Ovariectomy is protective against renal injury in the high-salt-fed older mRen2.Lewis rat

Estrogen-mediated mechanisms in hypertension and other cardiovascular diseases

Cardiovascular disease (CVD) is the leading cause of death globally for men and women. Premenopausal women have a lower incidence of hypertension and other cardiovascular events than men of the same age, but diminished sex differences after menopause implicates 17-beta-estradiol (E2) as a protective agent. The cardioprotective effects of E2 are mediated by nuclear estrogen receptors (ERα and ERβ) and a G protein-coupled estrogen receptor (GPER). This review summarizes both established as well as emerging estrogen-mediated mechanisms that underlie sex differences in the vasculature during hypertension and CVD. In addition, remaining knowledge gaps inherent in the association of sex differences and E2 are identified, which may guide future clinical trials and experimental studies in this field.

Hypertension after the Menopause: What Can We Learn from Experimental Studies?

Hypertension is the most prevalent cardiovascular disease of the adult population and is closely associated with serious cardiovascular events. The burden of hypertension with respect to vascular and other organ damage is greater in women. These sex differences are not fully understood. The unique feature in women is their transition to menopause accompanied by profound hormonal changes that affect the vasculature that are also associated with changes of blood pressure. Results from studies of hormone replacement therapy and its effects on the cardiovascular system are controversial, and the timing of treatment after menopause seems to be important. Therefore, revealing potential sex- and sex hormone-dependent pathophysiological mechanisms of hypertension in experimental studies could provide valuable information for better treatment of hypertension and vascular impairment, especially in postmenopausal women. The experimental rat models subjected to ovariectomy mimicking menopause could be useful tools for studying the mechanisms of blood pressure regulation after menopause and during subsequent therapy.

Biological Sex Modulates the Adrenal and Blood Pressure Responses to Angiotensin II

The relationship between biological sex and aldosterone on blood pressure (BP) is unclear. We hypothesized that sex would modify the interaction between aldosterone and vascular responses to salt intake and angiotensin II (AngII). To test this hypothesis, in 1592 subjects from the well-controlled Hypertensive Pathotype cohort, we compared responses of women and men to chronic (BP and aldosterone levels in response to dietary salt) and acute (BP, renal plasma flow, and aldosterone responses to AngII infusion) manipulations. Women had a 30% higher salt sensitivity of BP than men (P<0.0005) regardless of age or hypertension status, a greater BP response to AngII, and a 15% greater aldosterone response to AngII on both restricted and liberal salt diets (P<0.005). Furthermore, there was an interaction (P=0.003) between sex and aldosterone on BP response to AngII. Women also had a greater (P<0.01) increment in renal plasma flow in response to AngII than men. To assess potential mechanisms for this sex effect, we compared aldosterone responses to AngII or potassium from rat zona glomerulosa cells and observed greater aldosterone production in female than male zona glomerulosa cells basally and in response to both agonists (P<0.0001). In a rodent model of aldosterone-mediated cardiovascular disease induced by increased AngII and low NO, circulating aldosterone levels (P<0.01), myocardial damage (P<0.001), and proteinuria (P<0.05) were greater in female than male rats despite having similar BP responses. Thus, increased aldosterone production likely contributes to sex differences in cardiovascular disease, suggesting that women may be more responsive to mineralocorticoid receptor blockade than men.

Long- but not short-term estradiol treatment induces renal damage in midlife ovariectomized Long-Evans rats

Clinical recommendations limit menopausal hormone therapy to a few years, yet the impact of a shorter treatment duration on cardiovascular health is unknown. We hypothesized that both short- and long-term estradiol (E2) treatment exerts positive and lasting effects on blood pressure, vascular reactivity, and renal health. This study was designed to mimic midlife menopause, followed by E2 treatment, that either followed or exceeded the current clinical recommendations. Female Long-Evans retired breeders were ovariectomized (OVX) at 11 mo of age and randomized into three groups: 80-day (80d) vehicle (Veh>Veh), 40-day (40d) E2 + 40d vehicle (E2>Veh), and 80d E2 (E2>E2). In comparison to Veh>Veh, both the E2>Veh and E2>E2 groups had lower systolic blood pressure and enhanced mesenteric relaxation in response to estrogen receptor-α stimulation. Despite the reduced blood pressure, E2>E2 induced renal and cardiac hypertrophy, reduced glomerular filtration, and increased proteinuria. Interestingly, kidneys from E2>Veh rats had significantly fewer tubular casts than both of the other groups. In conclusion, long-term E2 lowered blood pressure but exerted detrimental effects on kidney health in midlife OVX Long-Evans rats, whereas short-term E2 lowered blood pressure and reduced renal damage. These findings highlight that the duration of hormone therapy may be an important factor for renal health in aging postmenopausal women.

