Subpressor doses of angiotensin II increase plasma F(2)-isoprostanes in rats

Predicting sex differences in the effects of diuretics in renal epithelial transport during angiotensin II-induced hypertension

Chronic angiotensin II (ANG II) infusion is an experimental model that induces hypertension in rodents. The natriuresis, diuresis, and blood pressure responses differ between males and females. This is perhaps not unexpected, given the rodent kidney, which plays a key role in blood pressure regulation, exhibits marked sex differences. Under normotensive conditions, compared with males, the female rat nephron exhibits lower Na+/H+ exchanger 3 (NHE3) activity along the proximal tubule but higher Na+ transporter activities along the distal segments. ANG II infusion-induced hypertension induces a pressure natriuretic response that reduces NHE3 activity and shifts Na+ transport capacity downstream. The goals of this study were to apply a computational model of epithelial transport along a rat nephron 1) to understand how a 14-day ANG II infusion impacts segmental electrolyte transport in male and female rat nephrons and 2) to identify and explain any sex differences in the effects of loop diuretics, thiazide diuretics, and K+-sparing diuretics. Model simulations suggest that the NHE3 downregulation in the proximal tubule is a major contributor to natriuresis and diuresis in hypertension, with the effects stronger in males. All three diuretics are predicted to induce stronger natriuretic and diuretic effects under hypertension compared with normotension, with relative increases in sodium excretion higher in hypertensive females than in males. The stronger natriuretic responses can be explained by the downstream shift of Na+ transport load in hypertension and by the larger distal transport load in females, both of which limit the ability of the distal segments to further elevate their Na+ transport.NEW & NOTEWORTHY Sex differences in the prevalence of hypertension are found in human and animal models. The kidney, which regulates blood pressure, exhibits sex differences in morphology, hemodynamics, and membrane transporter distributions. This computational modeling study provides insights into how the sexually dimorphic responses to a 14-day angiotensin II infusion differentially impact segmental electrolyte transport in rats. Simulations of diuretic administration explain how the natriuretic and diuretic effects differ between normotension and hypertension and between the sexes.

Deletion of vascular thromboxane A2 receptors and its impact on angiotensin II-induced hypertension and atherosclerotic lesion formation in the aorta of Ldlr-deficient mice

The thromboxane A2 receptor (TP) has been shown to play a role in angiotensin II (Ang II)-mediated hypertension and pathological vascular remodeling. To assess the impact of vascular TP on Ang II-induced hypertension, atherogenesis, and pathological aortic alterations, i.e. aneurysms, we analysed Western-type diet-fed and Ang II-infused TPVSMC KO/Ldlr KO, TPEC KO/Ldlr KO mice and their respective wild-type littermates (TPWT/Ldlr KO). These analyses showed that neither EC- nor VSMC-specific deletion of the TP significantly affected basal or Ang II-induced blood pressure or aortic atherosclerotic lesion area. In contrast, VSMC-specific TP deletion abolished and EC-specific TP deletion surprisingly reduced the ex vivo reactivity of aortic rings to the TP agonist U-46619, whereas VSMC-specific TP knockout also diminished the ex vivo response of aortic rings to Ang II. Furthermore, despite similar systemic blood pressure, there was a trend towards less atherogenesis in the aortic arch and a trend towards fewer pathological aortic alterations in Ang II-treated female TPVSMC KO/Ldlr KO mice. Survival was impaired in male mice after Ang II infusion and tended to be higher in TPVSMC KO/Ldlr KO mice than in TPWT/Ldlr KO littermates. Thus, our data may suggest a deleterious role of the TP expressed in VSMC in the pathogenesis of Ang II-induced aortic atherosclerosis in female mice, and a surprising role of the endothelial TP in TP-mediated aortic contraction. However, future studies are needed to substantiate and further elucidate the role of the vascular TP in the pathogenesis of Ang II-induced hypertension, aortic atherosclerosis and aneurysm formation.

The F2-isoprostane 8-iso-PGF2α attenuates atherosclerotic lesion formation in Ldlr-deficient mice - Potential role of vascular thromboxane A2 receptors

The F2-isoprostane 8-iso-PGF_2α (also known as 15-F_2t-isoprostane, iPF_2α-III, 8-epi PGF_2α, 15(S)-8-iso-PGF_2α, or 8-Isoprostane), a thromboxane A₂ receptor (TP) agonist, stable biomarker of oxidative stress, and risk marker of cardiovascular disease, has been proposed to aggravate atherogenesis in genetic mouse models of atherosclerotic vascular disease. Moreover, the TP plays an eminent role in the pathophysiology of endothelial dysfunction, atherogenesis, and cardiovascular disease. Yet it is unknown, how the TP expressed by vascular cells affects atherogenesis or 8-iso-PGF_2α-related effects in mouse models of atherosclerosis. We studied Ldlr-deficient vascular endothelial-specific (EC) and vascular smooth muscle cell (VSMC)-specific TP knockout mice (TP^ECKO/Ldlr KO; TP^VSMCKO/Ldlr KO) and corresponding wild-type littermates (TP^WT/Ldlr KO). The mice were fed a Western-type diet for eight weeks and received either 8-iso-PGF_2α or vehicle infusions via osmotic pumps. Subsequently, arterial blood pressure, atherosclerotic lesion formation, and lipid profiles were analyzed. We found that VSMC-, but not EC-specific TP deletion, attenuated atherogenesis without affecting blood pressure or plasma lipid profiles of the mice. In contrast to a previous report, 8-iso-PGF_2α tended to reduce atherogenesis in TP^WT/Ldlr KO and TP^{EC KO}/Ldlr KO mice, again without significantly affecting blood pressure or lipid profiles of these mice. However, no further reduction in atherogenesis was observed in 8-iso-PGF_2α-treated TP^{VSMC KO}/Ldlr KO mice. Our work suggests that the TP expressed in VSMC but not the TP expressed in EC is involved in atherosclerotic lesion formation in Ldlr-deficient mice. Furthermore, we report an inhibitory effect of 8-iso-PGF_2α on atherogenesis in this experimental atherosclerosis model, which paradoxically appears to be related to the presence of the TP in VSMC.

The ACE2/Ang (1-7)/MasR axis as an emerging target for antihypertensive peptides

Food protein-derived bioactive peptides, particularly antihypertensive peptides, are important constituents of functional foods or nutraceuticals. Most antihypertensive are identified as the inhibitors of angiotensin converting enzyme (ACE), a key enzyme responsible for the generation of angiotensin II (Ang II), which is a vasoconstricting peptide. Hence, ACE has long been used as a universal target to identify antihypertensive peptides. Angiotensin converting enzyme 2 (ACE2), is a homolog of ACE but uses Ang II as its key substrate to produce angiotensin (1-7), exerting vasodilatory activity via the mas receptor (MasR). Therefore, ACE2 functions in the opposite way as ACE and is an emerging novel target for cardiovascular therapy. The potential of food protein-derived bioactive peptides in targeting ACE2 has been rarely explored. While, recently we found that IRW, an egg white ovotransferrin-derived antihypertensive peptide, reduced blood pressure in spontaneously hypertensive rats via the ACE2/Ang (1-7)/MasR axis, indicating a new mechanism of food protein-derived bioactive peptides in reducing blood pressure. The objectives of this review are to summarize the functions of the ACE2/Ang (1-7)/MasR axis and to examine its potential roles in the actions of food protein-derived antihypertensive peptides. The interaction between antihypertensive peptides and the ACE2/Ang (1-7)/MasR axis will also be discussed.

No effect of the angiotensin receptor blocker candesartan on cerebrovascular autoregulation in rats during very high and low sodium intake

Autoregulation of cerebral blood flow (CBF) denotes that CBF is constant despite fluctuation of blood pressure within wide limits. Inhibition of the renin–angiotensin system (RAS) is known to decrease the lower and upper limits of CBF autoregulation. We have previously shown that this includes inhibition by the angiotensin receptor blocker (ARB) candesartan. In the present study we investigated the influence of the ARB candesartan on the lower limit of CBF autoregulation in two groups of Sprague-Dawley rats, on high (4.0% Na⁺) and low (0.004% Na⁺) sodium diet, respectively. Control animals were given the same diet, but no ARB. CBF was studied with the laser Doppler method. Blood pressure was lowered by controlled bleeding. Results revealed that both high and low sodium diet with low and high renin levels respectively block the influence of candesartan on CBF autoregulation. This was expected in rats on a high salt diet with a low renin level, but unexpected in rats with a low salt intake with a high renin level.

