Sodium excretion and intrarenal hemodynamics in thoracic inferior vena cava constriction

To investigate the relationship of intracortical blood flow distribution to the antinatriuretic effect of acute and chronic thoracic inferior vena cava (TIVC) constriction, anesthetized control dogs were infused with isotonic saline equal to 6% body wt. This caused an increase in the glomerular filtration rate (GFR), from 40.3 to 50.2 ml/min/100 g kidney, renal blood flow (RBF), from 267.4 to 390.8 ml/min/100 g kidney, and fractional clearance of sodium (FC[Na]), from 0.22 to 7.97%, and a drop in hematocrit (Hct), from 35 to 24%. A modification of the radioactive microsphere technique demonstrated a decrease in the percentage of outer cortical blood flow (%OCF), from 68.3 to 55.7%, and a corresponding increase in the percentage of inner cortical blood flow (%ICF), from 31.7 to 44.3%. Acute superimposition of TIVC constriction reduced the GFR, from 43.5 to 23.7 ml/min/100 g kidney, RBF, from 304.4 to 162.9 ml/min/100 g kidney, FC[Na], from 7.85 to 3.05%, but did not change the %OCF. Dogs with chronic TIVC constriction differed from normal controls only in a lower %OCF, 57.0 vs. 68.3%, and a higher %ICF, 43.0 vs. 31.7%. This pattern of flow distribution, however, was similar to that observed in saline infused normal animals. Infusion of saline into these dogs did not change the GFR, RBF, or %OCF, but did raise FC[Na] from 0.31 to 2.08%. These results indicate that changes in the intracortical blood flow distribution are not critical to the development of natriuresis or salt retention.