Renal water and sodium handling during gradated unilateral ureter obstruction.
OBJECTIVE
Unilateral complete obstruction of the ureter (UUO) is associated with characteristic changes in renal function. To improve the understanding of how urine concentration directly is affected by changes in pelvic pressure, changes in renal salt and water handling along the nephron and collecting duct were examined.


METHODS
Pelvic pressure was raised stepwise using an adjustable lever inserted in the right ureter. Urine samples were collected from the tip of the catheter by way of an overflow system. Water and sodium handling in the distal and proximal tubules were measured by the lithium clearance technique. Renal blood flow (RBF) was measured with implanted ultrasonic flow probes. Catheters were placed in both renal veins and glomerular filtration rate (GFR) and filtration fraction were calculated using renal extraction of (51)Cr-EDTA independent of urine sampling.


RESULTS
The sequence of changes for each parameter is provided. The parameters did not show a uniform pattern from which specific threshold values could be derived. However, the mean value of the following parameters were markedly changed at specific pressures: (1) at 10 cm H(2)O ipsilateral urine output decreased rapidly and distal absolute reabsorption of sodium (DAR(H2O)) decreased, (2) at 20 cm H(2)O GFR started to decline rapidly, (3) at 30 cm H(2)O urine output was impaired, and (4) at 40 cm H(2)O proximal absolute reabsorption of water (PAR(H2O)) showed a decreasing tendency in all pigs together with impairment in tubular sodium handling. Furthermore, free water clearance was slightly impaired (-0.26 +/- 0.15 at baseline and -0.15 +/- 0.08 ml/min at maximum pressure) and ipsilateral RBF decreased from 171.1 +/- 12.4 ml/min at baseline to 136.3 +/- 12.3 ml/min at ureteral pressure of 80 cm H(2)O (p < 0.05). Consistent with that, ipsilateral renal vascular resistance increased with increasing pressure in the renal pelvis.


CONCLUSIONS
Water reabsorption and sodium handling is progressively impaired with increasing pelvic pressure. GFR and RBF are reduced in parallel. The study shows that the kidney responds to ureteral obstruction is unique and individual.
Pedersen
T S
TS
Institute of Experimental Clinical Research, University of Aarhus, Aarhus University Hospital, Skejby, Aarhus N, Denmark.
Hvistendahl
J J
JJ
Djurhuus
J C
JC
Frøkiaer
J
J
D000818:Animals; D001834:Body Water / Q000378:metabolism*; D005919:Glomerular Filtration Rate; D007668:Kidney / Q000503:physiopathology*; D007684:Kidney Tubules / Q000502:physiology; D010388:Pelvis; D011312:Pressure; D012079:Renal Circulation; D012964:Sodium / Q000378:metabolism*; D013552:Swine; D014517:Ureteral Obstruction / Q000503:physiopathology*; D014556:Urine; D014655:Vascular Resistance
D012964:Sodium