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Nephrol Dial Transplant (1992) 7: 493-500
© 1992 European Renal Association-European Dialysis and Transplant Association

research-article

Tubular handling of amino acids after intravenous infusion of amino acids in healthy humans

I. N. Tietze1,, S. S. Sørensen1, H. Eiskjæer1, K. Thomsen2 and E. B. Pedersen1

1Department of Medicine and Nephrology, Skejby Hospital, Psychiatric Hospital Risskov, University Hospital in Aarhus Aarhus, Denmark 2The Psychopharmacology Research Unit, Psychiatric Hospital Risskov, University Hospital in Aarhus Aarhus, Denmark

Correspondence and offprint requests to: Correspondence and offprint requests to: Ida Nørager Tietze, Department of Medicine and Nephrology C, Skejby Hospital, 8200 Aarhus N Denmark.

To examine the fractional excretion of amino acids after an increase in the filtered load, and to study a possible coupling between proximal tubular reabsorption of individual amino acids and sodium/ water, eleven healthy subjects were examined before and during intravenous infusion of a mixture of essential and non-essential amino acids. Thirteen healthy subjects, who received isotonic glucose instead, participated in an identical time-control study. Glomerular filtration rate (GFR), renal plasma flow (RPF), and proximal and distal absolute and fractional tubular reabsorption of sodium and water (PARNa, PFRNa/Water, DARNa, and DFRNa) evaluated by the lithium clearance method were determined during four clearance periods of 30 min each. After amino acid infusion, GFR and RPF increased, whereas filtration fraction (FF) was unchanged. PARNa. was unchanged, but lithium clearance increased significantly (P<<0.05) and PFRNa/Water fell, indicating an increased delivery of sodium and water out of the proximal tubules. DARNa, increased, but DFRNa, was unchanged, thus no net increase was recorded in urinary sodium and water output. In the time-control study, no changes in kidney function were seen. Absolute excretion of amino acids increased for glutamic acid, serine, glutamic, glycine, threonine, histidine, alanine, arginine, tyrosine, valine, methionine, isoleucine, phenylalanine, leucine, and lysine (p<<0.01), and fractional excretion increased for all but glutamic acid, tyrosine, arginine, isoleucine, and leucine. Reabsorption of amino acids was enhanced uniformly and almost paralleled the filtered load without any sign of saturation of the reabsorption mechanisms. It is concluded that using the lithium clearance method in man no straightforward correlation seems to exist between absolute reabsorption of sodium in the proximal tubules and reabsorption of individual amino acids

Keywords: amino acid infusion; amino acid excretion; glomerular filtration rate; lithium clearance; sodium excretion


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