Atrial natriuretic peptide in patients with obstructive uropathy

Natural History of Postobstructive Nephropathy: A Single-Center Retrospective Study

BACKGROUND

There is extensive published material on the effects of experimental ureteric obstruction. In contrast, there is very little literature on the natural history of postobstructive renal disease in patients.

METHODS

Patients presenting with obstructive nephropathy and renal impairment in a tertiary renal unit, and whose obstruction was successfully relieved, were identified, and the Modification of Diet in Renal Disease equation was used to calculate the glomerular filtration rate (GFR) at presentation and after relief of obstruction.

RESULTS

104 patients were identified (79 male). There were 9 deaths at 12 months and a further 4 deaths by 3 years; losses to follow-up were 7 and 20 at the same time points. The mean GFR was 9.2 +/- (SEM) 0.9 ml/min at presentation (n = 104), 27.8 +/- 1.7 ml/min at 3 months (n = 98), 29.0 +/- 1.8 ml/min at 12 months (n = 79), and 30.0 +/- 2.2 ml/min at 3 years (n = 61). Of 28 patients initially requiring dialysis, 6 were dialysis dependent at 3 months; 3 further patients, all with GFR <10 ml/min after relief of obstruction, required dialysis by 12 months and 1 further patient by 3 years.

CONCLUSIONS

Progressive deterioration in renal function is unusual after relief of obstruction in the majority of patients over a 3-year period. This relative stability in human postobstructive nephropathy contrasts with the course of remnant nephropathy in animal models.

Voie excrétrice supérieure : physiologie, physiopathologie des obstructions et explorations fonctionnelles

The urine is transported from the renal papilla to the bladder through the upper urinary tract which allows this transport to be safe and comfortable, i.e., without any risk or pain for the kidney. This active transport depends on the smooth muscle contractile properties. The upper urinary tract is totally autonomous; this feature allows the preservation of its function after renal transplantation. However, despite its accessory role, the autonomous nervous system can modulate its activity. Upper urinary tract obstruction involves adaptative mechanisms which are different depending on the type (acute, chronic, acquired or congenital) of obstruction. Functional evaluations of the upper urinary tract are aimed at identify the urine transport conditions and the relationship between obstruction and clinical conditions such as hydronephrosis, pain or impaired renal function.

Acute ureteral obstruction and glomerulotubular function in rats

Urinary tract obstruction is a common cause of acute renal failure (ARF). During unilateral ureteral obstruction (UUO) arteriolar vasoconstriction, increase in tubular pressure, and ultrafiltrate retrodiffusion occur. We studied renal function of rats with surgical UUO for 24 hr. After this period of UUO, the contralateral kidney was removed and the right ureter was deobstructed. The control uninephrectomized group consisted of normal rats submitted to left uninephrectomy (UNx). Functional studies were performed 12 and 24 hr, and 7 days after deobstruction and UNx. We measured creatinine clearance, and fractional excretion of sodium and lithium. Using conventional formulas we calculated fractional proximal and distal sodium reabsorption. Initially we observed a reduction in glomerular filtration rate (GFR) after deobstruction (12 and 24 hr). However, after 7 days, the GFR was significantly higher in deobstructed rats than in controls (340.3 +/- 18.3 vs. 286.4 +/- 9.3 microL/min/100 g, p < 0.01). The dry kidney weight was also increased in these rats. The fractional sodium excretion was increased in deobstructed rats, mainly in early studies (12 and 24 hr). Whereas fractional proximal reabsorption was reduced in both groups, the fractional distal reabsorption was significantly decreased in the deobstructed group compared to UNX controls (93.9 +/- 0.9 vs. 98.9 +/- 0.1% after 24 hr, p < 0.01). Our data showed that UUO influenced both glomerular and tubular functions. A salient finding was the overcorrection of GFR 7 days after deobstruction. The renal release of hormones and growth factors could mediate these alterations in renal function through their vascular, tubular, and proliferative actions.

The pathophysiology of ureteral obstruction

Ureteral obstruction can have a variety of causes intrinsic or extrinsic to the kidney. The effects of obstruction are examined from the perspectives of duration, severity, totality, and the presence of complicating factors. There is a difference in the postobstructive pathophysiology depending on whether one or both ureters were obstructed. Atrial natriuretic peptide may be important in postobstructive diuresis, and preliminary evidence suggests a role for it as protection against nephron ischemia in acute obstruction. The potential for recovery of renal function after relief of obstruction depends on the duration and degree of obstruction, the condition of the contralateral kidney, and the presence or absence of infection. Ability to acidify the urine to pH < 6.0 preoperatively may be a good predictor of the recovery potential of an obstructed kidney. Urine concentrations of lysosomal enzymes such as N-acetylglucosaminidase also may be useful for this purpose, as may measurement of creatinine clearance in urine obtained from a nephrostomy tube.

Failure of atrial natriuretic peptide to induce natriuresis in aortocaval fistula dogs

Creation of an aortocaval fistula (ACF) in dogs induces salt and water retention, activation of the renin-angiotensin and adrenergic nervous systems and renal papillary ischemia associated with high levels of circulating atrial natriuretic peptide (ANP). The effects of intrarenal ANP (1.2 micrograms/min) infusion on systemic and renal hemodynamics, renal excretory function, renal output of renin and norepinephrine (NE) and papillary plasma flow (PPF) were studied in both normal and ACF dogs. ANP did not alter systemic hemodynamics in either group, but led to a significant increase in renal blood flow (RBF), glomerular filtration rate (GFR), urine flow rate (V), sodium excretion (UNaV) and fractional excretion of sodium (FENa), and a significant decrease in renal vascular resistance (RVR) and urine osmolality (UOsm) in normal dogs. GFR, RBF, RVR, V, UNaV, FENa and UOsm remained unchanged, however, in ACF dogs. In ACF dogs, both renal renin and NE output were significantly greater during baseline and remained significantly greater following ANP infusion, associated with a significantly lower PPF compared with normal dogs. These data suggest that ACF dogs are resistant to the renal effects of ANP, which can neither mitigate the hormonal mediators of sodium retention nor reverse the papillary ischemia observed in this model.

Acute hemodynamic and endocrinological effects of partial fetal bladder obstruction

The pathophysiology of fetal urinary obstruction has not been elucidated. Using a unique, reproducible and easily reversible animal preparation, we studied the acute hemodynamic and endocrinological responses to partial fetal bladder obstruction in 16 ovine fetuses at 115 days of gestation (term 147 days). After partial obstruction blood pressure and renal weight increased significantly for at least 72 hours. Renal blood flow trended upwards, particularly from 24 to 72 hours, although this change was not statistically significant. Plasma renin activity was significantly increased during the first 24 hours after obstruction but it returned to baseline thereafter. Plasma cortisol or catecholamine concentrations remained unchanged. The time course and pattern of hemodynamic changes in this fetal sheep preparation of partial urinary obstruction differ significantly from those reported in other preparations.