Contribution of the proximal tubule to urinary ammonia excretion by the dog

¹ Departments of Medicine, Duke University Medical Center and Veterans Administration Hospital, Durham, North Carolina

Measurements of ammonia concentration were performed on 48 samples of proximal tubular fluid from antidiuretic dogs during normal acid-base balance, and acute or chronic ammonium chloride acidosis. Measurable concentrations of ammonia (>0.3 mmoles/liter) were not detectable in proximal fluid during either normal acid-base balance or acute ammonium chloride acidosis. However, in both conditions, an ammonia concentration in proximal fluid of less than 0.3 mmoles/liter could still have accounted for a large percentage of urinary ammonia. For this reason, the present data can neither confirm nor deny the existence of ammonia addition to proximal tubular fluid during normal acid-base balance and acute metabolic acidosis. In contrast, chronic metabolic acidosis was accompanied by the definite appearance of ammonia in proximal fluid, its concentration averaging 0.82 ± .32 mmoles/liter. This observation demonstrates clearly that net ammonia addition can be observed along the proximal tubule under certain circumstances. It suggests further that the proximal tubule also contributes to the adaptive rise of urinary ammonia excretion during chronic acidosis.

Key Words: micropuncture • ammonim chloride acidosis

Submitted on February 4, 1965