Effects of increased ureteropelvic pressure on fluid and NaCl absorption across the jejunum

The aim of the present study was to elucidate the effects of an increased ureteropelvic pressure (UPP) on the net jejunal fluid, Na+, and Cl- absorption in anesthetized dogs. UPP was changed under hydrostatic pressure with warmed Ringer's solution. At a UPP of 0 mmHg, the net jejunal fluid, Na+, and Cl- absorption were 10.1 +/- 0.5 ml, 2.4 +/- 0.1, and 2.0 +/- 0.1 mEq, and were significantly reduced to 5.9 +/- 0.4 ml, 2.0 +/- 0.1, and 1.6 +/- 0.1 mEq, respectively, by an increase in UPP to 60 mmHg. After lowering the UPP to 0 mmHg, the net absorption recovered to the control values. The same experiments were performed after ipsilateral renal denervation. Ipsilateral renal denervation completely abolished this response. This result suggests that the afferent pathway of this response is the renal nerves. We also assessed the validity of the method using a jejunal loop by examining the effects of repetition of the absorption experiment on the net absorption. The net absorption was not altered by 6 times repetition of the absorption experiment. To determine the collection ratio, phenol red was used in the first and sixth absorption experiments. The collection ratios were 92.2 +/- 1.1 and 90.3 +/- 0.9%, respectively. There was no significant difference in collection ratio between the first and sixth values. This is the first report in which an increased UPP was found to inhibit the net jejunal fluid, Na+, and Cl- absorption.