The extravascular pool of albumin in the non-diuretic rat kidney estimated by means of radioactive tracers and quantitative immunochemistry.

The extravascular pool of albumin in the non-diuretic rat kidney was determined as the difference between total and intravascular albumin pools. The total pool of albumin was determined in two ways in the same kideny: 1. as the distribution volume of rat endogenous albumin measured immunochemically and 2. as the distribution volume of 125I-labelled rat albumin equilibrated for 4 days. The distribution volume of 131I human albumin after 1 min equilibration was taken as a measure of the intravascular pool. Total albumin pool estimated as rat endogenous albumin volume of distribution averaged 13.4, 25.1, and 43.0 mul per 100 mg tissue in cortex, outer and inner medulla, respectively. Similar figures were obtained using 125I-labelled rat albumin. Intravascular pool of albumin in the 3 zones averaged 7.2, 19.7, and 26.8 mul per 100 mg tissue. The calculated extravascular fraction of albumin averaged 0.44, 0.21, and 0.35 for cortex, outer and inner medulla, respectively.