The role of nutritional factors in the course of experimental renal failure

Renal effect of anti-hypertensive drugs depends on sodium diet in the excision remnant kidney model

Angiotensin converting enzyme inhibitors (ACEI) are believed to protect remnant kidney, but all previous studies used the ligation model which causes severe hypertension, and very few have compared drugs in rats having similar control of blood pressure (BP). We compared rats with uremia obtained by 70% excision of total renal mass, a model which causes mild, late hypertension. Study I compared the effects of enalapril (E), cicletanine (C) and placebo (P) in uremic (U) rats fed a 0.50% (normal-high) Na diet. Study II compared the effects of E, C, P, and guanfacine (G) in U rats fed a diet restricted to 0.25% Na (normal-low). In study I, UP rats developed progressive hypertension (140, 146, 160 and 166 mm Hg at 3, 6, 9 and 12 weeks), proteinuria (240 mg/day at 9 and 12 weeks) which were not affected by E or C. The occurrence of end-stage renal disease (ESRD) led to the sacrifice of all rats after three months. All three groups had similar severe renal lesions (over 25% sclerosed glomeruli in 5 of 10 UP, 9 of 14 UE, 7 of 14 UC rats, with huge cystic tubular dilatations). In study II, rats could be sacrificed later (6 months) and had evidence of less severe renal disease. All the drugs tested prevented hypertension throughout the study (P less than 0.001), with lowest values in UE rats. E and G, but not C, reduced proteinuria. Renal damage was reduced with E and G, but not with C, despite similar BP in C and G rats. Thus, in contrast with what was obtained in the ligation model, ACEI affected neither the BP nor the renal lesions of rats made uremic by renal excision and fed a 0.50% Na diet. Moderate Na restriction improved the consequences of nephron loss and restored the anti-hypertensive effect of drugs. However, these drugs had a different effect on renal preservation: it was dramatic with E, good with G, and undetectable with C.

The effect of protein intake on the lifelong changes in renal function of rats with a solitary kidney damaged at young age

Changes in renal function were followed lifelong in male rats with only 1 kidney either intact or damaged by ureteral obstruction or ischemia. After surgery the rats were given a low (12%) or a high (36%) protein diet. After a period with a stable glomerular filtration rate, which was longer on the low protein diet, there was a linear decline in rats with an intact single kidney. The rate of decline was highest on the high protein diet, resulting in a shorter survival time. A decrease in urine osmolality and an increase in protein excretion preceded the decrease in filtration rate, while it was followed by an increase in blood pressure. The glomerular filtration rate of the rats with a single damaged kidney initially recovered to 75 to 80% of that of rats with an intact single kidney on the same diet. There was a linear decrease in the glomerular filtration rate, with the highest rate of decrease on the high protein diet. The mean survival time was less than that of rats with a single intact kidney. Proteinuria preceded the decrease in filtration rate, while hypertension was observed later. We conclude that in rats with a solitary kidney renal failure eventually develops. A low protein diet postpones and attenuates this development but it does not prevent it.

Pathogenesis and significance of nonprimary focal and segmental glomerulosclerosis

Injury of the glomerular microvasculature by nonimmunologic processes is often the underlying mechanism of progressive deterioration of renal function in patients with a variety of renal disorders. The structural hallmark of this injury is focal and segmental glomerulosclerosis, often accompanied by entrapment of hyalin. Although such lesions are quite characteristic for diseases that primarily affect the glomerular podocyte, similar damage occurs in association with functional and structural adaptive changes that develop as a consequence of a significant loss of functioning nephrons or other systemic disorders. Experimental studies have revealed that such functional adaptations include intrarenal vasodilatation that through increases in glomerular capillary pressure and plasma flow leads to a significant compensatory hyperfiltration. This functional state is accompanied by a parallel increase in glomerular volume, attained chiefly by expansion of matrix components and an increase in the number of endothelial and mesangial cells, but not of podocytes. The persistence of the adaptive changes results in endothelial, mesangial, and epithelial cell dysfunction revealed clinically by proteinuria and structurally by the development of microthrombosis, microaneurysms, mesangial expansion, and occlusion of capillaries by hyalin accumulation. Although all these pathologic processes can lead to segmental collapse of the capillary tuft, it is the progressive hyalin deposition in capillaries with defective or detached podocytes that represents the major mechanism in the development of segmental and eventually global glomerulosclerosis. The inability of the highly differentiated podocyte to replicate in response to systemic or locally released trophic factors ultimately results in imperfections of the capillary wall that set the stage for permeability defects amplified and accentuated by greatly augmented hydrodynamic forces. These structural and functional microvascular changes acting in concert not only facilitate the transcapillary convection of macromolecules that results in albuminuria, but can also be anticipated to play a key role in the entrapment and accumulation of larger macromolecules in front of the lamina densa in the form of hyalin material. Continuing damage to the glomerular microvasculature exacerbates the adaptive changes in surviving nephrons, closing a positive-feedback loop that culminates in end-stage renal failure.

