Lisa C. Contino

Upregulation of renal endothelin receptors in rats with cyclosporine A-induced nephrotoxicity

Measurement of endothelin receptors by binding assay was performed in rats treated with cyclosporine A (CYA). Cyclosporine A administration at 50 mg/kg i.p. for 4 days resulted in renal function impairment as indicated by a significant increase in serum creatinine concentration (from 0.46 +/- 0.02 to 0.61 +/- 0.03 mg/dl. P less than 0.01) and a significant decrease in 24 h creatinine clearance (from 0.65 +/- 0.04 to 0.41 +/- 0.02 ml/min per 100 g, P less than 0.01). Renal endothelin (ET) receptor density was significantly higher in CYA-treated rats (312 +/- 34 vs. 196 +/- 26 fmol/mg protein, P less than 0.01). These data support the possible involvement for endothelin in the increased renal vascular resistance associated with CYA-induced nephrotoxicity.

Effect of nifedipine on cyclosporine A-induced nephrotoxicity, urinary endothelin excretion and renal endothelin receptor number

The aim of the present study was to determine the effect of a calcium channel blocker on renal function, urinary endothelin excretion and endothelin receptor number in rats. Administration of cyclosporine resulted in a significant impairment of renal function when measured by either [14C]inulin or 24 h creatinine clearances. This nephrotoxicity was associated with statistically significant (P less than 0.05) increases in urinary endothelin excretion and renal endothelin receptor number. Treatment with nifedipine attenuated cyclosporine A-induced renal dysfunction and reduced urinary endothelin excretion. The data provide further evidence of a role for endothelin in cyclosporine A-induced nephrotoxicity.

Increased endothelin excretion in rats with renal failure induced by partial nephrectomy.

1 Six weeks following partial nephrectomy in rats, significant increases in serum urea nitrogen and serum creatinine concentration and a significant decrease in creatinine clearance were observed. 2 Measurement of systolic blood pressure by tail plethysmography indicated that animals that had undergone partial nephrectomy were hypertensive. 3 Compared to sham‐operated animals, there were 4 fold increases in both urinary protein excretion and urinary endothelin excretion. 4 There was a significant correlation between urinary protein and urinary endothelin excretion (r = 0.77). There was also a correlation (r = 0.65) between urinary endothelin excretion and systolic blood pressure. 5 Plasma endothelin concentrations were not different in sham‐operated and partially nephrectomized rats. 6 The data indicate that there is an increased renal endothelin production in rats with chronic renal failure.

Comparison between carvedilol and captopril in rats with partial ablation-induced chronic renal failure

1 The effect of the novel β‐adrenoceptor antagonist and vasodilator, carvedilol (SK&F 105517, ∼ 70 mg kg−1 daily in the food), and captopril (∼ 38 mg kg−1 daily in the drinking fluid) on the progression of chronic renal failure in rats was studied. 2 Six weeks following partial renal ablation, the urinary protein excretion of the carvediol‐ (60 ± 21 mg day−1) and captopril‐treated (35 ± 9mgday−1) animals was less than 50% that of control rats (133 ± 27 mg d−1). 3 Serum creatinine (Scr) and urea nitrogen (SUN) concentrations of the carvedilol‐(Scr, 0.63 ± 0.09 mg dl−1; SUN, 11.3 ± 1.2 mg dl−1) and captopril‐treated (Scr, 0.82 ± 0.05 mg dl−1; SUN, 14.1 ± 1.5 mg dl−1) animals were also significantly (P < 0.05) lower than that observed in control animals (Scr, 1.4 ± 0.3 mg dl−1; SUN, 19.2 ± 3.9 mg dl−1), indicating that glomerular filtration rate was improved by both drugs. Plasma renin activity was significantly (P < 0.05) higher in captopril‐treated rats (24.7 ± 4.6 ng angiotensin I ml−1 h−1) than in either carvedilol‐treated (7.9 ± 1.4 ng angiotensin I ml−1 h−1) or control animals (7.4 ± 1.0 ng angiotensin I ml−1 h−1). 4 Histological examination of the kidneys demonstrated a significantly reduced glomerular hypertrophy and glomerulosclerosis in those animals receiving carvedilol or captopril compared to controls. 5 Serum carvedilol concentration measured every 6 h for 24 h was variable and ranged on average from 57 ± 13 ng ml−1 at 16 h 00 min to 121 ± 31 ng ml−1 at 03 h 00 min. These data indicate that the rats probably had 24 h systemic exposure to carvedilol. 6 The present study indicates that carvedilol is effective in attenuating the progression of chronic renal failure in rats.

