Effect of ipsilateral ureteric obstruction on contralateral kidney and role of renin angiotensin system blockade on renal recovery in experimentally induced unilateral ureteric obstruction.

AIMS: To study, the effects of ipsilateral ureteric obstruction on contralateral kidney and the role of renin angiotensin system (RAS) blockade on renal recovery in experimentally induced unilateral ureteric obstruction.
MATERIALS AND METHODS: Unilateral upper ureteric obstruction was created in 96 adult Wistar rats that were reversed after pre-determined intervals. Losartan and Enalapril were given to different subgroups of rats following relief of obstruction.
RESULTS: The severity of dilatation on the contralateral kidney varied with duration of ipsilateral obstruction longer the duration more severe the dilatation. There is direct correlation between renal parenchymal damage, pelvi-ureteric junction (PUJ) fibrosis, inflammation and severity of pelvi-calyceal system dilatation of contralateral kidney with duration of ipsilateral PUJ obstruction.
CONCLUSIONS: Considerable injury is also inflicted to the contralateral normal kidney while ipsilateral kidney remains obstructed. Use of RAS blocking drugs has been found to significantly improve renal recovery on the contralateral kidney. It can, thus, be postulated that contralateral renal parenchymal injury was mediated through activation of RAS.

INTRODUCTION

Ureteropelvic junction obstruction is the commonest cause of fetal hydronephrosis.[1-4] The pathophysiology of congenital obstructive uropathy[5-7] has been studied in animal models.[8-11] This study was initiated with the aim to create an ipsilateral ureteral obstruction for varying durations in rat models and to study the changes in contralateral kidney with respect to duration of obstruction. This artificially created ureteral obstruction was reversed and then reversal of pathological changes in contralateral kidney was studied. Effect of Losartan and Enalapril individually on the recovery of renal function in contralateral kidney were studied and then compared with each other.

MATERIAL AND METHODS

This prospective study was performed on 96 adult female Wistar rats (weighing 100-150 g). The rats were divided into four equal groups and each group was further subdivided in to three equal sub groups, depending on the duration for which the ureters were obstructed (7, 21 and 42 days respectively). The left ureter was ligated in each rat.[12-14] Group I acted as control to study the renal changes on contralateral (right) kidney on creating an ipsilateral (left) proximal ureteral obstruction. The rats were sacrificed at the end of 7, 14 and 21 days. Group II served to study the reversal of these changes on contralateral kidney upon reversing this ipsilateral ureteral obstruction. The ipsilateral ureteral obstruction was relieved at the end of 7, 21 and 42 days and the rats were then sacrificed 14 days following the reversal. Group III was used to demonstrate the benefit of adding an angiotensin receptor blocker Losartan (1 mg/kg/day for 14 days) during the recovery phase on contralateral kidney. Group IV was similar to Group III except for the use of Enalapril at a dose of 50 mg/kg/day instead of Losartan.

Morphometric measurements

The kidneys were split longitudinally and photographed along with a scale, using a 12.1 megapixels ×4 optical zoom digital camera kept vertically overhead at a distance of 25 cm and an angle of 15°. The various dimensions, i.e., the renal height, pelvic dimensions (antero-posterior, cranio-caudal and lateral) and renal cortical thickness at the upper and lower pole was measured with a least count of 0.01 mm using I-photo-measure software version 3.0.

Pathological grades

The slides were stained with hematoxylin, eosin and Masson's trichrome stains. The distances were measured with Image Pro Plus software with a least count of 0.00001 μm. The pathological grades were as shown in Tables 1–4.[15]

Table 1

Grade of renal parenchymal damage

Table 4

Inflammation at pelviureteric junction lamina propria

Statistical analysis

The data analysis was carried out using STATA software version 9.0 Stata Corp. LP Texas USA. Pre-operative and post-operative continuous data were compared using t-test and dichomatous data were compared using Chi-square test. A P value of <0.05 was considered statistically significant.

RESULTS

Morphometric analysis

Renal height

When comparisons were drawn on the basis of groups there was significant difference between days 7 and 21 (P < 0.05) and 7 and 42 (P < 0.0001) in group I. There was similar significant difference between days 7 and 21 (P < 0.004), days 7 and 42 (P < 0.0001) and days 21 and 42 (P < 0.0001) in group II. However, in groups III and IV there was no significant difference at various durations.

Pelvis diameters

After 42 days of obstruction, significant difference of antero-posterior diameter between group I and III, group I and IV, group II and III, group II and IV. There was no significant difference between groups after 7 days and 21 days of obstruction. This signifies antero-posterior diameter was affected late after obstruction than cranio-caudal diameter.

Volume of pelvis

The pelvic volume was calculated as the product of all three dimensions of the pelvis. The pelvic volumes were significantly different between group I and the other groups at 7 days. This signifies that if the obstruction is reversed early, the degree of hydronephrosis comes back to normal. There was no difference between group II and groups III, IV. At 42 days there was significant difference in the pelvic volumes between group I and group III (P < 0.0001) and group I and group IV (P < 0.0001). The difference between group I and II was not significant. However, there was no difference in this change brought about by Losartan (group III) and Enalapril (group IV) (P = 1.00).

Average cortical thickness: Renal height

The cortical thickness was measured at the upper and lower pole, and average of the two was drawn and this was shown as a ratio between the cortical thickness and the total renal size to avoid disparity borne by rat-to-rat kidney size variation. When comparisons were drawn on the basis of groups there was no significant difference between days 7 and 21 but significant difference between days 7 and 42 in group I. There was no significant difference between groups III and IV suggesting that the cortical thickness returns to normal levels once Losartan or Enalapril is added. There was no significant difference in the cortical thickness between the groups at day 7 and day 21 and day 42 except group II and IV at 7 days and group I and IV at 42 days. If we compare the cortical thickness and the pelvic volumes irrespective of the duration of obstruction we find that there is a significant difference between groups I and III, IV suggesting that simply reversing the obstruction does not suffice to reverse the morphometric indices and it's the addition of a renoprotective drug, which improves the renal damage. However, there is no significant difference between Losartan and Enalapril in this regard.

