Abstract P397: Preservation Of Renal Microvascular Function In Ischemia-reperfusion Induced Kidney Injury In Rats

Abstract

Proper renal blood flow and glomerular filtration rate are critical for maintaining normal kidney function by precisely adjusting preglomerular microvascular resistance. Renal ischemia-reperfusion (IR) insult markedly increased mRNA expression of the inflammatory chemokine (C-C motif) Ligand 2 (CCL2) in rat kidney tissues. We hypothesized that depletion of macrophages prevented IR-induced renal autoregulatory impairment via reduction of CCL2 in preglomerular microvessels (PGMV). IR was induced in male rats by 60-minute bilateral renal artery occlusion followed by reperfusion. Some IR rats were treated with the selective macrophage inhibitor, Liposome-encapsulated clodronate (LC) following reperfusion and repeated 72 hours post-IR. Afferent arteriolar autoregulatory reactivity was assessed using the in vitro blood-perfused juxtamedullary nephron preparation in sham, IR, and IR+LC rats on day 7. Afferent arterioles from sham-operated rats exhibited pressure-dependent vasoresponsiveness. The baseline arteriolar diameter averaged 13.4 ± 0.5 μm at renal perfusion pressure (RPP) of 100 mmHg. Diameter increased to 117 ± 4% of baseline at RPP of 65 mmHg and decreased to 69 ± 2% at 170 mmHg, respectively. In contrast, afferent arterioles from IR rats only increased to 104 ± 2% and decreased to 91 ± 5% of baseline at 65 and 170 mmHg, respectively (P < 0.05 vs sham), indicating the impaired autoregulatory capacity in IR rats. LC-treated IR rats, however, markedly improved the pressure-dependent vasoresponsiveness. A decrease in RPP to 65 mmHg resulted in a 124 ± 17% increase in the baseline diameter, whereas increasing RPP to 170 mmHg led to a 74 ± 7% decrease in diameter. Additionally, IR markedly increased CCL2 mRNA expression in isolated PGMV by 10-fold 7 days post-IR. IR also elevated NADPH oxidase subunits (gp91 phox , P67 phox , and P47 phox ). Significantly, LC treatment suppressed mRNA expression of CCL2, gp91 phox , P67 phox , and P47 phox in IR-PGMV. In conclusion, depletion of macrophages preserves afferent arteriolar autoregulatory capacity and reduces PGMV CCL2 mRNA expression in IR rats, suggesting a critical role of macrophages in mediating renal microvascular autoregulatory impairment in IR-induced kidney injury via the increase of CCL2 in PGMV.