equivalent quantity of whole or of hydrolyzed protein given orally (31,32). Because the latter patient maintained nitrogen equilibrium while receiving 100 grams of amino acids intravenously daily, it is suggested that during the protracted period of negative nitrogen balance he received an insufficient quantity of amino acids to fulfill the body protein requirements, particularly in view of the adequate caloric intake maintained throughout the study (4,200 calories daily).…”