Rodent vertical sleeve gastrectomy alters maternal immune health and fetoplacental development

Bariatric surgery is increasingly employed to improve fertility and reduce obesity-related co-morbidities in obese women. Surgical weight loss not only improves the chance of conception but reduces the risk of pregnancy complications including pre-eclampsia, gestational diabetes, and macrosomia. However, bariatric procedures increase the incidence of intrauterine growth restriction (IUGR), fetal demise, thromboembolism, and other gestational disorders. Using our rodent model of vertical sleeve gastrectomy (VSG), we tested the hypothesis that VSG in diet-induced, obese dams would cause immune and placental structural abnormalities that may be responsible for fetal demise during pregnancy. VSG dams studied on gestational day (G) 19 had reduced circulating T-cell (CD3+ and CD8+) populations compared with lean or obese controls. Further, local interleukin (IL) 1β and IL 1 receptor antagonist (il1rn) cmRNA were increased in placenta of VSG dams. Placental barrier function was also affected, with increased transplacental permeability to small molecules, increased matrix metalloproteinase 9 expression, and increased apoptosis in VSG. Furthermore, we identified increased placental mTOR signaling that may contribute to preserving the body weight of the fetuses during gestation. These changes occurred in the absence of a macronutrient deficit or gestational hypertension in the VSG dams. In summary, previous VSG in dams may contribute to fetal demise by affecting maternal immune system activity and compromise placental integrity.

Impaired Oxidative Status Is Strongly Associated with Cardiovascular Risk Factors

The main target of primary prevention is the identification of cardiovascular risk factors aimed at reducing of the adverse impact of modifiable factors, such as lifestyle and pharmacological treatments. In humans, an alteration of the oxidative status has been associated with several pathologies, including diabetes and cardiovascular diseases. However, the prognostic relevance of circulating oxidative stress biomarkers remains poorly understood. Our study explored, in a healthy population (n = 322), the relationship between oxidative status and cardiovascular risk factors. Here, we were successful in demonstrating that plasmatic oxidative status is significantly associated with traditional cardiovascular risk factors. We revealed a significant depletion in the efficacy of total plasma antioxidant barrier in high cardiovascular risk categories, and we confirmed an age-related alteration of oxidative status. The efficacy of total plasma antioxidant barrier is significantly depleted in relation to metabolic disorders. Interestingly, the cholesterol imbalance is the main factor in depleting the efficacy of total plasma antioxidant barrier. The oxidative status is also influenced by hypertension, and a slight increase in systolic blood pressure determines a highly significant effect. We showed that the first detectable event of a redox disturbance is the repairing intervention of the antioxidant barrier that is thus decreased as overutilized.

Oxidative status in the macula densa modulates tubuloglomerular feedback responsiveness in angiotensin II-induced hypertension

AIM

Tubuloglomerular feedback (TGF) is an important mechanism in control of signal nephron glomerular filtration rate. The oxidative stress in the macula densa, primarily determined by the interactions between nitric oxide (NO) and superoxide (O2-), is essential in maintaining the TGF responsiveness. However, few studies examining the interactions between and amount of NO and O2- generated by the macula densa during normal and hypertensive states.

METHODS

In this study, we used isolated perfused juxtaglomerular apparatus to directly measure the amount and also studied the interactions between NO and O2- in macula densa in both physiological and slow pressor Angiotensin II (Ang II)-induced hypertensive mice.

RESULTS

We found that slow pressor Ang II at a dose of 600 ng kg(-1) min(-1) for two weeks increased mean arterial pressure by 26.1 ± 5.7 mmHg. TGF response increased from 3.4 ± 0.2 μm in control to 5.2 ± 0.2 μm in hypertensive mice. We first measured O2- generation by the macula densa and found it was undetectable in control mice. However, O2- generation by the macula densa increased to 21.4 ± 2.5 unit min(-1) in Ang II-induced hypertensive mice. We then measured NO generation and found that NO generation by the macula densa was 138.5 ± 9.3 unit min(-1) in control mice. The NO was undetectable in the macula densa in hypertensive mice infused with Ang II.

CONCLUSIONS

Under physiological conditions, TGF response is mainly controlled by the NO generated in the macula densa; in Ang II induced hypertension, the TGF response is mainly controlled by the O2- generated by the macula densa.

A subpressor dose of angiotensin II elevates blood pressure in a normotensive rat model by oxidative stress

Oxidative stress is an imbalance between free radicals and antioxidants, and is an important etiological factor in the development of hypertension. Recent experimental evidence suggests that subpressor doses of angiotensin II elevate oxidative stress and blood pressure. We aimed to investigate the oxidative stress related mechanism by which a subpressor dose of angiotensin II induces hypertension in a normotensive rat model. Normotensive male Wistar rats were infused with a subpressor dose of angiotensin II for 28 days. The control group was sham operated and infused with saline only. Plasma angiotensin II and H2O2 levels, whole-blood glutathione peroxidase, and AT-1a, Cu/Zn SOD, and p22phox mRNA expression in the aorta was assessed. Systolic and diastolic blood pressures were elevated in the experimental group. There was no change in angiotensin II levels, but a significant increase in AT-1a mRNA expression was found in the experimental group. mRNA expression of p22phox was increased significantly and Cu/Zn SOD decreased significantly in the experimental group. There was no significant change to the H2O2 and GPx levels. Angiotensin II manipulates the free radical-antioxidant balance in the vasculature by selectively increasing O2(-) production and decreasing SOD activity and causes an oxidative stress induced elevation in blood pressure in the Wistar rat.

Inhibition of reactive oxygen species in hypothalamic paraventricular nucleus attenuates the renin-angiotensin system and proinflammatory cytokines in hypertension

AIMS

To explore whether reactive oxygen species (ROS) scavenger (tempol) in the hypothalamic paraventricular nucleus (PVN) attenuates renin-angiotensin system (RAS) and proinflammatory cytokines (PICs), and decreases the blood pressure and sympathetic activity in angiotensin II (ANG II)-induced hypertension.

METHODS AND RESULTS

Male Sprague-Dawley rats were infused intravenously with ANG II (10 ng/kg per min) or normal saline (NS) for 4 weeks. These rats were treated with bilateral PVN infusion of oxygen free radical scavenger tempol (TEMP, 20 μg/h) or vehicle (artificial cerebrospinal fluid, aCSF) for 4 weeks. ANG II infusion resulted in increased mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA). These ANG II-infused rats also had higher levels of gp91(phox) (a subunit of NAD(P)H oxidase), angiotensin-converting enzyme (ACE), and interleukin-1 beta (IL-1β) in the PVN than the control animals. Treatment with PVN infusion of TEMP attenuated the overexpression of gp91(phox), ACE and IL-1β within the PVN, and decreased sympathetic activity and MAP in ANG II-infused rats.

CONCLUSION

These findings suggest that ANG II infusion induces elevated PICs and oxidative stress in the PVN, which contribute to the sympathoexcitation in hypertension. Inhibition of reactive oxygen species in hypothalamic paraventricular nucleus attenuates the renin-angiotensin system, proinflammatory cytokines and oxidative stress in ANG II-induced hypertension.

Enhanced expression and activity of Nox2 and Nox4 in the macula densa in ANG II-induced hypertensive mice

NAD(P)H oxidase (Nox)2 and Nox4 are the isoforms of Nox expressed in the macula densa (MD). MD-derived superoxide (O₂⁻), primarily generated by Nox2, is enhanced by acute ANG II stimulation. However, the effects of chronic elevations in ANG II during ANG II-induced hypertension on MD-derived O₂⁻ are unknown. We infused a slow pressor dose of ANG II (600 ng·min⁻¹·kg⁻¹) for 2 wk in C57BL/6 mice and found that mean arterial pressure was elevated by 22.3 ± 3.4 mmHg (P < 0.01). We measured O₂⁻ generation in isolated and perfused MDs and found that O₂⁻ generation by the MD was increased from 9.4 ± 0.9 U/min in control mice to 34.7 ± 1.8 U/min in ANG II-induced hypertensive mice (P < 0.01). We stimulated MMDD1 cells, a MD-like cell line, with ANG II and found that O₂⁻ generation increased from 921 ± 91 to 3,687 ± 183 U·min⁻¹·10⁵ cells⁻¹, which was inhibited with apocynin, oxypurinol, or NS-398 by 46%, 14%, and 12%, respectively. We isolated MD cells using laser capture microdissection and measured mRNA levels of Nox. Nox2 and Nox4 levels increased by 3.7 ± 0.17- and 2.6 ± 0.15-fold in ANG II-infused mice compared with control mice. In MMDD1 cells treated with Nox2 or Nox4 small interfering (si)RNAs, ANG II-stimulated O₂⁻ generation was blunted by 50% and 41%, respectively. In cells treated with p22(phox) siRNA, ANG II-stimulated O₂⁻ generation was completely blocked. In conclusion, we found that a subpressor dose of ANG II enhances O₂⁻ generation in the MD and that the sources of this O₂⁻ are primarily Nox2 and Nox4.

