Effect of chronic angiotensin II inhibition on the nitric oxide synthase in the normal rat during aging

New Dawn for Atherosclerosis: Vascular Endothelial Cell Senescence and Death

Endothelial cells (ECs) form the inner linings of blood vessels, and are directly exposed to endogenous hazard signals and metabolites in the circulatory system. The senescence and death of ECs are not only adverse outcomes, but also causal contributors to endothelial dysfunction, an early risk marker of atherosclerosis. The pathophysiological process of EC senescence involves both structural and functional changes and has been linked to various factors, including oxidative stress, dysregulated cell cycle, hyperuricemia, vascular inflammation, and aberrant metabolite sensing and signaling. Multiple forms of EC death have been documented in atherosclerosis, including autophagic cell death, apoptosis, pyroptosis, NETosis, necroptosis, and ferroptosis. Despite this, the molecular mechanisms underlying EC senescence or death in atherogenesis are not fully understood. To provide a comprehensive update on the subject, this review examines the historic and latest findings on the molecular mechanisms and functional alterations associated with EC senescence and death in different stages of atherosclerosis.

Central arterial aging and the epidemic of systolic hypertension and atherosclerosis

The structure and function of central arteries change throughout the lifetime of humans and animals. Since atherosclerosis and hypertension are prevalent in epidemic proportion among older persons, it is reasonable to hypothesize that specific mechanisms that underlie the arterial substrate that has been altered by an "aging process" are intimately linked to arterial diseases. Indeed, recent studies reveal a profile of arterial cell and matrix properties that emerges with advancing age within the grossly normal appearing aortic wall of both animals and humans. This profile is proinflammatory, and is manifested by intimal infiltration of fetal cells, increased production of angiotensin II (Ang II)-signaling pathway molecules, eg, matrix metalloproteases (MMPs), and monocyte chemoattractant protein (MCP-1), transforming growth factor B1 (TGF-beta1), enhanced activation of MMPs, TGF-beta, and NADPH oxidase, and reduced nitric oxide (NO) bioavailability. This profile is similar to that induced at younger ages in experimental animal models of hypertension or atherosclerosis. In humans, this proinflammatory state, which occurs in the absence of lipid deposition, appears to be attributable to aging, per se. Other well known human risk factors, eg, altered lipid metabolism, smoking, and lack of exercise, interact with this arterial substrate that is altered by aging and render the aging human artery fertile soil for facilitation of the initiation and progression of arterial diseases. Therapies to reduce or retard this age-associated proinflammatory state within the grossly appearing arterial wall central arteries, in addition to slowing arterial aging, per se, may have a substantial impact on the quintessential age-associated arterial diseases of our society.

Role of the renin-angiotensin system in the pathogenesis of intimal hyperplasia: therapeutic potential for prevention of vein graft failure?

The saphenous vein remains the most widely used conduit for peripheral and coronary revascularization despite a high rate of vein graft failure. The most common cause of vein graft failure is intimal hyperplasia. No agents have been proven to be successful for the prevention of intimal hyperplasia in human subjects. The renin-angiotensin system is essential in the regulation of vascular tone and blood pressure in physiologic conditions. However, this system mediates cardiovascular remodeling in pathophysiologic states. Angiotensin II is becoming increasingly recognized as a potential mediator of intimal hyperplasia. Drugs modulating the renin-angiotensin system include angiotensin-converting enzyme inhibitors and angiotensin receptor blockers. These drugs are powerful inhibitors of atherosclerosis and cardiovascular remodeling, and they are first-line agents for management of several medical conditions based on class I evidence that they delay progression of cardiovascular disease and improve survival. Several experimental models have demonstrated that these agents are capable of inhibiting intimal hyperplasia. However, there are no data supporting their role in prevention of intimal hyperplasia in patients with vein grafts. This review summarizes the physiology of the renin-angiotensin system, the role of angiotensin II in the pathogenesis of cardiovascular remodeling, the medical indications for these agents, and the experimental data supporting an important role of the renin-angiotensin system in the pathogenesis of intimal hyperplasia.

Angiotensin II blockade upregulates the expression of Klotho, the anti-ageing gene, in an experimental model of chronic cyclosporine nephropathy

BACKGROUND

The Klotho gene plays a role in suppressing ageing-related disorders. It is suggested that activation of renin-angiotensin system (RAS) or oxidative stress suppresses Klotho in the kidney. This study evaluated the association between Klotho expression and RAS in cyclosporine (CsA)-induced renal injury.

