Renal function during experimental hydronephrosis: function during partial obstruction following contralateral nephrectomy in the dog

N-acetyl-glucosaminidase (NAG) excretion in partially obstructed weanling rats

The understanding of pathophysiology of obstructed uropathy has been facilitated by animal models with partial ureteric obstruction. Some studies on partially obstructed adult rats have drawn attention to a biphasic pattern of obstructive uropathy: an initial 'destructive' phase and a 'steady' phase in which renal deterioration no longer occurs and in which relief of obstruction would be of no advantage. We aimed to verify if this pattern applies also to younger (weanling) rats with more immature kidneys, resembling those of the human fetus. We measured the NAG-values in the urine samples of partially obstructed animals at different intervals of obstruction and in those of controls. The biphasic pattern proved to be the same as in adult rats as was previously documented, but the turning point occurred earlier (between 10 and 15 days of obstruction). Furthermore, there is evidence of low level values of N-Acetyl-Glucosaminidase (NAG) in the early phase of obstruction (5 days), demonstrating that the increase of tubular enzyme is not due to the operation itself. There is evidence that, if the 'destructive' phase can be precisely identified by biochemical studies, this could help identifying those subjects who could benefit from relief of obstruction.

Intrapelvic pressure monitoring in the partially obstructed porcine kidney

OBJECTIVES

The diagnosis of urinary obstruction in newborns and infants remains difficult because the diagnostic studies available at present are fraught with many problems. It is our premise that precise measurement of renal pelvic pressures under physiologic conditions in patients with urinary tract dilation will allow diagnosis of obstruction and prediction of further renal damage. This study evaluates an intrapelvic pressure monitoring system.

METHODS

Four porcine subjects had partial ureteropelvic junction obstruction created surgically; two subjects were used as controls. Doppler ultrasound and MAG-3 furosemide renography were performed preoperatively and each week pressures were measured with a Millar 5 F solid-state pressure transducer and the analog signals were converted on line to digital information to allow signal processing and later data analysis. Antegrade nephrostograms were obtained at the same sitting and showed that the model remained stable over time. Measurements were obtained at physiologic flow rates as well as at the standard Whitaker infusion rate of 10 cc/min.

RESULTS

Thirteen pressure studies were performed on 9 kidneys. Each study was classified as normal (4), partial obstruction (8), or total obstruction (1), based on ultrasound and nephrostogram criteria. The normal units had baseline pressures of 4.12 +/- 0.94 cm water (H2O), which increased to 9.12 +/- 1.38 cm H2O with infusion. In the partially obstructed group, baseline was 16.4 +/- 3.83 cm H2O and increased to 35.3 +/- 15.9 cm H2O with infusion. The kidney with total obstruction showed a baseline pressure of 27 cm H2O, which increased to 68 cm H2O with infusion. These pressure measurements were also compared to furosemide renography.

CONCLUSIONS

Intrapelvic pressures correlated well with conventional ultrasound and nephrostogram in the evaluation of partial obstruction. However, the results of furosemide renography and the Whitaker test were quite variable and did not accurately define partial obstruction or correlate with intrapelvic pressure. The Millar solid-state transducer monitoring system is an accurate method of evaluating the intrapelvic pressure and could possibly become a standard for diagnosing significant urinary obstruction against which other studies can be evaluated.

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.

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.

A new test to predict reversibility of hydronephrotic atrophy after stable partial unilateral ureteral obstruction

In previous studies we showed that hydronephrotic atrophy develops only in the first weeks after stable partial ureteral obstruction, and does not progress thereafter. Relief of obstruction only in the "destructive phase" and not in the later "steady-state phase" seems to improve or prevent hydronephrotic atrophy. Since the duration of partial ureteral obstruction is often not known, we studied urinary enzymes of rat kidneys after stable partial unilateral ureteral obstruction to identify the destructive phase. We chose as an example of the tubular lysosomal enzyme N-acetyl glucosaminidase (NAG) and as an example of the brush border enzyme gamma-glutamyl-transferase (Gamma-GT). NAG concentration but not so much Gamma-GT concentration was higher in the urine of the obstructed kidneys than in the urine of the contralateral control kidney, in the first two weeks after operation, and then returned to normal. These observations lead to the conclusion that the "destructive phase" after ureteral obstruction can be identified by the appearance of high urinary tubular lysosomal enzyme content. The clinical implication is that the timing of relief of asymptomatic stable partial ureteral obstruction of unknown duration can be based on the concentrations of urinary lysosomal enzymes.