Oxidative stress contributes to sex differences in angiotensin II-mediated hypertension in spontaneously hypertensive rats

NADPH oxidase has been implicated in ANG II-induced oxidative stress and hypertension in males; however, the contribution of oxidative stress to ANG II hypertension in females is unknown. In the present study, we tested the hypothesis that greater antioxidant capacity in female spontaneously hypertensive rats (SHR) blunts ANG II-induced oxidative stress and hypertension relative to males. Whole body and renal cortical oxidative stress levels were assessed in female and male SHR left untreated or following 2 wk of chronic ANG II infusion. Chronic ANG II infusion increased NADPH oxidase enzymatic activity in the renal cortex of both sexes; however, this increase only reached significance in female SHR. In contrast, male SHR demonstrated a greater increase in all measurements of reactive oxygen species production in response to chronic ANG II infusion. ANG II infusion increased plasma superoxide dismutase activity only in female SHR (76 ± 9 vs. 190 ± 7 Units·ml(-1)·mg(-1), P < 0.05); however, cortical antioxidant capacity was unchanged by ANG II in either sex. To assess the functional implication of alterations in NADPH enzymatic activity and oxidative stress levels following ANG II infusion, additional experiments assessed the ability of the in vivo antioxidant apocynin to modulate ANG II hypertension. Apocynin significantly blunted ANG II hypertension in male SHR (174 ± 2 vs. 151 ± 1 mmHg, P < 0.05), with no effect in females (160 ± 11 vs. 163 ± 10 mmHg). These data suggest that ANG II hypertension in male SHR is more dependent on increases in oxidative stress than in female SHR.

Osteopontin deficiency protects against aldosterone-induced inflammation, oxidative stress, and interstitial fibrosis in the kidney

Osteopontin (OPN) has been implicated in the pathology of several renal conditions. Recently, we demonstrated in vitro that aldosterone has important roles in collagen synthesis by inducing OPN (Irita J, Okura T, Kurata M, Miyoshi K, Fukuoka T, Higaki J. Hypertension 51: 507–513, 2008). The aim of the present study was to clarify the roles of OPN in aldosterone-mediated renal fibrosis by infusing aldosterone into either wild-type (WT) or OPN knockout mice (OPN−/−). We used uninephrectomized mice treated with aldosterone and high salt to exacerbate renal fibrosis. After 4 wk of treatment with aldosterone, we showed similar increases in systolic blood pressure in both strains of mice. Urine albumin excretion was greater in aldosterone-infused WT mice than in aldosterone-infused OPN−/− mice. Immunohistochemical analysis showed high levels of OPN expression in aldosterone-infused WT mice. Interstitial fibrosis and inflammatory infiltrations were increased in aldosterone-infused WT mice compared with either vehicle-infused WT or aldosterone-infused OPN−/− mice. These changes were ameliorated markedly by eplerenone treatment in aldosterone-infused WT mice. Aldosterone-infused WT mice also had increased expression of NADPH oxidase subunits compared with aldosterone-infused OPN−/− mice. We observed a marked increase in oxidative stress markers in aldosterone-infused WT mice compared with aldosterone-infused OPN−/− mice. These results indicate that OPN is a promoter of aldosterone-induced inflammation, oxidative stress, and interstitial fibrosis in the kidney and suggest that inhibition of OPN may be a potential therapeutic target for prevention of renal injury.

Hypertension in postmenopausal women: pathophysiology and treatment

Hypertension is the most common chronic disease in industrialized countries and represents the most common major cardiovascular risk factor after the fifth decade of life in both men and women. The prevalence of hypertension is lower in premenopausal women than men, whereas in postmenopausal women it is higher than in men. Mechanisms responsible for the increase in blood pressure are complex and multifactorial, including loss of estrogen, oxidative stress, endothelial dysfunction, modification in renin-angiotensin system spillover and sympathetic activation. In addition, postmenopausal hypertension can be considered an isolated disease, more typical of elderly women, or part of the metabolic syndrome, which is indeed more common in early postmenopausal women. In particular, metabolic syndrome may be considered a potentially unfavourable prognostic factor in hypertensive postmenopausal women, because it seems to worsen the severity of hypertension and reduce the capacity to respond to specific treatments. This article summarizes the different causes of postmenopausal hypertension and the specific treatment recommended by guidelines for this condition.

Role of superoxide and thromboxane receptors in acute angiotensin II-induced vasoconstriction of rabbit vessels

This study explored the hypothesis that a portion of angiotensin II-induced contractions is dependent on superoxide generation and release of a previously unidentified arachidonic acid metabolite that activates vascular smooth muscle thromboxane receptors. Treatment of rabbit aorta or mesentery artery with the thromboxane receptor antagonist SQ29548 (10 μM) reduced angiotensin II-induced contractions (maximal contraction in aorta; control vs. SQ29548: 134 ± 16 vs. 93 ± 10%). A subset of rabbits deficient in vascular thromboxane receptors also displayed decreased contractions to angiotensin II. The superoxide dismutase mimetic Tiron (30 mM) attenuated angiotensin II-induced contractions only in rabbits with functional vascular thromboxane receptors (maximal contraction in aorta; control vs. Tiron: 105 ± 5 vs. 69 ± 11%). Removal of the endothelium or treatment with a nitric oxide synthase inhibitor, nitro-l-arginine (30 μM) did not alter angiotensin II-induced contractions. Tiron and SQ29548 decreased angiotensin II-induced contractions in the denuded aortas by a similar percentage as that observed in intact vessels. The cyclooxygenase inhibitor indomethacin (10 μM) or thromboxane synthase inhibitor dazoxiben (10 μM) had no effect on angiotensin II-induced contractions indicating that the vasoconstrictor was not thromboxane. Angiotensin II increased the formation of a 15-series isoprostane. Isoprostanes are free radical-derived products of arachidonic acid. The unidentified isoprostane increased when vessels were incubated with the superoxide-generating system xanthine/xanthine oxidase. Pretreatment of rabbit aorta with the isoprostane isolated from aortic incubations enhanced angiotensin II-induced contractions. Results suggest the factor activating thromboxane receptors and contributing to angiotensin II vasoconstriction involves the superoxide-mediated generation of a 15-series isoprostane.

Hypertension alone or related to the metabolic syndrome in postmenopausal women

Cardiovascular risk is poorly perceived by women, especially during the peri- and postmenopausal period when susceptibility to cardiovascular events increases. Nevertheless in Europe, 55% of women versus 43% of men currently die of cardiovascular disease. Blood pressure is one of the most powerful and accurate determinants of cardiovascular status and risk. Despite its importance, hypertension is often underestimated and undiagnosed, especially in women. Various mechanisms are implicated to play a role in the blood pressure increase in women at the time of menopause. Hypertension can be considered an isolated disease, more typical of elderly women, or part of the metabolic syndrome, more frequent in early postmenopausal women. The metabolic syndrome, a clustering of lipid and nonlipid cardiovascular risk factors, is estimated to affect approximately 20-30% of the middle-aged population and its prevalence appears to be increasing in the worldwide population.

