Influence of irbesartan and enalapril on changes of renal function associated with the established phase of l-NAME hypertension.

OBJECTIVE: Reversibility of the systemic and renal alterations induced by N(omega)-nitro-L-arginine-methyl ester(L-NAME) was assessed by treatment with irbesartan and enalapril (30 and 10 mg/kg per 24 h, respectively) alone or in combination. DESIGN: L-NAME (20 mg/kg per 24 h) was given to rats for 6 weeks and treatments were administered during the last 2 weeks. Glomerular filtration rate and renal plasma flow [GFR and RPF per g of kidney weight (KW)] were determined using the clearance technique. RESULTS: Arterial pressure was similarly reduced by treatments. GFR was lower in L-NAME-treated rats than in controls (552 +/- 52 versus 1106 +/- 78 microl/min per g KW), whereas RPF was reduced to a larger extent, thus resulting in an increase in filtration fraction. GFR was normalized by irbesartan but not enalapril or the combination (1042 +/- 50, 790 +/- 79 and 725 +/- 38 microl/min per g KW, respectively). RPF returned to normal and filtration fraction fell markedly with the combination. All treatments reduced the lesions of preglomerular vessels and reversed L-NAME-induced albuminuria and cardiovascular hypertrophy. At a dose of 3 mg/kg per 24 h, irbesartan only reduced the lesions of the afferent arteriole. CONCLUSIONS: Through its effects on AT1 receptors, angiotensin II may play an important role in the maintenance of L-NAME hypertension and associated alterations. The lower GFR and filtration fraction observed with enalapril in the presence of irbesartan suggests the intervention of non-angiotensin II-mediated mechanism, and at the postglomerular level, in the effect of angiotensin-converting enzyme (ACE) inhibitors.

Endothelin blockade in angiotensin II hypertension: prevention and treatment studies in the rat.

1. The participation of endothelin (ET) in the development and maintenance of hypertension induced by angiotensin (Ang) II was assessed using the non-specific ET receptor antagonist bosentan (30 mg/kg per day). 2. In the prevention study, bosentan was given 24 h prior to and during the 17 day period of AngII infusion (200 ng/kg per min, s.c., osmotic pump), whereas in the treatment study, bosentan was administered from day 10 to day 17. Tail-cuff pressure (TCP) was measured before and on days 10 and 17 of AngII infusion. At the end of studies, heart weight index was calculated as the ratio of heart to bodyweight (HWI) and the wall thickness of the carotid artery (perfusion/fixation at 120 mmHg) was measured. Tail-cuff pressure increased from 129 +/- 3 to 179 +/- 7 and 189 +/- 9 mmHg on days 10 and 17 of AngII infusion, respectively. 3. Final TCP was markedly lowered in rats pretreated with bosentan, whereas TCP remained comparable with untreated hypertensive rats when bosentan was given from day 10 of AngII infusion (177 +/- 9 mmHg). 4. The increase in cardiac mass associated with AngII hypertension was similarly attenuated in the two groups receiving bosentan. 5. The HWI was 3.49 +/- 0.12 mg/g in untreated hypertensive rats and 3.18 +/- 0.08 and 3.11 +/- 0.09 mg/g in rats pretreated with bosentan and those receiving the antagonist from day 10. 6. The increase in carotid wall thickness induced by AngII was prevented, but not reversed, by bosentan. 7. These results support the hypothesis that endogenous ET participates only in the initial phase of AngII hypertension. In addition, the beneficial effect of bosentan of cardiac mass but not on arterial wall thickness is in favour of a role of ET as a local mediator of the cardiac hypertrophic effect of AngII, independently of the level of blood pressure and duration of hypertension.

[Cardiac and vascular hypertrophy in hypertension due to angiotensin II. Effect of losartan and bosentan]. / Hypertrophie cardiaque et vasculaire dans l'hypertension à l'angiotensine II. Influence du losartan et du bosentan.

