Determination of extracellular space and intracellular electrolytes in rat liver in vivo*

Uptake of a number of isotopically labelled extracellular tracers by rat liver in vivo was studied.2. A residual intravascular space of 3.0-3.5% following exsanguination was measured by use of (51)Crred cells. This space was significantly greater than that of skeletal muscle and was also greater in nephrectomized as compared to intact rats.3. (131)Ialbumin and polyvinylpyrolidine (PVP) were found to distribute initially in a space of 6-7% and this was followed by a delayed rise that was greater for PVP. The extravascular portion of this space is termed the large-molecule accessible space and is believed to correspond to the histological space of Disse.4. (14)Csucrose and inulin initially distribute in a space of 10-12% followed by a continued late increase. This initial space is termed the small molecule accessible space and is thought to include most of interstitial space.5. (36)Cl(-) and stable Na(+) and Cl(-) spaces were constant at 19-21% and can be used to put an upper limit on extracellular space.6. Operationally, the 1 hr inulin space in the nephrectomized rat was felt to be the best indicator of extracellular space.7. Total electrolytes were measured and intracellular values of 22, 165 and 22 m-mole/l. cell water for Na(+), K(+) and Cl(-), respectively, were calculated.8. By use of (14)CDMO, an intracellular pH of 7.25 and an intracellular HCO(3) (-) of 13 m-mole/l. cell water were calculated.