8-iso-prostaglandin-F2α stimulates chloride transport in thick ascending limbs: role of cAMP and protein kinase A

Salt reabsorption by the loop of Henle controls NaCl handling and blood pressure regulation. Increased oxidative stress stimulates NaCl transport in one specific segment of the loop of Henle called the thick ascending limb (TAL). The isoprostane 8-iso-prostaglandin-F2α (8-iso-PGF2α) is one of the most abundant nonenzymatic lipid oxidation products and has been implicated in the development of hypertension. However, it is not known whether 8-iso-PGF2α regulates transport or the mechanisms involved. Because protein kinase A (PKA) stimulates NaCl transport in several nephron segments, we hypothesized that 8-iso-PGF2α increases NaCl transport in the cortical TAL (cTAL) via a PKA-dependent mechanism. We examined the effect of luminal 8-iso-PGF2α on NaCl transport by measuring chloride absorption (J(Cl)) in isolated microperfused cTALs. Adding 8-iso-PGF2α to the lumen increased J(Cl) by 54% (from 288.7 ± 30.6 to 446.5 ± 44.3 pmol·min(-1)·mm(-1); P < 0.01), while adding it to the bath enhanced J(Cl) by 35% (from 236.3 ± 35.3 to 319.2 ± 39.8 pmol·min(-1)·mm(-1); P < 0.05). This stimulation was blocked by Na-K-2Cl cotransporter inhibition. Next, we tested the role of cAMP. Basal cAMP in the cTAL was 18.6 ± 1.6 fmol·min(-1)·mm(-1), and 8-iso-PGF2α raised it to 35.1 ± 1.4 fmol·min(-1)·mm(-1), an increase of 94% (P < 0.01). Because cAMP stimulates PKA, we measured J(Cl) using the PKA-selective inhibitor H89. In the presence of H89 (10 μM), 8-iso-PGF2α failed to increase transport regardless of whether it was added to the lumen (216.1 ± 16.7 vs. 209.7 ± 23.8 pmol·min(-1)·mm(-1); NS) or the bath (150.4 ± 32.9 vs. 127.1 ± 28.6 pmol·min(-1)·mm(-1); NS). We concluded that 8-iso-PGF2α stimulates cAMP and increases Cl transport in cTALs via a PKA-dependent mechanism.

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

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

Brain nuclear factor-kappa B activation contributes to neurohumoral excitation in angiotensin II-induced hypertension

AIMS

Angiotensin II (ANG II)-induced inflammatory and oxidative stress responses contribute to the pathogenesis of hypertension. In this study, we determined whether nuclear factor-kappa B (NF-kappaB) activation in the hypothalamic paraventricular nucleus (PVN) increases oxidative stress and contributes to the ANG II-induced hypertensive response.

METHODS AND RESULTS

Rats were infused intravenously with ANG II (10 ng/kg per min) or saline for 4 weeks. These rats received either vehicle or losartan (LOS, 20 microg/h), an angiotensin II type 1 receptor (AT1-R) antagonist; pyrrolidine dithiocarbamate (PDTC, 5 microg/h), a NF-kappaB inhibitor; tempol (TEMP, 80 microg/h), a superoxide scavenger; LOS (20 microg/h), and PDTC (5 microg/h); or TEMP (80 microg/h) and PDTC (5 microg/h), given intracerebroventricularly (ICV) via osmotic minipump. ANG II infusion resulted in increased mean arterial pressure, renal sympathetic nerve activity, plasma proinflammatory cytokines (PIC), norepinephrine, and aldosterone. These rats also had higher levels of Fra-LI (an indicator of chronic neuronal activation), PIC, phosphorylated IKKbeta, NF-kappaB subunits, AT1-R, superoxide, and gp91phox (a subunit of NADP(H) oxidase) and lower levels of IkappaBalpha in the PVN than control animals. ICV treatment with LOS, PDTC, or TEMP attenuated these changes, and combined treatment with ICV LOS and PDTC, or ICV TEMP and PDTC prevented these ANG II-induced hypertensive responses.

CONCLUSION

These findings suggest that an ANG II-induced increase in the brain renin-angiotensin system activates NF-kappaB in the PVN and contributes to sympathoexcitation in hypertension. The increased superoxide in the PVN contributes to NF-kappaB activation and neurohumoral excitation in hypertension.

Sex differences in control of blood pressure: role of oxidative stress in hypertension in females

In general, blood pressure is higher in normotensive men than in age-matched women, and the prevalence of hypertension in men is also higher until after menopause, when the prevalence of hypertension increases for women. It is likely then that the mechanisms by which blood pressure increases in men and women with aging may be different. Although clinical trials to reduce blood pressure with antioxidants have typically not been successful in human cohorts, studies in male rats suggest that oxidative stress plays an important role in mediating hypertension. The exact mechanisms by which oxidative stress increases blood pressure have not been completely elucidated. There may be several reasons for the discrepancies between clinical and animal studies. In this review, the data obtained in selected clinical and animal studies are discussed, and the hypothesis is put forward that oxidative stress may not be as important in mediating hypertension in females as has been shown previously in male rats. Furthermore, it is likely that differences in genetics, age, length of time with hypertension, endothelial dysfunction, and sex are all factored in to modulate the responses to antioxidants in humans. As such, future clinical trials should be designed and powered to evaluate the effects of oxidative stress on blood pressure separately in men and women.

Reactive oxygen species and glucocorticoid-induced hypertension

1. There is increasing evidence for a role of oxidative stress and nitric oxide deficiency in experimental glucocorticoid-induced hypertension, as evidenced by increased biomarkers of oxidative stress; the effectiveness of antioxidants or reduced NADPH oxidase antagonists in lowering blood pressure; and secondary upregulation of endogenous antioxidant enzymes in response to oxidative stress. 2. In the vasculature, the main sources of superoxide are NADPH oxidase, xanthine oxidase, uncoupled endothelial nitric oxide synthase (eNOS) and mitochondria. 3. NADPH oxidase plays a significant role in the pathogenesis of glucocorticoid-induced hypertension in the rats, but xanthine oxidase and uncoupled eNOS pathways are not important sources of reactive oxygen species in these models. The role of mitochondrial reactive oxygen species in glucocorticoid-induced hypertension remains to be clarified.

Long-term nebivolol administration reduces renal fibrosis and prevents endothelial dysfunction in rats with hypertension induced by renal mass reduction

OBJECTIVES

D/L-Nebivolol is a lypophilic beta1-adrenergic antagonist which is devoid of intrinsic sympathomimetic activity and can increase nitric oxide (NO) bioavailability with its subsequent vasodilating properties. The purpose of the present work was to assess the effect of long-term nebivolol administration on both renal damage and endothelial dysfunction induced by renal mass reduction (RMR) in rats. Atenolol, which does not increase NO bioavailability, was included in the study as a comparative beta-adrenoceptor antagonist.

METHODS

Rats were subjected to both right nephrectomy and surgical removal of two-thirds of the left kidney in order to retain approximately one-sixth of the total renal mass. One week after ablation, rats were distributed randomly according to the following experimental groups: control group containing RMR rats without treatment; RMR rats treated daily with nebivolol for 6 months (drinking water, 8 mg/kg per day); and RMR rats treated daily with atenolol for 6 months (drinking water, 80 mg/kg per day). A group of sham-operated animals was also included.

RESULTS

Administration of either nebivolol or atenolol similarly reduced arterial pressure in comparison with RMR untreated animals; however, animals receiving nebivolol presented lower levels of collagen type I expression as well as lower glomerular and interstitial fibrosis than those receiving atenolol. Urinary excretion of oxidative stress markers were also lower in animals receiving nebivolol than in rats treated with atenolol. Furthermore, nebivolol prevented RMR-induced endothelial dysfunction more efficiently than atenolol.

CONCLUSIONS

Nebivolol protects against renal fibrosis, oxidative stress and endothelial dysfunction better than equivalent doses, in terms of arterial pressure reduction, of atenolol in a hypertensive model of renal damage induced by RMR.

Biomarkers of oxidative stress and antioxidant status in children born small for gestational age: evidence of lipid peroxidation

Children born small for gestational age are known to be at increased risk for adult diseases such as hypertension, diabetes, and coronary heart disease. Oxidative stress is a common feature of these pathogenic conditions and can be the key link between size at birth and increased morbidity later in life. The purpose of this study was to analyze the parameters of lipoperoxidation and changes in antioxidant defense system as well as assess their relationship to birth weight. Concentrations of thiobarbituric-acid-reactive-substances and F2-isoprostanes, total antioxidant status, and the activity of both superoxide dismutase and glutathione peroxidase were measured in 65 children (33 boys, 32 girls; ages 8-13 y). Thiobarbituric-acid-reactive-substances and F2-isoprostane levels were significantly elevated in children born small for gestational age. Nevertheless, superoxide dismutase activity was significantly elevated in these children and the levels of both glutathione peroxidase activity and total antioxidant status were unchanged. Moreover, we found that systolic blood pressure was positively associated with thiobarbituric-acid-reactive-substances levels in race- and gender-adjusted models but not in a multivariable regression model. In conclusion, the current study revealed that there is evidence of oxidative stress in children born small for gestational age as supported by increased lipid peroxidation.

