Ammonia secretion in sweat

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Abstract
These studies were per-formed to investigate the mechanism of ammonia secretion in sweat (which in man has an ammonia concentration up to 6 m[image]) by comparing the pH of sweat to the S/B [NH3] (sweat-to-blood ammonia concentration ratio) and to the sweat PNH3. Sweat was obtained from adult human volunteers (12 studies in 8 subjects) after local iontophoresis of pilocarpine as well as after exposure to high ambient temperatures, and from the footpads of cats after injection of methacholine chloride. The mean pH of thermal sweat, pharmacologic sweat, and cat sweat, respectively, was 5.80, 6.80, and 7.65. The measured S/B [NH3] was inversely proportional to the sweat pH as might be expected if ionic trapping played role in determining the concentration of ammonia in sweat. The Pnh3 of sweat was found to be related to sweat pH of 4.84 to a PNH3 of 1,800 x 10-6 mm Hg at a sweat pH of 3.17. The sweat PNH3 exceeded blood PNH3 when the sweat pH was greater than 6 suggesting that ammonia in sweat is in equilibrium with an ammonia pool other than blood. In the volunteers, the blood ammonia concentration rose when total body sweating was induced after exposure to high ambient temperatures. The mean blood ammonia concentration rose from 0.084 m[image] before sweating to 0.127 m[image] during total body sweating. These results suggest that ammonia is produced by the sweat gland and diffuses as the free base into blood and sweat where it is trapped as ionic ammonium.