Renal effects of omapatrilat and captopril in salt-loaded, nitric oxide-deficient rats

Inhibition of nitric oxide synthases causes systemic hypertension and renal injury in rats. Our objective was to examine whether omapatrilat, a vasopeptidase inhibitor that inhibits both angiotensin-converting enzyme (ACE) and neutral endopeptidase, could induce better regression of renal injury than ACE inhibitor alone. Ten groups of rats were studied. They were fed either a normal (0.8% NaCl) or a high (4% NaCl) sodium diet. Eight of these groups received NG-nitro-L-arginine methyl ester (L-NAME, 20 mg x kg(-1) x d(-1)) in their drinking water. After 4 weeks, 1 group on each diet was killed and considered the L-NAME group, whereas the others received L-NAME alone, captopril (200 mg x kg(-1) x d(-1)) plus L-NAME, or omapatrilat (80 mg x kg(-1) x d(-1)) plus L-NAME for 4 additional weeks. In rats receiving L-NAME alone for 8 weeks, the mortality rate was approximately 90%, irrespective of the diet. In contrast, all rats survived in the captopril and the omapatrilat groups. In rats fed a normal-sodium diet, captopril and omapatrilat normalized systolic blood pressure and induced a complete regression of renal injury. Creatinine clearance and proteinuria were also normalized. In the high-sodium-diet groups, both treatments were less efficient: blood pressure remained elevated, and the regression of renal fibrosis was only partial. Although proteinuria decreased significantly with captopril or omapatrilat, creatinine clearance remained lower than in the controls. These results demonstrate that, in nitric oxide-deficient rats fed a normal-sodium diet, ACE and vasopeptidase inhibitors exhibit a marked renoprotective effect, whereas these treatments are less efficient in rats fed a high-sodium diet.     

Arterial function in nitric oxide-deficient hypertension: influence of long-term angiotensin II receptor antagonism.

OBJECTIVE: Since the effects of angiotensin II receptor antagonism on arterial function in nitric oxide (NO)-deficient hypertension are unknown, we investigated the influence of losartan therapy (20 mg kg-1 day-1) on the control of arterial tone in NG-nitro-L-arginine methyl ester (L-NAME; 20 mg kg-1 day-1)-induced hypertension. METHODS: Forty Wistar rats were divided into four groups: control, losartan, L-NAME, and losartan + L-NAME. The responses of isolated mesenteric arterial rings were examined in standard organ chambers after 8 treatment weeks. RESULTS: Losartan therapy prevented the development of L-NAME-induced hypertension and the associated impairments of endothelium-independent relaxations to nitroprusside, isoprenaline, and cromakalim, vasodilators acting via the formation of NO, activation of beta-adrenoceptors and opening of K+ channels, respectively. In addition, endothelium-dependent relaxations of noradrenaline-precontracted rings to acetylcholine during NO synthase inhibition in vitro were decreased in L-NAME rats, and clearly improved by losartan therapy. The inhibition of cyclooxygenase by diclofenac improved the responses to acetylcholine more effectively in L-NAME than losartan + L-NAME rats, but the relaxations remained decreased in L-NAME rats when compared with losartan + L-NAME rats. When hyperpolarization of smooth muscle was prevented by precontractions induced by high concentration of KCl, the responses to acetylcholine during combined NO synthase and cyclooxygenase inhibition were similar and almost abolished in all groups. Furthermore, superoxide dismutase, a scavenger of superoxide anions, enhanced the acetylcholine-induced relaxations more effectively in L-NAME than losartan + L-NAME rats, although plasma antioxidant capacity was similar in all study groups. CONCLUSION: Chronic L-NAME-induced hypertension was associated with attenuated arterial relaxation via endothelium-dependent and -independent mechanisms, both of which were improved by the losartan treatment. The mechanisms whereby losartan enhanced arterial relaxation in this model of experimental hypertension may have included enhanced hyperpolarization and increased sensitivity to NO in smooth muscle, and decreased vascular production of superoxide and vasoconstrictor prostanoids.     

