Effect of Iron-Deficiency Anemia on Percent Blood Volume in Growing Rats

In determining iron bioavailability as iron gained in hemoglobin relative to intake, blood volume is calculated for the iron-deficient animals at the initiation of a feeding trial and again on the iron-repleted animals at the termination of the trial. However, the effect of iron deficiency on percent blood volume in the rats commonly used in iron repletion studies has not been determined. In experiment 1, we noted the relationship between body weight and blood volume in 18 randomly selected healthy male rats with a weight range of 95–278 g. In experiment 2, the in vivo disappearance of Evans blue dye from the plasma of 17 rats and the precision of the dye dilution method for estimating known volumes of heparinized rat blood were studied. From this information, linear regression equations were developed to more accurately estimate blood volume in vivo. In experiment 3, we studied blood volume relative to body weight in 122 weanling male rats at four levels of anemia. These animals were fed a low iron diet and bled to achieve anemia in 7 days. In the subsequent repletion interval, the rats were fed diets supplemented with ferrous sulfate for periods of 0, 5, 10 or 15 days, after which hemoglobin and blood volume were determined, and the animals were killed. Though body weight and blood volume were linearly correlated (r = 0.78), no such association existed between body weight and percent blood volume (r = 0.058). Blood volume held constant at 7.5 ± 0.1 (mean ± SE) percent of body weight in weanling prepubescent rats of 30–45 days of age regardless of iron status.