The detailed mechanisms determining the course of congestive heart failure (CHF) in hypertensive subjects with associated renal dysfunction remain unclear. In Ren-2 transgenic rats (TGR), a model of angiotensin II (ANG II)-dependent hypertension, CHF was induced by volume overload achieved by creation of the aorto-caval fistula (ACF). In these rats we investigated the putative pathophysiological contribution of epoxyeicosatrienoic acids (EETs) and compared it with the role of the renin-angiotensin system (RAS). We found that untreated ACF TGR exhibited marked intrarenal and myocardial deficiency of EETs and impairment of renal function. Chronic treatment of these rats with cis-4-[4-(3-adamantan-1-yl-ureido)cyclohexyloxy]benzoic acid (c-AUCB, 3 mg/L in drinking water), an inhibitor of soluble epoxide hydrolase (sEH) which normally degrades EETs, increased intrarenal and myocardial EETs, markedly improved survival rate, and increased renal blood flow, glomerular filtration rate and fractional sodium excretion, without altering RAS activity. Chronic angiotensin-converting enzyme inhibition (ACEi) with trandolapril, (6 mg/L in drinking water) improved survival rate even more, and also inhibited the development of renal dysfunction; these beneficial actions were associated with significant suppression of the vasoconstrictor/sodium retaining axis and further activation of the vasodilatory/natriuretic axis of the systemic and intrarenal RAS, without modifying tissue availability of biologically active fatty acid epoxides. In conclusion, these findings strongly suggest that chronic sEH inhibition and chronic treatment with ACEi, each of them altering a different vasoactive system, delay or even prevent the onset of decompensation of CHF in ACF TGR, probably by preventing the development of renal dysfunction.

Abstract-Previous studies have shown that whereas the nonclipped kidney in two-kidney, one clip (2K1C) rats undergoes marked depletion of renin content and renin mRNA, intrarenal angiotensin II (Ang II) levels are not suppressed; however, the distribution and functional consequences of intrarenal Ang II remain unclear. The present study was performed to assess the plasma, kidney, and proximal tubular fluid levels of Ang II and the renal responses to intrarenal Ang II blockade in the nonclipped kidneys of rats clipped for 3 weeks. The Ang II concentrations in proximal tubular fluid averaged 9.19Ϯ1.06 pmol/mL, whereas plasma Ang II levels averaged 483Ϯ55 fmol/mL and kidney Ang II content averaged 650Ϯ66 fmol/g. Thus, as found in kidneys from normal rats with normal renin levels, proximal tubular fluid concentrations of Ang II are in the nanomolar range. To avoid the confounding effects of decreases in mean arterial pressure (MAP), we administered the nonsurmountable AT 1 receptor antagonist candesartan directly into the renal artery of nonclipped kidneys (nϭ10). The dose of candesartan (0.5 g) did not significantly decrease MAP in 2K1C rats (152Ϯ3 versus 148Ϯ3 mm Hg), but effectively prevented the renal vasoconstriction elicited by an intra-arterial bolus of Ang II (2 ng). Candesartan elicited significant increases in glomerular filtration rate (GFR) (0.65Ϯ0.06 to 0.83Ϯ0.11 mL ⅐ min Ϫ1 ⅐ g Ϫ1) and renal blood flow (6.3Ϯ0.7 to 7.3Ϯ0.9 mL ⅐ min Ϫ1 ⅐ g Ϫ1 ), and proportionately greater increases in absolute sodium excretion (0.23Ϯ0.07 to 1.13Ϯ0.34 mol ⅐ min Ϫ1 ⅐ g Ϫ1 ) and fractional sodium excretion (0.38Ϯ0.1% to 1.22Ϯ0.35%) in 2K1C hypertensive rats. These results show that proximal tubular fluid concentrations of Ang II are in the nanomolar range and are much higher than can be explained on the basis of plasma levels. Further, the data show that the intratubular levels of Ang II in the nonclipped kidneys of 2K1C rats remain at levels found in kidneys with normal renin content and could be exerting effects to suppress renal hemodynamic and glomerular function and to enhance tubular reabsorption rate. (Hypertension. 1999;33:102-107.) Key Words: renin-angiotensin system Ⅲ hypertension, renal Ⅲ angiotensin antagonist Ⅲ receptors, angiotensin Ⅲ glomerular filtration rate Ⅲ renal blood flow P revious studies have shown the pivotal role of the renin-angiotensin system (RAS) in the development and maintenance of two-kidney, one clip (2K1C) hypertension.