METHODS

Chronic CsA nephropathy was induced by administering CsA (30 mg/kg) to mice on a low-salt diet (LSD) for 4 weeks. A normal-salt diet (NSD) was used as the control. Reverse transcription-polymerase chain reaction, western blot and immunohistochemistry were performed for Klotho and intrarenal RAS activity was measured using immunohistochemistry for angiotensinogen and renin. Oxidative stress was measured with urinary excretion of 8-hydroxy-2'-deoxyguanosine (8-OHdG).

RESULTS

CsA treatment decreased Klotho mRNA and protein in mouse kidney in a dose-dependent and time-dependent manner, but a concurrent treatment with losartan, an angiotensin II type 1 (AT1) receptor blocker, reversed the decrease in Klotho expression with histological improvement. This finding was more marked in the LSD than the NSD. Klotho expression was correlated with angiotensinogen and renin expression, tubulointerstitial fibrosis score and urinary 8-OHdG excretion.

CONCLUSIONS

Angiotensin II may play a pivotal role in regulating Klotho expression in CsA-induced renal injury. AT1 receptor blocker may inhibit the ageing process by decreasing oxidative stress caused by CsA.

Age-related changes in redox signaling and VSMC function

Epidemiological studies have shown that advancing age is associated with an increased prevalence of cardiovascular disease (CVD). Vascular smooth muscle cells (VSMC) comprise the major arterial cell population, and changes in VSMC behavior, function, and redox status with age contribute to alterations in vascular remodeling and cell signaling. Over two decades of work on aged animal models provide support for age-related changes in VSMC and/or arterial tissues. Enhanced production of reactive oxygen species (ROS) and insufficient removal by scavenging systems are hallmarks of vascular aging. VSMC proliferation and migration are core processes in vascular remodeling and influenced by growth factors and signaling networks. The intrinsic link between gene regulation and aging often relates directly to transcription factors and their regulatory actions. Modulation of growth factor signaling leads to up- or downregulation of transcription factors that control expression of genes associated with VSMC proliferation, inflammation, and ROS production. Four major signaling pathways related to the transcription factors, AP-1, NF-kappaB, FoxO, and Nrf2, will be reviewed. Knowledge of age-related changes in signaling pathways in VSMC that lead to alterations in cell behavior and function consistent with disease progression may help in efforts to attenuate age-related CVD, such as atherosclerosis.

Signaling mechanisms of angiotensin II in regulating vascular senescence

Angiotensin (Ang) II, the major effector of the rennin-angiotensin-aldosterone system (RAAS), has multiple functions in regulating cardiovascular hemodynamics and structure. Recent evidence strongly supports that Ang II promotes the onset and progression of vascular senescence, which is associated with vascular functional and structural changes, contributing to age-related vascular diseases. The vast majority of the cardiovascular actions of Ang II, including vascular senescence, are mediated by the Ang II type-1 (AT(1)) receptor. Similar to its growth-promoting process, the signaling mechanisms of AT(1) receptor-mediated vascular senescence-promoting effects involve activation of small G-protein Ras such as Ki-ras2A, mitogen-activated protein kinases (MAPK) such as extracellular signal-regulated kinase 1/2, and transcription factors including nuclear factor (NF)-kappaB and activator protein (AP)-1, and increased generation of reactive oxygen species. Moreover, AT(1) receptor stimulation has been suggested to inactivate cyclin-dependent kinase complexes by up-regulation of cell cycle regulators such as p53 and p21, resulting in cellular senescence. Furthermore, the interaction between Ang II and aldosterone (Aldo) in their contribution to cardiovascular pathophysiology has been highlighted. Aldo can interact with Ang II signaling via a genomic mechanism mediated by the mineralocorticoid receptor (MR). Aldo via MR couples with the AT(1) receptor to elicit the Ras/NF-kappaB, AP-1/p53/p21 pathway involving oxidative stress, leading to synergistic promotion of vascular senescence. Although the precise mechanisms controlling cellular senescence are currently poorly understood, this article reviews recent findings on the signaling mechanisms elicited by RAAS from the perspective of AT(1) receptor blockers and/or MR blockers in the treatment of age-related vascular diseases.

