Measurement of extracellular fluid volume in nephrectomized dogs.

The volumes of distribution of a number of substances of widely varying molecular size and chemical properties, including sulfate, thiosulfate, mannitol, sucrose, and inulin, have been found to represent 15 to 25 per cent of body weight of man, dog, and other mammals. The apparently equal volumes of distribution of these dissimilar substances has suggested that the distribution of each of these substances measures the same portion of body fluid and has led to efforts to identify this volume of body fluid with the extracellular fluid volume. In a series of individuals, however, there is a considerable range in the fraction of body weight which the volume of distribution of any one of these substances represents. In only a few instances have the distributions of two of these substances been compared simultaneously in the same individual. Schwartz (1) reported a ratio of thiosulfate volume to simultaneously measured mannitol volume of 0.90 (0.87 to 0.96) in four normal dogs, a ratio of 1.02 and 0.98 in two normal human subjects, and a ratio of inulin to simultaneously measured mannitol volume of 0.97 (0.93 to 1.02) in six normal human subjects (2). Walser, Seldin, and Grollman (3) reported a ratio of radiosulfate volume to simultaneously measured inulin volume of 0.95 (S.D. + 0.11) in nine normal human subjects. Deane, Schreiner, and Robertson (4) measured volumes of sucrose and inulin in each of four normal human subjects on separate occasions and found an average ratio of sucrose volume to inulin volume of 0.97 (0.94 to 1.03). Most of these comparisons depend on quantitative recovery in the urine of infused inulin. Kruhaffer's (5) data indicate a larger volume of distribution for sucrose than inulin in nephrectomized rabbits. Raisz, Young, and Stinson (6) have reported a ratio of inulin volume to thio-