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

A partial obstruction of the left ureter was created in six-week-old rats. The effects on renal function were studied after three, nine and 15 weeks, first in normal hydration, and then after extracellular volume expansion. Moderate hydronephrosis without parenchymal weight reduction developed within three weeks. The hydronephrotic kidney i) excreted during normal hydration less urine and sodium than the intact one, because of increased reabsorption, ii) was capable of reacting fully on volume expansion and iii) had, after volume expansion, a higher renal blood flow and GFR but also a higher reabsorption of water, sodium, potassium and osmoles, resulting in excretions similar to those on the intact side. The differences noted were small (less than 20%) except for sodium excretion. The hydronephrotic kidney seemed to tolerate an increase in ureteral resistance better than the intact one would do. There were no significant differences between the three, nine and 15-week groups, with regard to the effects on the hydronephrotic kidney. Thus, except for a tendency to sodium retention, the effects of partial ureteric obstruction in young rats seem to be relatively harmless and do not increase with time.

Experimental obstructive hydronephrosis in newborn rats. VI. Long-term effects on glomerular filtration and distribution

Partial obstruction of one ureter was created in newborn rats and its effects were studied after the rats matured. The obstructed pelvis was found to be considerably enlarged. The parenchymal weight was 19 per cent lower and the whole kidney glomerular filtration rate was 43 per cent lower than on the contralateral intact side (p less than 0.001); however, these figures probably include a compensatory increase on the intact side. In the central part of the cortex, the glomerular filtration rate/mg. cortex was 21 per cent lower in the hydronephrotic kidney (p less than 0.02), but there was no intracortical redistribution. The glomerular density in this region was 24 per cent higher on the hydronephrotic side (p less than 0.001), because the glomeruli were crammed together in the distended cortex. No redistribution of glomeruli was found. The results are discussed and compared with previous findings from our laboratory. In this model, partially obstructive uropathy was found to cause only a moderate depression, but no redistribution, of the filtration.

The growing rabbit with a solitary, partially-obstructed kidney. Analysis of an experimental model with reference to the renal concentrating ability

The systemic and renal effects of high partial ureteral obstruction were investigated in a new model of experimental hydronephrosis. The test group comprised 12 contralaterally nephrectomized growing male New Zealand rabbits. As compared to the pyelographic findings in 6 unilaterally nephrectomized control animals, the test group could be divided into partially obstructed but non-hydronephrotic and obstructed-hydronephrotic subgroups. Animals of all 3 groups were capable of increasing their weight during the first 2 postoperative months. The mean plasma creatinine concentration remained normal in the obstructed group and even hydronephrosis was compatible with a normal serum creatinine level. As studied during forced hypotonic expansion, the renal response to a vasopressin analogue was significantly different in all 3 animal groups. Reciprocal but less marked differences were noted in the animals' ability to retain water during this test. We conclude that in this experimental model the magnitude of the antidiuretic response is inversely related to the radiologically defined degree of obstruction.

Pathophysiological changes in rat kidneys with partial ureteral obstruction since infancy