Cytochrome P450 enzymes: Central players in cardiovascular health and disease

Cardiovascular disease (CVD) is a human health crisis that remains the leading cause of death worldwide. The cytochrome P450 (CYP) class of enzymes are key metabolizers of both xenobiotics and endobiotics. Many CYP enzyme families have been identified in the heart, endothelium and smooth muscle of blood vessels. Furthermore, mounting evidence points to the role of endogenous CYP metabolites, such as epoxyeicosatrienoic acids (EETs), hydroxyeicosatetraenoic acids (HETEs), prostacyclin (PGI(2)), aldosterone, and sex hormones, in the maintenance of cardiovascular health. Emerging science and the development of genetic screening have provided us with information on the differences in CYP expression among populations and groups of individuals. With this information, a link between CYP expression and activity and CVD, such as hypertension, coronary artery disease (CAD), myocardial infarction, heart failure, stroke, and cardiomyopathy and arrhythmias, has been established. In fact many currently used therapeutic modalities in CVD owe their therapeutic efficacy to their effect on CYP metabolites. Thus, the evidence for the involvement of CYP in CVD is numerous. Concentrating on treatment modalities that target the CYP pathway makes ethical sense for the affected individuals and decreases the socioeconomic burden of this disease. However, more research is needed to allow the integration of this information into a clinical setting.

Sexual dimorphism in the renin-angiotensin system in aging spontaneously hypertensive rats

In young adult spontaneously hypertensive rats (SHR), mean arterial pressure (MAP) is higher in males than in females and inhibition of the renin-angiotensin system (RAS) eliminates this sex difference. After cessation of estrous cycling in female SHR, MAP is similar to that in male SHR. The purpose of this study was to determine the role of the RAS in maintenance of hypertension in aging male and female SHR. At 16 mo of age, MAP was similar in male and female SHR (183+/-5 vs. 193+/-8 mmHg), and chronic losartan (40 mg.kg-1.day-1 po for 3 wk) reduced MAP by 52% (to 90+/-8 mmHg, P<0.05 vs. control) in males and 37% (to 123+/-11 mmHg, P<0.05 vs. control) in females (P<0.05, females vs. males). The effect of losartan on angiotensin type 1 (AT1) receptor blockade was similar: MAP responses to acute doses of ANG II (62.5-250 ng/kg) were blocked to a similar extent in losartan-treated males and females. F2-isoprostane excretion was reduced with losartan more in males than in females. There were no sex differences in plasma renin activity, plasma angiotensinogen or ANG II, or renal expression of AT1 receptors, angiotensin-converting enzyme, or renin. However, renal angiotensinogen mRNA and protein expression was higher in old males than females, whereas renal ANG II was higher in old females than males. The data show that, in aging SHR, when blood pressures are similar, there remains a sexual dimorphism in the response to AT1 receptor antagonism, and the differences may involve sex differences in mechanisms responsible for oxidative stress with aging.

Enhanced superoxide generation modulates renal function in ANG II-induced hypertensive rats

This study was performed to examine the role of superoxide formation in the regulation of renal hemodynamic and excretory function and to assess its contribution in the pathogenesis of ANG II-dependent hypertension. Renal responses to acute intra-arterial infusion of the O2− scavenger tempol (50 μg·min−1·100 g body wt−1) with or without catalase (1,500 U·min−1·100 g−1; both native and polyethylene glycol-catalase), which reduces H2O2, were evaluated in anesthetized male Sprague-Dawley rats treated chronically with ANG II (65 ng/min) for 2 wk and compared with nontreated control rats. In ANG II-treated hypertensive rats, tempol caused increases in medullary (13 ± 2%), cortical (5 ± 2%), and total renal blood flow (9 ± 2%) without altering systemic arterial pressure. There were also increases in glomerular filtration rate (9 ± 2%), urine flow (17 ± 4%), and sodium excretion (26 ± 5%). However, tempol infusion in nontreated normotensive rats did not cause significant changes in any of these renal parameters. Coinfusion of catalase with tempol did not alter the responses observed with tempol alone, indicating that the observed renal responses to tempol in ANG II-treated rats were attributed to its O2− scavenging effects without the involvement of H2O2. Tempol infusion also significantly decreased 8-isoprostane excretion in ANG II-treated rats (39 ± 6%) without changes in H2O2 excretion. However, coinfusion of catalase reduced H2O2 excretion in both ANG II-treated (41 ± 6%) and nontreated rats (28 ± 5%). These data demonstrate that enhanced generation of O2− modulates renal hemodynamic and tubular reabsoptive function, possibly leading to sodium retention and thus contributing to the pathogenesis of ANG II-induced hypertension.

Testosterone supplementation in aging men and women: possible impact on cardiovascular-renal disease

Treatment of aging men and women with testosterone supplements is increasing. The supplements are given to postmenopausal women mainly to improve their libido and to aging men to improve muscle mass and bone strength, to improve libido and quality of life, to prevent and treat osteoporosis, and, with the phosphodiesterase-5 inhibitors, such as sildenafil, to treat erectile dysfunction. The increased use of testosterone supplements in aging individuals has occurred despite the fact that there have been no rigorous clinical trials examining the effects of chronic testosterone on the cardiovascular-renal disease risk. Studies in humans and animals have suggested that androgens can increase blood pressure and compromise renal function. Androgens have been shown to increase tubular sodium and water reabsorption and activate various vasoconstrictor systems in the kidney, such as the renin-angiotensin system and endothelin. There is also evidence that androgens may increase oxidative stress. Furthermore, the kidney contains the enzymes necessary to produce androgens de novo. This review presents an overview of the data from human and animal studies in which the role of androgens in promoting renal and cardiovascular diseases has been investigated.

Cardiovascular alteration and treatment of hypertension: do men and women differ?

Cardiovascular disease is one of the most common causes of mortality affecting both men and women in industrialized nations. Sex-related differences have been well established with regard to heart and vascular function as well as cardiovascular disease processes. Nevertheless, the precise mechanisms of action behind these gender-related differences are poorly understood. Premenopausal women have a relatively lower arterial blood pressure compared to age-matched men and post-menopausal women, suggesting a role of ovarian hormones in blood pressure regulation. Sex-related differences in vasculature and neuroendocrine systems are also present that can affect hemostasis, vascular reactivity, and vascular tone. Treatment for cardiovascular disease and hypertension has been challenging and unsatisfactory. Men and women may require different antihypertensive regimens due to differences in the progression and presentation of hypertension. Additionally, hormone replacement therapy in postmenopausal women has been controversial, producing both beneficial and detrimental effects. Therefore, this review will focus on sex-related differences in the heart and vasculature, and treatments for cardiovascular disease, such as hypertension.

Animal models of hypertension: an overview

Hypertension is a multifactorial disease involving complex interactions between genetic and environmental factors. Development of experimental models of hypertension allowed dissection and isolation of various factors associated with regulation of blood pressure, inheritance of hypertensive traits, and cellular responses to injury. The phenotype-driven approach is taking advantage of selective breeding of animals (primarily rats) that exhibit a desired phenotype, like the useful SHR. Genotype-driven models include transgenic techniques, in which mice are the most successful for selective deletion or overexpression of target genes. Notably, a combination of comparative genomics strategies and phenotypic correlates enhances the utility of hypertension models and their clinical relevance. Indeed, experimental models enabled development of targeted interventions aimed at decreasing not only blood pressure but also target organ injury. Continued utilization of experimental models simulating human hypertension, particularly those that combine other clinically relevant comorbidities like obesity or hypercholesterolemia, may afford development of effective strategies to address this common disease. Nevertheless, a cautious approach is mandatory when experimental findings in these models are extrapolated to human hypertension.

Antihypertensive response to prolonged tempol in the spontaneously hypertensive rat

INTRODUCTION

Tempol is a permeant nitroxide superoxide dismutase (SOD) mimetic that lowers mean arterial pressure (MAP) in spontaneously hypertensive rats (SHRs). We investigated the hypothesis that the antihypertensive response entails a negative salt balance, blunting of plasma renin activity (PRA), endothelin-1 (ET-1), or catecholamines or correction of oxidative stress as indexed by 8-isoprostane prostaglandin F(2alpha) (PGF(2alpha)) (8-Iso).

METHODS

Groups (N= 6 to 8) of SHRs were infused for 2 weeks with vehicle or tempol (200 nmol/kg/min) or given tempol (2 mmol/L) in drinking water.

RESULTS

Tempol infusion reduced the MAP of anesthetized SHRs (150 +/- 5 vs. 126 +/- 6 mm Hg) (P < 0.005). Oral tempol did not change the heart rate but reduced the MAP of conscious SHRs (-23 +/- 6 mm Hg) (P < 0.01) but not Wistar-Kyoto (WKY) rats. Tempol infusion increased the PRA (2.2 +/- 0.2 vs. 5.0 +/- 0.9 ng/mL/hour) (P < 0.005), did not change excretion of nitric oxide (NO) [NO(2)+ NO(3) (NOx)], ET-1, or catecholamines but reduced excretion of 8-Iso (13.2 +/- 1.4 vs. 9.6 +/- 0.9 ng/24 hours; P < 0.01). Cumulative Na(+) balance and gain in body weight were unaltered by tempol infusion. Tempol prevented a rise in MAP with high salt intake.

