Impaired nephrogenesis in rats with congenital obstructive uropathy

Alterations caused by renal obstruction in developing kidneys are of particular interest in basic research of congenital obstructive uropathy. In rats nephrogenesis mainly occurs 7 to 10 days postnatally. Therefore, surgically induced neonatal ureteral obstruction in rats has been suggested to be analogous to congenital obstruction in the fetus. An attempt less prone to surgical artifacts and assessing even earlier developmental stages is to monitor the development of obstructed kidneys in rats with congenital obstructive uropathy.

Rats from an inbred strain with congenital renal obstruction in 70% of their littermates were observed. Morphologically, significant hydronephrosis was not detected before day 5 post partum and progressed with age. Unilateral obstructed kidneys were compared with contralateral kidneys and kidneys from healthy control animals at ages of 1, 5, 10, 18 and 32 days. A total of 72 renal units were investigated. The renal messenger RNA expression of renin and transforming growth factor-beta1 (TGF-beta1) was quantified by competitive quantitative reverse transcription polymerase chain reaction using a gene specific complementary RNA standard.

In controls the gene expression of renin decreased from day 1 to day 18 and remained stable. TGF-beta1 expression increased during the first 10 days and then decreased again. Renin expression of the obstructed kidneys was reduced (p <0.05) on day 1, increased to a maximum versus controls (p <0.01) on day 10 and decreased to an unchanged elevated level (p <0.01) on days 18 and 32. Renin expression of the contralateral kidneys showed no significant alterations to control kidneys. Messenger RNA expression of TGF-beta1 of obstructed kidneys stayed decreased during the first 10 days (p <0.05), then increased excessively on day 18 (p <0.01) and slightly decreased on day 32. TGF-beta1 expression of the contralateral kidneys was parallel to controls on a slightly elevated level, increased on day 18 and returned to control level on day 32.

Within the postpartum period of nephrogenesis gene expression of renin and TGF-beta1 was decreased in obstructed kidneys compared to controls. As the renin angiotensin system and TGF-beta1 have important functions in normal kidney development, these results suggest impaired nephrogenesis of congenital obstructed kidneys even before the onset of morphological signs of hydronephrosis. These features differ from surgical induced unilateral ureteral obstruction at birth and promise new insights into the pathophysiology of congenital obstructive uropathy.