Characterization of acidification by the isolated perfused rat kidney: evidence for adaptation by the distal nephron to a high bicarbonate diet.

Characterization of acidification by the isolated perfused rat kidney: Evidence for adaptation by the distal nephron to a high bicarbonate diet. To characterize acidification by the distal nephron of the intact kidney independent of alterations in buffer availability, we subjected isolated rat kidneys perfused with glucose as the sole substrate to stepwise acidification of the perfusate. In response to progressive perfusate acidification with hydrochloric acid, a maximal pH gradient between urine and perfusate, which averaged 1.71 ± 0.12, was achieved at a mean perfusate pH of 6.89 ± 0.04. The maximum pH gradient was increased when sulfuric acid rather than hydrochloric acid was used to acidify the perfusate, and it was decreased by 0.67 when amiloride (10 -5 M) was added to the perfusate. Thus, hydrogen ion transport by the distal nephron of the intact rat kidney appears to be amenable to study, and it responds similarly to the hydrogen ion pump of anuran urinary epithelia. Kidneys from animals subjected to a variety of dietary regimens were studied in response to stepwise perfusate acidification with hydrochloric acid. Ammonium excretion averaged 0.49 ± .03 µmoles/min and did not differ significantly between any of the dietary groups. Chronic acidosis and the ingestion of either a low or high salt diet had no influence on the maximal pH gradient. Neither a low nor a high potassium diet affected the pH gradient, suggesting that the difference in urine pH between these two conditions in vivo is the result of differences in ammonia production. Ingestion of a high bicarbonate diet significantly decreased the pH gradient to 1.20 ± 0.09. Thus, an adaptive change in distal nephron hydrogen ion transport occurs in the rat kidney in response to chronic ingestion of alkali. Caracteristiques de l'acidification par le rein de rat isole perfuse: Preuve de l'adaptation du nephron distal a un regime riche en bicarbonate. Afin de caracteriser l'acidification par le nephron distal du rein intact independamment des modifications de la disponibilite en tampons, des reins de rats perfuses avec du glucose comme seul substrat ont ete soumis a une acidification progressive du perfusat. En reponse a l'acidification progressive du perfusat par d'acide chlorhydrique un gradient maximal de pH entre l'urine et le plasma, en moyenne de 1,71 ± 0,12, a ete obtenu pour un pH moyen de perfusat de 6,89 ± 0,04. Le gradient maximum de pH a augmente quand d'acide sulfurique a ete utilise a la place d'acide chlorhydrique pour acidifier le perfusat et a diminue quand de l'amiloride (10 -5 M) a ete ajoute au perfusat. Ainsi le transport d'ions hydrogene par le nephron distal du rein intact de rat parait pouvoir etre etudie et repondre de facon semblable a la pompe a hydrogene de l'epithelium urinaire des anuriens. Des reins d'animaux soumis a divers regimes ont ete etudies au cours de l'acidification progressive de perfusat par d'acide chlorhydrique. L'excretion d'ammonium etait en moyenne de 0,49 ± 0,03 µmoles/min et ne differait pas significativement entre les groupes. L'acidose chronique et l'ingestion d'un regime soit pauvre soit riche en sel n'a pas eu d'influence sur le gradient maximal de pH. Le contenu en potassium du regime n'a pas affecte le gradient maximal de pH ce qui suggere que la difference de pH urinaire, in vivo, entre ces deux situations est le resultat d'une difference de production d'ammoniac. L'ingestion d'un regime riche en bicarbonate diminue significativement le gradient a 1,20 ± 0,09. Ainsi une modification adaptative dans le transport d'ions hydrogene par le nephron distal survient elle dans le rein de rat en reponse a l'ingestion chronique de bases.