Ammonium excretion during stopped flow: a hypothetical ammonium countercurrent system

¹ Department of Physiology, University of Kansas Medical Center, Kansas City, Kansas

Successive ureteral occlusions were performed on chronically acidotic animals infused first with HCl and then with NaHCO₃. Peak ammonium concentrations developed in very distal samples of each occlusion were compared with urine pH. In successive occlusions on any one dog, the line relating peak ammonium concentration to urine pH closely followed the slope predicted by the theory of nonionic diffusion when urine pH was above 6.0. When urine pH was below 6.0 in successive occlusions, the slope was significantly less than the theoretical. In these latter experiments, doubling occlusion time resulted in small increases in ammonium concentration. Glutamine infusions raised ammonium concentrations and tended to shift the slope towards the theoretical at urine pH's down to 5.6. In alkalotic animals, the ratio [NH₄]_u/ [NH₄]_b was much greater than predicted by theory, and urine concentrations of the free base NH₃ were as much as fourfold greater than renal venous blood concentrations. A counter-current mechanism for ammonium is proposed to explain the ability of the kidney to concentrate NH₃ in alkaline urine.

Key Words: pH effect on ammonium excretion • nonionic diffusion theory • acid excretion

Submitted on December 16, 1964