A partial ureteral obstruction (PUO) was created in 5-day-old rats by implanting the left ureter in the psoas muscle. The surgical technique was modified to produce mild or severe hydronephrosis [Hn (m) and Hn (s)]. The rats were studied at ages between 45 and 65 days with regard to kidney weight, number of functioning glomeruli, mean arterial blood pressure (MAP), total glomerular filtration rate (GFR), nephron filtration rate (SNGFR), tubular free-flow pressure (PT, and stop-flow pressure (SFP). Total GFR was determined after the release of obstruction. The other studies were performed in the obstructed state. Reference values were obtained from sham-operated and untouched control rats. The number of functioning nephrons was depressed 38% in Hn (m) and 73% in Hn (s). Total GFR was preserved in Hn (m) and depressed 54% in Hn (s). SNGFR in the remaining nephrons was significantly elevated in Hn (m) and normal in Hn (s). SFP was significantly elevated in Hn (s). The Hn (s) rats were hypertensive. The glomerular density was lower in the hydronephrotic than in the contralateral kidneys. This suggests a compensatory growth of the remaining nephrons in the Hn kidneys. We conclude that PUO present since infancy will either destroy the nephrons or elicit an adaptive response that will tend to preserve GFR.

Recovery of radiologically functionless obstructed kidneys

Eleven patients had radiologically non-functioning and unilaterally obstructed kidneys with normal kidneys on the other side. The kidneys were divided into three groups according to the urinary pH of the obstructed kidney at operation: Group 1 (pH 6.0 or less); Group 2 (pH 6.1-7.1); Group 3 (pH greater than 7.1). The obstruction was corrected in all patients despite the pre-operative radiological findings or the morphological appearance at operation. Radiological recovery was assessed 2 months post-operatively and was found to be good in all patients in Group 1. In Group 2, recovery was good in one patient, moderate in two and absent in one. In Group 3 there was no evidence of radiological recovery in either patient.

Changes in urinary pH and glomerular filtration rate in partially obstructed canine kidney

The creatinine clearance and urinary pH changes were studied in 12 male dogs in whom the ureters were unilaterally obstructed for periods ranging from 2 days to 27 weeks. The obstruction was then released and the recovery was studied. Using the contralateral kidney as control, significant drop in the creatinine clearance was observed to be consistently associated with failure to produce acidic urine. The obstructed kidneys with urinary pH above 7.00 had significant reduction in creatinine clearance when compared with obstructed kidneys with urinary pH 7.00 or less (p less than 0.005). The marked drop in the creatinine clearance and rise in urinary pH was observed to occur in kidneys obstructed for more than 3 weeks. With obstruction for shorter periods, the ability to produce acidic urine is preserved and the recovery potential is good.

Experimental partial ureteric obstruction in newborn rats. IV. Do the morphological effects progress continuously?

Partial obstruction of the ureter was created in newborn rats, and its effects were studied after 1, 2, 3, 6 and 9 weeks--that is, until adult age. Within 1 week, a considerable hydronephrosis had appeared. Within 2 weeks, parenchymal weight was found slightly reduced (8 per cent) on the obstructed side, and, within 3 weeks, equivalently increased on the contralateral, intact side. After these points in time, there was no further deterioration. Histological examination revealed marked deformation of the papilla and minor foci of degeneration and inflammation within 1 to 2 weeks which tended to become chronic in type after 3 to 9 weeks. Arterial hypertension was not noted. Thus, the effects of partial ureteric obstruction on the renal parenchyma are 1) discrete, 2) not in proportion to the degree of hydronephrosis, 3) fully compensated by contralateral hypertrophy and 4), after reaching an early maximum, not increasing with time.

Experimental obstructive hydronephrosis in newborn rats. III. Long-term effects on renal function

A partial obstruction of 1 ureter was created in newborn rats and its effects were studied in the adult rat. The obstructed pelvis was found to be considerably enlarged. Nevertheless, the GFR (glomerular filtration rate) was only slightly decreased (10 per cent), completely compensated by increase on the contralateral, non-obstructed side. The reduction in GFR was less than the reduction in number of glomeruli (19 per cent), indicating a raised filtration rate per glomerulus. Water excretion was slightly increased and potassium excretion moderately decreased; sodium and osmolar excretion were not significantly affected. There was no correlation between these changes and the degree of pelvic enlargement. Thus, in this model, in which there is no urinary tract infection or pyelonephritis, partial obstructive uropathy caused less damage to the kidney function than might have been expected.