Effect of dietary lipids on renal function in rats with subtotal nephrectomy

Female rats with 1-3/4 nephrectomy were divided in two groups and pair fed for five weeks diets differing in their linoleic acid content. Five weeks after subtotal nephrectomy, values for glomerular filtration rate and renal plasma flow were significantly higher and the values of blood pressure significantly lower in rats fed a diet rich in linoleic acid. Systolic blood pressure averaged 156 +/- 5.6 mm Hg in high and 215 +/- 8.1 mm Hg in low linoleic acid-fed rats. Differences in the values of blood pressure between the two groups were observed three weeks after subtotal renal ablation and persisted throughout the period of observation. Inulin clearance averaged 0.89 +/- 0.07 ml/min in the high and 0.44 +/- 0.05 ml/min in the low linoleic acid group. Protein excretion in the urine was significantly less in rats fed the high linoleic acid diet (36.9 +/- 4.4 mg/24 hr) than in those fed the low linoleic acid diet (90.1 +/- 12.5 mg/24 hr). The weight of the remnant kidney five weeks after subtotal renal ablation was greater in rats fed a low linoleic acid diet as compared to those fed a high linoleic acid diet (P less than 0.05). Glomerular lesions were more severe in rats fed a low linoleic acid diet than in those fed a high linoleic acid diet. Feeding high linoleic acid diets to normal and subtotally nephrectomized rats increased the content of linoleic and arachidonic acid in renal cortex and medulla.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidemic renal disease of unknown etiology in the Zuni Indians

An epidemic of renal disease is occurring among the Zuni Indians in western New Mexico. In 1985, 1.6% of Zunis had clinically recognized renal disease and 1% had renal insufficiency. The incidence of end-stage renal disease (ESRD) in 1984 and 1985 was 14 times the rate for US whites, and three times the rates of other Indians in ESRD network 6. One third of the cases of renal disease and ESRD is due to type 2 diabetes, but the etiology of disease in most of the remainder is unknown. Affected subjects range from early childhood to old age. Early signs are hematuria, mild to moderate proteinuria, normal BP, and low total hemolytic complement, normal or low C3 and C4 levels, in about 40% of the cases. The clinical course varies from benign to rapidly progressive renal failure. Biopsies usually reflect an immune-complex mediated mesangiopathic glomerulonephritis, with IgA, IgG, IgM, and C3 variably present in the mesangium. In some cases, there is a very strong familial pattern suggesting autosomal dominant inheritance or a marked communal exposure effect. This may be a genetic disease educed by the consanguinity in the ethnically homogeneous Zuni population. Mesangiopathic renal disease is common in some Oriental populations, and this phenomenon may reflect the American Indians' Oriental ancestry. This disease may also be due to toxic exposures related to jewelry-making, potting, Zuni water, Zuni salt, or herbal or other products used for medicinal or religious purposes. This epidemic is much morbidity and generating huge costs for ESRD treatment. Further study is needed to better understand its etiology.

Influence of different protein intake on renal growth in young rats

We have examined the effect of high protein intake on kidney growth and function in growing rats. The rats were kept on an isocaloric diet containing 12%, 21% and 50% protein, from weaning (16 days) until the time of investigation (18, 20, 24, 40 or 80 days). There was no significant difference between the 12% and 21% protein groups in any of the parameters studied. 50% protein increased body weight (BW) and kidney weight (KW). The increase in kidney weight was already evident after 2 days and exceeded the increase in body weight in all age groups. At 24 days renal cortical DNA and the protein/DNA ratio were significantly increased in the 50% protein group. At 40 days the cortical DNA content, but not the protein/DNA ratio, was significantly increased in the 50% group. The glomerular filtration rate GFR) was studied at 40 days. Total GFR as well as GFR/BW was significantly higher in the 50% group than in the 21% group. In one protocol the diet was discontinued at age 40 days and the rats were studied at age 80 days. In these rats all parameters of renal size and function were the same as in the rats that had had a normal (21%) protein intake from weaning. We conclude that in young rats high protein intake reversibly increases GFR out of proportion to BW and selectively and reversibly stimulates kidney growth by stimulating cell proliferation.