CONCLUSION

Tempol corrects hypertension without a compensatory sympathoadrenal activation or salt retention. The response is independent of nitric oxide, endothelin, or catecholamines and occurs despite increased PRA. It is accompanied by a reduction in oxidative stress and is maintained during increased salt intake.

Effects of captopril on the renin angiotensin system, oxidative stress, and endothelin in normal and hypertensive rats

There is substantial evidence suggesting that angiotensin II plays an important role in elevating blood pressure of spontaneously hypertensive rats, despite normal plasma renin activity, and that converting enzyme inhibitors (captopril) can effectively normalize blood pressure in the spontaneously hypertensive rats. One mechanism by which angiotensin II induces hypertension is via oxidative stress and endothelin, as seen in subpressor angiotensin II-induced hypertension. In fact, it has been shown that antioxidants lower mean arterial pressure in spontaneously hypertensive rats. However, the relationship between angiotensin II, oxidative stress, and endothelin in the spontaneously hypertensive rats is still relatively undefined. This study examines the relationship between mean arterial pressure, plasma renin activity, angiotensin II, oxidative stress, and endothelin in spontaneously hypertensive rats compared with normotensive Wistar Kyoto rats, and the effects of captopril on this association. Untreated spontaneously hypertensive rats had increased plasma angiotensin II levels despite normal plasma renin activity, oxidative stress, and endothelin. Captopril treatment in spontaneously hypertensive rats lowered mean arterial pressure, angiotensin II, oxidative stress, and endothelin, and increased plasma renin activity. In contrast, captopril increased plasma renin activity (suggesting effective captopril treatment) but did not significantly alter mean arterial pressure, angiotensin II, oxidative stress, or endothelin of Wistar Kyoto rats. These results suggest that in spontaneously hypertensive rats, angiotensin II is a primary instigator of hypertension, and that captopril selectively lowers angiotensin II, oxidant stress, and endothelin, which in turn may contribute to the blood pressure-lowering efficacy of captopril in spontaneously hypertensive rats.

Enhanced oxidative stress in coronary heart disease and chronic heart failure as indicated by an increased 8-epi-PGF(2alpha)

The role of oxidation injury as an important factor in the pathophysiology of cardiomyopathy (CMP) has recently gained increasing interest. Semiquantitative analysis for isoprostane, 8-epi-prostaglandin F(2alpha) (8-epi-PGF(2alpha)), and oxidised low-density lipoprotein (ox-LDL) of coronary vascular tissue samples derived from CMP patients revealed an increased extent and intensity of uptake as compared to the respective controls. To evaluate oxidative stress in vivo, we examined plasma, serum, salivary, and urinary 8-epi-PGF(2alpha) in patients with dilated CMP (n=20) and ischemic CMP (n=20) with decreased left ventricular ejection fraction (LVEF). Patients with coronary heart disease (CHD) (n=20) and 20 healthy, age-matched, and sex-matched controls were investigated in parallel. 8-Epi-PGF(2alpha) levels were correlated with the functional severity of heart failure [New York Heart Association (NYHA) classification] and LVEF. 8-Epi-PGF(2alpha) levels were matched according to risk factors (smoking and hypercholesterolemia) and were significantly higher in patients with CMP as compared to healthy controls and patients with CHD in all investigated compartments. A positive correlation between NYHA stages and 8-epi-PGF(2alpha), as well as a negative correlation to LVEF, could be demonstrated in a subgroup analysis. These findings reflect the enhanced oxidation injury in patients with CMP and, to a lesser extent, in CHD as compared to healthy controls, thus highly indicating the relevance of oxidative stress for the pathogenesis and progression of cardiovascular disease.

Vascular effects of 15-F2t-isoprostane in spontaneously hypertensive rats

F2-isoprostanes are a family of compounds derived from arachidonic acid by free radical-catalyzed peroxidation. Among F2-isoprostanes, 15-F2t-IsoP is a vasoconstrictor in animal and human vascular beds. Several recent studies found increased 15-F2t-IsoP levels in animal models of hypertension. However, no data is available on the vascular effect of 15-F2t-IsoP in such models. The contractile responses of 15-F2t-IsoP (10–9 to 3 × 10–5 mol/L) were tested on rat thoracic aortic rings in spontaneously hypertensive rats (SHR) compared with Wistar-Kyoto (WKY) rats. The contraction induced by 15-F2t-IsoP was not significantly different in aortic rings from WKY rats and SHR (Emax 139% ± 5% vs. 134% ± 6%, respectively) and was mediated through thromboxane A2–prostaglandin H2 receptor activation as shown by the rightward shift of the concentration-contraction curves in presence of GR 32191, a specific thromboxane A2–prostaglandin H2 receptor antagonist. Endothelial denudation increased the maximal contraction compared to intact rings induced by 15-F2t-IsoP in both WKY rats (170% ± 20% vs. 139% ± 5%, p < 0.05) and SHR (194% ± 11% vs. 134% ± 6%, p < 0.01), whereas pretreatment with Nω-nitro-L-arginine (10–4 mol/L) or with indomethacin (10–5 mol/L) increased the maximal contraction to 15-F2t-IsoP in WKY rats but not in SHR. SHRs treated with an angiotensin-converting enzyme inhibitor, enalapril, for four weeks showed decreased maximal contraction to 15-F2t-IsoP in vessels with and without endothelium compared with untreated SHR. In conclusion, 15-F2t-IsoP-induced vasoconstriction is similar in SHR compared with WKY rats. Endothelium modulates 15-F2t-IsoP contraction in both strains. However, whereas this effect is mediated through nitric oxide- and cyclooxygenase-dependent pathways in WKY rats, other mediators are implicated in SHR. Key words: isoprostane, hypertension, lipid peroxidation, vascular reactivity, angiotensin-converting enzyme (ACE) inhibitors.

F2-Isoprostane level is associated with the angiotensin II type 1 receptor -153A/G gene polymorphism

Recent studies have shown that F2-isoprostane levels-a marker for lipid peroxidation-are increased in human renovascular hypertension but not in essential hypertension. Angiotensin II specifically stimulates F2-isoprostane production through activation of the AT1 receptor. The objective was to determine whether there is a relationship between the level of oxidative stress evaluated by measuring urinary F2-isoprostanes levels and polymorphisms of genes involved in the renine angiotensin aldosterone system (RAAS) regulation. The population studied included 100 subjects, 65 of whom were healthy normotensives; the other 35 were suffering from untreated, essential hypertension. The polymorphisms studied concern the genes encoding angiotensin I-converting enzyme (ACE/in16del/ins), angiotensin II receptor type I (AGTR1/A+39C[A+1166C] and AGTR1/A-153G), angiotensinogen (AGT/M235T), and aldosterone synthase (CYP11B2/T344C). Oxidative stress was evaluated by measuring urinary F2-isoprostanes levels. The characteristics of the population were as follows: men/women = 46/56; age = 50 +/- 10 years; BMI = 24 +/- 3 kg/m2; SBP = 131.7 +/- 17.2 mm Hg; DBP = 84.6 +/- 10.4 mm Hg. In univariate analysis, urinary F2-isoprostane levels were significantly lower in the presence of the G allele of AGTR1/A-153G (56 +/- 17 vs 76 +/- 39 pmol/mmol creatinine; P < 0.001, and P < 0.01 after Bonferroni correction for 10 tests). In multivariate analysis, taking into account BP, age, gender, BMI, plasma glucose, and total cholesterol, the G allele of AGTR1/A-153G is linked independently to urinary F2-isoprostanes level (P < 0.01). Our data suggest that F2-isoprostane level depends at least in part on the A-153G polymorphism of the angiotensin II AT1 receptor gene. The clinical and prognostic relevance of this polymorphism requires further investigation.

