Apparent and Osmotic Volumes of Distribution of Sodium, Chloride, Sulfate and Urea

Abstract

Vols. of distr. of Na, chloride, sulfate, and urea were detd. in anesthetized, nephrectomized dogs and cats from the ratio of the injd. load of these substances to the increment in plasma concn. produced. Exptl. and theoretical analysis is presented to account for the widely divergent vols. of distr. calculated by the usual dilution formula for the different ions of a loaded salt (NaCl, Na2SO4) largely confined to the extracellular fluid. On the basis of this analysis, a quantitative distinction is drawn between "apparent" and "osmotic" vols. of distr. Total body water is approximated by the osmotic vol. of distr., for chloride is less than the total body water by a calculated amt,, which accords with the theory that body cells as a whole, under the conditions of these expts., act essentially like a perfect osmometer.