Endothelin receptor A blockade reduces proteinuria and vascular hypertrophy in spontaneously hypertensive rats on high-salt diet in a blood-pressure-independent manner

The renal endothelin (ET) system is involved in the pathogenesis of kidney fibrosis as well as blood pressure control by regulating tubular sodium excretion. Long-term effects of ETA receptor blockade on blood pressure and kidney function in spontaneously hypertensive rats (SHRs) on a high-salt diet are unknown. We treated SHRs on a 6% (w/v) NaCl sodium diet (SHR-S) for 48 weeks with the ETA antagonist LU 135252 (whose selectivity for ETA is 150 times greater than for ETB) with 10, 30 and 100 mg . kg(-1) . day(-1) or placebo. The ETA antagonist had at no time-point any effect on blood pressure. Glomerular filtration rate was normal in SHR-S and not altered by LU 135252. However, urinary albumin excretion was markedly reduced by the ETA antagonist (SHR-S, 145+/-50 mg/day; SHR-S+ 10 mg . kg(-1) . day(-1) LU 135252, 33+/- 11 mg/day, P < 0.05 versus SHR-S; SHR-S+30 mg . kg(-1) . day(-1) LU 135252, 55+/- 16 mg/day and SHR-S+ 100 mg . kg(-1) . day(-1) LU 135252, 32+/- 11 mg/day, P < 0.05 versus SHR-S at both concentrations). Total urinary protein excretion was likewise significantly reduced by treatment with 10 mg . kg(-1) . day(-1) LU 135252 (SHR-S, 0.25+/-0.06 g/day; SHR-S+ 10 mg . kg(-1) . day(-1) LU 135252, 0.089+/-0.01 g/day, P < 0.05 versus SHR-S). The higher dosages of LU 135252 showed only a trend towards reduction of total urinary protein excretion. Computer-aided image analysis after haematoxylin/eosin and periodic acid-Schiff staining revealed that treatment with 10 mg . kg(-1) . day(-1) LU 135252 significantly reduces the media/lumen ratio of intrarenal arteries. Higher dosages of LU 135252 were less effective. Renal matrix protein synthesis in SHR-S was not altered by LU 135252. In conclusion, the renal ET system contributes in a blood-pressure-independent manner to the regulation of urinary protein excretion and renal vascular hypertrophy in SHR-S. Lower doses of the ETA antagonist were more effective, indicating that a potential additional blockade of the ETB receptor using higher doses of LU 135252 seems to oppose the beneficial effects of a sole ETA blockade. Urinary protein excretion is an independent risk factor of chronic renal failure, thus ETA antagonists might be a therapeutic tool to prevent proteinuria-induced chronic renal failure.