AbstractTo define the relationship between portal hypertension and renal excretion of salt and water, two acute animal models of portal hypertension were investigated. In both models, it was necessary for systemic and renal hemodynamics to remain unchanged during the creation of portal hypertension so as to eliminate the effects of change in these parameters on renal excretion.In eight dogs, portal hypertension was induced by controlled tightening of a ligature around the superior hepatic vein and changes in hemodynamics were prevented by controlled i.v. titration with canine plasma. Rises in portal pressure 9.3 ± 2.6 to 15.6 ± 2.3 cm H2O were associated with significant decreases in urine volume 1.57 ± 0.53 to 0.66 ± 0.21 ml per min (p<0.05) and urinary sodium excretion [340 ± 82 to 145 ±75 mEq per min (p<0.05)]. In contrast, similar experiments in five dogs in which the portal vein was partially ligated with increases in portal pressure from 8.3 ± 0.6 to 18.6 ± 0.5 cm H2O resulted in no change in urinary volume or sodium excretion.Acute reversible portal hypertension induced by hepatic vein constriction is associated with acute reversible retention of water and salt in the absence of changes in renal blood flow and creatinine clearance which only occur when the liver is involved and not with portal vein const