Decreased endothelium-dependent NO-cGMP vascular relaxation and hypertension in growth-restricted rats on a high-salt diet

Low birth weight caused by placental insufficiency increases the risk of hypertension in young adults, particularly while ingesting a high-salt diet; however, the vascular mechanisms involved are unclear. We tested whether intrauterine fetal growth restriction results in salt-sensitive offspring that exhibit impaired endothelium-dependent relaxation, enhanced vascular contraction, and hypertension during high-salt diet feeding. Male offspring of control pregnant rats and pregnant rats with reduced uterine perfusion pressure (intrauterine growth restricted [IUGR]) were fed either a normal-sodium (NS, 1%) or a high-sodium (HS, 8%) diet. Body weight was less in IUGR/NS and IUGR/HS than in NS and HS rats. Arterial pressure was greater in IUGR/NS (144+/-4 mm|Hg) than in NS (131+/-3 mm|Hg) rats and far greater in IUGR/HS (171+/-12 mm|Hg) than in HS (129+/-2 mm|Hg) rats. In isolated, endothelium-intact aortic strips, phenylephrine (Phe, 10(-5) mol/L) caused an increase in active stress that was greater in IUGR/NS (13.9+/-0.9 N/m2) than in NS (8.5+/-0.6 N/m2) animals and far greater in IUGR/HS (18.2+/-1.2 N/m2) than in HS (9.4+/-0.8x10(4) N/m2) rats. Acetylcholine caused relaxation of the Phe-mediated contraction and induced vascular nitrite/nitrate production that was less in IUGR/NS than in NS animals and far less in IUGR/HS than in HS rats. N(G)-nitro-L-arginine methyl ester, which inhibits nitric oxide (NO) synthase, or ODQ, which inhibits cGMP production in smooth muscle, inhibited acetylcholine relaxations and enhanced Phe contractions in NS and HS rats but not in IUGR/NS or IUGR/HS rats. Endothelium removal enhanced Phe-induced stress in NS and HS rats but not in IUGR/NS or IUGR/HS rats. Thus, endothelium-dependent relaxation via the NO-cGMP pathway is inhibited in systemic vessels of IUGR rats, particularly during intake of an HS diet. This might explain the increased vasoconstriction and arterial pressure in low-birth-weight offspring during ingestion of an HS diet.     

Contractility and endothelium-dependent relaxation of resistance vessels in polycystic kidney disease rats

Hypertension and vascular disease are common complications in autosomal-dominant polycystic kidney disease (ADPKD). The role of changes in morphology and reactivity of resistance vessels in this disease have not previously been studied. Mesenteric resistance arteries were dissected from 8- to 14-week-old heterozygous Han:SPRD polycystic kidney disease (PKD) rats, homozygous normal Han:SPRD littermates (HSPRD) and Sprague-Dawley rats (SD). The morphology, noradrenaline (NA) contractility, endothelium-dependent acetylcholine (ACh) relaxation before and after incubation with L(G)-nitro-L-arginine methyl ester (L-NAME), and endothelium-independent 3-morphollino-sydnonimine (SIN-1) relaxation were studied with the Mulvany-Halpern myograph. Blood pressure and morphology of vessels were the same in all groups of rats, apart from a slightly higher media/lumen ratio in heterozygous PKD rats (p < 0.05). Active wall tension and contractile sensitivity to NA were higher in both heterozygous PKD rats and HSPRD than SD rats (p < 0. 05). The maximum endothelium-dependent relaxation rate was markedly decreased in heterozygous PKD (19 +/- 9%) and HSPRD (34 +/- 12%) compared to SD rats (75 +/- 11%) (p < 0.05). After incubation with L-NAME, ACh-induced relaxation was significantly attenuated in SD rats, less attenuated in HSPRD, and not significantly changed in heterozygous PKD rats. SIN-1-induced endothelium-independent relaxation was similar in all three groups. In conclusion, hyperreactivity to NA and impaired endothelium-dependent relaxation were present in resistance vessels from Han:SPRD rats, especially in animals with PKD. These abnormalities in resistance vessels from PKD rats may be important for the development of hypertension and vascular disease.     

Haemodynamic effects of dual blockade of the renin-angiotensin system in spontaneously hypertensive rats: influence of salt

OBJECTIVE: To elucidate the mechanisms responsible for the adverse renal effects induced by dual blockade of the renin-angiotensin system (RAS) and the role of salt therein. METHODS: The effects of enalapril, losartan and their combination on blood pressure, renal haemodynamics, renal function and RAS were investigated over a wide range of doses in spontaneously hypertensive rats fed either a low-sodium or a high-sodium diet. RESULTS: In rats fed the low-sodium diet, the losartan-enalapril combination induced the same dose-dependent haemodynamic and hormonal changes as did three- to 10-fold greater doses of enalapril or losartan alone. When a strong decrease (> 50%) in blood pressure was achieved (with 10 mg/kg enalapril plus 10 mg/kg losartan, 100 mg/kg enalapril or 100 mg/kg losartan), a massive renal vasoplegia occurred and renal insufficiency developed. In addition, because of the huge release of renin, angiotensinogen concentrations were reduced, leading to a decrease in intrarenal angiotensins. In rats fed the high-sodium diet, those treated with the enalapril 30 mg/kg plus losartan 30 mg/kg combination, despite complete functional RAS blockade, exhibited smaller decreases in blood pressure and renal resistance, lesser release of renin and angiotensinogen consumption, and a normal renal function. These effects were similar to those produced by 100 mg/kg of enalapril or losartan in rats fed the high-salt diet, or by 10 mg/kg of enalapril or of losartan in rats fed the low-salt diet. CONCLUSIONS: Dual RAS blockade could be either beneficial, when sodium intake is unrestricted, or dangerous, when sodium intake is restricted.     

