Long-term follow-up of a human subject with a remnant kidney

Does significant renal ablation truly and invariably lead to hyperfiltration and progressive chronic kidney disease?

It is generally believed that significant renal ablation leads to hyperfiltration and eventually progressively worsening chronic kidney disease. The data behind this belief have not been scrutinized intensively. More importantly, the above belief leads many physicians to manage patients differently than they otherwise would manage. Here, we examine the data behind whether hyperfiltration occurs when patients lose kidney mass (by excision or by disease) and whether the hyperfiltration is uniformly injurious.

Renal hemodynamic effects of lovastatin in a renal ablation model

OBJECTIVES

Patients with renal mass reduction of more than 50% are at increased risk for progressive renal failure. Lipid-lowering agents have been shown to preserve renal function in various models of chronic renal failure. This study was performed to evaluate the hemodynamic effects of lovastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, in the remnant kidney model.

METHODS

Two groups of animals were studied. Group 1 (n = 9) served as controls and group 2 (n = 14) received lovastatin, 15 mg/kg/day orally, for 2 weeks after renal ablation. Glomerular filtration rate (GFR, inulin clearance), renal blood flow (RBF, ultrasonic flow probe), and 24-hour protein excretion were measured in anesthetized rats.

RESULTS

Two weeks after renal ablation, GFR was 0.28 +/- 0.09 mL/min/gkw (gram kidney weight) in group 1, whereas in group 2, lovastatin preserved GFR at 0.58 +/- 0.3 mL/min/gkw (P < 0.05). RBF in group 1 was 1.2 +/- 0.2 mL/min/gkw and increased to 2.1 +/- 0.4 mL/min/gkw in group 2 (P < 0.05), representing a 43% increase. Protein excretion decreased significantly to 13 +/- 1.7 mg/24 hr in group 2. The lovastatin-treated group had a lower serum cholesterol (59 +/- 3 mg/dL versus 71 +/- 2 mg/dL, P < 0.05), but serum triglyceride levels were not different between the two groups.

CONCLUSIONS

Lovastatin preserves renal function in a renal ablation model after 2 weeks of treatment. It specifically increased total RBF. Therefore, in addition to its known cholesterol lowering effect, lovastatin also has the direct renal hemodynamic effect of increasing RBF and maintaining GFR.

Hemodynamic theory of progressive renal disease: a 10-year update in brief review

Experimental studies have suggested that glomerular hypertension is ultimately damaging to the kidney. Prevention of glomerular hypertension by dietary protein restriction or antihypertensive therapy lessens glomerular injury in several experimental models of chronic renal disease. Glomerular hypertension and hyperfiltration also occur in humans with diabetes mellitus, solitary or remnant kidneys, and various forms of acquired renal disease. Clinical studies are beginning to show that dietary protein restriction and antihypertensive therapy may slow progression in these disorders. Large multicenter trials are currently under way to better define the effects of these therapeutic maneuvers on the progression of chronic renal disease.

Unilateral nephrectomy and progression of renal failure

Extensive ablation of renal mass in experimental animals leads to progressive glomerulosclerosis and chronic renal failure (CRF). Clinical studies are far from answering the question whether patients with reduced renal mass are at risk of developing progressive CRF. The aim of our study was to examine the morphological and functional aspects of the remnant kidney in a group of patients who underwent unilateral nephrectomy for renal tuberculosis: 313 patients (161 M, 152 F) mean age 57.2 +/- 10.7, were examined after a period ranging from 13.56 to 591.2 months. All patients were on ad libitum diet. Hypertension was found in 34.19% of the patients; SBP was 155.29 +/- 19.9 mmHg and DBP was 92.74 +/- 13.07 mmHg. Estimation of renal size performed by ultrasound scanner gave the following results: length 116.78 +/- 8.99 mm; width 58.24 +/- 7.21 mm; thickness 17.88 +/- 1.96 mm. Kidney function assessed by serum creatinine levels showed a mean level of 1.28 +/- 0.53 mg%. Forty-two patients (13.41%) had serum levels > 1.5 mg% but 18 of them had nonconcomitant systemic or renal involvement. Microalbuminuria determined by RIA assay was found in 50.5% of the patients. In our group of patients renal functional impairment was low and hyperfiltration expressed as microalbuminuria does not appear to be a primary factor in the progression of renal failure.