Persistent vascular congestion in male spontaneously hypertensive rats contributes to delayed recovery of renal function following renal ischemia perfusion compared with females.

Acute kidney injury (AKI) due to ischemia is a serious and frequent clinical complication with mortality rates as high as 80%. Vascular congestion in the renal outer medulla occurs early after ischemia reperfusion (IR) injury, and congestion has been linked to worsened outcomes following IR. There is evidence implicating both male sex and preexisting hypertension as risk factors for poor outcomes following IR. The present study tested the hypothesis that male spontaneously hypertensive rats (SHR) have greater vascular congestion and impaired renal recovery following renal IR vs. female SHR and normotensive male Sprague-Dawley rats (SD). Thirteen-week-old male and female SHR and SD were subjected to sham surgery or 30 min of warm bilateral ischemia followed by reperfusion. Rats were euthanized 24 h or 7 days post-IR. IR increased renal injury in all groups vs. sham controls at 24 h. At 7 days post-IR, injury remained elevated only in male SHR. Histological examination of SD and SHR kidneys 24 h post-IR showed vascular congestion in males and females. Vascular congestion was sustained only in male SHR 7 days post-IR. To assess the role of vascular congestion on impaired recovery following IR, additional male and female SHR were pretreated with heparin (200 U/kg) prior to IR. Heparin pretreatment reduced IR-induced vascular congestion and improved renal function in male SHR 7 days post-IR. Interestingly, preventing increases in blood pressure (BP) in male SHR did not alter sustained vascular congestion. Our data demonstrate that IR-induced vascular congestion is a major driving factor for impaired renal recovery in male SHR.

Sodium bicarbonate loading limits tubular cast formation independent of glomerular injury and proteinuria in Dahl salt-sensitive rats.

Sodium bicarbonate (NaHCO3) slows the decline in kidney function in patients with chronic kidney disease (CKD), yet the mechanisms mediating this effect remain unclear. The Dahl salt-sensitive (SS) rat develops hypertension and progressive renal injury when fed a high salt diet; however, the effect of alkali loading on kidney injury has never been investigated in this model. We hypothesized that NaHCO3 protects from the development of renal injury in Dahl salt-sensitive rats via luminal alkalization which limits the formation of tubular casts, which are a prominent pathological feature in this model. To examine this hypothesis, we determined blood pressure and renal injury responses in Dahl SS rats drinking vehicle (0.1 M NaCl) or NaHCO3 (0.1 M) solutions as well as in Dahl SS rats lacking the voltage-gated proton channel (Hv1). We found that oral NaHCO3 reduced tubular NH4+ production, tubular cast formation, and interstitial fibrosis in rats fed a high salt diet for 2 weeks. This effect was independent of changes in blood pressure, glomerular injury, or proteinuria and did not associate with changes in renal inflammatory status. We found that null mutation of Hv1 also limited cast formation in Dahl SS rats independent of proteinuria or glomerular injury. As Hv1 is localized to the luminal membrane of TAL, our data suggest that alkalization of the luminal fluid within this segment limits cast formation in this model. Reduced cast formation, secondary to luminal alkalization within TAL segments may mediate some of the protective effects of alkali loading observed in CKD patients.