Preservation of renal function in the rat remnant kidney model of chronic renal failure by blood pressure reduction

Arginase inhibition slows the progression of renal failure in rats with renal ablation

Exogenous arginine slows the progression of chronic renal failure (CRF) in remnant rats through a nitric oxide (NO)-dependent mechanism. We tested whether the inhibition of arginase could induce similar results through the increased availability of endogenous arginine. Three groups of remnant rats were studied for 8 wk: 1) untreated rats (REM); 2) remnant rats treated with 1% l-arginine (ARG); and 3) remnant rats administered a Mn(2+)-free diet to inhibit arginase (MNF). Normal rats (NOR) were used as controls. Liver arginase activity was depressed in MNF rats (-35% vs. REM, P < 0.01). No difference in metabolic data was detected among the groups throughout the study; blood pressure was significantly lower in MNF vs. ARG and REM rats after 6 wk (P < 0.001). The glomerular filtration rate (GFR) was greatly depressed in REM rats (-47% vs. NOR, P < 0.03) but was higher in ARG and MNF rats (+40 and +43% vs. REM, respectively, P < 0.05), with comparable changes in renal hemodynamics. Despite the better GFR, proteinuria was decreased in both ARG and MNF rats (-42%, P < 0.05, and -57%, P < 0.01, respectively, vs. REM rats). Arginine plasma levels, significantly reduced in REM rats (-41% vs. NOR, P < 0.01), were partially restored in MNF rats (+38% vs. REM), and urinary nitrite excretion, greatly depressed in REM rats (-76% vs. NOR, P < 0.01), was significantly increased in MNF rats (+209% vs. REM, P < 0.05). At the renal level, arginase activity was only slightly depressed in MNF rats (-18% vs. REM), but intrarenal concentrations of arginine were lower in this latter group (P < 0.05 vs. other groups). Beyond the hemodynamic modifications, MNF rats showed a lower glomerular sclerosis index (P < 0.05 vs. REM and ARG). Inhibition of arginase slows the progression of CRF in remnant rats similarly to arginine-treated rats; the better histological protection in MNF rats, however, suggests that additional factors are involved in these modifications.

Effects of antihypertensive therapy on intrarenal angiotensin and bradykinin levels in experimental renal insufficiency

BACKGROUND

Whereas angiotensin converting enzyme inhibitors and angiotensin type 1 receptor antagonists have beneficial effects in the remnant model of renal failure, calcium channel blockers do not consistently improve renal disease in this model. This study examined whether these different means of blood pressure reduction have different effects on renal levels of angiotensin (Ang) and bradykinin peptides.

METHODS

Rats subjected to five-sixths nephrectomy were divided into groups with similar hypertension and proteinuria at 4 to 5 weeks. They then received either no treatment, or enalapril, losartan or nifedipine for 2 weeks. Following repeat measurements of proteinuria and blood pressure, Ang II and bradykinin peptides were measured in the remnant kidney and renin, Ang II, and aldosterone were measured in the plasma.

RESULTS

All three drugs had equivalent blood pressure-lowering effects. Enalapril and losartan reduced proteinuria but nifedipine did not. Reduction of proteinuria in rats treated with enalapril and losartan was associated with a reduction in Ang II levels in both the peri-infarct and intact portions of the remnant kidney. By contrast, nifedipine increased Ang II levels in the intact portion of the remnant kidney. Losartan reduced bradykinin levels in the peri-infarct portion of the remnant kidney while enalapril reduced bradykinin levels in the intact portion of the remnant kidney. Nifedipine had no effect on intrarenal bradykinin levels.

CONCLUSIONS

The differential effects of enalapril, losartan and nifedipine on proteinuria and intrarenal Ang II and bradykinin levels suggest that the ability of an antihypertensive to decrease proteinuria may depend on its ability to decrease kidney Ang II and bradykinin levels.

Renal protective effects of efonidipine in partially nephrectomized spontaneously hypertensive rats

