Source and function of urinary ammonia in the alligator

¹ Department of Biochemistry, Louisiana State University School of Medicine, New Orleans, Louisiana

The rate of renal deamination of 18 amino acids was determined by injecting them into alligators and measuring the ammonia excreted. Not only did glycine, alanine, glutamine and leucine account for nearly half of the plasma amino acids, they were also deaminated more rapidly than any of the others. In view of this it was concluded that these four amino acids are the natural precursors of urinary NH₃ in the alligator. Increased NH₃ and CO₂ excretion following glycine injections resulted in increased renal reabsorption of Na and Cl when NaCl was injected and increased Na reabsorption when NaHCO₃ or Na phosphate solutions were injected. The fact that excess NH₄HCO₃ excretion enhances salt reabsorption independent of plasma pH makes it probable that the excretion of N is the chief function of the ammonia mechanism and that salt conservation is incidental. Insulin decreased the plasma amino acid level and drastically reduced the NH₃ excretion. With the decrease in ammonia, NaCl and NaHCO₃ were excreted in increased amounts.