Influence of acute hyponatremia on renal ammoniagenesis in dogs with chronic metabolic acidosis.

The purpose of this study was to determine how acute hyponatremia might augment the excretion of ammonium in dogs with chronic metabolic acidosis. The excretion of ammonium was higher during hyponatremia because the proportion of ammonium produced that was excreted in the urine increased from 66% in controls to 77%. Effects on the production of ammonium are more complex. The rate of renal ammoniagenesis was not increased during hyponatremia in absolute terms nor when expressed per millimole of oxygen consumption. In contrast, this rate was somewhat higher during hyponatremia if expressed per millimole of sodium reabsorbed (9.8 vs. 10.3 mumol). The rate of oxygen consumption by the kidney did not fall, as anticipated, during hyponatremia; when this rate was expressed per millimole of sodium reabsorbed it rose from 46 to 55 mumol. There was no significant change in the rate of extraction of glutamine by the kidney, but there was a significant decrease in the rate of release of alanine during hyponatremia. Hence there appears to be more oxidation (yielding more ammonium) and less transamination of glutamine. We conclude that the renal events which led to a higher rate of excretion of ammonium during hyponatremia were a larger than expected rate of ammonium production owing to a greater rate of oxygen consumption together with lesser rate of transamination of the glutamine extracted by the kidney. In addition, more of the ammonium produced was transferred to the urine.