Angiotensin receptor blockade has protective effects on the poststenotic porcine kidney

Abstract

Angiotensin-converting enzyme inhibitors/angiotensin II receptor blockers (ARBs) may induce an acute decrease of glomerular filtration rate (GFR) in the stenotic kidney in renal artery stenosis, but most patients tolerate these drugs well. We hypothesized that angiotensin-converting enzyme inhibitors/ARBs stabilize stenotic kidney function during prolonged treatment by conferring protective effects. We tested this in control domestic pigs and pigs with renal artery stenosis untreated or treated with Valsartan, or triple therapy (seven pigs in each group) for 4 weeks starting 6 weeks after stenosis induction. Renal function, oxygenation, tubular function, and microcirculation were assessed by multi-detector computed tomography (CT), blood oxygen level-dependent magnetic-resonance imaging, and micro-CT. Valsartan and triple therapy decreased blood pressure similarly; however, Valsartan did not change the GFR of the stenotic kidney compared with renal artery stenosis and was similar to triple therapy. Both Valsartan and triple therapy stimulated microvascular density and improved tubular function. Valsartan also caused a greater increase of angiogenic factors and a decrease in oxidative stress, which were related to higher cortical perfusion and tubular response than triple therapy. Thus, Valsartan did not decrease stenotic kidney GFR, but improved cortical perfusion and microcirculation. These beneficial effects may partly offset the hemodynamic GFR reduction in renal artery stenosis and preserve kidney function.

Figure 1

1-1 Mean arterial pressure (MAP) assessed by telemetry over 10 weeks of observation in Normal, renal artery stenosis (RAS), RAS+Valsartan, and RAS+triple therapy (TT). MAP increased 1 week after induction of RAS and remained elevated in untreated RAS for the duration of the study. Valsartan and TT similarly lowered, but not normalized, MAP. 1–2: A–C Perfusion, renal blood flow (RBF) and glomerular filtration rate (GFR) assessed by MDCT at 10 weeks. All RAS groups had lower perfusion, RBF, and GFR compared to Normal, but Valsartan improved cortical perfusion compared to untreated RAS. 1–3 Representative images of stenotic kidney blood oxygen level dependent (BOLD) MRI before (top) and after (bottom) furosemide injection, and R2* in the cortex (A) and medulla (B) before and after furosemide. C: Delta-R2* in medulla. Both Valsartan and TT restored medullary tubular response to furosemide, but Valsartan elicited a greater improvement than TT. Arrows (white) indicate the approximate size of the medullary regions. *P<0.05 vs. Normal; **P<0.01 vs. Normal; $P<0.05 vs. RAS; ‡ P<0.05 vs. 6 wks; § P<0.05 vs. Pre-furosemide.

Figure 2

2–1 A–D Representative 3-dimensional images of the renal cortical microvasculature in Normal, renal artery stenosis (RAS), RAS+Valsartan and Triple therapy (TT) pig kidneys. E–F: quantification in the outer and inner cortex. RAS induced loss of small (20–40μm) and medium (40–200μm) microvessels in both the outer and inner cortex. TT improved small vessels in the outer cortex, while Valsartan normalized small vessels and improved medium-size vessels as well. 2-2 A–B Renal expression of angiogenic and angiostatic markers. Both Valsartan and TT stimulated angiogenesis, but Valsartan stimulated more angiogenic factors, while TT also upregulated the angiogenic inhibitor. Protein bands were quantified relative to GAPDH. Two representative bands from each group are shown. * P<0.05 vs. Normal; $ P<0.05 vs. RAS; †P<0.05 vs. RAS+Valsartan.

Figure 3

3–1 Representative dihydroethidium (DHE) images [40×, positive DHE staining (pink), nuclei (blue)], its quantification (A) and renal protein expression of P47 (B). Renal oxidative stress was increased in renal artery stenosis (RAS) and restored only by Valsartan. 3–2. Representative tumor necrosis factor (TNF)-alpha staining images [40×] and quantification. TNF-alpha positive cells (green, blue nuclei) were increased in the renal tubules and interstitium of RAS pigs. Both Valsartan and triple therapy (TT) attenuated TNF-alpha expression. 3-3. Representative trichrome staining (20×) and quantification. Both Valsartan and TT alleviated fibrosis compared to RAS. 3–4. Renal expression of fibrogenic markers. Valsartan and TT showed a similar anti-fibrotic effect. Protein bands were quantified relative to GAPDH. Two representative bands per group are shown. * P<0.05 vs. Normal; $ P<0.05 vs. RAS; †P<0.05 vs. RAS+Valsartan.

Figure 4

Renal expression of angiotensin receptors AT1R and AT2R. Valsartan alone increased AT1R, while AT2R was increased in all RAS groups. Protein bands were quantified relative to GAPDH. Two representative bands from each group are shown. *P<0.05 vs. Normal; $ P<0.05 vs. RAS.