Experimental obstructive hydronephrosis in newborn rats. II. Long-term effects on renal blood flow distribution

Partial obstruction of one ureter was created in newborn rats. The weights and blood flows (using the 86Rb-extraction method) of the cortex and outer and inner medulla were examined nine weeks later, i.e., in the adult. The obstructed pelvis was found to be enlarged 7-fold. The whole kidney blood flow on the hydronephrotic side was reduced by 10%; this was compensated by an increase on the contralateral side. There was a tendency to redistribution of flow from the cortex to the outer medulla; no other effects on regional flow were observed. The weight of the hydronephrotic kidneys was the same as that of the kidneys in control rats; hence no apparent atrophy was present. In contrast, the contralateral intact kidney was hypertrophied. The weight distribution of the different regions remained unaltered. Thus, the inner medullary weight was unaffected also on the obstructed side, although it showed considerable deformation. In the discussion, it is proposed that atrophy of the hydronephrotic kidney was probably present, but it was not detected because of the biological variation and the small number of observations. This presumed atrophy was uniform in all the regions and parallel with the reduction of whole kidney blood flow; hence the regional flows were relatively unaffected. It is concluded that unilateral partial obstruction in the newborn rat causes (i) discrete, parallel reductions of hydronephrotic kidney weight and flow, which are (ii) unrelated to the size of the obstructed pelvis and (iii) completely compensated by increases in the contralateral intact kidney.

Kidney function and histopathological changes in unilateral hydronephrosis with special reference to bilharzial ureter

Fifty-six patients with unilateral hydronephrosis were the subject of this study. The patients were classified into 4 groups according to the stage of hydronephrosis as assessed by radiological criteria. Split kidney function, histopathological studies, and measurement of intraureteral pressure were performed. Urinary Bilharziasis was held responsible for obstructive nephropathy in 77% of cases. Complicating urinary infection was present in 66%. The study has shown that creatinine excretion was slightly decreased in early, moderate, and moderately advanced hydronephrosis. On the other hand, a marked lowering of urine osmolality was found even in the early stages of hydronephrosis. The hydronephrotic kidney was found to be a salt losing one only in early, moderate, and moderately advanced hydronephroses, but not in the very advanced cases. The histopathological changes were mainly tubular, but some cases showed proliferative changes in the glomeruli. Eradication of urinary Bilharziasis and early treatment of this disease would markedly contribute to the prevention of obstructive nephropathies in countries where this disease is endemic.

Diagnosis of obstruction in experimental hydroureteronephrosis

A canine model with partial ureteral obstruction and progressive hydroureteronephrosis was utilized to validate and compare the accuracy of several diagnostic methods currently used to assess urinary tract obstruction. Tests of renal function and measurements of intrapelvic pressure were not helpful in following the progress of hydroureteronephrosis but did provide insight into the mechanisms by which incomplete ureteral occlusion impairs renal function. Serial intravenous pyelography, diuretic radionuclide urography, and perfusion pressure flow studies were frequently accurate in assessing obstruction, but each was subject to potential and, at times, regular misinterpretation. In applying the results of these laboratory studies to the problems of evaluating human hydroureteronephrosis, the clinician must recognize the pitfalls and limitations of these methods in order to ensure an accurate diagnosis of partial urinary obstruction.

Renal function in experimental chronic hydronephrosis. II. Backflow studies with radionuclides

Studies of backflow in experimental unilateral chronic hydronephrosis in dogs with a known residual renal function and renal pelvic volume were performed with radioactively labelled substances with molecular weights of ca. 600, 5 200 and 68 000 placed in the hydronephrotic renal pelvis. Three different pressure levels in the renal pelvis were used. Isotope concentrations were determined in the thoracic duct lymph, 0lood and urine from the contralateral kidney. The greater part of the test substances appeared to pass to the blood circulation, while a smaller part was found in the lymphatic ducts. The largest molecule, however, was only able to leave the renal pelvis to any appreciable extent at the highest pressure. In kidneys with a low grade of hydronephrosis and well preserved function, a relatively large amount of test substance left the renal pelvis (ca. 10-15%). In more advanced grades of hydronephrosis with greater impairment of renal function, the backflow was considerably less.