Isoprostanes and the kidney

Isoprostanes are not mere bystanders of oxidative injury, but possess potent biological activity and may thus contribute to the pathophysiology of various disorders associated with an increase in free radical formation. 15-F2t-IsoP (8-iso-prostaglandin F2) and 15-E2t-IsoP (8-iso-prostaglandin E2), two of the most abundant isoprostanes, are potent vasoconstrictors in various vascular beds, including the kidney. Since their discovery, numerous studies have aimed to define the receptors through which isoprostanes exert their effects. Whether the thromboxane receptor and/or other prostaglandin receptors mediate the actions of isoprostanes, or whether these compounds interact with their own unique receptors, remains to be clarified. Regardless of their exact mode of action, isoprostanes are being implicated in the pathophysiology of a variety of diseases, and their discovery might give rise to novel therapies for these diseases. Here we describe early studies that defined the vasoactive properties of isoprostanes in the kidney, and subsequent discoveries relating to their renal actions and pathophysiologic significance.

Systemic arterial pressure response to two weeks of Tempol therapy in SHR: involvement of NO, the RAS, and oxidative stress

The roles of nitric oxide (NO) and plasma renin activity (PRA) in the depressor response to chronic administration of Tempol in spontaneously hypertensive rats (SHR) are not clear. The present study was done to determine the effect of 2 wk of Tempol treatment on blood pressure [mean arterial pressure (MAP)], oxidative stress, and PRA in the presence or absence of chronic NO synthase inhibition. SHR were divided into four groups: control, Tempol (1 mmol/l) alone, nitro-L-arginine methyl ester (L-NAME, 4.5 mg x g(-1).day(-1)) alone, and Tempol + L-NAME or 2 wk. With Tempol, MAP decreased by 22%: 191 +/- 3 and 162 +/- 21 mmHg for control and Tempol, respectively (P < 0.05). L-NAME increased MAP by 16% (222 +/- 2 mmHg, P < 0.01), and L-NAME + Tempol abolished the depressor response to Tempol (215 +/- 3 mmHg, P < 0.01). PRA was not affected by Tempol but was increased slightly with L-NAME alone and 4.4-fold with L-NAME + Tempol. Urinary nitrate/nitrite increased with Tempol and decreased with L-NAME and L-NAME + Tempol. Tempol significantly reduced oxidative stress in the presence and absence of L-NAME. In conclusion, in SHR, Tempol administration for 2 wk reduces oxidative stress in the presence or absence of NO, but in the absence of NO, Tempol is unable to reduce MAP. Therefore, NO, but not changes in PRA, plays a major role in the blood pressure-lowering effects of Tempol. These data suggest that, in hypertensive individuals with endothelial damage and chronic NO deficiency, antioxidants may be able to reduce oxidative stress but not blood pressure.

Central Tempol alters basal sympathetic nerve discharge and attenuates sympathetic excitation to central ANG II

In the present study, we established dose-response relationships between central administration of 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (Tempol, a superoxide dismutase mimetic) and the level of renal sympathetic nerve discharge (SND) and tested the hypothesis that intracerebroventricular (icv) Tempol pretreatment would attenuate centrally mediated changes in SND produced by icv ANG II administration. Urethane-chloralose-anesthetized, baroreceptor-denervated, normotensive rats were used. We found that icv Tempol administration produced dose-dependent sympathoinhibitory, hypotensive, and bradycardic responses. Mean arterial pressure and SND values were significantly increased after icv ANG II (150 ng/kg) administration, and these responses were abrogated after icv pretreatment with Tempol (75 μmol/kg) or losartan. Brain superoxide levels tended to be higher in ANG II-treated rats compared with rats treated with Tempol and ANG II. Tempol pretreatment did not prevent increases in SND level that were produced by acute heat stress, which indicates specificity in the effect of Tempol in reducing sympathoexcitation. These results demonstrate that icv Tempol administration influences central sympathetic neural circuits in a dose-dependent manner and attenuates SND responses to central ANG II infusion.

Role of endothelin in mediating postmenopausal hypertension in a rat model

Cardiovascular disease is the leading cause of death in women after menopause. Hypertension, a major cardiovascular risk factor, becomes more prevalent after menopause. The mechanisms responsible for the increase in blood pressure (BP) in postmenopausal women are unknown. We have recently characterized the aged, postestrous-cycling (PMR) spontaneously hypertensive rats (SHR) as a model of postmenopausal hypertension. The purpose of the present study was to determine whether endothelin plays a role in the increased BP in PMR. Premenopausal female SHR, aged 4-5 mo (YF), and PMR, aged 16 mo, were studied. Expression of preproendothelin-1 mRNA was not different in either renal cortex or medulla between PMR and YF (n = 7-8/group). In contrast, ET-1 peptide expression was significantly higher in renal cortex of PMR than in renal cortex of YF, but there was no difference in medullary ET-1. Expression of endothelin ET(A) receptor (ET(A)R) mRNA was lower in renal cortex and medulla of PMR than of YF. Additional groups of rats (n = 6-7/group) were treated for 3 wk with the ET(A)R antagonist ABT-627 (5 mg.kg(-1).day(-1)). BP was significantly higher in PMR than in YF. ET(A)R antagonist reduced BP in PMR by 20% to the level found in control YF. ET(A)R antagonist had no effect on BP in YF. These data support the hypothesis that the increase in BP in PMR is mediated in part by endothelin and the ET(A)R.

The role of reactive oxygen species in the regulation of tubular function

The phrase reactive oxygen species covers a number of molecules and atoms, including the quintessential member of the group, O2-; singlet oxygen; H2O2; organic peroxides; and OONO-. While nitric oxide (NO) is also technically a member of the reactive oxygen species family, it is generally considered with a different class of compounds and will not be considered here. To our knowledge, there are currently no published data reporting the effects of reactive oxygen species on net transepithelial flux in the proximal nephron. However, there is evidence that OONO- regulates Na+/K+ adenosine triphosphatase (ATPase) activity as well as paracellular permeability. While it is easy to speculate that such an effect on the pump would decrease net transepithelial solute and water reabsorption, one cannot do so without knowing how other transporters are affected. O2- stimulates NaCl absorption by the thick ascending limb by activating protein kinase C and blunting the effects of NO. The effects of O2- on thick ascending limb NaCl absorption may be important for the initiation of salt-sensitive hypertension. To our knowledge, there are no published data concerning the role of reactive oxygen species in the regulation of solute absorption in either the distal convoluted tubule or the collecting duct. However, OONO- inhibits basolateral K+ channels in the cortical collecting duct, although the net effect of such inhibition is unknown.

CONCLUSION

While the regulation of tubular transport by reactive oxygen species is important to overall salt and water balance, we know very little about where and how these regulators act along the nephron.

Acute angiotensin II increases plasma F2-isoprostanes in salt-replete human hypertensives

Angiotensin (Ang) II induces oxidative stress in vitro and in animal models of hypertension. We tested the hypothesis that Ang II increases oxidative stress in human hypertension, as assessed by plasma F2-isoprostane concentrations. Plasma F2-isoprostanes, hemodynamic and endocrine parameters were measured at baseline and following a 55 min infusion of 3 ng/kg/min Ang II in 13 normotensive and 13 hypertensive volunteers ingesting a high- (200 mmol/d) or low- (10 mmol/d) sodium diet. Mean arterial pressure (MAP) and body mass index were higher in hypertensive subjects. Ang II infusion increased MAP (p<.001) and plasma aldosterone concentrations (p<.001) and decreased plasma renin activity (p<.001) and renal plasma flow (p<.001) to a similar extent in both groups. Plasma F2-isoprostane concentrations were similar at baseline. There was no effect of Ang II on F2-isoprostane concentrations during low-salt intake in either group (normotensive 51.7 +/- 7.1 to 53.7 +/- 6.5 pg/ml and hypertensive 52.2 +/- 8.2 to 56.2 +/- 10.0 pg/ml; mean +/- SE). During high-salt intake, Ang II increased F2-isoprostane concentrations in the hypertensive group (52.3 +/- 7.2 to 63.2 +/- 10.4 pg/ml, p=0.010) but not in the normotensive group (54.2 +/- 4.4 to 58.9 +/- 6.6 pg/ml, p=0.83). Acute Ang II infusion increases oxidative stress in vivo in hypertensive humans. The renin-angiotensin system may contribute to oxidative stress in human cardiovascular disease.