Pathological analysis

The parenchymal damage, fibrosis at pelvi-ureteric junction (PUJ), ureteral muscular hypertrophy, and inflammation at contralateral PUJ were graded with duration of obstruction at day 7, day 21, and day 42 [Tables 1–4]. Parenchymal damage in contralateral kidney after 42 days of ipsilateral upper ureteric obstruction and reversal of changes after reversing the obstruction were shown in Figure 1a and b, respectively. There is a significant difference between the various groups at any duration of obstruction except ureteral muscular hypertrophy [Table 5]. The changes in ureter muscle may require prolonged period of obstruction. The pathological changes in contralateral kidney set in as soon as the ipsilateral ureter is obstructed and the changes worsen significantly with increasing duration of obstruction. The P values are significant when the groups are compared with each. Histopathological changes specifically parenchymal damage and inflammation at PUJ were reversed significantly on addition of reno-protective drugs [Table 6] and enalapril had better trend of reno-protective action than losartan. Significant fibrosis at PUJ of contralateral kidney seen after prolonged ipsilateral PUJ obstruction, i.e., at least 42 days and this pathology resolves significantly by renin angiotensin system (RAS) blocking drugs.

Figure 1

(a) Pathological changes (parenchymal damage) in contralateral kidney after 42 days of ipsilateral upper ureteric obstruction (H and E, ×20) (b) Reversal of changes in contralateral kidney seen after reversing the obstruction (H and E, ×20)

Table 5

The P values comparing the various pathological changes amongst the groups separately at 7, 21 and 42 days

Table 6

The changes in histopathological grades of contralateral kidney with different duration of ipsilateral ureteral obstruction in the various groups

DISCUSSION

The activation of the renin-angiotensin system is a major factor in normal development of kidneys and in partial obstruction.[16] Administration of the angiotensin-converting enzyme (ACE) inhibitor enalapril not only maintained renal blood flow in partially obstructed kidneys at 3 weeks post-obstruction but also prevented the histological changes of glomerulosclerosis[17] and the effects of obstruction are not all ischemic. Obstruction can mimic renal artery stenosis, and because of its intense vasoconstrictor action, the resulting increase in angiotensin II (AII) leads to decreases in glomerular filtration rate (GFR). It is becoming increasingly clear, however, that AII profoundly affects the expression of growth factors in the developing kidney that ultimately are responsible for the changes in the histology. Up regulation of TGF is apparent in these infiltrating cells and the degree of up regulation correlates directly with fibrosis and collagen deposition in obstructed kidneys.[18] The fibrotic changes in the kidney are due to the expression of nuclear factor kappa B (NF-kB) resulted due to increase in AII.

In the current study, histological changes in renal parenchyma, fibrosis, and inflammation were seen in the contralateral kidney after ipsilateral ureteral obstruction and these changes after reversal of experimentally induced ipsilateral obstruction were further reversed by reno-protective drugs like losartan and enalapril.

Degree of hydronephrosis in contralateral kidney as indicated by increased pelvic volume starts within 7 days of creating an ipsilateral upper ureteral obstruction and was due to compensatory hyperfunction in contralateral kidney in response to ipsilateral obstruction. So hydronephrosis of contralateral kidney was reverted back by relieving the ipsilateral obstruction and thereby decreasing the overload on the contralateral kidney. Parenchymal thinning in contralateral kidney occurs after at least 3 weeks of creating the obstruction and worsens with duration. Reversing the obstruction alone does not improve the cortical thickness. Addition of a reno-protective drug however, significantly improves the cortical thickness.

The pathological changes also vary with duration of obstruction with long standing obstruction causing significant and consistent histopathological changes in contralateral kidney. The reversal of obstruction alone helps in resolution of this damage but addition of losartan or enalapril has a significantly better result in this recovery. In the experimental study by Sinha et al.,[19] the histopathological changes in ipsilateral obstructed kidney reversed after removal of obstruction but recovery was significantly better after addition of losartan or enalapril. So RAS blockade reverses the changes in ipsilateral obstructed kidney. This activated RAS after ipsilateral ureteral obstruction also affects the contralateral kidney and this was proved when the histopathological changes reverted in the contralateral kidney after addition of losartan or enalapril. Although, there is no significant difference between the two drugs, there appears to be trend of better recovery in the enalapril treated rats.

These observations support our contention[5] that RAS is the major culprit responsible for the functional renal loss in obstructive pathologies as follows: The renal parenchymal damage occurring in pelvi-ureteric junction obstruction (PUJO) is secondary to RAS activation. The damage can more effectively be controlled by use of any agent acting on the RAS, as has been demonstrated earlier.[14] ACE inhibitor (Enalapril) shows a better trend in this regard and this study supports the earlier observations[52021] that early detection of RAS activation can serve to discriminate pathological from non-pathological obstruction. It has been recently demonstrated that use of RAS blockade can retard the pace of clinical renal damage[22] as well as minimize experimentally created damage.[14] The present study, further provides proof of mechanism that use of drugs acting on RAS could be useful in reversing pathological changes in contralateral kidney caused after a period of experimentally created ipsilateral obstruction.

Table 2

Grade of fibrosis at pelvi-ureteric junction

Table 3

Hypertrophy at upper ureter