Genetic susceptibility to renal injury in hypertension

Role of renal perfusion pressure versus angiotensin II on renal oxidative stress in angiotensin II-induced hypertensive rats

Renal oxidative stress is thought to contribute to both the etiology and the associated renal injury in angiotensin (Ang) II-dependent hypertension. The contribution of Ang II versus elevated renal perfusion pressure (RPP) on albuminuria and renal oxidative stress in this model of hypertension was explored in the present study by chronically servocontrolling RPP to the left kidney and comparing responses with the right uncontrolled kidney and the left kidney of sham rats. Hypertension was produced in Sprague-Dawley rats fed a 4% NaCl diet by chronic IV infusion of Ang II (25 ng/kg per minute). The RPP to the left kidney was servocontrolled to mean daily pressures averaging approximately 120 mm Hg, whereas the uncontrolled kidneys averaged approximately 170 mm Hg over 14 days of Ang II infusion. Ang II infusion resulted in a 2.4-fold increase in albuminuria, which was RPP dependent. Kidneys exposed to both elevated RPP and Ang II (uncontrolled kidneys) displayed a 3.5-fold increase in malondialdehyde excretion and a 37% and 27% increase in renal cortical and outer medullary superoxide production, respectively. Elevated RPP significantly contributed to global renal oxidative stress (70% increase in malondialdehyde excretion) and outer medullary superoxide production. Elevated circulating levels of Ang II, per se, were responsible for a 1.5-fold and 2.0-fold increase in renal cortical and outer medullary NADPH oxidase activity, respectively. In summary, this study demonstrates that elevated RPP is directly responsible for the excess albuminuria in Ang II-infused rats, whereas both elevated RPP and Ang II directly contribute to the observed renal oxidative stress.

Hypertension-induced renal fibrosis and spironolactone response vary by rat strain and mineralocorticoid receptor gene expression

Introduction. Aldosterone promotes renal fibrosis via the mineralocorticoid receptor (MR), thus contributing to hypertension-induced nephropathy. We investigated whether MR gene expression influences renal fibrosis and MR antagonist response in a two-kidney, one-clip hypertensive rat model.

Materials and methods. Brown Norway (BN), Lewis, and ACI rats were randomised to spironolactone 20 mg/kg/day or water by gavage, starting four weeks after left renal artery clipping. Blood pressure was measured bi-weekly by tail cuff. After eight weeks of treatment, right kidneys were removed and examined for fibrosis and gene expression. Rats of each strain undergoing no intervention served as controls.

Results. Blood pressure increased similarly among strains after clipping and was unaffected by spironolactone. Hypertension caused the greatest renal fibrosis in BN rats (p < 0.001 by ANOVA compared to other strains). Real-time PCR analysis showed greater renal collagen type I and MR gene expression in untreated, hypertensive BN rats (both p < 0.05 compared to other strains). Spironolactone attenuated fibrosis, with similar fibrosis among strains of spironolactone-treated rats.

Conclusion. Hypertension-induced renal fibrosis was greatest in rats with the highest MR gene expression. Spironolactone abolished inter-strain differences in fibrosis. Our data suggest that MR genotype may influence aldosterone-induced renal damage, and consequently, renal response to aldosterone antagonism.

Differential effects of salt on renal hemodynamics and potential pressure transmission in stroke-prone and stroke-resistant spontaneously hypertensive rats

Salt-supplemented stroke-prone spontaneously hypertensive rats (SHRsp) develop more severe hypertension-induced renal damage (HIRD) compared with their progenitor SHR. The present studies were performed to examine whether in addition to increasing the severity of hypertension salt also enhanced the transmission of such hypertension to the renal vascular bed in the SHRsp. "Step" and "dynamic" renal blood flow (RBF) autoregulation (AR) were examined in approximately 12-wk-old SHR and SHRsp after 3-5 days of an 8% NaCl diet. During step AR under anesthesia (n = 8-11), RBF was significantly higher in the SHRsp at all perfusion pressures (P < 0.01), but AR capacity was not different. Similarly, in separate conscious chronically instrumented rats (n = 8 each), both blood pressure (BP) and RBF were modestly but significantly higher at baseline before salt in the SHRsp (P < 0.05). However, transfer function analysis did not show significant differences in the admittance gain parameters. However, after 3-5 days of salt, although average BP was not significantly altered in either strain, RBF increased further in the SHRsp and there was a significantly greater transfer of BP into RBF power in the SHRsp. This was reflected in the significantly higher admittance gain parameters at most frequencies including the heartbeat frequency (P < 0.05 maximum). These differential hemodynamic effects of salt have the potential to enhance BP transmission to the renal vascular bed and also contribute to the more severe HIRD observed in the salt-supplemented SHRsp.

Gene expression profiling in hypertension research: a critical perspective

Recent advances in molecular biology and technology have made it possible to monitor the expression levels of virtually all genes simultaneously. As the tools for gene expression profiling have become more widely available, the number of investigators applying this technology in hypertension research, as in other fields of biomedical research, has grown rapidly. At the same time, numerous articles have been published that discuss the technical aspects of gene profiling and its promise for advancing research on the pathogenesis and treatment of multiple clinical disorders. However, much of the research carried out with gene expression profiling has been of a correlational or descriptive nature, and the true value of this technology is unclear. Despite the initial wave of enthusiasm for gene expression profiling, its actual utility for studying multifactorial disorders like hypertension remains to be established. In this review, we offer a critical perspective on the use of gene expression profiling in hypertension research and discuss some emerging strategies for taking this technology beyond the limits of correlational and descriptive studies.