Chronic bosentan treatment improves renal artery vascular function in diabetes

OBJECTIVE: Endothelin-1 (ET-1) has been suggested to play an important role in the pathogenesis of diabetes-induced vascular complications. The primary purpose of the present study was to examine the potential beneficial effects of chronic ET receptor blockade (with bosentan) on vascular function in renal arteries from streptozotocin (STZ)-induced diabetic rats. DESIGN: Wistar rats were divided into four groups: control (C), control bosentan-treated (CB), diabetic (D) and diabetic bosentan-treated (DB). Following 10 weeks of bosentan treatment, vascular responses to norepinephrine (NE), ET-1, acetylcholine (ACh) were determined in vascular segments of renal arteries, both with and without the endothelium denuded, according to the following protocol: (1) a cumulative dose-response curve (DRC) to NE in the absence and presence of the nitric oxide synthase (NOS) inhibitor L-NAME (2) cumulative DRC to ET-1 and (3) cumulative DRC to ACh in precontracted arteries. In addition, plasma ET-1 was assayed and ET-1-like immunoreactivity was determined in vascular tissues by immunohistochemistry. RESULTS: The maximum contractile responses to NE and ET-1 were markedly exaggerated in endothelium-intact renal arteries from untreated D rats while ACh responses were preserved. Arteries denuded of endothelium did not exhibit exaggerated responses to NE or ET-1. L-NAME treatment did not affect responses to NE in arteries with or without endothelium. Strikingly, responses to NE and ET-1 (in arteries with endothelium) were completely normalized following long-term bosentan treatment. In addition, plasma ET-1 levels did not differ between C and D groups. However, renal arteries isolated from the D group exhibited increased ET-1-like immunoreactivity (local ET-1 content). CONCLUSION: These data uncover, for the first time, beneficial effects of mixed ETA/ETB receptor blockade on renal artery vascular function in diabetes. Alterations in the production and/or action of ET-1 may have important implications in the development of vascular dysfunction in experimental diabetes.     

Relationship between hypercholesterolaemia, endothelial dysfunction and hypertension.

OBJECTIVES: We have previously shown that in the rat a diet high in cholesterol and deficient in vitamin E and selenium results in hypercholesterolaemia and increased lipid oxidation. We utilized this model to determine whether rats given this diet develop impaired endothelium-dependent relaxation mediated by nitric oxide (NO) in mesenteric and in renal vessels. In addition, we tested whether the impairment is due to (i) decreased endothelial NO synthase activity, (ii) increased NO inactivation and/or (iii) increased production of the endothelium-derived constricting factors thromboxane A2/prostaglandin H2 and endothelin-1. We also investigated whether endothelial dysfunction induced by dyslipidaemia increases the sensitivity for the development of hypertension in response to high dietary salt. METHODS: Male Dahl salt-sensitive (DSS) rats were divided into three groups and received a standard diet (control group), a high (4%) cholesterol diet (HChol), or a high cholesterol diet deficient in the anti-oxidants vitamin E and selenium (HChol-Def). The NaCl content of these diets was 0.5%. After 18 weeks we studied endothelium-dependent relaxation in response to acetylcholine (ACh) in aortas and in isolated perfused preparations of mesenteric arteries and kidneys. In some experiments, ifetroban, a thromboxane A2/prostaglandin H2 receptor antagonist, was added to the organ bath or the perfusion buffer. Vascular responses to endothelin-1 as well as to BQ-123, an endothelin A receptor blocker, were studied in the isolated perfused kidneys. In addition, two extra groups of rats were fed a diet high in sodium chloride (2%): one of the groups received the normal cholesterol diet whereas the other group received the diet high in cholesterol and deficient in vitamin E and selenium. RESULTS: Compared to normocholesterolemic rats, responses to ACh were significantly impaired in aortas, mesenteric arteries and kidneys of HChol-Def rats (P < 0.01). Endothelial NO synthase activity (conversion of [14C]L-arginine to [14C]L-citrulline) was similar in aortas of control, HChol and HChol-Def rats; thus suggesting that impaired endothelium-dependent relaxation in the HChol-Def rats was not due to decreased cNOS catalytic activity. Ifetroban improved the impaired endothelium-dependent relaxation in mesenteric vessels, but not in aortas and kidneys. Endothelin-1 (ET-1: 10(-13)-10(-11) mol/l) elicited NO-mediated relaxations in kidneys of control rats but not in kidneys of HChol-Def; blockade of ET-1 with BQ-123, an ET(A) receptor blocker, did not improve NO-mediated relaxation of HChol-Def. Despite impaired endothelium-dependent relaxation in renal and mesenteric vessels, HChol-Def DSS rats failed to develop hypertension (systolic blood pressure 144 +/- 1 in control and 150 +/- 2 mmHg in HChol-Def) but manifested a significant increase in sensitivity to the pressor effects of a high (2% NaCl) dietary salt content during the initial 10 weeks of the study, although the final blood pressure at 18 weeks was similar in both groups. CONCLUSION: These studies support the notion that (i) products of lipid oxidation may reduce NO bioactivity without affecting endothelial NO synthase mass or catalytic activity, (ii) the mechanisms involved in the endothelial dysfunction induced by hypercholesterolaemia and oxidized lipids may differ among vascular beds, and (iii) decreased NO bioavailability does not necessarily result in systemic hypertension, but it may enhance the sensitivity to the hypertensinogenic effect of dietary salt.     