1. Hypertension plays a critical role in the progression of chronic kidney disease (CKD) to end-stage renal disease (ESRD), but it has also been postulated that antihypertensive drugs that block the renin-angiotensin system (RAS) show class-specific renoprotective actions beyond their blood pressure (BP)-lowering effects. 2. Because this notion has recently been questioned, in the present study we compared the effects of a RAS-dependent antihypertensive therapy (a combination of trandolapril, an angiotensin-converting enzyme inhibitor (ACEI) and losartan, an angiotensin-II (AngII) receptor subtype 1A receptor antagonist) with a 'RAS-independent' antihypertensive therapy (a combination of labetalol, an alfa- and beta-adrenoreceptor antagonist with the diuretics, hydrochlorothiazide and furosemide) on the progression of CKD after 5/6 renal ablation (5/6 NX) in Ren-2 renin transgenic rats (TGR), a model of AngII-dependent hypertension. Normotensive transgene-negative Hannover Sprague-Dawley (HanSD) rats after 5/6 NX served as controls. 3. RAS-dependent and -independent antihypertensive therapies normalized BP and survival rate, and prevented the development of cardiac hypertrophy and glomerulosclerosis to the same degree in 5/6 NX HanSD rats and in 5/6 NX TGR. The present findings show that renoprotection, at least in rats after 5/6 NX, is predominantly BP-dependent. When equal lowering of BP was achieved, leading to normotension, cardio- and renoprotective effects were equivalent irrespective of the type of antihypertensive therapy. 4. These findings should be taken into consideration in attempts to develop new therapeutic approaches and strategies aimed to prevent the progression of CKD and to lower the incidence of ESRD.

In the present study, we examined the effects of soluble epoxide hydrolase (sEH) inhibition on the development of angiotensin II-dependent hypertension and on renal function in transgenic rats with inducible expression of the mouse renin gene (strain name Cyp1a1-Ren-2). Hypertension was induced in these rats by indole-3-carbinol (I3C; 0.3% in the diet) for 12 days. The sEH inhibitor cis-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (c-AUCB) was given in two doses (13 or 26 mg l-1) in drinking water. Blood pressure (BP), body weight (BW) and renal excretory parameters were monitored in conscious animals during the experiment. Renal haemodynamics was assessed at the end of treatment in anaesthetized rats. I3C administration resulted in severe hypertension with a rise in systolic BP from 118 ± 2 to 202 ± 3 mmHg, a loss of BW from 266 ± 5 to 228 ± 4 g and a rise in proteinuria from 14 ± 2 to 34 ± 3 mg day-1. Both doses of c-AUCB significantly attenuated the development of hypertension (systolic BP of 181 ± 4 and 176 ± 4 mmHg, respectively), the loss in BW (256 ± 4 and 259 ± 3 g, respectively) and the degree of proteinuria (27 ± 2 and 25 ± 3 mg day-1, respectively) to a similar extent. Moreover, c-AUCB prevented the reduction in renal plasma flow (5.4 ± 0.4 vs. 4.6 ± 0.3 ml min-1 g-1) and significantly increased sodium excretion (0.84 ± 0.16 vs. 0.38 ± 0.08 μmol min-1 g-1) during I3C administration. These data suggest that the oral administration of c-AUCB displays antihypertensive effects in Ren-2 transgenic rats with inducible malignant hypertension via an improvement of renal function.

The present study was undertaken to evaluate the effects of chronic treatment with cis-4-[4-(3- adamantan-1-yl-ureido)cyclohexyl-oxy]benzoic acid (c-AUCB), a novel inhibitor of soluble epoxide hydrolase (sEH), which is responsible for the conversion of biologically active epoxyeicosatrienoic acids (EETs) to biologically inactive dihydroxyeicosatrienoic acids (DHETEs), on blood pressure (BP) and myocardial infarct size in male heterozygous Ren-2 transgenic rats (TGR) with established hypertension. Normotensive Hannover Sprague-Dawley (HanSD) rats served as controls. Myocardial ischemia was induced by coronary artery occlusion. Systolic BP was measured in conscious animals by tail-plethysmography. c-AUCB was administrated in drinking water. Renal and myocardial concentrations of EETs and DHETEs served as markers of internal production of epoxygenase metabolites. Chronic treatment with c-AUCB, which resulted in significant increases in the availability of biologically active epoxygenase metabolites in TGR – assessed as the ratio of EETs/DHETEs – was accompanied by a significant reduction in BP and significantly reduced infarct size in TGR as compared with untreated TGR. The cardioprotective action of c-AUCB treatment was completely prevented by acute administration of a selective EETs antagonist (14,15-epoxyeicosa5(Z)-enoic acid), supporting the notion that the improved cardiac ischemic tolerance conferred by sEH inhibition is mediated by EETs actions at the cellular level. These findings indicate that chronic inhibition of sEH exhibits antihypertensive and cardioprotective actions in this transgenic model of angiotensin II-dependent hypertension.