Effects of ANG II type 1 and 2 receptors on oxidative stress, renal NADPH oxidase, and SOD expression

Oxidative stress accompanies angiotensin (ANG) II infusion, but the role of ANG type 1 vs. type 2 receptors (AT1-R and AT2-R, respectively) is unknown. We infused ANG II subcutaneously in rats for 1 wk. Excretion of 8-isoprostaglandin F2alpha (8-Iso) and malonyldialdehyde (MDA) were related to renal cortical mRNA abundance for subunits of NADPH oxidase and superoxide dismutases (SODs) using real-time PCR. Subsets of ANG II-infused rats were given the AT1-R antagonist candesartan cilexetil (Cand) or the AT2-R antagonist PD-123,319 (PD). Compared to vehicle (Veh), ANG II increased 8-Iso excretion by 41% (Veh, 5.4 +/- 0.8 vs. ANG II, 7.6 +/- 0.5 pg/24 h; P < 0.05). This was prevented by Cand (5.6 +/- 0.5 pg/24 h; P < 0.05) and increased by PD (15.8 +/- 2.0 pg/24 h; P < 0.005). There were similar changes in MDA excretion. Compared to Veh, ANG II significantly (P < 0.005) increased the renal cortical mRNA expression of p22phox (twofold), Nox-1 (2.6-fold), and Mn-SOD (1.5-fold) and decreased expression of Nox-4 (2.1-fold) and extracellular (EC)-SOD (2.1-fold). Cand prevented all of these changes except for the increase in Mn-SOD. PD accentuated changes in p22phox and Nox-1 and increased p67phox. We conclude that ANG II infusion stimulates oxidative stress via AT1-R, which increases the renal cortical mRNA expression of p22phox and Nox-1 and reduces abundance of Nox-4 and EC-SOD. This is offset by strong protective effects of AT2-R, which are accompanied by decreased expression of p22phox, Nox-1, and p67phox.

Role of oxidative stress in angiotensin-induced hypertension

Infusion of ANG II at a rate not sufficient to evoke an immediate vasoconstrictor response, produces a slow increase in blood pressure. Circulating levels of ANG II may be within ranges found in normotensive individuals, although inappropriately high with respect to sodium intake. When ANG II levels are dissociated from sodium levels, oxidative stress (OXST) occurs, which can increase blood pressure by several mechanisms. These include inadequate production or reduction of bioavailability of nitric oxide, alterations in metabolism of arachidonic acid, resulting in an increase in vasoconstrictors and decrease in vasodilators, and upregulation of endothelin. This cascade of events appears to be linked, because ANG II hypertension can be blocked by inhibition of any factor located distally, blockade of ANG II, OXST, or endothelin. Such characteristics are shared by other models of hypertension, such as essential hypertension, hypertension induced by reduction in renal mass, and renovascular hypertension. Thus these findings are clinically important because they reveal 1) uncoupling between ANG II and sodium, which can trigger pathological conditions; 2) the various OXST mechanisms that may be involved in hypertension; and 3) therapeutic interventions for hypertension developed with the knowledge of the cascade involving OXST.

Thromboxane synthase and TP receptor mRNA in rat kidney and brain: effects of salt intake and ANG II

A TP receptor (TP-R) mimetic causes salt-sensitive hypertension and renal afferent arteriolar vasoconstriction. TP-Rs mediate effects of ANG II on renal vascular resistance and drinking. Therefore, we investigated the hypothesis that thromboxane A(2) synthase (TxA(2)-S) and/or TP-R expression is regulated by salt and/or ANG II. Rats (n = 6) received high-salt (HS) or low-salt (LS) diets. Additional HS-diet rats received ANG II while other HS- and LS-diet rats received the AT(1) receptor (AT(1)-R) antagonist losartan. Excretion of thromboxane B(2) by conscious rats was increased with the HS diet compared with the LS diet (126 +/- 10 vs. 48 +/- 5 pmol/24 h, respectively; P < 0.01). The mRNA abundance for TP-Rs (relative to beta-actin) in the kidney cortex was enhanced 30% by the HS diet (P < 0.001) and was reduced 50% by the addition of ANG II (P < 0.001). However, during losartan administration, the effects of salt were reversed; mRNA more than doubled during the LS diet (P < 0.001). Similarly, the mRNA abundance for TP-Rs in the brain stem was reduced by 50% with the addition of ANG II (P < 0.001) and during losartan administration was almost doubled by the LS diet (P < 0.001). The mRNA abundance for TxA(2)-S in the kidney cortex also was increased many times with the HS diet (P < 0.001). In contrast, the mRNA for TxA(2)-S in the brain was unaffected by salt. ANG II did not affect TxA(2)-S at either site. During losartan administration, TxA(2)-S increased modestly in the brain stem with the LS diet. mRNA abundance for TP-Rs in the kidney cortex and brain stem is suppressed by ANG II acting on AT(1)-Rs. In the absence of AT(1)-Rs, expression of TP-Rs at both sites is enhanced by LS intake. In contrast, ANG II does not affect the mRNA abundance for TxA(2)-S. Expression of TxA(2)-S is enhanced by HS intake in the kidney cortex but by LS intake in the brain stem only during losartan administration. Thus TP-Rs are strongly dependent on ANG II acting on AT(1)-Rs, whereas TxA(2)-S is regulated differentially in the kidney cortex and brain stem by salt intake.

Superoxide contributes to vascular dysfunction in mice that express human renin and angiotensinogen

This study examined vascular function and the role of superoxide in mice that chronically express human renin (R+) and human angiotensinogen (A+). Responses of aortas from R+/A+ mice and from their normotensive littermates (RA- mice) were examined in vitro. Endothelium-dependent relaxation to acetylcholine was impaired in vessels from R+/A+ mice (e.g., maximal relaxation to 100 microM acetylcholine was 45 +/- 5% and 65 +/- 3% in R+/A+ and RA- mice, respectively; P < 0.05). Relaxation was also impaired to the endothelium-independent dilators authentic nitric oxide and nitroprusside in vessels from R+/A+ mice. Maximal vasorelaxation to the endothelium-independent, non-nitric oxide dilator papaverine was similar in R+/A+ and RA- mice. Incubation of vessels from R+/A+ mice with Tiron (1 mM), a superoxide scavenger, improved relaxation to acetylcholine, nitric oxide, and nitroprusside. In contrast, incubation with diethyldithiocarbamate (1 mM), an inhibitor of copper-containing SODs, reduced acetylcholine- and nitroprusside-induced relaxation in vessels from both R+/A+ and RA- mice. Basal superoxide levels, measured with lucigenin-enhanced chemiluminescence (5 microM lucigenin) and hydroethidine-based fluorescent confocal microscopy, were higher in vessels from R+/A+ mice and were Tiron and polyethylene glycol-SOD sensitive. These results suggest that increased superoxide contributes to impaired nitric oxide-mediated relaxation in this genetic model of chronic angiotensin II-dependent hypertension.

Involvement of TP and EP3 receptors in vasoconstrictor responses to isoprostanes in pulmonary vasculature

Although isoprostanes generally act on smooth muscle via TXA(2)-selective prostanoid receptors (TPs), some suggest other prostanoid receptors or possibly even a novel isoprostane-selective receptor might be involved. We studied contractions to several isoprostanes in porcine pulmonary vasculature using organ bath techniques. 8-iso-prostaglandin E(2) (PGE(2)) was the most potent and efficacious of the isoprostanes, with a log EC(50) of -7.0 +/- 0.2 in the pulmonary artery and -6.8 +/- 0.2 in the pulmonary vein. The responses to all the isoprostanes were essentially completely blocked by the TP receptor antagonist ICI 192605 [4(Z)-6-[(2,4,5-cis)2-(2-chlorophenyl)-4-(2-hydroxyphenyl)1,3-dioxan-5-yl]hexenoic acid], and the equilibrium dissociation constants for ICI 192605 competing with U46619 or 8-iso-PGE(2) were both approximately 2 nM, indicating that isoprostane-evoked responses involve primarily TP receptors. Only 8-iso-PGE(2) was able to evoke substantial contractions in the presence of ICI 192605 and only in the pulmonary vein. The EC(50) of these ICI 192605-insensitive responses was -6.1 +/- 0.2. Using a variety of prostanoid agonists, we found the pulmonary vein lacked excitatory PGF(2alpha)-selective prostanoid receptor (FP) or PGD(2)-selective prostanoid receptor (DP) but expressed excitatory EP(3) receptors. The ICI 192605-insensitive responses to 8-iso-PGE(2) were unaffected by the EP(1) antagonist SC-19220 [8-chloro-debenz[b,f][1,4]oxazepine-10(11H)-carboxy-(2-acetyl) hydrazine; 10(-5) M] but were antagonized by the less selective DP/EP(1)/EP(2) antagonist AH6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid; 10(-5) M) or by cyclopiazonic acid (10(-5) M; depletes the internal Ca(2+) store). Our data indicate that, whereas 8-iso-PGE(2) constricts pulmonary vasculature primarily through TP receptors, a substantial portion of this response is also directed through EP(3) receptors or possibly a novel isoprostane receptor.