Systemic and renal effect of chronic omapatrilat in sodium-restricted, one-kidney, one-clip hypertensive rats

OBJECTIVE: The systemic and renal effect of omapatrilat was evaluated and compared with that of enalapril (30 and 10 mg/kg per day) in sodium-depleted, one-kidney, one-clip hypertensive rats. Participation of kinins was assessed by concomitant infusion of Hoe140 (300 microg/kg per day). DESIGN: Four weeks after clipping and uninephrectomy, dietary sodium was withdrawn for 2 weeks and rats were treated during the last 6 days of the study. METHODS: Tail-cuff pressure and sodium excretion were determined in conscious rats. Glomerular filtration rate (GFR) and renal plasma flow (RPF) were determined in anesthetized rats using clearance methods. The heart weight index was calculated. RESULTS: Omapatrilat was as effective as enalapril in reducing arterial pressure, and Hoe140 had no influence. Natriuresis increased to a similar extent with omapatrilat and enalapril. Hoe140 prevented the sodium loss only in enalapril-treated rats. Compared with untreated rats, GFR was reduced to a lesser extent by omapatrilat than enalapril (694 +/- 93 and 364 +/- 40 versus 848 +/- 43 microl/min per g kidney weight). Hoe140 had no influence on GFR in omapatrilat-treated animals but attenuated the reduction of GFR in enalapril-treated rats (662 +/- 22 and 543 +/- 62 microl/min per g kidney weight). Since RPF was not significantly affected, reduction of the filtration fraction was more marked in enalapril- than omapatrilat-treated rats (60 and 28%, respectively). Heart weight index was lower in omapatrilat-treated rats than in untreated or enalapril-treated rats. Hoe140 failed to significantly obliterate the antihypertrophic effect of omapatrilat. CONCLUSION: These results suggest that accumulation of natriuretic peptides due to neutral endopeptidase inhibition participated in the antihypertrophic effect of omapatrilat and tended to counteract the deleterious effect of ACE inhibition on renal function.     

Comparison of angiotensin-converting enzyme (ACE), neutral endopeptidase (NEP) and dual ACE/NEP inhibition on blood pressure and resistance arteries of deoxycorticosterone acetate-salt hypertensive rats

