Partial ureteric obstruction in the pubescent rat. I. Long-term effects on renal function

The antenatally detected pelvi-ureteric junction stenosis: advances in renography and strategy of management

This review includes an analysis of new developments in the field of renography, the predictive factors suggesting the need for pyeloplasty in cases of pelvi-utereric stenosis detected antenatally and integration of the pelvi-ureteric junction stenosis within the framework of antenatally detected hydronephrosis.

Ureteropelvic junction obstruction causes histologic alterations in contralateral kidney

BACKGROUND/PURPOSE

Ureteropelvic junction (UPJ) obstruction causes histologic alterations both in ipsilateral and contralateral kidney. Because these alterations directly affect the fate of renal damage, definition of these alterations is of utmost importance from the clinical point of view. Thus, an experimental study is designed to determine the alterations of renal histology in response to partial and complete UPJ obstruction.

METHODS

Fifteen adult female New Zealand rabbits were assigned randomly into 3 groups (each containing 5 rabbits) according to the degree of unilateral UPJ obstruction as group I, sham operation was performed and served as the control group; group II, partial UPJ obstruction was made; group III, complete UPJ obstruction was made. The animals in group I and II were killed after 3 weeks, and animals in group III were killed after 2 weeks. Tissue samples were prepared and processed according to routine light microscopic tissue processing.

RESULTS

UPJ obstruction led to glomerulosclerosis, dilatation of proximal and distal tubules of loops of Henle, and dilatation of collecting tubes consistent with necrotic and apoptotic changes in ipsilateral kidneys. Severity of these degenerative changes depended on degree of obstruction. UPJ obstruction also led to histologic alterations on the contralateral kidneys such as glomerular edema, congested blood vessels, dilated tubuli, and necrotic and apoptotic changes in epithelia, which were more prominent in group III than group II.

CONCLUSIONS

It is well known that compensating changes including increased blood flow and parenchymal hypertrophy occurs in contralateral kidney as a response to unilateral UPJ obstruction. However histologic findings of this study confirmed progression of parenchymal damage and presence of apoptosis in contralateral kidney for the first time.

The protective effects of captopril and nitric oxide on solitary kidney after chronic partial ureteric obstruction

OBJECTIVE

To determine whether vasodilator agents (captopril and nitric oxide) change the morphological and functional effects of chronic partial ureteric obstruction in solitary kidney tissue in unilaterally nephrectomized rats.

MATERIALS AND METHODS

Each of 50 prepubertal Wistar albino rats underwent right nephrectomy and were then assigned to one of five groups. Rats in group 1 underwent a sham operation (control) and in the other groups the ureter of the remaining kidney was partially obstructed by surgery. In group 2, no drug treatments were given; in groups 3, 4 and 5 captopril, L-arginine methyl ester (L-Arg) or NG- nitro-L-arginine-methyl ester, respectively, were given for 3 weeks. In all rats, diuretic scintigraphy was used to measure kidney perfusion, glomerular filtration rate (GFR) and concentration. Blood urea nitrogen (BUN), serum creatinine levels, kidney parenchymal weight and pelvic volume were measured and the kidneys evaluated histopathologically.

RESULTS

Renal perfusion was significantly greater in both group 3 and 4 than in group 2. The GFR was 18% greater in group 3 and 22.3% greater in group 4 than in group 2. The GFR was decreased by 67% in group 5 compared with the control group. The mean parenchymal weight, mean pelvic volume, BUN and serum creatinine in the four groups with a partially obstructed ureter were significantly different from the control group. There also were significant differences between group 2 and groups 3--5, and between group 2 and group 3. Histological damage was severe in all four groups with partial ureteric obstruction, but in the drug-treated groups, medullary fibrosis was less frequent.

CONCLUSION

After 3 weeks of treatment, captopril and L-Arg both improved kidney perfusion, GFR, BUN and serum creatinine levels, but were less effective in preventing parenchymal atrophy and changes in pelvic volume.

Duplex Doppler evaluation of acute renal obstruction

Patients with possible acute renal obstruction often undergo numerous types of radiological examinations. Renal Doppler ultrasound is a quick and noninvasive way to assess for physiological and hemodynamic changes that accompany acute obstruction. The renal Doppler study may provide unique data not available from conventional sonography. Most, but not all, clinical and laboratory studies regarding Doppler of acute renal obstruction have reported encouraging results. As limitations to the Doppler examination in this clinical setting are delineated, a proper role for renal Doppler will continue to emerge.

