Abstract
Most observes have found that circulating red cell volume deduced from measurement of plasma volume and venous hematocrit demonstrates a higher value than that measured by direct method. The most reasonable explanation for this phenomenon is that the cell percentage of the blood in small vessels is lower than that in the large arteries and veins.
When both plasma and cell volumes are determined simultaneously, one obtains a true measure of total blood volume and can calculate the overall cell percentage. If the ratio of overall cell percentage/large vessel cell percentage, or Fcells value is constant in large physiological variation of rats, one can be safely used to deduce blood volume from a large vessel hematocrit and an estimation of plasma volume.
Normal and splenectomized rats with wide range of body weight and with different levels of protein in the diets were used for the experiment. With the use of <sup>51</sup> Cr and T-1824, red cell and plasma volumes are measured simultaneously in the rat. Red cell and plasma volumes per unit body weight are decreased in accordance with the increase in body weight, and they are also reduced by feeding a low protein diet.
Fcells value of the rats shows neither significant difference with body weight, nor nutritional status, and is unchanged by splenectomy.
