Mechanism by which enhanced ammonia production reduces urinary potassium excretion

Mechanism by which enhanced ammonia production reduces urinary potassium excretion. To determine the mechanism whereby an increase in ammonia production decreases urinary potassium excretion, we perfused isolated rat kidneys at a pH of either 7.0 or 7.4. After 45min of perfusion at either pH, glutamine or ammonium chloride was added to the perfusate to result in concentrations of 5 and 0.8mM, respectively and observations were continued for 50min. Control kidneys were perfused at both pH's without further additions to the perfusate. At pH 7.0, glutamine increased ammonia production and increased urinary ammonium excretion strikingly; whereas the addition of ammonium chloride did not change ammonia production but increased urinary ammonium excretion to a comparable degree. Both maneuvers resulted in a reciprocal fall in urinary potassium excretion in comparison with control perfusions. The decrease in potassium excretion could not be accounted for by differences in perfusate or urinary acid-base parameters, or by changes in urinary sodium, water, or chloride excretion. At pH 7.4, glutamine also significantly increased ammonia production and perfusate ammonia concentration. In contrast to the studies at pH 7.0 in which the urine pH was acid (5.9), the urine remained alkaline (pH 7.2), and both urinary ammonium excretion and urinary potassium excretion were unaltered. Thus, potassium sparing is not a nonspecific effect of glutamine, its metabolism to ammonia, or perfusate ammonia concentration but is directly related to an increase in urinary ammonium excretion. Mecanisme par lequel une augmentation de la production d'ammoniaque reduit l'excretion urinaire de potassium. Afin de determiner le mecanisme par lequel une augmentation de la production d'ammoniaque diminue l'excretion urinaire de potassium, des reins de rats isoles ont ete perfuses soit a pH 7,0, soit a pH 7,4. Apres 45min de perfusion a l'un ou l'autre pH, de la glutamine ou du chlorure d'ammonium ont ete ajoutes au perfusat afin d'obtenir des concentrations respectivement de 5.0 et 0,8mM, puis la preparation a encore ete etudiee pendant 50min. Des reins temoins ont ete perfuses aux deux pH sans autres additions au perfusat. A pH 7,0 la glutamine augmente la production d'ammoniaque et augmente considerablement l'excretion d'ammoniaque alors que l'addition de chorure d'ammonium ne modifie pas la production d'ammoniaque mais augmente de facon comparable l'excretion urinaire. Les deux manoeuvres ont pour consequence une diminution de l'excretion urinaire de potassium par comparaison avec les perfusions controles. La diminution de l'excretion de potassium ne peut pas etre expliquee par des differences d'etat acido-basique du perfusat ou de l'urine ou par des modifications de l'excretion urinaire de sodium, d'eau ou de chlore. A pH 7,4 la glutamine augmente aussi la production d'ammoniaque et la concentration d'ammoniaque dans le perfusat. Cependant, a la difference des etudes a pH 7,0 au cours desquelles le pH de l'urine etait acide (5,9), l'urine est restee alcaline (pH 7,2) et l'excretion urinaire d'ammoniaque de meme que l'excretion de potassium n'ont pas ete modifiees. Ainsi l'economie de potassium n'est pas un effet non specifique de la glutamine, de son metabolisme en ammoniaque ou de la concentration en ammoniaque du perfusat, mais est directement lieea l'augmentation de l'excretion urinaire de potassium.