Losartan improves impaired nitric oxide synthase-dependent dilatation of cerebral arterioles in type 1 diabetic rats

We examined whether activation of angiotensin-1 receptors (AT1R) could account for impaired responses of cerebral arterioles during type 1 diabetes (T1D). First, we measured responses of cerebral arterioles in nondiabetic rats to eNOS-dependent (acetylcholine and adenosine diphosphate (ADP)) and -independent (nitroglycerin) agonists before and during application of angiotensin II. Next, we examined whether losartan could improve impaired responses of cerebral arterioles during T1D. In addition, we harvested cerebral microvessels for Western blot analysis of AT1R protein and measured production of superoxide anion by brain tissue under basal conditions and in response to angiotensin II in the absence or presence of losartan. We found that angiotensin II specifically impaired eNOS-dependent reactivity of cerebral arterioles. In addition, while losartan did not alter responses in nondiabetics, losartan restored impaired eNOS-dependent vasodilatation in diabetics. Further, AT1R protein was higher in diabetics compared to nondiabetics. Finally, superoxide production was higher in brain tissue from diabetics compared to nondiabetics under basal conditions, angiotensin II increased superoxide production in nondiabetics and diabetics, and losartan decreased basal (diabetics) and angiotensin II-induced production of superoxide (nondiabetics and diabetics). We suggest that activation of AT1R during T1D plays a critical role in impaired eNOS-dependent dilatation of cerebral arterioles.

Protective effect of long-term angiotensin II inhibition

Experimental studies indicate that angiotensin II (ANG II) through its type 1 receptor (AT(1)) promotes cardiovascular hypertrophy and fibrosis. Therefore, the aim of this study was to analyze whether chronic long-term inhibition of the renin-angiotensin system (RAS) can prevent most of the deleterious effects due to aging in the cardiovascular system of the normal rat. The main objective was to compare two strategies of ANG II blockade: a converting enzyme inhibitor (CEI) and an AT(1) receptor blocker (AT(1)RB). A control group remained untreated; treatment was initiated 2 wk after weaning. A CEI, enalapril (10 mg.kg(-1).day(-1)), or an AT(1)RB, losartan (30 mg.kg(-1).day(-1)), was used to inhibit the RAS. Systolic blood pressure, body weight, and water and food intake were recorded over the whole experimental period. Heart, aorta, and mesenteric artery weight as well as histological analysis of cardiovascular structure were performed at 6 and 18 mo. Twenty animals in each of the three experimental groups were allowed to die spontaneously. The results demonstrated a significant protective effect on the function and structure of the cardiovascular system in all treated animals. Changes observed at 18 mo of age in the hearts and aortas were quite significant, but each treatment completely abolished this deterioration. The similarity between the results detected with either enalapril or losartan treatment clearly indicates that most of the effects are exerted through AT(1) receptors. An outstanding finding was the significant and similar prolongation of life span in both groups of treated animals compared with untreated control animals.

Effects of ovariectomy and growth hormone administration on body composition and vascular function and structure in old female rats

Aging and estrogen-deprivation induce deleterious effects on body composition and vascular function in females. On the other hand, growth hormone (GH), whose production is reduced by age, exerts several vascular effects. The aim of this study was to investigate the effect of long-term estrogen deprivation and GH administration on body composition, vascular function and structure in aged female rats.

METHODS

Twelve female Wistar rats were ovariectomized at 10 months of age. At 20 months of age, half of the ovariectomized rats were treated with GH for 4 weeks. The remaining ovariectomized rats animals and one group of six intact females were used as control groups. After the treatment period, animals were sacrificed and Specific Gravity Index (SGI) and periuterine fat weigh, as well as vascular reactivity and morphometry in aortic rings, were studied.

RESULTS

No significant differences were found in SGI and periuterine fat weigh between ovariectomized and intact control rats. SGI was significantly increased by GH, and periuterine fat was reduced by the treatment. Dose-dependent relaxing responses to acetylcholine and isoproterenol were significantly diminished in ovariectomized rats as compared with intact animals, and GH treatment improved these responses. Ovariectomized animals showed significantly higher contracting responses to phenylephrine, acetylcholine + L-NAME and angiotensin-I than intact rats, and treatment with GH reduced them significantly. Media cross-sectional area was increased in ovariectomized rats as compared to intact animals, and GH reduced this area, but differences did not reach significance.

CONCLUSION

GH has beneficial effects in body composition and endothelial function in old ovariectomized female rats.

