Impairment of Whole Kidney Blood Flow Autoregulation in the Transition from Acute to Chronic Kidney Disease in Ischemia‐Reperfusion Rats

Abstract

Efficient autoregulation of renal blood flow (RBF) is an essential mechanism of renal microcirculation to protect against glomerular injury. Patients surviving an episode of acute kidney injury (AKI) develops chronic kidney disease (CKD). Renal ischemia-reperfusion (IR) is a major cause of AKI and triggers inflammation and reactive oxygen species (ROS) accumulation. We hypothesized that IR‑induced inflammation and ROS accumulation leads to a persistent reduction of RBF and impairment of RBF autoregulation contributing to CKD progression. Whole kidney RBF autoregulation was assessed in vivo in Sprague-Dawley male IR induced by bilateral arterial ischemia for 60 minutes followed by 24 hours, 1-week and 4‑weeks of reperfusion. Plasma creatinine increased in IR at 24 hours (3.9±0.2 vs. 1.0±0.1 mg/dl in sham, P<0.05, n=6-7/group) and week 1 (1.4±0.1 vs. 1.1±0.0 mg/dl in sham, P<0.05, n=7-8/group). Systolic blood pressure was similar between sham and IR over the 4 weeks post-IR (113-135 mmHg). IR reduced baseline RBF (5.8±0.5 vs. 9.1±0.5 ml/min.gkw in sham, P<0.05, n=6/group) at 24 hours and further decreased RBF at week 1 (3.7±0.7 vs. 9.1±1.1 ml/min.gkw in sham, n=5-6/group). At week 4, RBF was still significantly low in IR (6.9±0.4 vs. 10.4±0.3 ml/min.gkw in sham, P<0.05, n=6/group). RBF remained stable during step reduction of renal perfusion pressure (RPP) from 120 to 100 mmHg in all shams with autoregulatory index (AI) less than 0.2, indicating intact autoregulation. RBF autoregulation, however, was completely impaired in IR at 24 hours, week 1 and week 4 as RBF passively decreased during reduction of RPP, yielding AI of 0.8±0.2, 1.1±0.2 and 0.9±0.3, respectively. Preglomerular microvessels (PGMV) were collected for mRNA measurement (n=6-8/group). IR elevated mRNA expression of p67phox 7‑fold at 24 hours and 2‑fold at week 1 (P<0.05 vs. respective shams). IR also elevated gp91phox mRNA expression 5-fold at 24 hours and 2-fold at week 1 (P<0.05 vs. shams). IR tended to elevate p47phox mRNA expression at 24 hours and reached a significance at week 1 (2-fold, P<0.05 vs. sham). Inflammatory mediators, monocyte chemoattractant protein-1 (MCP-1) and vascular cell adhesion protein-1 (VCAM-1), were also assessed in PGMV. MCP-1 mRNA expression was increased in IR with a peak of 10-fold at 24 hours and then decreased at week 1 but still elevated compared to shams (2-fold, P<0.05). VCAM-1 mRNA expression remained unchanged at 24 hours but increased 2-fold at week 1 (P<0.05). We also assessed profibrotic markers (TGF-β, collagen IV and fibronectin). TGF-β mRNA expression started to increase in IR at 24 hours (2-fold) and reached a significance at week 1 (3-fold, P<0.05 vs. sham) and further increased at week 4 (4-fold). IR also increased mRNA expression of collagen IV 5-fold at week 1 and 4-fold at week 4 (P<0.05). Fibronectin mRNA expression was also increased in IR 4-fold at week 1 and remained at the same level at week 4 (P<0.05). In conclusion, these results demonstrate that IR leads to a persistent reduction of RBF and impairment of RBF autoregulation in male rats and suggest that renal hemodynamic dysfunction might be associated with activation of NADPH oxidase, MCP-1 and TGF-β in PGMV of IR.