Edward A. Murphy

Apparent Free Amino Acids in Deproteinized Plasma of Normal and Uremic Persons

Not all clinical manifestations of severe uremia can be explained on the basis of abnormalities of the water balance or of electrolyte patterns. Many patients die with the uremic syndrome even as the plasma levels of all known electrolytes are normal (1, 2). Even though it appears unlikely that retention of the known end products of protein metabolism is responsible for the clinical picture of uremia (3), it is probable that the toxicity of the uremic syndrome is related to a disturbance of protein metabolism. Measurement and comparison of free amino acid concentrations in the body fluids of uremic persons with the amino acid patterns in normal body fluids is prerequisite to further investigations of protein metabolism in uremia. If one or more of the essential amino acids were found deficient in uremic body fluids such a finding might serve to explain certain clinical features of the uremic syndrome which suggest decreased protein synthesis. Abnormally high concentrations of individual amino acids in uremic body fluids would raise the question of their contribution to the uremic toxicity. Consistently abnormal amino acid patterns in uremia would call for explorations of the mechanisms underlying this abnormality. Such investigations might fill in and define our presently so vacuous and chimerical picture of the derangements of chemical and physiological processes which are the basis for the uremic syndrome. Animal experiments from our laboratories (4) have demonstrated deficiencies of apparent free methionine and threonine, with simultaneous excess of apparent free arginine and glycine in the blood plasma of nephrectomized uremic dogs. The present report extends our studies of plasma amino acid levels in uremia to human patients.

Free and apparent amino acids in deproteinized plasma of normal and uremic (nephrectomized) dogs.

Summary 1. Microbiological assay procedures were found to be applicable to the determination of free amino acids in depro-teinized plasma but only in the absence of interfering substances. The apparent (relative) values obtained in the presence of interfering substances were shown to be meaningful but only when determined over a wide range of concentration of plasma filtrates. 2. It was concluded that the concentration of some free amino acids (histidine, isoleucine, leucine, ly-sine, phenylalanine. proline, serine and val-ine) was not significantly different but that of some apparent amino acids was higher (ar-ginine and glycine) and others (methionine and threonine) lower in the deproteinized plasma of uremic (nephrectomized) compared to normal dogs.

Influence of Environment on Preweaning Growth of the Rat. I. Dietary Regimen of the Young.

Summary The shape of the preweaning growth curve of the rat is profoundly affected by the lack or availability of solid food. The divergence from conformity to Zuckers growth equation of rats raised on the Anderson and Smith diet may be due to the natural transition from a liquid (milk) to a solid diet and does not appear to be explained by a qualitative deficiency in this diet.

Effect of ethionine on amino acid composition of rat tumors.

Summary 1. Percentages of total and “free” amino acids in viable tissues of Sarcoma R-1 and Walker carcinosarcoma 256 grown in control and ethionine-treated male and female rats of the Wistar strain have been determined by microbiological assay methods. 2. Ethionine treatment induced no change in total amino acids but caused an increase or decrease in concentration of some “free” amino acids in viable tissue but was without marked effect on methionine. 3. It was concluded that inhibition of tumor growth by ethionine probably results largely from indirect effects on utilization of amino acids other than methionine.

Effect of Ethionine in Castrated Male Rats, with and without Testosterone.

Summary 1. The per cent tumor inhibition, change in carcass weight, and concentration of nonprotein methionine in the liver, resulting from administration of ethionine to normal, castrated, and testosterone-treated castrated male rats, has been determined. 2. Tumor inhibition by ethionine, and the toxi-city of this substance, was greater in castrated than in normal or testosterone-treated castrated male rats and closely resembled that observed in female rats. 3. The concentration of free nonprotein methionine in the liver of castrated male rats was similar to that found in female rats and differed from that observed in normal male or testosterone-treated castrated male rats. The presence of a methionine conjugate was indicated in the liver of castrated male and normal female rats following ethionine administration while such a conjugate was lacking in the liver of normal male or testosterone-treated castrated male rats. 4. It was concluded that the sex difference observed in tumor inhibition, toxicity, and concentration of nonprotein methionine in the liver of ethionine-treated rats was mediated by the androgens.

Amino Acid Composition of Rat and Mouse Tumors.

Summary 1. Percentages of total amino acids in viable tissues of the Walker carcinosarcoma 256 (rat), Sarcoma 180 (mouse), and Taylor tumor (mouse) have been determined by both column and paper chromatography. 2. Values obtained by column chromatography agreed satisfactorily with those determined in the same laboratory by microbiological assay while the majority of values determined by paper chromatography were in poor agreement with those of the other two methods. 3. There was no significant difference in the total amino acid content of tumors from rats or mice.