Temocapril, an Angiotensin converting enzyme inhibitor, ameliorates age-related increase in carotid arterial stiffness in normotensive subjects

BACKGROUND/AIMS

Oxidative stress plays an important role in vascular ageing. The close relationship of the renin-angiotensin system with mechanisms of oxidative stress suggests its possible involvement in the deleterious effects of ageing. The present study was designed to investigate whether inhibition of the renin-angiotensin system improves the age-related increase in arterial stiffness.

METHODS

Normotensive elderly subjects in a geriatric nursing home (n = 24; male/female = 7/17; 86 +/- 9 years, mean +/- SD) were randomly assigned to receive either an angiotensin converting enzyme inhibitor, temocapril (n = 12, 1 mg daily) or nothing (n = 12). Carot id arterial stiffness parameter beta and circulating levels of malondialdehyde-modified low-density lipoprotein were measured before and 6 months after randomization.

RESULTS

Temocapril decreased beta (from 7.0 +/- 1.0 to 4.9 +/- 0.9, p < 0.05) and malondialdehyde-modified low-density lipoprotein levels (from 73.2 +/- 19.9 to 61.3 +/- 18.4 U/l, p < 0.05) without changing the blood pressure. The changes in beta and malondialdehyde-modified low-density lipoprotein levels were significantly correlated (rho = 0.600, p < 0.05).

CONCLUSION

These results suggest that temocapril ameliorates the age-related increase in carotid arterial stiffness in healthy, normotensive elderly subjects.

Protective effect of the inhibition of the renin-angiotensin system on aging

Experimental studies indicate that chronic long-term inhibition of the renin-angiotensin system (RAS) can prevent most of the deleterious effects due to aging in the cardiovascular system and in the kidney of the normal mouse and rat. In this review, all the information available on this subject provided by several studies performed by our research group during the last years is been described. Treatment was initiated either after weaning or at 12 months of age that is about half the normal life span of the rat. A converting enzyme inhibitor: enalapril or an angiotensin II type 1 (AT1) receptor blocker: losartan were used to inhibit the RAS. Cognitive behaviour, emotionality, and locomotor activity were also determined at 10 and 18 months of age in treated since weaning and untreated control rats to elucidate the participation of angiotensin II in memory disfunction. A similar observation was obtained in animals treated from 12 to 18 months of age. Results have demonstrated a significant protective effect on the function and the structure of the cardiovascular system, the kidney and the brain in all the treated animals. Damage observed at 12 months of age was not very significant, but treatment stop further deterioration that was evident in untreated animals. The similarity of the results detected with either enalapril or losartan treatment, clearly indicates that most of the effects are exerted through AT1 receptors. Analysis of the nitric oxide and antioxidant enzymes systems suggest that the protective effect is related to an antioxidant action of the RAS inhibitors and a reduced formation of reactive oxygen species. AngII inhibition might produce changes in the mechanisms of oxidative stress specially at the mitochondrial level. Prevention of mitochondrial decrease and/or damage would be related with the delay of the normal aging process.

Endothelium-derived hydrogen peroxide accounts for the enhancing effect of an angiotensin-converting enzyme inhibitor on endothelium-derived hyperpolarizing factor-mediated responses in mice

Background- We have recently identified that endothelium-derived hydrogen peroxide (H2O2) is an endothelium-derived hyperpolarizing factor (EDHF) in animals and humans, for which endothelial nitric oxide synthase (eNOS) is an important source. Angiotensin-converting enzyme (ACE) inhibitors are known to enhance EDHF-mediated responses. In this study, we examined whether endothelium-derived H2O2 accounts for the enhancing effect of an ACE inhibitor on EDHF-mediated responses and, if so, what mechanism is involved.

METHODS AND RESULTS

Control and eNOS-/- mice were maintained with or without temocapril (10 mg/kg per day orally) for 4 weeks, and isometric tensions and membrane potentials of mesenteric arteries were recorded. In control mice, temocapril treatment significantly enhanced EDHF-mediated relaxations and hyperpolarizations to acetylcholine (n=8 each). Catalase, a specific scavenger of H2O2, abolished the beneficial effects of temocapril, although it did not affect endothelium-independent relaxations to sodium nitroprusside or NS1619, a direct opener of K(Ca) channels (n=6 each). Western blot analysis demonstrated that the temocapril treatment significantly upregulated the expression of eNOS. By contrast, this enhancing effect of temocapril was absent in eNOS-/- mice (n=6).

CONCLUSIONS

These results indicate that endothelium-derived H2O2 accounts for the enhancing effect of temocapril on EDHF-mediated responses caused in part by eNOS upregulation, further supporting our H2O2 theory.