We investigated the effects of a calcium antagonist, efonidipine, which was reported to dilate not only afferent arterioles but also efferent alterioles, on progression of renal failure in salt-loaded partially nephrectomized spontaneously hypertensive rats (SHR). Forty-four SHR's with 5 of 6 nephrectomy were divided into four groups: group 1 as control (n=20); group 2, efonidipine-treated (n=8); group 3, enalapril-treated (n=8); and group 4, nifedipine-treated (n=8). The rats were given these drugs and a high-salt diet (5% NaCl) for 8 weeks. During the experiment, systolic blood pressure (SBP) and daily urinary protein excretion were measured every 2 weeks. At the end of the study, serum creatinine was determined, and renal tissues were obtained for light microscopic examination. SBP was markedly reduced by 8-week antihypertensive treatment. (control, 267+/-7 mmHg; efonidipine, 181+/-7 mmHg; enalapril, 200+/-12 mmHg; nifedipine, 184+/-6 mmHg). Glomerular sclerosis developed markedly in the control group, but was partially prevented in all treated groups. Similarly, urinary protein excretion (UPE) was suppressed by efonidipine (180+/-16 mg/day) and enalapril (186+/-16 mg/day vs. 301+/-28 mg/day for control). In contrast, nifedipine failed to prevent the increase in urinary protein excretion (258+/-22 mg/day). In conclusion, efonidipine attenuates SBP increase and ameliorates glomerular injury as well as nifedipine and enalapril. Furthermore, beneficial effects of efonidipine, but not nifedipine, on proteinuria suggest that different mechanisms mediate the improvement of proteinuria; one possible mechanism could be efferent arteriolar dilation, not reported in nifedipine.

Renoprotective effects of felodipine and/or enalapril in spontaneously hypertensive rats with and without L-NAME

To determine the renoprotective effects of a calcium antagonist (felodipine) and an angiotensin-converting enzyme (ACE) inhibitor (enalapril), alone or in combination, 10 groups of 19-week-old spontaneously hypertensive rats (SHR) (with or without N(G)-nitro-L-arginine methyl ester [L-NAME]) were studied using renal micropuncture techniques. Group 1 (control), group 2 (felodipine, 30 mg x kg(-1) x d[-1]), group 3 (enalapril, 30 mg x kg(-1) x d[-1]), and group 4 (felodipine plus enalapril, 15 mg x kg(-1) x d(-1) each agent) were studied after 3 weeks of treatment without L-NAME. L-NAME (50 mg/L) cotreatment was administered in drinking water to groups 6 through 10 using the same doses of each agent as in groups 1 through 4: group 5 (only L-NAME), group 6 (felodipine), group 7 (enalapril), and group 8 (felodipine plus enalapril). Groups 9 and 10 received L-NAME initially for 3 weeks followed by felodipine or felodipine plus enalapril, respectively, for the subsequent 3 weeks. All three treatments resulted in reductions in mean arterial pressure and total peripheral vascular resistance (P<.001) that were associated with important structural and functional renal microcirculatory improvements. Thus, the pathological nephrosclerosis (subcapsular and juxtamedullary) glomerular and arteriolar injury scores were improved (P<.05 at least) in association with normalization of afferent and efferent arteriolar resistances, and single-nephron glomerular filtration rate, plasma flow, and blood flow were significantly improved, as well as the ultrafiltration coefficient (compared with group 5, L-NAME). Thus, the calcium antagonist felodipine, alone or in combination with an ACE inhibitor, not only prevented but also reversed L-NAME-exacerbated hypertensive nephrosclerosis in SHR.

Renal effects of antihypertensive therapy in uninephrectomized diabetic rats

Diabetic nephropathy is a major cause of chronic renal failure. The evidence available indicates that renal hemodynamics are altered in clinical and experimental diabetes mellitus. In these circumstances, an increased glomerular filtration rate (GFR) is associated with albuminuria and eventually with glomerulosclerosis. We studied the renal and hemodynamic effects of long-term treatment (5 months) using an angiotensin-converting enzyme inhibitor (trandolapril, 0.7 mg/g b.w. per day) and a calcium antagonist (verapamil, 20 mg/g b.w. per day), and the combination of the two (veratran) at the same dose, on streptozotocin-diabetic uninephrectomized rats. A moderate degree of hyperglycemia (2-4 g/l) was maintained with daily insulin. Mean arterial pressure (MAP) was measured monthly using the tail-cuff method. Determinations were made of urinary protein excretion, creatinine clearance, urinary electrolyte excretion and, at the end of treatment, renal and cardiac hypertrophy. MAP was similar in control and untreated diabetic rats. Trandolapril and veratran reduced MAP whereas verapamil alone had no effect on these animals. All groups showed a slight proteinuria that increased with verapamil treatment. The GFR of diabetic animals was higher than in the control group (mainly the first 2 months), except for veratran group, in which it was similar to the control value. Urinary electrolyte excretion increased in all diabetic groups with no significant differences among them. Veratran induced a protective effect against cardiac hypertrophy. None of the treatments affected renal hypertrophy. It is concluded that in a murine model of diabetes without hypertension or proteinuria, a combination of verapamil and trandolapril prevents hyperfiltration whereas verapamil alone increases proteinuria.