We assessed the role of angiotensin (Ang) II type 1 receptor (AT1) and endothelin type A and B (ETA & ETB) receptor in cardiovascular hypertrophy associated with angiotensin II-induced hypertension (200 ng/kg.min s.c. for 10 or 17 days). Antagonism of AT1 receptors was obtained by oral administration of losartan (10 or 30 mg/kg.day) and blockade of ETA and ETB receptors was obtained by oral administration of bosentan (30 mg/kg.day). Losartan and bosentan were administered 24 h before and during the 10 days of angiotensin II (prevention) or they were given after the development of hypertension i.e. from day 10 to 17 of angiotensin II (treatment). Tail-cuff pressure (TCP) was measured before and at the end of the period of administration of antagonists. At the end of experiments, cross sectional area (CSA, mm2) of the carotid was measured after perfusion and fixation at 100 mmHg and heart weight index (HWI, mg/g body weight) was determined. Results are mean +/- SEM. [table: see text] In addition to its blood pressure lowering effect, both doses of losartan prevented and reversed the cardiovascular hypertrophy induced by angiotensin II. Similarly, bosentan prevented and reversed the effect of angiotensin II on cardiovascular structure independently of arterial pressure. These results indicate that the effect of angiotensin II on blood pressure, heart and carotid structure is exclusively mediated by AT1 receptors. The influence of bosentan suggests that endothelin plays an important role in local action of angiotensin II independently of blood pressure level.

Chronic bradykinin infusion and receptor blockade in angiotensin II hypertension in rats.

The influence of endogenous bradykinin(BK) on the control of arterial pressure and the development of cardiac hypertrophy was assessed in chronically angiotensin II(Ang II)-infused rats (200 ng. kg-1. min-1) through the effects of concomitant infusion of 3 doses of BK (15 ng. kg-1. d-1, 100 ng. kg-1. d-1 and 100 ng. kg-1. min-1 ie, 144 000 ng. kg-1. d-1) or BK-blockade by Hoe140 (300 microg. kg-1. d-1) for 10 days. In Ang II-infused rats, tail-cuff pressure increased from 124+/-3 to 174+/-6 mm Hg (P<0.001). The pressor effect of Ang II was not affected by simultaneous infusion of BK or Hoe140. At the end of the experiments, cardiac mass was higher in rats infused with Ang II alone (3.56+/-0.10 versus 2.89+/-0.05 mg/g in untreated controls, P<0.01) and the development of cardiac hypertrophy was not modified by administration of the 3 doses of BK or Hoe140. In addition, the fall in cardiac output associated with Ang II was prevented only by the moderate and high doses of BK, mainly through an increase in stroke volume and a decrease in total peripheral resistance. In the same way, the renal vasoconstrictor effect of Ang II was abolished by the medium and high dose of BK. Hoe140 did not affect cardiac output or renal blood flow in this model. No influence of BK or Hoe140 on the increase in albuminuria induced by Ang II was detected. In conclusion, exogenous BK may oppose the effect of Ang II on vascular tone, but it cannot prevent hypertension and target-organ damage associated with this experimental model of hypertension, even at a very high dose.

[Effect of chronic bradykinin infusion on angiotensin II hypertension in rats]. / Effet de l'administration chronique de bradykinine dans l'hypertension induite par l'angiotensine II chez le rat.

In previous studies, we demonstrated that in ANG II-treated rats, prevention of cardiac hypertrophy (CH) by enalapril was blunted by bradykinin (BK) blockade by Hoe140. The putative role of BK was assessed by chronic exogenous BK infusion and in 46 male Sprague-Dawley rats infused with ANG II. ANG II (200 ng/kg/min) alone and associated with BK at low (BKlow, 15 ng/kg/day), mid (BKmid, 100 ng/kg/day) and high doses (BKhigh, 100 ng/kg/min) were delivered by Alzet osmotic pumps for 10 days and compared to control animals (Veh). Values of systolic arterial pressure (SAP, mmHg) in conscious rats and heart weight (HW, mg/g bw) at the end of the study are reported below. Results were submitted to ANOVA and are expressed as mean +/- SEM.

[Renal alterations in L-NAME hypertension: influence of losartan and bosentan]. / Altérations rénales dans l'hypertension artérielle au L-NAME: influence du losartan et du bosentan.

