What is the Role of Urinary Ammonium Excretion?
There are different views on the true role of NH4+ excretion in urine. How can the renal excretion of ammonium which has a pK of 9.2 represent H+ excretion from the body? One school says the production of ammonium from glutamine in the tubule cells results in production of alpha-ketoglutarate which is then metabolised in the tubule cell to new bicarbonate which is returned to the blood. The net effect is the return of one bicarbonate for each ammonium excreted in the urine. By this analysis, the excretion of ammonium is equivalent to the excretion of acid from the body as one plasma H+ would be neutralised by one renal bicarbonate ion for each ammonium excreted. Thus an increase in ammonium excretion as occurs in metabolic acidosis is an appropriate response to excrete more acid. The other school says this is not correct. The argument is that metabolism of alpha-ketogluarate in the proximal tubule cells to produce this new HCO3- merely represents regeneration of the HCO3 that was neutr