Effects of perindopril and hydrochlorothiazide on the long-term progression of lithium-induced chronic renal failure in rats

Administration of lithium in the diet to new-born rats induces chronic renal failure associated with hypertension, proteinuria and irreversible tubulo-interstitial morphological changes. In the present study we induced chronic renal failure by administration of lithium for 16 weeks to new-born rats, and examined the spontaneous course of this nephropathy and the effects of antihypertensive treatment with either perindopril (12 mg/kg diet) or hydrochlorothiazide (500-1000 mg/kg diet) during a 24 weeks follow up period without lithium. In the placebo group, progression to terminal uraemia occurred in all rats with severe renal failure (initial Purea > 15 mM) (10 of 18). Rats with mild-moderate renal failure (Purea 9-15 mM) showed no deterioration in renal function despite persistent systolic hypertension and irreversible structural renal changes. Perindopril normalized the blood pressure in all rats but did not prevent the progression to terminal uraemia (8 to 18). Hydrochlorothiazide partially controlled the hypertension and accellerated the progression of uraemia without increasing the mortality (7 of 17). Irrespective of treatments, the predominant quantitative structural changes (e.g. decreased volume of proximal tubular cells) showed significant correlations with the degree of renal dysfunction, but not with systolic blood pressure in the surviving rats. It is concluded that progression of lithium-induced nephropathy to terminal uraemia occurs when the nephrotoxic insult results in a more than 50% reduction of the glomerular filtration rate, judged from Purea levels. The failure of effective antihypertensive treatment with an angiotension-converting enzyme inhibitor to modify the progression suggests that in this model, systemic or glomerular hypertension may not be an important pathophysiological factor. The structural and functional deterioration observed in Li-uraemic rats during treatment with hydrochlorothiazide remains unexplained.

Angiotensin converting enzyme inhibition and protein restriction in progression of experimental chronic renal failure

This study examined whether the effects of protein restriction and angiotensin converting enzyme (ACE) inhibition on the progression of renal failure are common or additive. Male Sprague Dawley rats (12 wks of age) underwent 5/6 nephrectomy and were randomized to 20% protein diet (PD) (n = 9), 20% PD+enalapril (5 mg/kg/day) (n = 10), 20% PD+felodipine (30 mg/kg/day) (n = 9), 6% PD (n = 9), 6% PD+enalapril (n = 9) or 6% PD+felodipine (n = 10). Protein restriction, enalapril or felodipine treatment all retarded progression of renal failure and development of glomerular lesions. Protein restriction and enalapril appeared to have additive effects in preventing glomerular sclerosis.

Radiotelemetric BP monitoring, antihypertensives and glomeruloprotection in remnant kidney model

The mechanisms by which antihypertensives exert a glomeruloprotective effect in the remnant kidney model remain controversial. Based on periodic tail-cuff BP measurements, the variable glomeruloprotective efficacy of antihypertensive agents has been ascribed to mechanisms other than or in addition to their ability to lower BP. To more precisely define the relationship between BP control and glomeruloprotection, systolic BP was continuously monitored radiotelemetrically at 10-minute intervals for approximately 65 days in rats after approximately 5/6 renal ablation. Rats with remnant kidneys received either no therapy or one of three antihypertensive regimens in their drinking water after the first week: enalapril, a triple therapy regimen (reserpine, hydralazine, hydrochlorothiazide); or a high dose triple therapy regimen. Although all antihypertensive regimens significantly lowered BP, considerable interanimal variability was observed. Additionally, marked lability of BP was present in both untreated and treated rats. Glomerular injury in individual animals (N = 34) was very strongly correlated with their overall averaged systolic BP during the final eight weeks (r = 0.91) and with the frequency of systolic BP readings > 150 mm Hg (r = 0.89). These data do not provide evidence of a therapeutic advantage for any of the regimens independent of their antihypertensive effects but indicate that the glomeruloprotective efficacy of these antihypertensive regimens is directly proportional to their antihypertensive efficiency.

