Letter | Published:

Evidence for a Non-Plasma Source of Urea in Sweat

Naturevolume 214page506 (1967) | Download Citation



THE ratio of the concentration of urea in the sweat to that in the plasma (s/p) is known to be greater than unity. Schwartz1 attributed this gradient to back diffusion of water because he found that raising the plasma urea concentration had little effect on the s/p ratio for urea. Recent evidence2,3 suggests that (a) s/p for urea is not entirely independent of plasma urea concentration; (b) s/p for urea is independent of s/p osmolality in man and the cat (for example, the s/p urea is greater than 1 in the hyperosmotic sweat obtained from the hairless footpad of the cat); (c) compounds related to urea by virtue of similar volumes of distribution (ethanol, antipyrine, creatinine) or similar molecular configuration (thiourea, methylurea, acetamide) all behave differently from urea in sweat in that none of these compounds is present in sweat at higher concentrations than in plasma.

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  1. 1

    Schwartz, I. L., Thaysen, J. H., and Dole, V. P., J. Exp. Med., 97, 429 (1953).

  2. 2

    Brusilow, S. W., and Gordes, E. H., Amer. J. Physiol., 209, 1213 (1965).

  3. 3

    Brusilow, S. W., and Gordes, E. H., Fed. Proc., 25, 468 (1966).

  4. 4

    Walser, M., and Bodenlos, L. J., J. Clin. Invest., 38, 1617 (1959).

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  1. Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland



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