Reabsorption of Certain Amino Acids and Derivatives by the Kidney Tubules

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Evidence has been presented previously showing a marked variation in the extent of the excretion of different amino acids after their intravenous administration. This study was designed to measure the rates of tubular reabsorption of 1-tyrosine, N-acetyl-1-tyrosine, N-methyl-1-tyrosine and 1-histidine. The results were obtained by using sodium ferrocyanide to measure the rate of glomerular filtration during the period of study of each substance. The procedure is an adaptation of one elaborated by Van Slyke, Hiller and Miller. Dogs received an intraperitoneal injection of 200 cc of a solution containing a suitable amount of sodium ferrocyanide together with the compound being studied. After a lapse of 15 minutes the bladder was emptied by catheterization and washed with distilled water. The urine was collected for a period of approximately one hour. Tyrosine and its derivatives were determined by the Folin-Ciocalteu phenol reagent; histidine by the Jorpes modification of the Koessler-Hanke method. A sample of blood was obtained about 15 minutes after the beginning and again 15 minutes before the end of the experimental period. The average of the values for the 2 samples of blood was used in each calculation. Volume of glomerular filtrate was obtained by dividing 100 × mg of ferrocyanide excreted by the average mg % of ferrocyanide in the plasma. By using this volume of glomerular filtrate and the plasma concentration of amino acid it was possible to calculate the amount of amino acid in the glomerular filtrate. Knowing the amount of amino acid excreted one obtained by difference the amount of the amino acid reabsorbed by the tubules. From Table I it appears that only a small fraction of the acetyl derivative is reabsorbed whereas approximately two-thirds of the methyl derivative is taken up under similar conditions.