Volume Expansion Enhances the Recovery of Renal Function and Prolongs the Diuresis and Natriuresis After Release of Bilateral Ureteral Obstruction: A Possible Role for Atrial Natriuretic Peptide

Plasma atrial natriuretic peptide (ANP) levels are elevated in patients with bilateral ureteral obstruction (BUO). To further evaluate the role of ANP in postobstructive diuresis, natriuresis and recovery of renal function, 3 groups of dogs were studied: Group 1, 6 dogs that underwent 48 hours of unilateral ureteral obstruction (UUO); Group 2, 6 dogs that underwent 48 hours of BUO; and Group 3, 6 dogs volume replete with normal saline during 48 hours of BUO. All 3 groups underwent hourly hemodynamic and clearance studies for 15 hours after the release of obstruction. Group 1 experienced no increase in either urine output or sodium excretion from the ipsilateral or contralateral kidney after release of obstruction. Groups 2 and 3 both experienced an initial diuresis and natriuresis after BUO (p < 0.01). However, in Group 2 diuresis and natriuresis after BUO ceased at 5 and 2 hours, respectively, while in Group 3 both persisted for 10 and 9 hours, respectively. Before obstruction the GFR was similar in all three groups. In Group 1 the GFR decreased significantly in the ipsilateral kidney (34.5 +/- 1.4 to 14.48 +/- 1.5 ml. per minute, (p < 0.01)) and increased significantly in the contralateral kidney (32.4 +/- 2.8 to 44.4 +/- 2.0 ml. per minute, (p < 0.05)) and remained so throughout the postobstruction period. The GFR in Groups 2 and 3 decreased to a similar level 1 hour after release (13.3 +/- 1.7 and 17.5 +/- 3.4 ml. per minute, respectively); however, Group 2 remained decreased during the period after release while group 3 increased to 23.4 +/- 3.4 ml. per minute (p < 0.01) at 11 hours after release of obstruction. In Group 2 the control plasma ANP level was 17.9 +/- 3.7 pg./ml. and was not altered by BUO, whereas ANP increased significantly after 48 hour BUO in Group 3, from 30.6 +/- 6.7 to 63.7 +/- 11.7 pg./ml. (p < 0.01). Before and after 48 hours of BUO, the pulmonary capillary wedge pressure was 5.0 +/- 2.0 mm. Hg and 7.0 +/- 1.0 mm. Hg (NS) in Group 2, while it increased from 7.18 +/- 1.5 mm. Hg to 11.6 +/- 1.9 mm. Hg (p < 0.01) in Group 3. We conclude that volume expansion during BUO enhances postobstructive diuresis and natriuresis and allows a greater recovery of GFR after release of the obstruction. This effect may be mediated through elevated plasma levels of ANP as measured in this study.