Nifedipine versus fosinopril in uninephrectomized diabetic rats

Antihypertensive agents have been shown to exert inequivalent effects on glomerular injury in experimental renal disease models. To compare the consequences of dissimilar antihypertensive regimens on the development of diabetic glomerulopathy, studies were performed in three groups of uninephrectomized moderately hyperglycemic diabetic rats. One group (DM) received no therapy except insulin. The remaining groups received insulin and either the angiotensin I converting enzyme inhibitor, fosinopril (FOS), or the calcium channel blocker, nifedipine (NIF). Both drugs lowered blood pressure comparably. At four to eight weeks, DM rats exhibited elevation of the single nephron glomerular filtration rate (SNGFR), due to elevations of the glomerular capillary plasma flow rate (QA) and the glomerular capillary hydraulic pressure (PGC). Neither NIF nor FOS affected values for SNGFR or QA. However, while FOS lowered PGC and increased Kf, NIF did not affect these parameters. In longer term (8 month) studies, DM rats exhibited progressive albuminuria and glomerular sclerosis. FOS markedly limited development of albuminuria and glomerular injury, but NIF was ineffective in limiting either parameter of glomerular injury. Thus, in contrast to the beneficial effects of converting enzyme inhibitors, chronic calcium channel blockade with nifedipine fails to limit PGC or glomerular injury in diabetic rats. These findings lend further support to the concept that different classes of antihypertensive agents are not equally effective in protecting against diabetic glomerulopathy.

Long-term enalapril and verapamil in rats with reduced renal mass

The effect of long-term treatment with either enalapril or high dose verapamil on survival, proteinuria, blood pressure and renal morphology was studied in female Wistar rats with markedly reduced renal mass. Four weeks were allowed for remnant kidney hypertrophy before determining the response to renal ablation of individual animals regarding proteinuria and hypertension. At this time, five groups of 18 rats were formed with equal levels of proteinuria and hypertension. Groups E1 and E2 were treated with enalapril, groups V1 and V2 with verapamil, and one group served as control. The daily food allowance was 14 g/rat of a standard rat diet, containing 30% protein and 100 mmol NaCl/kg food in groups E1 and V1. NaCl content was reduced to 20 mmol/kg food in groups E2, V2 and control. The drugs were added to the drinking water, enalapril at a dose of 0.1 g/liter, verapamil at 0.5 to 0.7 g/liter. Drug intake thus amounted to 10 to 25 mg/kg for enalapril and 50 to 140 mg/kg for verapamil. Treatment was continued for 15 weeks. Three of the 18 control rats did not survive up to 15 weeks. Mortality was lower in the enalapril treated groups with a single nonsurvivor in group E1. In contrast, mortality was higher in the verapamil treated animals with seven nonsurvivors in group V1 and eight in group V2. Blood pressure control was excellent in both enalapril treated groups. and proteinuria decreased in most animals of group E1 and all of group 22. Glomerulosclerosis did not develop in the majority of the enalapril treated animals. Despite the high dose, verapamil barely lowered blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Progression of renal insufficiency: role of blood pressure

The effect of blood pressure on progression of renal insufficiency was examined in a large group of patients who eventually required dialysis. Out of 198 consecutive new chronic dialysis patients, 86 had sufficient data predialysis to determine rates of progression of renal insufficiency by reciprocal creatinine versus time plots. Average plasma creatinine at first contact was 3.8 +/- 0.2 mg/dl and at the time of dialysis was 11.4 +/- 0.4 mg/dl. Mean duration of follow-up was 33.4 +/- 2.5 months and the average rate of decline in reciprocal creatinine was -0.009 +/- 0.001 dl/mg month. Patients were stratified by average value of diastolic blood pressure measured in clinic. Patients in the lowest quartile had a rate of decline in reciprocal creatinine of -0.007 +/- 0.001 dl/mg month, which was slower than that of patients in the third and fourth quartiles, -0.010 +/- 0.001 and -0.011 +/- -0.002 dl/mg month, respectively (P less than 0.05). In individual patients, a mean diastolic BP of less than 90 mm Hg was associated with a rate of decline in reciprocal creatinine of -0.006 +/- 0.001 dl/mg month which was significantly less than the rate of -0.009 +/- 0.001 when the diastolic BP was greater than 90 mm Hg. Thus, in a large group of patients who have progressed to ESRD, there is an association between control of diastolic blood pressure and a slower rate of decline in renal function.

Atrial natriuretic factor in chronic renal failure: studies in man and the rat

1. Plasma concentration and atrial content of atrial natriuretic factor (ANF) were measured in rats with chronic renal failure induced by subtotal nephrectomy. 2. Plasma ANF was higher, and atrial ANF content lower in rats with renal failure when compared with sham-operated controls. 3. Plasma renin activity (PRA) and ANF were elevated at 1 week following subtotal nephrectomy. After 1 month plasma ANF had risen further, but PRA was suppressed to below control values. 4. Plasma ANF was also measured in six patients with chronic renal failure undergoing routine haemodialysis. 5. Elevated plasma ANF levels in patients with renal failure were lowered by haemodialysis, although extraction of ANF across the dialysis membrane was negligible. 6. Secretion of ANF is increased in chronic renal failure in man and the rat, possibly mediated by increased intravascular volume.