Excretion of ammonia by rat kidney during metabolic alkalosis

In rat kidney, proximal tubular and final urinary ammonia concentration are finite. They are lower in animals with metabolic alkalosis than in controls. A positive correlation between ammonia concentration and water removal (as indicated by fluid to plasma ratios for inulin) was found. A comparison of tubular fluid to plasma concentration ratios for inulin and ammonia indicates that more ammonia enters proximal tubular fluid than appears in the final urine. These observations indicate that ammonia is probably secreted primarily at the level of the proximal tubule and then undergoes reabsorption at distal sites of the nephron.