Background: We have previously shown that animals with hydronephrosis due to chronic partial unilateral ureteral obstruction (PUUO) develop salt-sensitive hypertension. The incidence of hydronephrosis due to ureteropelvic junction obstruction is approximately 1%. During the last decade the management of hydronephrosis has become much more conservative, but the long-term physiological consequences of this policy are not clear.

Aim: In this study the effects of ipsi- and contralateral nephrectomy and ureterovesicostomy on blood pressure were studied in hydronephrotic animals.

Methods: PUUO was created in 3-week-old male Sprague-Dawley rats and 4-6 weeks later blood pressure was measured with telemetry, with normal and high salt diet, before and after uninephrectomy or ureterovesicostomy. Plasma renin concentration was analyzed during both diets, before and after ipsilateral nephrectomy.

Results: All hydronephrotic animals developed salt-sensitive hypertension, of different degrees. Before nephrectomy the plasma renin concentration was significantly higher in the hydronephrotic animals than in controls (160 ± 15 vs 96 ± 12 mGU/ml respectively), but after the ipsilateral nephrectomy no differences were found. In the hydronephrotic animals both ipsilateral nephrectomy and ureterovesicostomy reduced the blood pressure and salt-sensitivity but the former still differed significantly from the controls. In contralaterally nephrectomized hydronephrotic animals the salt-sensitive hypertension became more pronounced.

Conclusion: Hydronephrosis in rats causes salt-sensitive hypertension that can be markedly reduced by nephrectomy or by ureterovesicostomy. The mechanisms appear to be intrarenal and primarily located in the diseased kidney, but a secondary mechanism is also present.