Measurement of the liver extracellular space in vivo in dogs.

To obtain a reasonable estimate in vivo of the liver extracellular space (ECS) in intact, non-exsanguinated dogs, the distribution volumes of a variety of radioactive tracers were obtained as a function of time. 36Cl, 14C- and 3H-inulin, 125I-albumin, 51Cr-red cells, and endogenous 35Cl distribution volumes were obtained in liver from 5 min to 4 h. The 36Cl space was stable and reproducible at 29.0%, a value similar to the endogenous 35Cl (28.2%) and 5 min 14C-inulin (29.9%) spaces. The 36Cl space may be used as the upper limit of liver ECS, whereas the inulin space exceeds this value after 5 min and progressively increases. Electrolyte concentrations in liver cell water are calculated using the 36Cl space of 29% as the liver ECS. The advantages of using 36Cl over other methods to determine liver ECS in intact animals are discussed.