Isotonic saline loading and intrarenal distribution of glomerular filtration in dogs.

Isotonic saline loading and intrarenal distribution of glomerular filtration in dogs. Na-14C-ferrocyanide has been used to measure the ratio of the glomerular filtration rate (SNGFR) of the superficial (SUP) and juxtamedullary (JM) glomeruli of dogs. Using Hanssen's technique, a 0.25 to 1.0 ml single pulse injection of a 15% Na ferrocyanide solution containing 500 jiCi of '4C-ferrocyanide was rapidly injected through a small catheter inserted into the aorta above the renal arteries. Nine or 10 seconds later, the renal pedicles were clamped, the kidneys removed immediately, frozen and immersed in FeCI3. The amount of radioactivity associated with the Prussian blue precipitate within the lumen of the proximal tubule is proportional to the filtration rate of the nephron. In each kidney, at least five SUP and JM proximal tubules from five different regions were dissected and the ratio of the radioactivity of SUP/JM nephrons of each zone was determined. In kidneys of six normally hydrated dogs, this ratio was 0.8 0.03. During continuous saline diuresis (Ringer 3 mI/mm/kg x 30 mm followed by urine volume replacement) the total kidney GFR remained unchanged and the ratio of the SUP/JM SNGFR was 0.83 0.03 which is not different from control values. These results corroborate micropuncture data in the dog which indicate that the SNGFR of the SUP nephrons varies proportionately with total kidney GFR during saline diuresis. This study also indicates that a redistribution of gbmerular filtration towards SUP nephrons is not responsible for the natriuresis observed in these conditions. This finding is also in agreement with the data which demonstrate that the vasodibatation occurring in the kidney following isotonic saline loading is observed throughout the whole cortex.