Freeze-dissection analysis of 133Xe distribution to measure regional renal blood flow

To verify the freeze-dissection technique for measuring renal blood flow (RBF) distribution in anesthetized dogs we compared the sum of all compartment flow rates with total RBF, compared compartment flow distribution with intercepts, and determined recirculated 133Xe. By dissection, we found that the cortex, delineated by its granular brownish red appearance, comprised 69%, whereas the outer medulla (the reddish portion) was 18% of the total kidney weight. Average cortical flow was 3.77 ml X g-1 X min-1 and the y-intercept for 133Xe washout was 85% of the initial radioactivity distribution. Outer medullary flow was 2.01 ml X g-1 X min-1 with a y-intercept of 13%. In a 100-g kidney, total cortical flow would be 259.8 ml/min (3.77 ml X g-1 X min-1 X 68.9 g) and total outer medullary flow would be 36.0 ml/min. These calculations indicate that 86% of the total flow is distributed to the cortex and 13% to the outer medulla, as the intercept-calculated percentages indicated. Summing whole cortical and medullary flows results in a flow that agrees with the electromagnetically measured flow of 292 ml/min for a 100-g kidney.