OBJECTIVES : Omapatrilat, an inhibitor of neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE), is an effective antihypertensive agent. Here, we studied the relative roles of NEP and ACE inhibition and their effect on resistance artery structure and function of deoxycorticosterone acetate (DOCA)-salt hypertensive rats. METHODS : Omapatrilat (40 mg/kg per day), the NEP inhibitor CGS 25462 (CGS, 100 mg/kg per day) and the ACE inhibitor enalapril (10 mg/kg per day), were given for 3 weeks to DOCA-salt hypertensive rats. Effects on small mesenteric resistance arteries were studied on a pressurized myograph. Collagen deposition was evaluated by confocal microscopy. RESULTS : Systolic blood pressure of DOCA-salt rats was significantly reduced (P < 0.05) by omapatrilat and CGS. Omapatrilat and CGS treatment increased lumen diameter and decreased media width and media/lumen ratio of small arteries of DOCA-salt rats (P < 0.05). Small artery relaxation responses to acetylcholine improved under omapatrilat or CGS treatment. The stress-strain curve shifted leftward in mesenteric arteries from DOCA-salt rats compared to control rats. Omapatrilat or CGS treatment resulted in a rightward shift, which was significantly different from that induced by enalapril. Omapatrilat and CGS decreased collagen deposition in the vessel wall of DOCA-salt rats. Enalapril had no effect on blood pressure, vascular structure, endothelial function or collagen deposition in the vessel wall of DOCA-salt rats. CONCLUSIONS : Dual inhibition of ACE/NEP in DOCA-salt hypertensive rats resulted in potent anti-hypertensive effects, prevented vascular remodelling and improved endothelial function of resistance arteries. NEP inhibition is involved to a large extent in the effect of omapatrilat in DOCA-salt rats. These actions of omapatrilat may confer protection against end-organ damage characteristic of severe hypertension.     

Vasopeptidase Inhibition Prevents Endothelial Dysfunction of Resistance Arteries in Salt-Sensitive Hypertension in Comparison With Single ACE Inhibition

-To determine whether natriuretic peptides in addition to the renin-angiotensin system are involved in functional and structural vascular changes in salt-sensitive hypertension, we compared equipotent hypotensive treatment with the dual neutral endopeptidase/ACE inhibitor omapatrilat (35 mg. kg(-1). d(-1)) or the ACE inhibitor captopril (100 mg. kg(-1). d(-1)). The reactivity and geometry of mesenteric resistance arteries from Dahl salt-sensitive rats were studied in vitro under perfused and pressurized conditions. Chronic salt administration increased systolic blood pressure by 57+/-4 mm Hg, whereas concentrations of atrial natriuretic peptide were reduced in heart and in plasma (P:<0.05). In addition, the medial cross-sectional area of small mesenteric arteries was increased and endothelium-dependent relaxation in response to acetylcholine and contraction in response to endothelin-1 were impaired in the mesenteric arteries of salt-sensitive rats on a high-salt diet (P:<0.05). Concomitant treatment with either omapatrilat or captopril reduced the increase in systolic blood pressure and hypertrophic remodeling to a similar degree (P:<0.05) but affected plasma and cardiac atrial natriuretic peptide levels differently (P:<0.05). In addition, omapatrilat normalized endothelium-dependent relaxations to a greater extent than captopril (P:<0.05). Furthermore, vasopeptidase inhibition increased cGMP levels compared with captopril (P:<0.05). Contractions to endothelin-1 were normalized by either antihypertensive drug. These results suggest that in the Dahl rat, with similar reductions in systolic blood pressure, omapatrilat is superior to captopril in preventing impaired endothelial function in small resistance arteries. Thus, vasopeptidase inhibition may have therapeutic advantages of the prevention of changes in vascular function and structure in salt-sensitive forms of hypertension.     

老年大鼠主动脉内皮依赖性舒张反应的研究

为探讨血管老化对血管内皮依赖性舒张反应的影响,本实验观察了离体青年和老年大鼠主动脉对乙酰胆碱(ACh)和硝普钠(SNP)的舒张反应及血管组织环化-磷酸鸟苷(cGMP)含量的变化。结果发现,老年大鼠主动脉对ACh的内皮依赖性舒张反应减弱(P<0.01),而对SNP的非内应依赖性舒张反应无明显受损;老年大鼠主动脉组织的基础cGMP含量和ACh刺激后的cGMP含量均低于青年大鼠(P<0.01)。提示血管老化引起的内皮依赖性舒张反应减弱可能与内皮功能不全、内皮衍生的舒张因子生成或释放减少有关。     

Vasopeptidase inhibition exhibits endothelial protection in salt-induced hypertension

