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

Abstract

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.