Effect of AT1 receptor antagonism on vascular and circulating inflammatory mediators in SHR: role of NF-κB/IκB system

We investigated the role of angiotensin II in vascular and circulating inflammatory markers in spontaneously hypertensive rats (SHR). IL-1β, IL-6, and TNF-α aortic mRNA expression and plasma levels were measured in adult SHR untreated or treated with the angiotensin II receptor antagonist candesartan (2 mg·kg−1·day−1) or antihypertensive triple therapy (TT; in mg·kg−1·day−1: 20 hydralazine + 7 type 1 hydrochlorothiazide + 0.15 reserpine) for 10 wk. Likewise, aortic expression of NF-κB p50 subunit precursor p105 and its inhibitor (IκB) were measured. Age-matched Wistar-Kyoto rats (WKY) served as normotensive reference. High blood pressure levels were associated with increased ( P < 0.05) aortic mRNA expression of IL-1β, IL-6, and TNF-α. Hypertension was also accompanied by increased IL-1β and IL-6 plasma levels. No differences were observed in circulating TNF-α levels between SHR and WKY. SHR presented elevated aortic mRNA expression of the transcription factor NF-κB and reduction in its inhibitor, IκB. Candesartan decreased ( P < 0.05) blood pressure levels, aortic mRNA expression of IL-1β, IL-6, and TNF-α, and ( P < 0.05) IL-1β and IL-6 plasma concentration. However, although arterial pressure decrease was comparable for the treatments, TT only partially reduced the increments in inflammatory markers. In fact, candesartan-treated rats showed significantly lower levels of circulating and vascular inflammatory markers than TT-treated animals. The treatments increased IκB mRNA expression similarly. However, only candesartan reduced NF-κB mRNA expression. In summary, 1) SHR presented a vascular inflammatory process; 2) angiotensin II, and increased hemodynamic forces associated with hypertension, seems to be involved in stimulation of inflammatory mediators through NF-κB system activation; and 3) reduction of inflammatory mediators produced by candesartan in SHR could be partially due to both downregulation of NF-κB and upregulation of IκB.

Enalapril increases mitochondrial nitric oxide synthase activity in heart and liver

Heart and liver mitochondria isolated from rats treated with enalapril, 3-30 mg/kg/day in the drinking water for 7-120 days, showed a time- and dose-dependent increased nitric oxide (NO) production in the range of 14-250%. Heart and liver mitochondria from control rats produced 0.69 and 0.50 nmol of NO/min/mg of protein, respectively, as determined by dual wavelength spectrophotometry (577-591 nm) following hemoglobin oxidation to methemoglobin. The response to enalapril treatment, attributed to a gene-mediated up-regulation of mitochondrial nitric oxide synthase (mtNOS) activity, was half-maximal at 5-6 days and was maintained up to 120 days. Enalapril-treated animals showed an increased mtNOS functional activity in heart mitochondria that inhibited state 3 O(2) uptake (from 22% in control rats to 43%) and increased state 4 hydrogen peroxide (H(2)O(2)) production (from 30% in control rats to 52%). Calculated heart intramitochondrial NO and H(2)O(2) steady-state concentrations were increased 66% and 20%, respectively, by enalapril treatment. Signaling pathways dependent on mitochondrial NO and H(2)O(2) may account for the beneficial effects of enalapril in aging mammals.

Enalapril prevents impaired nitric oxide synthase-dependent dilatation of cerebral arterioles in diabetic rats

BACKGROUND AND PURPOSE

Our goal was to identify the effects of chronic treatment with enalapril on cerebrovascular dysfunction and endothelial nitric oxide synthase (eNOS) protein in diabetic rats.

METHODS

Rats were assigned to 1 of 4 groups: nondiabetic, diabetic, nondiabetic/enalapril-treated, and diabetic/enalapril-treated groups. Rats assigned to the nondiabetic groups were injected with vehicle (sodium citrate buffer), and rats assigned to the diabetic groups were injected with streptozotocin (50 mg/kg IP). Enalapril (10 mg/kg per day) was administered in the drinking water and coincided with the injection of vehicle or streptozotocin. Two to 3 months later, we examined responses of pial arterioles to nitric oxide synthase (NOS)-dependent agonists (acetylcholine and ADP) and a NOS-independent agonist (nitroglycerin). After these functional studies, we harvested cerebral microvessels for Western blot analysis of eNOS protein.