Omapatrilat represents a new class of drugs capable of inhibiting both ACE and neutral endopeptidase 24.11, the so-called vasopeptidase inhibitors. It therefore contributes to neurohumoral modulation, which might improve endothelial function in cardiovascular diseases. This study investigated the effect of omapatrilat in comparison to the ACE inhibitor captopril on systolic blood pressure and endothelial function in salt-induced hypertension. Dahl salt-sensitive rats (n=6/group) on standard or salt-enriched (4% NaCl) chow were treated for 8 weeks with either omapatrilat (36+/-4 mg/kg per day), captopril (94+/-2 mg/kg per day), or placebo. Aortic rings were then isolated and suspended in organ chambers for isometric tension recording. Systolic blood pressure of salt-fed, placebo-treated animals increased to 196+/-6 mm Hg, which was prevented by omapatrilat (162+/-5 mm Hg, P<0.05) and captopril (164+/-7 mm Hg, P<0.05) to a comparable degree. In control rats, acetylcholine (10(-10) to 10(-5) mol/L) induced endothelium-dependent relaxation (97+/-4%), which was reduced by high-salt diet to 30+/-5% (P<0.005; n=6). Omapatrilat improved relaxation to a greater extent (86+/-5%) than did captopril (57+/-6%; P<0.05). eNOS protein expression and aortic nitrite/nitrate content were reduced in hypertensive rats and improved by both omapatrilat and captopril. Aortic endothelin-1 levels were increased in salt-fed animals and unaffected by omapatrilat or captopril. These data suggest that despite comparable blood pressure, omapatrilat is superior to captopril in improving endothelium-dependent relaxation in salt-sensitive hypertension.     

Olmesartan ameliorates renovascular injury and oxidative stress in Zucker obese rats enhanced by dietary protein

BACKGROUND: The metabolic syndrome is a risk factor for the development of renal and vascular complications. Dietary protein intake aggravates renal injury in Zucker obese rats, a model of the metabolic syndrome. This study investigated whether dietary protein intake enhances renal and vascular injuries by oxidative stress, and assessed effects of olmesartan, an angiotensin II type 1 receptor blocker, in this model. METHODS: Zucker obese rats were fed either a standard protein diet, high protein diet (OHP), or high protein diet containing olmesartan or hydralazine for 12 weeks. We examined the glomerulosclerosis score, endothelium-dependent relaxation response in the aorta, 4-hydroxy-2-nonenal (HNE) contents in the kidney and aorta, and mRNA expression of NAD(P)H oxidase components (p22phox and p47phox) in the renal cortex. RESULTS: The OHP rats developed proteinuria, glomerulosclerosis, and endothelial dysfunction. Olmesartan prevented the development of all these damages in OHP rats, whereas hydralazine improved only glomerulosclerosis. The high protein diet also augmented HNE accumulation in glomeruli, renal arteries, and aortas, and increased the mRNA expressions of p22phox and p47phox in the renal cortex in obese rats. Olmesartan, but not hydralazine, inhibited all these changes. CONCLUSIONS: These results suggested that increased dietary protein intake exacerbates renal and vascular injuries, and augments oxidative stress in a rat model of the metabolic syndrome. Olmesartan ameliorated these injuries, presumably through its antioxidative effects, whereas hydralazine improved only glomerulosclerosis through its antihypertensive action. Dietary protein-enhanced injuries in the metabolic syndrome may be associated with hypercholesterolemia and the activated renin-angiotensin system.     

Dual angiotensin-converting enzyme/neutral endopeptidase inhibition on cardiac and renal fibrosis and inflammation in DOCA-salt hypertensive rats

OBJECTIVES: The relative roles of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) inhibition on cardiac and renal fibrosis in deoxycorticosterone acetate (DOCA)-salt hypertensive rats were studied. METHODS: The ACE/NEP inhibitor omapatrilat (40 mg/kg per day), the ACE inhibitor enalapril (10 mg/kg per day) and the NEP inhibitor CGS 25462(100 mg/kg per day) were administrated for 3 weeks to DOCA rats. Collagen was stained with Sirius red, and mediators of inflammation were identified by immunolabeling (vascular cell adhesion molecule, nuclear factor-kappaB, infiltrating ED-1-positive macrophages and monocyte chemotactic protein-1) or by western blot (platelet-endothelial cell adhesion molecule-1). RESULTS: Elevated systolic blood pressure of DOCA rats was significantly reduced (P < 0.05) by omapatrilat and CGS 25462. Omapatrilat and CGS 25462 significantly (P < 0.05) decreased interstitial collagen density in the left ventricle of DOCA rats compared with untreated DOCA rats. Enalapril only decreased the subepicardial collagen of DOCA rats. Omapatrilat significantly (P < 0.05) decreased renal mesangial collagen deposition in DOCA rats. Cardiac and renal expression of surface adhesion molecules, nuclear factor-kappaB, monocyte chemotactic protein and ED-1-positive cells were decreased in omapatrilat-treated DOCA rats compared with untreated DOCA rats. Enalapril and CGS 25462 did not alter mesangial collagen of DOCA rats. CONCLUSIONS: Dual ACE/NEP inhibition was more effective than ACE or NEP inhibition in decreasing inflammatory mediators, and improving cardiac and renal fibrosis. This suggests a role for NEP inhibition added to blockade of the renin-angiotensin system that may explain the greater efficacy of omapatrilat.     

