DETERMINATION OF BLOOD AND PLASMA VOLUME PARTITIONS IN THE GROWING RAT

Abstract

Plasma dilution of the di-azo blue dye T-1824 affords a comparatively simple, relatively accurate method for determining the blood and plasma vol. partitions in the rat. The method is advantageous in a chronic expt. where repeated detns. are desirable. A single sample technique was used. The mortality was 2.5%. The dye was injected into the exposed jugular bulb. 0.6-0.8 ml. of blood was obtained by heart puncture 3.5.4.0 min. after inj. Relative optical density of the plasma diluted dye was measured in the Klett-Summerson photoelectric colorimeter. Plasma vol. was calculated from the dye conc. The hematocrit, necessary to estimate the blood vol., was calculated from the detd. Hb conc. in g. A factor, 2.95, was employed. The derivation of the factor and the calculation were suggested by gravimetric relationships and based upon the assumption that cell gravity and Hb conc. within the cells is nearly constant; or that changes in cell gravity and Hb are usually parallel. This assumption would appear to be valid in the rat. The error between the observed conventional and the calculated hematocrit was 0.4%. Plasma, blood, and cell vols. were detd. at 3 stages of growth in 34 growing Sherman-strain rats maintained on an adequate purified diet. The values obtained were related to body size. The relationship was not linear. When these values were adjusted to a unit of size (surface area) it was apparent that the unit plasma and blood vols. attained maximal values in the 70-90g pubescent rat. The data suggest that it is necessary in rats to consider the blood vol. partitions in relation to body size and stage of growth.