The influence of losartan and the endothelin A and B receptor antagonist, bosentan was assessed on the alterations in renal hemodynamic and function as well as urinary albumin excretion (taken as an index of renal lesions) associated with L-NAME hypertension. L-NAME was given for 4 weeks (20 mg/100 mL in the drinking (fluid) followed by a 2-week period of concomitant treatment with L-NAME and losartan or bosentan (30 and 30 mg/kg, gavage). A group of rats received L-NAME without additional treatment and a group of rats were not given L-NAME and served as normotensive controls. Systolic arterial pressure (SAP) was measured before L-NAME, and before and every 5 days of losartan or bosentan treatment period. Urinary excretion of albumin (UAlb) was determined before and at the end of treatment period. Under anesthesia, glomerular filtration rate (GFR) and renal plasma flow (RPF) were estimated by the clearance method and the filtration fraction was calculated [FF = 100* (GFR/RPF)].

Prevention of the cardiovascular and renal effects of angiotensin II by endothelin blockade.

Angiotensin II (Ang II) stimulates the release and gene expression of endothelin-1 in isolated vascular smooth muscle cells. In 47 Sprague-Dawley rats, we assessed the influence of concomitant treatment by the mixed ET(A)/ET(B) endothelin receptor antagonist bosentan (30 mg/kg per day, gavage) on the effect of a 10-day infusion of Ang II (200 ng/kg per minute, SC, osmotic pump) on arterial pressure, renal hemodynamics (microsphere method), albuminuria, cardiac weight, and carotid structure. Ang II increased systolic arterial pressure (SAP) by 49+/-7 mm Hg. Although bosentan alone did not affect SAP, the development of Ang II-induced hypertension was entirely prevented by the endothelin antagonist. In addition, the reduction in renal blood flow induced by Ang II (4.9+/-0.3 versus 7.4+/-0.2 mL x min-1 x g-1 in control rats) was prevented by concomitant administration of bosentan (8.8+/-0.8 mL x min-1 x g-1). The marked increase in albuminuria observed in rats infused with Ang II (2524+/-961 versus 91+/-6 microg/24 h in control rats) was prevented by bosentan. Similarly, bosentan abolished the increase in heart weight index (from 2.96+/-0.03 to 3.41+/-0.08 mg/g body weight) and carotid media thickness (from 73+/-14 to 108+/-6 microm) induced by Ang II infusion. Of interest, the dipsogenic action of Ang II was not influenced by bosentan. In conclusion, endogenous endothelin contributes to the cardiovascular and renal effects of Ang II.

Bosentan prevents preglomerular alterations during angiotensin II hypertension.

The present study was performed to characterize structurofunctional alterations of preglomerular vessels during chronic angiotensin II (Ang II)-induced hypertension (Ang II group: 400 ng x kg[-1] x min[-1], 10 days) and to assess the role of endothelin-1 in rats receiving Ang II and the mixed receptor antagonist bosentan (Ang II+B group: 30 mg x kg[-1] x d[-1], 10 days). Systolic blood pressure rose by 56+/-3 and 54+/-6 mm Hg in Ang II and Ang II+B rats, respectively. Albuminuria increased similarly in both Ang II-treated groups, reflecting glomerular barrier dysfunction. Preglomerular vessels were isolated after HCI maceration and comprised arcuate arteries and their branches, interlobular arteries (ILA), and afferent arterioles (AA). In the Ang II group, focal vascular lesions affected 36+/-6%, 20+/-5%, and 4+/-1% of arcuate arterial branches, ILA, and AA, respectively. They were characterized by 74% increased media thickness and accumulation of Sudan black-positive (SB+) lipid droplets, and media cell proliferation was documented through immunohistochemistry. The occurrence of SB+ lesions was strikingly reduced with bosentan. Autoregulatory responses (AR) were assessed along ILA and AA with the use of blood-perfused juxtamedullary nephron preparations. AR were elicited by raising blood perfusion pressure from 60 to 160 mm Hg and quantified through videomicroscopy as pressure-induced constrictions. AR were inhibited in Ang II-treated rats along ILA and AA; Ang II-induced AR changes were prevented by bosentan. Maximal relaxation induced by Mn2+ revealed equal basal tone in Ang II-treated, Ang II+B-treated, and control vessels. Chronic Ang II-induced hypertension is therefore associated with the development of SB+ lesions and selective impairment of AR in juxtamedullary nephrons. Endothelin-1 likely mediates the structurofunctional alterations of preglomerular vasculature during Ang II hypertension.

