The Importance of Sodium Ions for the Excretion of Ammonium and Hydrogen Ions in the Urine

Abstract

Summary.The aim of the present work has been to investigate whether the urinary excretion of NH4 and H+ takes place by an exchange with positive ions from the urine. pH in the urine and the excretion of NH4 were investigated under conditions, where the amount of positive ions reaching the distal part of the tubules was reduced. The following results were found: At high values of the excretion of NHJ, a cation deficiency resulted in a decrease in this quantity. Simultaneously a very large reduction in the urinary excretion of Na+ and a more moderate decrease in the excretion of the other cations were found. The pronounced reduction in the urinary excretion of Na+ was absent in the beginning of an acidosis, when the formation of ammonia was small. The hydrogen ion concentration of the urine varied with the content of Na+ over a considerable range of concentration. When Na+ or K+ were ingested, pH decreased in spite of the increasing diuresis. The experiments support the idea that NHt and H+ are excreted by exchange with cations from the tubular fluid. It is emphasized that the privileged position apparently occupied by the sodium ion is not necessarily associated with the exchange process itself but may be due to an active transport of this ion from the tubular cells to the interstitial fluid.The possible effects of an active transport of sodium on the migration of other ions are discussed.