Influence of nonionic diffusion on absorption of NH₄⁺ and HCO₃^– from the bladder

¹ Department of Medicine, Tufts University School of Medicine, and Renal Laboratory, Pratt Clinic, New England Center Hospital, Boston, Massachusetts

Studies have been carried out to compare the losses of NH₄⁺ and of HCO₃^– from the dog bladder in vivo when: 1) each of these ions was present separately as the salt of a strong electrolyte, and 2) both ions were present together as ammonium bicarbonate. The initial concentration of electrolyte in each experiment was 100 mmoles/liter. After instillation of ammonium chloride (pH 8), [NH₄⁺] fell by a mean of 20 mEq/liter in 8 hr, whereas after instillation of ammonium bicarbonate, [NH₄⁺] fell by a mean of 67 mEq/liter (P < .001). After instillation of sodium bicarbonate, [HCO₃^–] fell by only 10 mEq/liter, whereas in the ammonium bicarbonate experiments it fell by 58 mEq/liter (P < .001). It is proposed that the larger loss of NH₄⁺ and HCO₃^– which occurred in the ammonium bicarbonate experiments resulted from the simultaneous and rapid diffusion of NH₃ and CO₂ with continuous regeneration of each nonionic species at the expense of the ionic member of each buffer pair. These observations suggest that nonionic diffusion, under some conditions, may lead to significant transfers of weak electrolytes across the bladder wall.