[Bosentan attenuates the hypertensive effect of angiotensin II in rats]. / Le bosentan atténue l'effet hypertenseur de l'angiotensine II chez le rat.

The influence of nonspecific blockade of endothelin receptors by bosentan (30 mg/kg per day, gavage) was assessed on hypertension induced by infusion of angiotensin II (AngII 200 ng/kg/min sc for 10 days) in rats. Tail-cuff pressure was measured before and every second day of AngII-infusion period. At the end of experiments, mean arterial pressure (MAP, mmHg), cardiac output (CO ml/min/kg body weight) and renal blood flow (RBF ml/min/g kidney weight) were determined (microspheres technique) in conscious rats, and total peripheral and renal vascular resistances were calculated (TPR = MAP/CO and RVR = MAP/RBF). [table: see text] Tail-cuff pressure increased from 126 +/- 4 to 164 +/- 8 mmHg in rats infused with AngII alone whereas it did not change (basal: 132 +/- 3 and final: 135 +/- 3 mmHg: p = NS) when bosentan was coadministered with AngII. At the end of study in conscious rats, the AngII-induced rise in MAP was accompanied by a reduction in CO and RBF and a marked increased in TPR and RVR. In AngII-perfused rats, CO, RBF, TPR and RVR were restored by bosentan to values observed in untreated rats. These results indicate that blockade of endothelin A and B receptors by bosentan prevents the development of AngII-induced hypertension through attenuation of the effect of AngII on vascular tone and suggest that endothelin is an important mediator of the vasoconstrictor action of angiotensin II in rats.

Cardioprotective effect of enalapril in renovascular and angiotensin II hypertension.

The influence of chronic treatment with enalapril or losartan (10 or 30 mg/kg/24h, respectively) on cardiac mass was evaluated in one-kidney, one clip (1K-1C) hypertensive rats submitted to sodium restriction 3 weeks after clipping and in rats infused for 10 days with angiotensin II (ANGII: 200 ng/kg/min). In 1K-1C hypertension, cardiac mass and arterial pressure were reduced to a similar extent by enalapril and losartan. In ANGII hypertension, enalapril and losartan blunted the increase in cardiac mass whereas losartan but not enalapril prevented the development of hypertension. The cardioprotective effect of enalapril was attenuated by concomitant blockade of bradykinin receptors (Hoe140: 300 micrograms/kg/24h) in both models. The beneficial influence of enalapril on cardiac mass appears to be independent of its effect on blood pressure and ANGII generation and seems partly mediated by endogenous bradykinin in these high ANGII models of hypertension.

Preglomerular sudanophilia in L-NAME hypertensive rats: involvement of endothelin.

To characterize alterations of renal vessels occurring during systemic hypertension elicited in rats by 5, 10, and 25 days of treatment by the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME)(20 mg/kg daily), preglomerular vasculatures, consisting of arcuate arteries and their branches, interlobular arteries, and afferent arterioles, were isolated by HCl maceration. Blockade of nitric oxide synthase significantly increased tail-cuff systolic blood pressure by 21 +/- 2% and 42 +/- 3% after 5 and 25 days, respectively. Medias of hypertensive arcuate arterial branches and interlobular arteries but not of afferent arterioles had focal deposits of Sudan black-positive lipid droplets. At 25 days, vessel wall thickness increased by 72 +/- 6% along the sudanophilic areas. Immunostaining of sudanophilic lesions with a panel of antibodies unveiled medial cell proliferation, macrophage invasion, immunoreactive vascular cell adhesion molecule-1, and low-density lipoprotein. The frequency of sudanophilic lesions increased with time to affect 26 +/- 2% and 36 +/- 3% of arcuate arterial branches and interlobular arteries, respectively, at 25 days. Hypertensive L-NAME-treated rats developed glomerular injury probed by albuminuria and glomerular immunostaining for alpha-smooth muscle actin. Administration of the nonselective endothelin antagonist bosentan (30 mg/kg daily) blunted the development of sudanophilic lesions during L-NAME treatment without affecting arterial hypertension or degree of glomerular injury. Therefore, L-NAME hypertension leads to rapid development of focal, inflammatory, proliferative, and sudanophilic lesions along preglomerular vessels, suggesting atherosclerosis-like processes. Furthermore, endothelin is a likely mediator in the development of these lesions.

