Which of the following is TRUE in unilateral ureteric obstruction (UUO)?
A. Renal blood flow (RBF) increases during the first 1 1/2 to 4 hours along with an increase in the ureteric pressureAnswer D
In UUO, RBF increases during the first 0–90 minutes and is accompanied by a high collecting system pressure because of the obstruction. In the second phase lasting up to 5 hours, both RBF and collecting system pressure remain elevated but RBF begins to gradually decline. A third phase beginning about 5 hours after obstruction is characterised by a further decline in RBF, now paralleled by a decrease in collecting system pressure.
Infusion of the angiotensin-converting enzyme (ACE) inhibitor Captopril attenuates the declines in RBF and GFR in UUO, suggesting that angiotensin II is an important mediator of the preglomerular vasoconstriction in the second and third phases of UUO. Endothelin antagonists limit the reduction of RBF and GFR in rats during and after release of UUO.