Congenital unilateral hydronephrosis in a rat model: continuous renal pelvic and bladder pressures

We investigated a rat model with inbred unilateral congenital hydronephrosis. Simultaneous bladder and renal pelvic pressures were measured during different urinary flows, and during bladder filling and voiding in these congenitally hydronephrotic rats (approximately 45 days old) and normal nonhydronephrotic rats from the same colony. Differential pressures between pelvis and proximal ureter were determined. Upon termination of the experiment the urinary tract was removed and processed for histological examination. Hydronephrotic rats had significantly higher renal pelvic pressures throughout bladder filling at all urinary flow rates than normal rats. These elevated renal pelvic pressures exceeded bladder pressures at high flows (for example bladder pressure at 50% capacity was 8.9 +/- 3.1 cm. water and corresponding pelvic pressure was 20.8 +/- 2.1 [hydronephrosis] versus pelvic pressure 7.4 +/- 1.1 [control]). While pressures in the proximal ureter were higher than in the pelvis in normal rats the hydronephrotic rats showed significantly higher pressures in the pelvis, suggesting that the site of obstruction is the ureteropelvic junction. Histological evaluation of the excised kidneys revealed only minimal tubular changes. This study represents a unique animal model with unilateral hydronephrosis from a partially obstructing ureteropelvic junction. Moreover, the data indicate that partial urinary obstruction and the associated renal pelvic pressures should be defined with reference to bladder fullness and urinary flow rates.

Response of the newborn ureteropelvic junction complex to induced and later reversed partial ureteral obstruction in the rabbit model

The clinical controversy regarding the timing of surgery for asymptomatic newborns with obstructed hydronephrosis was addressed using a model of reversible partial ureteral obstruction in the newborn rabbit. The histomorphometric changes in the ureteropelvic junction complex (for example, pelvis, ureteropelvic junction and upper ureter) and kidney in 44 normal cases were determined and compared with the effects of 47 cases of ongoing partial obstruction and timed reversal of partial obstruction at 1 week in 9 cases, at 2 weeks in 10 or at 4 weeks in 10 (end of the study at age 8 weeks). After partial obstruction hydronephrosis appeared by 1 week postoperatively. There were progressive increases in the thickness of the lamina muscularis and mass index of smooth muscle and collagen (all p < 0.001). However, since the per cent surface area of smooth muscle did not change significantly in comparison to normal, there was disproportionately more collagen. For reversals at 1 week the muscle and collagen in the lamina muscularis were not significantly different from normal. For reversals at 2 weeks the mass index of collagen was greater than normal (p < 0.05) and reversal at 1 week (p < 0.05). For reversals at 4 weeks the lamina muscularis was thicker, and the mass index of collagen and muscle was greater than the earlier reversal groups and normal (all p < 0.05). In conclusion, partial ureteral obstruction causes progressive thickening of the lamina muscularis by collagen and muscle with a disproportionately greater increase in collagen than muscle. The earlier the obstruction can be reversed, the more normal is the ureteropelvic junction complex histology. The functional significance of these changes needs to be determined.

Long-term partial ureteral obstruction and its effects on kidney function

Previously it has been shown that partial ureteral obstruction present in young rats for 12 weeks results in small morphological changes in the kidney as well as slightly decreased kidney function. In the present study the aim was to examine whether rats obstructed for one year had more advanced changes in morphology and kidney function. The first group of animals examined after three weeks of obstruction showed only modest changes in kidney function with a reduced potassium concentration in the urine but no reduction in the glomerular filtration rate. After one year there was a reduction in urine flow as well as in the excretion of both potassium and sodium. Urine osmolality was also reduced. Glomerular filtration rate measured in this group of animals was reduced in the obstructed kidney by about 60% compared to the contralateral one. There were only small changes in the morphology with no loss in parenchymal weight or compensatory hypertrophy, but there was a significant deformation of the papilla and an increase in inflammatory cells in the parenchyma. In conclusion hydronephrosis during a shorter period is not harmful to kidney function but if sustained for an extended time period kidney function will deteriorate.

