Back
Renin-angiotensin system (RAS) is activated during ischemic acute kidney injury. Via AT2R, angiotensin II, promotes vasodilatory, anti-inflammatory and antifibrotic actions and participates in tissue repair. We previously described that 40 min of renal ischemia followed by 1 day of reperfusion in male rats induced severe tissue damage and a decrease in glomerular filtration rate (GFR) that were partially prevented with a high dose of the AT2R agonist, C21 (1 mg/kg/day). Sex differences in the development of renal ischemia-reperfusion (IR) injury and in RAS components expression have been reported. Research is limited on female animals. Our aim was to characterize renal IR damage in female rats and to study the effects of pretreatment with the AT2R agonist, C21.
Female Wistar rats (n=6 per group) were subjected to 40 min of unilateral renal ischemia followed by 1 day of reperfusion (I). Controls underwent sham operation (C).
Another groups received C21 (Vicore Pharma, 0.3 mg/kg/day, i.p.) 2 days prior to I (IC) or sham operation (CC). The last dose was administered 1h before the ischemic insult. Urine was collected in metabolic cages. Blood was collected from cava vein and postischemic kidney was excised. Urea in plasma and creatinine in plasma and urine were measured with commercial kits. GFR was estimated by creatinine clearance. Urinary Kim-1 (uKIM), a marker of proximal tubular injury, was measured by Elisa. uKIM was expressed as pg related to urine flow or relative to urinary creatinine concentration. For histological studies, kidneys were fixed and stained with PAS. Data was analyzed using ANOVA followed by Newman-Keuls contrast.
We found no statistically significant differences in GFR, and in plasma creatinine and urea levels between groups. uKIM was increased in I and C21 attenuated this increase (C: 5.4±1; CC: 3.9±0.5; I: 66.1±21*; IC: 21.3±12*# pg/min.100 g body weight, *p<0.05 vs C; #p<0.5 vs I). Similar results were obtained when uKIM levels were related to urinary creatinine concentration. Histological studies showed moderate tissue damage in I (injury score: 25-50%), evidenced by multifocal necrosis, areas with moderate brush border loss, vacuolization of tubular cell cytoplasm, cellular desquamation into the lumen, intratubular casts. Pretreatment with C21 induces a better preservation of the tubular architecture. The injury was of mild to normal in IC (injury score <25%).
In agreement with other studies, we found that IR damage in female rats was less severe than in males. uKIM was elevated before changes in GFR and plasma creatinine, representing a sensitive biomarker to evidence minor tissue damage in female rats. We previously demonstrated that a dose of 1 mg/kg/day of C21 have renoprotective effects against the severe damage induced by IR in male rats. Based on the lower damage found in female, we tested a lower C21 dose (0.3 mg/kg/day). We described for the first time a renoprotective effect of C21 against ischemic injury in female rats, and increase evidence supporting that stimulation of AT2R triggers cytoprotective mechanisms against an ischemic event. The present study evidence the need of further sex specific studies.