Red cell and plasma volumes of the rat and of tissues during cold acclimation

¹ Department of Anatomy, University of Washington School of Medicine, Seattle, Washington

Red cell and plasma volumes of the total rat and of its individual tissues and organs were determined for animals exposed to 5 C for 4 hr, 24 hr, 2 weeks, and 6 weeks. In addition, the tissue hematocrit ratios were determined. These values were compared with those of rats kept at 24 C. Fe⁵⁹-labeled erythrocytes and I¹³¹-labeled albumin were given intravenously, and after mixing the rats were frozen in liquid nitrogen. The organs and tissues were removed in the frozen state, assayed for radioactivity, and blood cell and plasma volumes were calculated on a unit weight basis. Significant changes in blood cell and plasma volumes were observed for the total rat and for many of the individual organs. There was a significant increase in the red cell content of the total rat within 24 hr of cold exposure. After 6 weeks, total blood volume was increased by approximately 20% over the control level and the increase in erythrocyte volume was slightly more than the increase in plasma volume. The hematocrit ratio of heart blood was 44.8 after 6 weeks exposure compared with 41.5 for controls. In general, it can be said that the somatic parts of the body showed increases in blood volume whereas the visceral parts had decreased volumes.