Chronic kinin blockade and effect of ramipril in renal adaptation to sodium restriction.

The contribution of endogenous kinins to impairment in renal adaptation to a 6-day period of dietary sodium withdrawal associated with treatment with ramipril (5 mg/kg per day) and losartan (30 mg/kg per day) was evaluated by use of concomitant chronic administration of the bradykinin B2-receptor antagonist Hoe 140 (150 or 300 micrograms/kg per day via subcutaneous osmotic pump). A similar level of higher cumulative sodium excretion was observed in ramipril- and losartan-treated rats compared with untreated animals, and the effect of ramipril was not affected by Hoe 140. Similarly, the fall in arterial pressure and the renal vasodilatation associated with ramipril and losartan were not modified by Hoe 140. Glomerular filtration rate (785 +/- 73 microL/min per g KW in untreated sodium-depleted rats) decreased to a larger extent in ramipril-treated rats compared with losartan-treated rats (371 +/- 78 and 550 +/- 55 microL/min per g KW, respectively). Hoe 140 markedly prevented the alteration in glomerular filtration rate associated with ramipril, thus resulting in a final glomerular filtration rate (543 +/- 41 microL/min per g KW) similar to that observed with losartan. These findings demonstrate that despite a lack of influence on arterial pressure and sodium balance, accumulation of kinins markedly contributes to deterioration of the glomerular filtration rate induced by ramipril in sodium-depleted rats.

[Sodium intake and angiotensin in hypertension induced by chronic NO synthase inhibition in the rat]. / Apport sodé et angiotensine dans l'hypertension induite par inhibition chronique de la NO syntéthase chez le rat.

The influence of dietary sodium restriction and angiotensin II blockade on hypertension induced by a 25-day period of administration of the inhibitor of nitric oxide synthesis NG-nitro-L-arginine methyl ester (L-NAME: 10 mg/kg twice daily by gavage) was assessed in Wistar rats fed a normal or low sodium diet. In addition, the angiotension II receptor blocker, losartan (30 mg/kg once daily by gavage) was administered prior to and during L-NAME in rats fed the normal sodium diet. Results expressed as mean +/- ESM are presented in the following table: [table: see text] At the end of studies, conscious systolic arterial pressure increased similarly in L-NAME-treated groups maintained on NS or LS intake. Moreover, a 25% reduction in cardiac output due to a decrease in stroke volume was observed in both groups. A slight but significant cardiac hypertrophic response was observed in hypertensive rats irrespective of sodium intake. Losartan totally prevented the development of hypertension as well as the decrease in cardiac output and the cardiac hypertrophy associated with L-NAME treatment in rats on normal sodium intake. In conclusion, hypertension resulting from chronic blockade of nitric oxide synthesis was not affected by dietary sodium restriction. A crucial role for the renin-angiotensin system was demonstrated in this new model of hypertension.

Sodium and angiotensin in hypertension induced by long-term nitric oxide blockade.

The influence of dietary sodium restriction and angiotensin II blockade on hypertension induced by a 25-day period of administration of the inhibitor of nitric oxide synthesis NG-nitro-L-arginine-methyl ester (10 mg/kg twice daily by gavage) was assessed in Wistar rats fed a normal or low sodium diet. In addition, the angiotensin II receptor blocker losartan (30 mg/kg once daily by gavage) was administered before and during NG-nitro-L-arginine-methyl ester in rats fed the normal sodium diet. At the end of the studies, conscious systolic arterial pressure increased similarly in NG-nitro-L-arginine-methyl ester-treated groups maintained on normal or low sodium intake. Moreover, a 25% reduction in cardiac output due to a decrease in stroke volume was observed in both groups. A slight but significant cardiac hypertrophic response was observed in hypertensive rats irrespective of sodium intake. At the completion of studies, plasma renin activity was similar to corresponding controls in the hypertensive groups on normal or low sodium intake. Losartan totally prevented the development of hypertension as well as the decrease in stroke volume and cardiac hypertrophy associated with NG-nitro-L-arginine-methyl ester treatment in rats on normal sodium intake. In conclusion, hypertension resulting from long-term blockade of nitric oxide synthesis was not affected by dietary sodium restriction. A crucial role for the renin-angiotensin system was demonstrated in this new model of hypertension.