Renal venous pressure and volume natriuresis in the rat

Anesthetized rats were surgically prepared so that left renal venous pressure could be maintained at its normal level (near 1 mmHg) (1 mmHg = 133.322 Pa) while right renal venous pressure was free to change in response to acute isoncotic blood volume expansion (n = 10). The purpose of the study was to test whether the renal venous pressure changes normally accompanying a 33% blood volume expansion have an effect on inulin clearance (CIn) and on the rates of excretion of water (V) or sodium (UNaV) by the kidneys. In 10 control rats blood volume was not expanded. The results showed that the volume expansion used resulted in a peak pressure of 5.3 +/- 0.5 (SEM) mmHg in the right renal vein. Both kidneys showed significant increases in CIn, V, and UNaV over their respective preexpansion values. However, there were no significant differences between these parameters measured in the right or in the left kidney even though the differences between the two renal venous pressures were highly significant during the infusion and for the next 20 min. In a further six rats, a caval snare was placed superior to the right renal vein so that both renal venous pressures could be held at normal during blood volume expansion. The ensuing diuresis and natriuresis were not different from those observed in the preceding group. It is concluded that changes in renal venous pressure, of the magnitude associated with volume expansion, have no significant effect on renal excretion rates.