51Cr EDTA determinations of the extracellular fluid volume in hemorrhage: a study with fed and starved rats

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Abstract
Extracellular fluid [ECF] volumes were determined in fed and 24- to 30-h starved rats, before and after 60 min of hemorrhagic hypotension at 70 mm Hg. Bilateral renal vascular ligation was carried out to prevent clearance of the isotope tracer used, 51Cr-EDTA. The time taken for a bolus of the tracer to distribute itself in its space was determined in fed and starved animals after the standard period of hypotension. This was found to be 37 min for fed animals and 50 min for starved animals. When the isotope ECF space was compared before and after hemorrhage in fed animals, it was unchanged, despite an estimated blood volume loss of 39%. The isotope ECF space was reduced 5.5% after hemorrhage in animals which were starved. Apparently, fed rats mobilized intracellular fluid to the interstitium in hemorrhage, whereas starved animals did not. This finding of variable fluid homeostasis is ascribed to the different nutritional status of the animals investigated and has considerable implications.