Posthemorrhagic changes in plasma water and extracellular fluid volumes in the rat

Anesthetized rats were submitted to a standardized hemorrhage to 40 mm Hg by withdrawing 35 to 40% of the total blood volume. The plasma water and the extracellular fluid volumes of the whole animal and selected tissues were estimated with 125 I human serum albumin and 51Cr EDTA, respectively, after recovery periods of 10 and 90 minutes. The plasma water volume of the whole animal decreased, but approximately 50% of the shed plasma water was restored within 10 minutes after the hemorrhage. The extracellular fluid volume of the whole animal did not change significantly after hemorrhage, whereas this fluid compartment was regionally reduced in the liver, spleen, and subcutaneous fat after a 10-min recovery period but only in the liver after a 90-min recovery period.