Comparison of inulin and chromium-EDTA spaces in the nephrectomized baboon

Validation of [57Co]cyanocobalamin as an extracellular fluid marker and measurement of albumin exclusion from the interstitium in the rabbit

The use of [57Co]cyanocobalamin as an extracellular marker has been validated. Its simultaneous use with 51Cr-labeled erythrocytes and 125I-human serum albumin allows quantitative measurement of tissue water and the fractional exclusion of albumin from the interstitial compartment. The extravascular extracellular spaces of rabbit tissue are lung, 32 +/- 4%; heart, 25 +/- 2%; gut, 24 +/- 4%; and muscle, 13 +/- 1%. The fractional excluded albumin spaces are lung, 0.78 +/- 0.05; heart, 0.37 +/- 0.03; gut, 0.69 +/- 0.05; and muscle 0.58 +/- 0.03. The oversimplification that the extravascular extracellular space is a homogeneous region defined by a small tracer molecule and has the composition of lymph must be reconsidered. Albumin has a vastly different distribution in the interstitial spaces of different organs. Use of the three tracers reported here allows efficient measurement of blood volume, interstitial space, and interstitial albumin exclusion in whole tissues and organs, and thus can lead to further understanding of the in vivo changes occurring in various physiologic and disease states.

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

Extracellular fluid volumes have been determined in fed and 24-30 h starved rats, before and after 60 min of hemorrhagic hypotension at 70 mmHg. 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 those which had been starved. 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 had been starved. It is concluded that fed rats mobilised 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.

Induced hyperosmolality effects on extracellular fluid volume, lymph flow and osmolar equilibrium: studies in the rat

The effects of experimentally induced hyperosmolality has been studied in rats. Renal vascular pedicle ligation was performed on all animals to prevent renal clearance of the infused solute, xylose, and allow accurate ECF space determinations with 51Cr EDTA. Small volume hyperosmolar xylose infusions caused parallel elevation of the osmolality of thoracic duct lymph and arterial plasma. A positive correlation was obtained between lymph osmolality and flow alterations. The maximal osmolality elevation of 22 mosm X kg-1 H2O was associated with an intracellular fluid mobilisation which was equal to 7.1% of the ECF space. The infused and mobilised fluid volumes were distributed unequally between the intra and extra vascular compartments of the ECF.

Plasma water and 51Cr EDTA equilibration volumes of different tissues in the rat

The EDTA space and the plasma water volume of the whole animal and selected tissues were investigated with constant EDTA infusions of different duration in the rat. The calculated EDTA space increased with the duration of the infusion both in the whole animal and the tissues sampled. The plasma water volume remained constant, and therefore the calculated increase of the EDTA space suggests a slow intracellular accumulation of the tracer. As intracellular accumulation of EDTA increases with experimental time, it is necessary to use as short an experimental interval as possible to reduce this error when determining extracellular fluid volumes.