Unfavorable Reduction in the Ratio of Endothelin B to A Receptors in Experimental 5/6 Nephrectomy and Adenine Models of Chronic Renal Insufficiency.

Chronic renal insufficiency (CRI) is characterized by increased endothelin 1 (ET-1) synthesis. We studied rat kidney endothelin receptor A (ETA) and receptor B (ETB) expressions after 12 and 27 weeks of 5/6 nephrectomy, and after 12 weeks of 0.3% adenine diet, representing proteinuric and interstitial inflammation models of CRI, respectively. Uric acid and calcium-phosphate metabolism were modulated after 5/6 nephrectomy, while ETA blocker and calcimimetic were given with adenine. Endothelin receptor mRNA levels were measured using RT-qPCR and protein levels using autoradiography (5/6 nephrectomy) or ELISA (adenine model). Both 12 and 27 weeks after 5/6 nephrectomy, kidney cortex ETA protein was increased by ~60% without changes in ETB protein, and the ETB:ETA ratio was reduced. However, the ETB:ETA mRNA ratio did not change. In the adenine model, kidney ETA protein was reduced by ~70%, while ETB protein was suppressed by ~95%, and the ETB:ETA ratio was reduced by ~85%, both at the protein and mRNA levels. The additional interventions did not influence the observed reductions in the ETB:ETA ratio. To conclude, unfavorable reduction in the ETB:ETA protein ratio was observed in two different models of CRI. Therefore, ETA blockade may be beneficial in a range of diseases that cause impaired kidney function.

Endothelin A receptor blocker and calcimimetic in the adenine rat model of chronic renal insufficiency.

BACKGROUND: We studied whether endothelin receptor antagonist and calcimimetic treatments influence renal damage and kidney renin-angiotensin (RA) components in adenine-induced chronic renal insufficiency (CRI). METHODS: Male Wistar rats (n = 80) were divided into 5 groups for 12 weeks: control (n = 12), 0.3% adenine (Ade; n = 20), Ade + 50 mg/kg/day sitaxentan (n = 16), Ade + 20 mg/kg/day cinacalcet (n = 16), and Ade + sitaxentan + cinacalcet (n = 16). Blood pressure (BP) was measured using tail-cuff, kidney histology was examined, and RA components measured using RT-qPCR. RESULTS: Adenine caused tubulointerstitial damage with severe CRI, anemia, hyperphosphatemia, 1.8-fold increase in urinary calcium excretion, and 3.5-fold and 18-fold increases in plasma creatinine and PTH, respectively. Sitaxentan alleviated tubular atrophy, while sitaxentan + cinacalcet combination reduced interstitial inflammation, tubular dilatation and atrophy in adenine-rats. Adenine diet did not influence kidney angiotensin converting enzyme (ACE) and AT4 receptor mRNA, but reduced mRNA of renin, AT1a, AT2, (pro)renin receptor and Mas to 40-60%, and suppressed ACE2 to 6% of that in controls. Sitaxentan reduced BP by 8 mmHg, creatinine, urea, and phosphate concentrations by 16-24%, and PTH by 42%. Cinacalcet did not influence BP or creatinine, but reduced PTH by 84%, and increased hemoglobin by 28% in adenine-rats. The treatments further reduced renin mRNA by 40%, while combined treatment normalized plasma PTH, urinary calcium, and increased ACE2 mRNA 2.5-fold versus the Ade group (p < 0.001). CONCLUSIONS: In adenine-induced interstitial nephritis, sitaxentan improved renal function and tubular atrophy. Sitaxentan and cinacalcet reduced kidney renin mRNA by 40%, while their combination alleviated tubulointerstitial damage and urinary calcium loss, and increased kidney tissue ACE2 mRNA.

Vasopeptidase Inhibition Corrects the Structure and Function of the Small Arteries in Experimental Renal Insufficiency.

BACKGROUND: We studied whether vasopeptidase inhibition corrects the structure and function of the small arteries in experimental chronic renal insufficiency (CRI). METHODS: After 5/6 nephrectomy (NX) surgery was performed on rats, there was a 14-week follow-up, allowing CRI to become established. Omapatrilat (40 mg/kg/day in chow) was then given for 8 weeks, and the small mesenteric arterial rings were investigated in vitro using wire and pressure myographs. RESULTS: Plasma and ventricular B-type natriuretic peptide (BNP) concentrations were increased 2- to 2.7-fold, while systolic blood pressure (BP) increased by 32 mm Hg after NX. Omapatrilat treatment normalized the BNP and reduced the BP by 45 mm Hg in the NX rats. Endothelium-dependent vasorelaxation was impaired but the response to acetylcholine was normalized after omapatrilat treatment. Vasorelaxations induced by nitroprusside, isoprenaline and levcromakalim were enhanced after omapatrilat, and the responses were even more pronounced than in untreated sham-operated rats. Arterial wall thickness and wall-to-lumen ratio were increased after NX, whereas omapatrilat normalized these structural features and improved the strain-stress relationship in the small arteries; this suggests improved arterial elastic properties. CONCLUSION: Omapatrilat treatment reduced BP, normalized volume overload, improved vasorelaxation and corrected the dimensions and passive elastic properties of the small arteries in the NX rats. Therefore, we consider vasopeptidase inhibition to be an effective treatment for CRI-induced changes in the small arteries.

Phosphate binding reduces aortic angiotensin-converting enzyme and enhances nitric oxide bioactivity in experimental renal insufficiency.

BACKGROUND: Disturbed calcium-phosphorus metabolism is associated with increased kidney angiotensin-converting enzyme (ACE) in experimental chronic renal insufficiency (CRI). However, information about the effects of phosphate binding and loading on vascular ACE is lacking. METHODS: Fifteen weeks after 5/6 nephrectomy (NX), rats were placed on a phosphate-binding (NX+Ca, 3.0% Ca), phosphate-loading (NX+Pi, 1.5% Pi), or control diet for 12 weeks (NX and sham). RESULTS: Aortic ACE, blood pressure, plasma phosphate, and parathyroid hormone were increased in the NX and NX+Pi groups, but were reduced with phosphate binding. Endothelium-mediated relaxations of isolated mesenteric conduit artery rings to acetylcholine were impaired in the NX and NX+Pi groups, but did not differ from sham in NX+Ca rats. Experiments with nitric oxide (NO) synthase inhibition in vitro suggested that the NO-mediated component of acetylcholine response was lower in the NX and NX+Pi groups, but did not differ from sham in NX+Ca rats. In all NX groups, aortic endothelial NO synthase (eNOS) was reduced, while plasma and urine concentrations of NO metabolites were increased. Aortic nitrated proteins and calcification were increased in the NX and NX+Pi groups when compared with the NX+Ca and sham groups. CONCLUSION: Hypertension in the NX model of CRI was associated with reduced vasorelaxation, decreased eNOS, and increased ACE and nitrated proteins in the aorta. Phosphate binding with calcium carbonate enhanced vasorelaxation via endogenous NO and suppressed elevation of ACE and nitrated proteins, suggesting reduced vascular oxidative stress. Our findings support the view that correction of the calcium-phosphorus balance prevents CRI-induced vascular pathophysiology.