Much of the metabolic acid in the urine under ordinary circumstances is neutralized by ammonia. From 300 to 500 cc. of tenth-normal acid is excreted in the course of twenty-four hours combined in this way. A quarter of a century ago Nash and Benedict1 demonstrated that the kidney is the site of formation of the ammonia present in fresh urine. Although it has not been demonstrated in the mammal, it seems likely from experiments in amphibians2 that the distal portion of the renal tubule secretes the ammonia, which there is substituted for the fixed base in combination with the metabolic acid being excreted.
The generally inverse relationship between the urea nitrogen and ammonia nitrogen in the urine under various metabolic alterations led to the view that urea was the material from which the urinary ammonia arose. However, urease is not found in the kidney; more recent studies3
FORMATION OF AMMONIA. JAMA. 1947;135(12):775. doi:10.1001/jama.1947.02890120029015
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