A comparative analysis of extracellular fluid volume of several tissues as determined by six different markers

The uptake and distribution of 6 different extracellular markers were analyzed in ten tissues of the rat. The saccharides, ³H-mannitol, ³H-raffinose, ³H-inulin, and ¹⁴C-inulin, reached a steady-state distribution in all tissues within ≈15 min after intraperitoneal injection; ²²Na and ³⁶Cl followed similar kinetics in all tissues except the choroid plexuses and the thyroid, which required > 1 hr to obtain a steady-state plateau. In most tissues, the steady-state spaces of ³H-raffinose, ³H-inulin, and ¹⁴C-inulin (60 min) were not significantly different; however, the ³H-mannitol, ²²Na and ³⁶Cl spaces were on average 45, 54, and 79%, respectively, greater than the ³H-inulin space.