Objective In the present study, we compared the effects of treatment with the novel soluble epoxide hydrolase (sEH) inhibitor (c-AUCB) with those of the AT1 receptor antagonist losartan on blood pressure (BP), autoregulation of renal blood flow (RBF) and on glomerular filtration rate (GFR) and the pressure–natriuresis relationship in response to stepwise reduction in renal arterial pressure (RAP) in Cyp1a1-Ren-2 transgenic rats. Methods Hypertension was induced in Cyp1a1-Ren-2 rats through dietary administration for 11 days of the natural xenobiotic indole-3-carbinol (I3C) which activates the renin gene. Treatment with c-AUCB and losartan was started 48 h before initiating administration of the diet containing I3C. Rats were prepared for renal functional studies to evaluate in-vivo renal autoregulatory efficiency when RAP was gradually decreased by an aortic clamp. Results I3C administration resulted in the development of severe hypertension which was associated with markedly lower basal RBF and GFR and substantially impaired autoregulatory efficiency as well as a suppression of the pressure–natriuresis relationship when compared with noninduced rats. Treatment with c-AUCB significantly decreased BP, improved autoregulatory efficiency of RBF and GFR and the slope of pressure–natriuresis relationship. Treatment with losartan completely prevented the impaired autoregulation and pressure–natriuresis relationship as well as the development of hypertension in I3C-induced rats. Conclusion Our present findings indicate that chronic treatment with the sEH inhibitor c-AUCB substantially attenuates the development of malignant hypertension in I3C-induced rats likely via improvement of the renal autoregulatory efficiency and the pressure–natriuresis relationship.

Abstract-The aims of this study were to delineate the relative contribution of angiotensin II (ANG II) subtype 1A (AT 1A ) and 1B (AT 1B ) receptors to the development of two-kidney, one-clip (2K1C) Goldblatt hypertension in mice, to examine if increased nitric oxide synthase (NOS) activity counteracts the vasoconstrictor influences of ANG II in 2K1C hypertensive mice, and to determine the role of ANG II type 2 (AT 2 ) receptors in 2K1C hypertension in mice. AT 1A ANG II receptor knockout (AT 1A Ϫ/Ϫ) and wild-type (AT 1A ϩ/ϩ) mice underwent clipping of the right renal artery. Systolic blood pressure (SBP) was significantly lower in AT 1A Ϫ/Ϫ compared with AT 1A ϩ/ϩ mice, and neither clip placement nor AT 2 receptor blockade with PD 123319 (PD) altered SBP in AT 1A Ϫ/Ϫ mice. A significant and sustained rise in SBP from 119Ϯ5 to 163Ϯ6 mm Hg was observed in the 2K1C AT 1A ϩ/ϩ mice from day 10 to day 26. Chronic PD infusion did not alter the course of hypertension in 2K1C/AT 1A ϩ/ϩ. Acute PD infusion did not alter mean arterial Key Words: mice Ⅲ receptors, angiotensin II Ⅲ hypertension, renovascular Ⅲ nitric oxide synthase Ⅲ nitric oxide I t is well recognized that the renin-angiotensin system plays the pivotal role in the development and maintenance of two-kidney, one-clip (2K1C) Goldblatt hypertension. 1 Previous studies have shown that activation of angiotensin II (ANG II) type 1 (AT 1 ) receptors predominantly mediates the effect of ANG II on the renal vasculature and is largely responsible for the development of hypertension in ANG II-dependent models of hypertension. 2-4 However, two subtypes for AT 1 receptors have been identified in mouse and rat (AT 1A and AT 1B ). 5 It has been demonstrated that the AT 1A receptors are the predominant subtype in most tissues, with the exception of the adrenal cortex, pituitary gland, and glomerulus, where the AT 1B receptors are also highly expressed. 6,7 The critical role of AT 1A receptors in blood pressure (BP) regulation has been confirmed by the development of AT 1A receptor knockout mice (AT 1A Ϫ/Ϫ). The AT 1A Ϫ/Ϫ mice exhibit markedly lower BP and impaired ability for normal sodium handling by the kidney and urinary concentrating ability compared with their wild-type controls (AT 1A ϩ/ϩ). 8 -11 In contrast, the AT 1B receptor knockout mice (AT 1A Ϫ/Ϫ) exhibit no abnormal phenotype. 12 However, it has been shown that in the absence of AT 1A receptors, AT 1B receptors may partially replace the function of AT 1A receptors in BP regulation. 13 Moreover, it has been also demonstrated that when AT 1A receptors are absent, AT 1B receptors can play an important role in mediating ANG II effects in the renal vasculature. 14,15 Taken together, these results indicate that under certain conditions, AT 1B receptors partially compensate for the absence of AT 1A receptors. In view of this information, we hypothesized that activation of AT 1B might contribute to the development of 2K1C Goldblatt hypertension. Since the binding signatures of the AT 1A and AT 1B receptors are ident...

Plasma and kidney angiotensin II levels were lower in anaesthetized transgenic rats but, in contrast, were higher in decapitated transgenic rats when compared with Hannover Sprague-Dawley rats, suggesting that the kidney function of prehypertensive transgenic rats is under inappropriately high angiotensin II-dependent influence.