Renal ammoniagenesis in an early stage of metabolic acidosis in man

Total renal ammonia production and ammonia precursor utilization were evaluated in patients under normal acid-base balance and in patients with 24-h NH₄Cl acidosis by measuring (a) ammonia excreted with urine and that added to renal venous blood, and (b) amino acid exchange across the kidney. In 24-h acidosis not only urinary ammonia excretion is increased, but also total ammonia production is augmented (P <0.005) in comparison with controls. By evaluating the individual role of acid-base parameters, urine pH and urine flow in influencing renal ammonia production, it was shown that the degree of acidosis and urine flow are likely major factors stimulating ammoniagenesis. Both urine pH and urine flow are determinant in the preferential shift of ammonia into urine. In 1-d acidosis, renal extraction of glutamine was not increased and the total ammonia produced/glutamine N extracted ratio was higher than in controls (P <0.005) and was inversely correlated with the log of arterial bicarbonate concentration (P <0.001). In the same condition, renal glycine and ornithine uptake took place; the more severe the acidosis, the greater was the renal extraction of these amino acids (P <0.001). These data indicate that at the early stages of metabolic acidosis, in spite of a brisk increase in ammonia production, the mechanisms responsible for the increased glutamine use, which are operative in chronic acidosis, are not activated and other ammonia precursors, besides glutamine, are probably used for ammonia production.