SODIUM AND WATER REABSORPTION IN DIFFERENT PARTS OF NEPHRON IN RATS WITH EXPERIMENTAL RENAL HYPERTENSION

Four weeks after clamping one renal artery, the perfusion pressure of the clamped kidney was normal whereas the mean arterial pressure had increased to 188 mm Hg. Urinary excretion of sodium and water of the clamped kidney had not changed while that of the untouched kidney increased considerably. Glomerular filtration rate (per g kidney), intratubular pressure, tubular diameter, transit time of Lissamine green and fractional sodium and water reabsorption of the proximal tubule were normal in both the clamped and the untouched kidney. In the untouched kidney, the transit time through Henle's loop was shortened and the sodium and water reabsorption in it was significantly reduced. These changes, although partly compensated by higher reabsorption in the distal tubule and collecting duct, are responsible for the increased sodium and water excretion of the untouched kidney. They are probably due to an increased medullary blood flow. In the clamped kidney, fractional sodium and water reabsorption of the whole nephron did not differ significantly from normal values. However, sodium reabsorption was lower in the distal tubule and higher in the collecting duct. Sodium transport in the distal tubule seemed to be impaired; throughout its length sodium TF/P ratio averaged 0.6. These results may explain the different urinary excretion found in human hypertension following unilateral renal artery stenosis (Howard-Test). © 1968 Springer-Verlag.