Intrarenal distribution of ammonia during diuresis and antidiuresis

Abstract

The intrarenal distribution of ammonia was evaluated in the dog during antidiuresis and osmotic (mannitol) diuresis at various levels of urine pH. During antidiuresis, the concentration of ammonia in renal tissue water rose progressively from the cortex to the tip of the papilla. In contrast, the corticomedullary ammonia gradient was completely obliterated by osmotic diuresis. In both experimental groups, a close relationship was observed between urine pH and the logarithm of the ratio between the urine and papillary concentrations of ammonia. The data are compatible with a proposal that a medullary countercurrent exchange system is responsible for medullary ammonia accumulation, and that diffusion equilibrium exists between the pNH₃ of loop of Henle fluid, vasa recta blood, and collecting duct fluid.