Verapamil protects against progression of experimental chronic renal failure

Chronic administration of verapamil (Ver) decreases nephrocalcinosis and tubular ultrastructural abnormalities in the remnant model of chronic renal disease. In the present study, the effect of chronic Ver administration on renal function, renal histology and mortality after subtotal nephrectomy was examined. Fourteen days after staged subtotal nephrectomy rats were paired according to renal functional impairment, mean arterial pressure (MAP), and body weight. Rats were pair fed and received either Ver (0.1 micrograms/g sc bid, N = 10) or saline (0.1 ml sc bid, N = 10) for up to 23 weeks. Both members of each pair were sacrificed shortly before the uremic death of controls. At sacrifice, rats treated with Ver had a lower serum creatinine (2.29 vs. 2.99 mg/dl, P less than 0.05) and a higher creatinine clearance (318 vs. 164 microliters/min, P less than 0.05) than controls. In a second experiment, survival was superior in rats treated with Ver than in controls from week seven (P less than 0.0025 by week 14). Serum creatinine was higher at week 10 in control rats (1.68 vs. 1.10 mg/dl, P less than 0.05). MAP was no different between the two groups, irrespective of the time between Ver administration and the measurement of MAP. Histological damage and nephrocalcinosis were worse, and renal and myocardial calcium content was higher in controls. In conclusion, independent of any effect on systematic MAP, chronic administration of Ver protects against renal dysfunction, histological damage, nephrocalcinosis and myocardial calcification, and improves survival in the remnant model of chronic renal disease.

Role of amount and nature of carbohydrates in the course of experimental renal failure

The renal effects of carbohydrates (CHO) were studied in two experiments. 1) The effects of CHO-energy restriction was evaluated by comparing uremic growing rats (initial weight: 80 g) fed "ad lib" (L rats) or CHO-restricted (starch and glucose) but receiving identical amounts of all other nutrients (R rats). R rats showed reduced growth, slower increase in plasma creatinine, lower mortality rate, and less histological renal damage than L rats. 2) Two types of CHO restriction, low glucose (R1 rats) or low starch (R2 rats) were compared to "ad lib" feeding (L1 rats) in adult rats (initial weight: 130 g). Growth was identically reduced in R1 and R2 rats. Mean plasma creatinine levels at week four was lower in R1 than in L1 rats. The overall rate mortality was higher for L1 and R2 than in R1 rats (79%, 81%, 53%) but included deaths from other causes than renal failure. Actuarial survival excluding these deaths was 27%, 83% and 10% in L1, R1 and R2 rats, respectively. Diffuse renal lesions were found in 25 of 30 L1, 5 of 15 R1, and 12 of 15 R2 rats (R1 vs. R1 and R2, P less than 0.01). The results show that CHO restriction may preserve the renal parenchyma, and suggest that restriction of "simple" rather than "complex" CHO restriction may be beneficial, a finding which could be of clinical importance if confirmed by further investigations.

Dietary protein prior to renal ischemia dramatically affects postischemic kidney function

Male Sprague-Dawley rats were maintained on high protein (60%), normal protein (20%), low protein (5%), or no protein (0%) diets for two or four weeks prior to 45 minutes of renal ischemia induced by renal pedicle clamping. Most (93%) of the rats on the high protein diet died within three days following renal ischemia. In addition, 69% of the rats on normal protein diets also died, most before the fourth day following ischemic insult. In contrast, 88% of the rats on the low protein diet lived, although some exhibited elevated serum creatinine levels for up to one to two weeks following ischemia. Finally, all of the rats on no protein diets lived, and most (75%) exhibited normal serum creatinine levels by the fourth day following ischemia. Shifting the diets of high protein and normal protein adapted rats to no protein diets immediately following ischemia did not improve postischemic survival. Also, changing the diets of no protein adapted rats to high protein diets immediately following ischemia did not significantly affect postischemic recovery. When rats were maintained on no protein diets for shorter periods of time prior to ischemia, it was found that approximately a week on this diet is necessary to provide maximum protection from postischemic acute renal failure. These findings demonstrate a dramatic effect of dietary protein prior to ischemic induced acute renal failure, and suggests that preoperative dietary protein intake should be an important consideration in those situations which are predisposed to postoperative acute renal failure.

Evaluation of renal function and acute renal failure in the neonate

The diagnosis of renal dysfunction in the neonate can be a challenging problem for the practicing pediatrician. Although there are real differences in renal function between term and preterm infants, overall function is quite adequate in both groups when fluid intake and environmental conditions are carefully controlled. When confronted with an infant with a pathologic decrease in urine output, the clinician must provide adequate fluid resuscitation for the infant with prerenal oliguria without inducing fluid overload in the infant with established, intrinsic renal failure. In addition, the infant with obstruction to urine flow must be distinguished. This requires careful assessment of physical findings and a few key laboratory determinations. Once the diagnosis of renal failure is made, frequent clinical monitoring with anticipation of potential complications is critical. Long-term management of renal failure in infancy and intervention for suspected urinary tract malformation in the fetus have emerged as difficult medical and ethical problems as our technology has advanced.