Hydrogen peroxide-induced inhibition of vasomotor activity: evaluation of single and combined treatments with vitamin A and insulin in streptozotocin-diabetic rats

A positive correlation has been established between increased oxidative stress and cardiovascular diseases in diabetes mellitus. We evaluated the effects of single or combined treatments with vitamin A (retinol acetate, 30 mg/kg/day, for 12-weeks) and insulin (8-10 IU/rat/day for the final 6-week) on vasomotor activity, oxidative stress and retinol metabolism in 12-week streptozotocin diabetic rats. The vasomotor activity was determined by measuring in vitro responsiveness of aorta rings to phenylephrine (PE) and acetylcholine (ACh) in the absence or in the presence of hydrogen peroxide (H2O2). Preincubation with H2O2 (10 microM) produced a significant decrease in PE (1 mM)-induced contraction in untreated-diabetic but not in control rats. Single treatment with insulin counteracted this effect of H2O2 and also reversed the increased contractile response of diabetic aorta to PE, while vitamin A was found to be ineffective. H2O2 (10 microM) also inhibited ACh (1 mM)-stimulated endothelium-dependent relaxation two fold more in diabetic than in control aorta. In the prevention of H2O2-induced inhibition of vascular relaxation to ACh, vitamin A alone was markedly effective while insulin alone was not. The combination of vitamin A plus insulin removed the inhibitory action of H2O2 in diabetic aorta. Diabetic animals displayed an increased level of aorta thiobarbituric acid reactive substance (TBARS) in association with decreased levels of plasma retinol and retinol-binding protein (RBP). Single treatment with insulin, in spite of allowing recovery of normal growth rate and improved glucose and retinol metabolism in diabetic rats, was unable to control TBARS production to the same extent as vitamin A alone. Our findings suggest that the maintenance of ACh-stimulated endothelium-dependent vasorelaxant tone in normal physiological levels depends largely on the prevention and/or inhibition of peroxidative stress, which is achieved by combined treatment with vitamin A plus insulin. The use of vitamin A together with insulin provides a better metabolic control and more benefits than use of insulin alone in the reduction of diabetes-induced vascular complications.     

NO contributes to EDHF-like responses in rat small arteries: a role for NO stores

OBJECTIVES: Responses to EDHF are usually characterised in the presence of nitric oxide synthase (NOS) and cyclooxygenase (COX) inhibitors. The contribution of NO to endothelium-dependent relaxation in the presence of NOS inhibitors was assessed using NO scavengers with the objective of testing (i) whether any residual NO produces endothelium-dependent relaxation in a manner similar to EDHF and (ii) to identify the source of the residual NO. METHODS: Small rat hepatic and mesenteric arteries were mounted in a tension myograph for either isometric or membrane potential measurements. RESULTS: Relaxation to ACh was unaffected by pre-treatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 300 microM), and indomethacin (Indo, 5 microM) in the absence or presence of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 1 microM), nitro-L-arginine (300 microM) or L-nitro-mono-methyl-arginine (L-NMMA, 300 microM). Addition of OxyHb (20 microM) or carboxy-PTIO (300 microM) produced a significant suppression of ACh-induced relaxations ( approximately 40%). In L-NAME+Indo treated arteries ACh-induced hyperpolarisation (delta16.3+/-2.1 mV, n=8) was significantly suppressed with the addition of OxyHb (Delta10.2+/-1.6 mV, n=12). ACh-induced relaxation, in the presence of L-NAME+Indo+OxyHb, was abolished by raised extracellular K(+), or the combination of charybdotoxin (CTX, 100 nM)+apamin (100 nM). In contrast whilst L-NAME+indo+barium+ouabain suppressed ACh-induced relaxation, the presence of OxyHb had no additional effect. Ultraviolet light induced a relaxation in arteries treated with L-NMMA+Indo (37.0+/-5.2%, n=9) which was sensitive to OxyHb (15.2+/-10.9%, n=4), and barium+ouabain (6.39+/-2.7%, n=4), but not CTX+apamin (37.8+/-2.4%, n=4). CONCLUSIONS: These findings suggest that NO contributes significantly to the "EDHF-like" response seen in rat small arteries and that the source of this NO may be preformed vascular stores.     