RESULTS

We found that acetylcholine- and ADP-induced dilatation of pial arterioles was impaired in diabetic compared with nondiabetic rats. In addition, while enalapril did not alter responses in nondiabetic rats, enalapril prevented diabetes-induced impairment of NOS-dependent vasodilatation. Furthermore, eNOS protein was higher in diabetic than in nondiabetic rats, and enalapril did not produce a further increase in eNOS protein in enalapril-treated diabetic rats compared with untreated diabetic rats.

CONCLUSIONS

These results suggest that enalapril prevents cerebrovascular dysfunction in diabetic rats. We speculate that the protective role of enalapril may be independent of an alteration in eNOS protein in cerebral microvessels.

Effects of AT1 Receptor Block Begun Late in Life on Normal Cardiac Aging in Rats

The goal of this study was to determine how short-term (12 weeks) angiotensin type I (AT1) block begun late in life affects aspects of myocardial biology and physiologic function altered by normal aging. Exercise capacity, myocardial morphology, histopathology, and coronary vascular function (degree of coronary vasodilation in response to adenosine) were evaluated in 53 Fischer 344 rats. Adult (6 months of age) and old (21 months of age) rats were studied after 12 weeks of either control drinking water, a low dose of candesartan that did not significantly lower blood pressure (1 mg/kg/d), or a high dose of candesartan (10 mg/kg/d). Significant age-associated changes in exercise capacity (38% decrease), coronary dilation in response to adenosine (41% decrease), and histopathology occurred but were not affected by candesartan treatment. Age-associated myocardial hypertrophy occurred as indicated by an increase in heart weight-to-tibia length ratio from 0.27 g/cm +/- 0.01 in the adult controls to 0.34 g/cm +/- 0.02 in the old controls (P < 0.05). This hypertrophy in the aged hearts was significantly attenuated by both low-dose (0.30 g/cm +/- 0.01) and high-dose (0.29 g/cm +/- 0.01) candesartan (P < 0.05). Echocardiographic measurements indicate that the candesartan-induced decrease in hypertrophy occurred concomitantly with slight decreases in septal wall thickness and left ventricular (LV) chamber diameter. It is concluded that short-term AT1 block, even when initiated late in life, can decrease age-associated LV hypertrophy independent of blood pressure-lowering effects.

Effect of treatment with losartan on cardiovascular autonomic and large sensory nerve fiber function in individuals with diabetes mellitus: a 1-year randomized, controlled trial

This study evaluated the effect of losartan, an angiotensin II receptor antagonist, on cardiovascular autonomic function and large sensory nerve fiber function in individuals with diabetes mellitus. In a double-blind placebo-controlled trial, individuals were randomly assigned to treatment with a daily oral dose of 50-mg losartan (n=24) or placebo (n=20) for 12 months. Tests of cardiovascular autonomic function (i.e., RR-variation during deep breathing and the Valsalva maneuver) and of large sensory nerve fiber function (i.e., vibratory thresholds) were measured at baseline and at 12 months. No significant difference at baseline was found for duration of diabetes, glycemic control, blood pressure, or body mass index (BMI) between the two groups. After 12 months, the decline in RR-variation that occurs over time appeared to be less for those taking losartan. There was, however, no statistically significant change in the results for any of the tests of cardiovascular autonomic function or vibratory thresholds between the groups. Multivariate analyses in the losartan study group revealed an independent association of duration of diabetes, change in (reduced) systolic blood pressure (SBP), and improved vibratory thresholds. This association was particularly noted for women. Pharmacologic agents may affect cardiovascular autonomic function by favorable or detrimental changes in the electrophysiology of the heart. The results of this study indicate that, although losartan may have slowed the normal decline in RR-variation, it did not result in any significant improvement in cardiovascular autonomic nerve fiber function. An association of vibratory thresholds and SBP was observed.

Effect of AT1 receptor blockade on hepatic redox status in SHR: possible relevance for endothelial function?