Long-term follow-up of renal function in rats with unilateral hydronephrosis

In order to obtain more information on the long-term changes in renal function of hydronephrotic kidneys, we have measured the glomerular filtration rate (GFR) in rats with a congenital or an experimental unilateral hydronephrotic kidney (HK). In Brown Norway rats, with congenital hydronephrosis, the presence of an HK affected neither the total GFR nor the contribution of that kidney to the total GFR, during a follow-up of 70 weeks. In Wistar rats with experimental unilateral hydronephrosis two groups could be distinguished on the basis of the contribution of the HK to the total GFR. In the first, the contribution of the HK to the total GFR was not different from that of controls. This contribution as well as the total GFR remained similar to that of controls during the follow-up. In the second group, the contribution of the HK to the total GFR was reduced to 25%. In these rats the total GFR was slightly less than that of controls. The contribution of the HK to the total GFR remained unchanged for the next 56 weeks. It is concluded that the long lasting presence of unilateral hydronephrosis in rats does not necessarily result in a progressive loss of renal function with time.

Hydronephrotic atrophy after stable mild or severe partial ureteral obstruction: natural history and recovery after relief of obstruction

After stable mild or severe partial unilateral ureteral obstruction in rats, the ratio of renal dry weight to whole body weight changes in two phases. In a "destructive phase" of two to six weeks, slight weight reduction occurs in the kidneys with mild obstruction and pronounced weight reduction occurs in those with severe obstruction. Then, in a "steady-state phase", there is no further weight reduction in kidneys with either mild or severe obstruction. Relief of ureteral obstruction during the steady-state phase does not result in an increase in renal dry weight. We conclude that the development of hydronephrotic atrophy after stable mild or severe partial unilateral ureteral obstruction can not be influenced by relief of obstruction in the steady-state phase.

Experimental obstructive hydronephrosis in newborn rats. XI. A one-year follow-up study of renal function and morphology

Partial obstruction of the left ureter was created in two-day-old rats and its effects on kidney function were studied with 99mTc-DMSA and 99mTc-DTPA after one, two, three and six weeks, and after one year. Kidneys from animals sacrificed at the age of six weeks or one year were also examined histologically. The obstructed renal pelvis was enlarged by about 35 times and there was a delayed excretion of 99mTc-DTPA during forced diuresis, indicating significant, chronic obstruction. The renal DMSA-uptake ratio (left kidney/(left and right kidney] was reduced to about 40% from the first week of obstruction. The parenchymal weight ratio (expressed as above) was reduced to about 45% after both six weeks and one year. The glomerular filtration rate, examined during forced diuresis and calculated on the basis of uptake capacity, was lowered to 42% after six weeks but was not significantly reduced after one year of obstruction. The incidence figures for medullary hemorrhage or accumulation of iron pigment, and chronic inflammatory changes in the cortex were somewhat higher after one year of obstruction than after 6 weeks, but the lesions were patchy in both groups. We conclude that partial unilateral ureteric obstruction, created in the neonatal period, leads to a slight but permanent functional disturbance and parenchymal weight reduction without prominent structural parenchymal damage.

Experimental partial ureteric obstruction in newborn rats. VII. Are the long term effects on renal morphology avoided by release of the obstruction?

Partial obstruction of the left ureter was created in newborn rats. The obstruction was either permanent or was released after two or seven days. The effects were studied at the age of six weeks. The permanently obstructed kidneys characteristically exhibited considerable enlargement (X 18) of pelvic volume and prominent deformation of the papilla, frequently associated with moderate widening of collecting ducts and convoluted tubuli, and focal inflammatory and degenerative lesions. The weight difference between the hydronephrotic and the contralateral, intact kidney was significantly higher than in a sham operated group, although the combined kidney weight was unchanged, indicating a reduction on the obstructed side and a compensatory contralateral hypertrophy. In the group released after seven days, the pelvic volume had returned to normal; nevertheless the parenchymal weight pattern and the histological lesions were similar to those found in animals obstructed for six weeks. In the group released after two days, the pelvic volume had normalized, and the histological changes were less prominent than in animals obstructed for seven days or six weeks. Yet there was a significant difference in parenchymal weight between the hydronephrotic and the contralateral kidney, almost entirely caused by hypertrophy on the nonobstructed side. Thus, the ureteric obstruction must be released very early to avoid parenchymal weight reduction and curb the tissue lesions. On the other hand, the resulting parenchymal damage is moderate and does not seem to progress with time.