Renoprotective effects of carvedilol in hypertensive‐stroke prone rats may involve inhibition of TGFβ expression

The effect of carvedilol on renal function, structure and expression of TGFβ and the matrix proteins fibronectin, collagen I and collagen III, was evaluated in spontaneously hypertensive stroke‐prone (SHR‐SP) rats fed a high fat, high salt diet. Carvedilol treatment for 11 to 18 weeks did not alter systolic blood pressure in SHR‐SP rats, however, it resulted in a significant reduction in heart rate. Carvedilol treatment reduced renal fibrosis and total, active and chronic renal damage to levels approaching those of WKY rats on a normal diet. Urinary protein excretion was higher in SHR‐SP rats (51±10 mg day−1) than WKY rats (18±2 mg day−1) and this was further increased when SHR‐SP rats were fed a high fat, high salt diet (251±120 mg day−1). Treatment with carvedilol resulted in significantly lower urinary protein excretion (37±15 mg day−1). The expression of TGFβ mRNA was significantly higher in SHR‐SP rats compared to WKY rats and a further increase was observed when rats were fed a high fat, high salt diet. Renal TGFβ expression was significantly reduced by treatment with carvedilol. The expression of fibronectin and collagen I and collagen III mRNA showed a pattern similar to that observed with TGFβ mRNA expression. Collagen I mRNA expression followed a pattern similar to renal fibrosis. These data indicate that carvedilol can provide significant renal protection in the absence of any antihypertensive activity and that the mechanisms involved in this action may include reduced expression of profibrotic factors such as TGFβ.

ANGIOTENSIN-CONVERTING ENZYME INHIBITION ATTENUATES PROTEINURIA AND RENAL TGF-BETA 1 MRNA EXPRESSION IN RATS WITH CHRONIC RENAL DISEASE

Evidence suggests that transforming growth factor beta 1 (TGF-β1), a multifunctional cytokine, induces renal extracellular matrix production and glomerular hypertrophy. The aim of the present study was to investigate the effect of captopril on the expression of TGF-β1 mRNA in a rat model of chronic renal failure: five-sixths nephrectomy. Chronic renal disease was induced by removal of the right kidney and ligation of three blood vessels supplying the left kidney. Sham-operated animals were used as controls. RNA was extracted from the viable remnant kidney of rats 1 day and 1 and 2 weeks following five-sixths nephrectomy and from the kidneys of rats who underwent sham sugery. TGF-β1 mRNA was induced within 24 h of partial nephrectomy, similar to that reported for early-onset genes. Subsequently, TGF-β1 mRNA expression continued to increase over the next 2–4 weeks. The upregulation of TGF-β1 correlated with the degree of proteinuria. Both the increase in TGF-β1 mRNA and proteinuria were abrogated by captopril treatment. In addition, no change in expression of ALK-5 or type II TGF-β receptors following five-sixths nephrectomy was observed. These data suggest that captopril may protect against development of glomerulosclerosis and proteinuria by reducing TGF-β1 expression and hence matrix production.

Prevention of cyclosporine A-induced renal vasoconstriction by the endothelin receptor antagonist SB 209670

Administration of endothelin to inactin-anesthetized rats resulted in a significant renal vasoconstriction as evidenced by a reduction in both renal plasma flow and glomerular filtration rate. Infusion of the novel nonpeptide endothelin ETA/ETB receptor antagonist, (+/-)-SB 209670, [(1RS-2SR,3RS)-3-(2-carboxymethoxy-4-methoxy-phenyl)-5 -(prop-1-yloxy)indane-2-carboxylic acid], significantly attenuated the renal vascular effects of endothelin-1. Intravenous administration of cyclosporine A (50 mg/kg) caused a significant reduction in renal plasma flow and glomerular filtration rate and urine flow and a dramatic increase in renal vascular resistance. Concomitant infusion of (+/-)-SB 209670 abolished the cyclosporine A-induced reduction in renal plasma flow and glomerular filtration rate and attenuated the cyclosporine A-induced fluid retention. The data indicate that endothelin is involved in the acute renal effects of cyclosporine A.