The study investigated whether the amelioration of endothelial dysfunction by candesartan (2 mg.kg-1.day-1; 10 wk) in spontaneously hypertensive rats (SHR) was associated with modification of hepatic redox system. Systolic arterial pressure (SAP) was higher (P < 0.05) in SHR than in Wistar-Kyoto rats (WKY) and was reduced (P < 0.05) by candesartan in both strains. Acetylcholine (ACh) relaxations were smaller (P < 0.05) and contractions induced by ACh + NG-nitro-l-arginine methyl ester (l-NAME) were greater (P < 0.05) in SHR than in WKY. Treatment with candesartan enhanced (P < 0.05) ACh relaxations in SHR and reduced (P < 0.05) ACh + l-NAME contractions in both strains. Expression of aortic endothelial nitric oxide synthase (eNOS) mRNA was similar in WKY and SHR, and candesartan increased (P < 0.05) it in both strains. Aortic mRNA expression of the subunit p22phox of NAD(P)H oxidase was higher (P < 0.05) in SHR than in WKY. Treatment with candesartan reduced (P < 0.05) p22phox expression only in SHR. Malonyl dialdehyde (MDA) levels were higher (P < 0.05), and the ratio reduced/oxidized glutathione (GSH/GSSG) as well as glutathione peroxidase activity (GPx) were lower (P < 0.05) in liver homogenates from SHR than from WKY. Candesartan reduced (P < 0.05) MDA and increased (P < 0.05) GSH/GSSG ratio without affecting GPx. Vessel, lumen, and media areas were bigger (P < 0.05) in SHR than in WKY. Candesartan treatment reduced (P < 0.05) media area in SHR without affecting vessel or lumen area. The results suggest that hypertension is not only associated with elevation of vascular superoxide anions but with alterations of the hepatic redox system, where ANG II is clearly involved. The results further support the key role of ANG II via AT1 receptors for the functional and structural vascular alterations produced by hypertension.

Enalapril and losartan attenuate mitochondrial dysfunction in aged rats

Renin-angiotensin system (RAS) inhibition can attenuate the effects of aging on renal function and structure; however, its effect on mitochondrial aging is unknown. To investigate whether an angiotensin-converting enzyme inhibitor (enalapril) or an angiotensin II receptor blocker (losartan) could mitigate age-associated changes in kidney mitochondria, male Wistar rats (14 mo old) received during 8 mo water containing either enalapril (10 mg/kg/day) (Enal), or losartan (30 mg/kg/day) (Los), or no additions (Old). Four-month-old untreated rats (Young) were also studied. In Old rats mitochondrial respiratory control, ADP/O, nitric oxide synthase activity, and uncoupling protein 2 levels were lower (46, 42, 27, and 76%, respectively), and Mn-SOD activity was higher (70%) than in Young, Enal, and Los rats. In Old rats mitochondrial hydrogen peroxide production was higher than in both Young (197%) and Enal or Los (40%) rats. In Old rats, kidney GSH/GSSG was lower than in both Young (80%) and Enal (57%) or Los (68%) rats. In Old rats electron microscopy showed effacement of microvilli in tubular epithelial cells, ill-defined mitochondrial cristae, lower mitochondrial numbers, and enhanced number of osmiophilic bodies relative to Young, Enal, or Los rats. In conclusion, enalapril and losartan can protect against both age-related mitochondrial dysfunction and ultrastructural alterations, underscoring the role of RAS in the aging process. An association with oxidative stress modulation is suggested.

Male gender increases sensitivity to renal injury in response to cholesterol loading

Males are at greater risk for renal injury than females. This may relate to nitric oxide (NO) availability, because female rats have higher renal endothelial NO synthase (NOS) levels. Previously, our laboratory found susceptibility to proteinuria induced by NOS inhibition in male compared with female rats. Dyslipidemia and hypercholesterolemia dose dependently decreased renal NOS activity and caused renal injury in female rats. We hypothesized that exposure of male rats to hypercholesterolemia would lead to more renal injury in male than in female rats due to an a priori lower renal NO system. Female and male rats were fed no, low-dose, or high-dose cholesterol for 24 wk. Cholesterol feeding dose dependently increased proteinuria in both female and male rats, but male rats developed more proteinuria at similar plasma cholesterol (P < 0.001). Control males had lower renal NOS activity than control females (4.44 +/- 0.18 vs. 7.46 +/- 0.37 pmol. min(-1). mg protein(-1); P < 0.05), and cholesterol feeding decreased renal NOS activity in males and in females (P < 0.05). Cholesterol-fed males developed significantly more vascular, glomerular, and tubulointerstitial monocyte/macrophage influx and injury than females. Thus under baseline conditions, male rats have lower renal NOS activity than female rats. This may explain why male rats are more sensitive to renal injury by factors that decrease NO availability, such as hypercholesterolemia.