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

Abstract

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.

Keywords: calcium; chronic kidney disease; chronic renal insufficiency; cinacalcet; creatinine; endothelin receptor A; endothelin receptor B; paricalcitol; phosphate; sitaxentan; uric acid.

Figure 1

Kidney medullary ETB (A) and ETA (B) receptor protein content, and the ETB:ETA protein ratio (C); and kidney cortical ETB (D) and ETA (E) receptor protein content, and the ETB:ETA receptor protein ratio (F) quantified using autoradiography in the twelve-week 5/6 nephrectomy model; NX, 5/6 nephrectomy; Sham, sham-operation; OXO, 2.0% oxonic acid diet; n = 12/group. Values are mean ± 95% confidence interval of the mean. Two-way ANOVA p-values for NX, OXO and their interaction are presented in the figures.

Figure 2

Representative original tracings of kidney ETB and ETA receptor autoradiography in the sham-operated and 5/6 nephrectomized rats in the twelve-week 5/6 nephrectomy model.

Figure 3

Kidney medullary ETB (A) and ETA (B) receptor protein content, and the ETB:ETA protein ratio (C); and kidney cortical ETB (D) and ETA (E) receptor protein content, and the ETB:ETA receptor protein ratio (F) quantified using autoradiography in the twenty-seven-week 5/6 nephrectomy model; NX, 5/6 nephrectomy; Sham, sham-operation; Ca, 3.0% calcium diet; Pi, 1.5% phosphate diet; Pari, 100 ng/rat of intraperitoneal paricalcitol three times weekly; n = 7−13/group. Values are mean ± 95% confidence interval of the mean. * p < 0.05 vs. Sham.

Figure 4

Kidney ETB (A) and ETA (B) receptor protein content, and the ETB:ETA receptor protein ratio (C) quantified using ELISA in the twelve-week adenine model; Control, control diet; Ade, 0.3% adenine diet; S, sitaxentan50 mg/kg/day; C, cinacalcet 20 mg/kg/day; SC, sitaxentan+cinacalcet; n = 12–20/group. Values are mean ± 95% confidence interval of the mean. * p < 0.05 vs. Control.