Eprosartan reduces cardiac hypertrophy, protects heart and kidney, and prevents early mortality in severely hypertensive stroke-prone rats

OBJECTIVE Eprosartan is a selective angiotensin II type I receptor antagonist approved for the treatment of hypertension. In the present studies, eprosartans ability to provide end-organ protection was evaluated in a model of cardiomyopathy and renal failure in stroke-prone rats (SP). METHODS SP were fed a high fat (24.5% in food) and high salt (1% in water) diet (SFD). Eprosartan (60 mg/kg/day) or vehicle (saline control) (n = 25/group) was administered by intraperitoneally-implanted minipumps to these SP on the SFD for 12 weeks. Normal diet fed SP and WKY rats (n = 25/group) were also included for comparison (i.e. served as normal controls). Mortality, hemodynamics, and both renal and cardiac function and histopathology were monitored in all treatment groups. RESULTS Eprosartan decreased the severely elevated arterial pressure (-12%; P < 0.05) produced by SFD but did not affect heart rate. Vehicle-treated SP-SFD control rats exhibited significant weight loss (-13%; P < 0.05) and marked mortality (50% by week 6 and 95% by week 9; P < 0.01). Eprosartan-treated SP-SFD rats maintained normal weight, and exhibited zero mortality at week 12 and beyond. Eprosartan prevented the increased urinary protein excretion (P < 0.05) that was observed in vehicle-treated SP-SFD rats. Echocardiographic (i.e. 2-D guided M-mode) evaluation indicated that SP-SFD vehicle control rats exhibited increased septal (+22.2%) and posterior left ventricular wall (+30.0%) thickness, and decreased left ventricular chamber diameter (-15.9%), chamber volume (-32.7%), stroke volume (-48.7%) and ejection fraction (-22.3%), and a remarkable decrease in cardiac output (-59.3%) compared to controls (all P < 0.05). These same parameters in eprosartan-treated SP-SFD rats were normal and differed markedly and consistently from vehicle-treated SP-SFD rats (i.e. treatment prevented pathology; all P < 0.05). Cardiac-gated MRI data confirmed the ability of eprosartan to prevent cardiac pathology/remodeling (P < 0.05). Histopathological analysis of hearts and kidneys indicated that eprosartan treatment significantly reduced end-organ damage (P < 0.01) and provided corroborative evidence that eprosartan reduced remodeling of these organs. Vehicle-treated SP-SFD rats exhibited a 40% increase in the plasma level of pro-atrial natiuretic factor that was reduced to normal by eprosartan (P < 0.05). CONCLUSION These data demonstrate that eprosartan, at a clinically relevant dose, provides significant end-organ protection in the severely hypertensive stroke-prone rat. It preserves cardiac and renal structural integrity, reduces cardiac hypertrophy and indices of heart failure, maintains normal function of the heart and kidneys, and eliminates premature mortality due to hypertension-induced end-organ failure.

Parathyroid Hormone-1 Receptor Down-Regulation in Kidneys from Rats with Chronic Renal Failure

Although secondary hyperparathyroidism is a common complication of chronic renal failure, few studies have examined the characteristics of parathyroid hormone (PTH) binding to the kidney or the regulation of the PTH receptor in chronic renal disease. In this study we measured PTH binding to the PTH-1 receptor in renal cortical membranes from normal rats and from rats with experimentally induced chronic renal failure. In normal rats, analysis of saturation binding experiments using 125I PTH-related peptide (chicken, cPTHrP) revealed apparent Kd and Bmax values of 1.16 ± 0.14 nmol/l and 338 ± 22.7 fmol/mg, respectively. Three weeks following induction of renal failure there was no change in the affinity of the PTH-1 receptor (Kd = 1.51 ± 0.24 nmol/l) but the Bmax was reduced by 45% (183 ± 32.5). In normal rats which had undergone thyroparathyroidectomy, the Kd was unchanged (1.17 ± 0.09) while the Bmax increased to 459 ± 31 fmol/mg. We conclude that chronic renal failure is accompanied by a downregulation of renal PTH-1 receptors.

Involvement of Nitric Oxide Synthase in Proteinuria Associated with Chronic Renal Disease in Rats

The present study demonstrates that the nitric oxide synthase inhibitor, aminoguanidine, can attenuate the proteinuria observed in a predominantly noninflammatory model of chronic renal disease in the rat. These data suggest that nitric oxide synthase may be involved in progressive renal disease.