Dietary sodium loading increases plasma brain natriuretic peptide levels in man.

The effect of dietary sodium loading on plasma human brain natriuretic peptide-like immunoreactivity (hBNP-li) was examined in 11 normotensive subjects aged 20-23 years. Plasma hBNP-li increased significantly with increasing dietary sodium intake, with levels of 1.33 +/- 0.17 pmol/l on day 5 of a normal-sodium diet (24-h urinary sodium excretion of 171 +/- 16 mmol) and 2.04 +/- 0.10 pmol/l (P less than 0.05, versus normal-sodium diet) on day 5 of a high-sodium diet (24-h urinary sodium excretion 503 +/- 36 mmol). Corresponding plasma atrial natriuretic factor levels were 5.6 +/- 1.7 pmol/l and 11.0 +/- 2.0 pmol/l (P less than 0.05, versus normal-sodium diet) on the normal- and high-sodium diets, respectively. These results suggest that, in addition to atrial natriuretic factor, BNP may be a new and important natriuretic peptide which regulates sodium homeostasis in man during increased sodium intake.     

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.     

Protein restriction during pregnancy induces hypertension and impairs endothelium-dependent vascular function in adult female offspring

Intrauterine undernutrition plays a role in the development of adult hypertension. Most studies are done in male offspring to delineate the mechanisms whereby blood pressure may be raised; however, the vascular mechanisms involved in female offspring are unclear. Female offspring of pregnant Sprague-Dawley rats fed either a control (C; 18%) or a low-protein (LP; 6%) diet during pregnancy were used. Birth weight and later growth were markedly lower in LP than in C offspring. LP offspring exhibited impaired estrous cyclicity with increased mean arterial pressure. Hypotensive response to acetylcholine (ACh) and the hypertensive response to phenylephrine (PE) were greater in LP than in C rats. N-nitro-L-arginine methyl ester (L-NAME) induced greater hypertensive responses in C than in LP rats. Endothelium-intact mesenteric arteries from LP offspring exhibited increased contractile responses to PE and reduced vasodilation in response to ACh. In endothelium-denuded arteries, relaxation responses to sodium nitroprusside were similar in both groups. Basal and ACh-induced increase in vascular nitrite/nitrate production was lower in LP than in C offspring. L-NAME or 1H-1,2,4-oxadiazolo-4,3-quinoxalin-1-one inhibited ACh relaxations and enhanced PE contractions in C offspring, but had minimal effect in LP rats. The decreased NO-mediated vascular response might explain the increased vascular contraction and arterial pressure in female offspring with low birth weight.     

Angiotensin II receptor antagonist improves age-related endothelial dysfunction

BACKGROUND : We previously demonstrated that the angiotensin converting enzyme (ACE) inhibitor, enalapril, prevents the age-related impairment of endothelium-dependent hyperpolarization and relaxation mediated by endothelium-derived hyperpolarizing factor (EDHF). OBJECTIVE : To test whether angiotensin II type 1 (AT1) receptor antagonists would also improve age-related endothelial dysfunction. METHODS : Normotensive Wistar-Kyoto (WKY) rats were treated for 3 months with either the AT1 receptor antagonist, candesartan cilexetil (3.5 mg/kg per day; candesartan group), or the ACE inhibitor, enalapril (20 mg/kg per day; enalapril group), from 9 to 12 months of age. Untreated 12-month-old WKY rats (old group) served as controls (n = 7-12). RESULTS : The two treatments decreased systolic blood pressure comparably. EDHF-mediated hyperpolarization in response to acetylcholine (ACh; 10(-5) mol/l) in the presence of norepinephrine in mesenteric arteries was improved in both the candesartan and enalapril groups to a similar extent compared with the old group (candesartan group, -24 +/- 3 mV; enalapril group, -21 +/- 2 mV; old group, -13 +/- 2 mV). EDHF-mediated relaxation was similarly improved in the candesartan and enalapril groups (maximum relaxation: candesartan group, 70 +/- 7%; enalapril group, 63 +/- 8%; old group, 33 +/- 9%). Hyperpolarization and relaxation responses to levcromakalim, an ATP-sensitive K+-channel opener, were similar in all groups. CONCLUSIONS : These findings suggest that the AT1 receptor antagonist is as effective as the ACE inhibitor in improving the age-related decline in EDHF-mediated hyperpolarization and relaxation in normotensive rats. Thus AT1 receptor antagonists might serve as novel tools with which to prevent endothelial dysfunction associated with aging.