Salt Loading Promotes Kidney Injury via Fibrosis in Young Female Ren2 Rats

BACKGROUND/AIMS

It is increasingly recognized that there is sexual dimorphism in kidney disease progression; however, this disparity is lost in the presence of diabetes where women progress at a similar rate to men. The renin-angiotensin-aldosterone system (RAAS) is known to regulate diabetes-induced kidney injury, and recent literature would suggest that gender differences exist in RAAS-dependent responses in the kidney. In this regard, these gender differences may be overcome by excessive salt intake. Thereby, we hypothesized that salt would promote proteinuria in transgenic female rats under conditions of excess tissue angiotensin (Ang) II and circulating aldosterone.

MATERIALS AND METHODS

We utilized young female transgenic (mRen2)27 (Ren2) rats and Sprague-Dawley (SD) littermates and fed a high-salt diet (4%) over 3 weeks.

RESULTS

Compared to SD and Ren2 controls, female Ren2 rats fed a high-salt diet displayed increases in proteinuria, periarterial and interstitial fibrosis as well as ultrastructural evidence of basement membrane thickening, loss of mitochondrial elongation, mitochondrial fragmentation and attenuation of basilar canalicular infoldings. These findings occurred temporally with increases in transforming growth factor-β but not indices of oxidant stress.

CONCLUSIONS

Our current data suggest that a diet high in salt promotes progressive kidney injury as measured by proteinuria and fibrosis associated with transforming growth factor-β under conditions of excess tissue Ang II and circulating aldosterone.

Role of estrogen in diastolic dysfunction

The prevalence of left ventricular diastolic dysfunction (LVDD) sharply increases in women after menopause and may lead to heart failure. While evidence suggests that estrogens protect the premenopausal heart from hypertension and ventricular remodeling, the specific mechanisms involved remain elusive. Moreover, whether there is a protective role of estrogens against cardiovascular disease, and specifically LVDD, continues to be controversial. Clinical and basic science have implicated activation of the renin-angiotensin-aldosterone system (RAAS), linked to the loss of ovarian estrogens, in the pathogenesis of postmenopausal diastolic dysfunction. As a consequence of increased tissue ANG II and low estrogen, a maladaptive nitric oxide synthase (NOS) system produces ROS that contribute to female sex-specific hypertensive heart disease. Recent insights from rodent models that mimic the cardiac phenotype of an estrogen-insufficient or -deficient woman (e.g., premature ovarian failure or postmenopausal), including the ovariectomized congenic mRen2.Lewis female rat, provide evidence showing that estrogen modulates the tissue RAAS and NOS system and related intracellular signaling pathways, in part via the membrane G protein-coupled receptor 30 (GPR30; also called G protein-coupled estrogen receptor 1). Complementing the cardiovascular research in this field, the echocardiographic correlates of LVDD as well as inherent limitations to its use in preclinical rodent studies will be briefly presented. Understanding the roles of estrogen and GPR30, their interactions with the local RAAS and NOS system, and the relationship of each of these to LVDD is necessary to identify new therapeutic targets and alternative treatments for diastolic heart failure that achieve the cardiovascular benefits of estrogen replacement without its side effects and contraindications.

Estrogen therapy, independent of timing, improves cardiac structure and function in oophorectomized mRen2.Lewis rats

OBJECTIVE

mRen2.Lewis rats exhibit exacerbated increases in blood pressure, left ventricular (LV) remodeling, and diastolic impairment after the loss of estrogens. In this same model, depletion of estrogens has marked effects on the cardiac biopterin profile concomitant with suppressed nitric oxide release. With respect to the establishment of overt systolic hypertension after oophorectomy (OVX), we assessed the effects of timing long-term 17β-estradiol (E2) therapy on myocardial function, myocardial structure, and the cardiac nitric oxide system.

METHODS

OVX (n = 24) or sham operation (Sham; n = 13) was performed in 4-week-old female mRen2.Lewis rats. After randomization, OVX rats received E2 immediately (OVX + E2-early; n = 7), E2 at 11 weeks of age (OVX + E2-late; n = 8), or no E2 at all (OVX; n = 9).

RESULTS

E2-early was associated with lower body weight, less hypertension-related cardiac remodeling, and decreased LV filling pressure compared with OVX rats without E2 supplementation. E2-late similarly attenuated the adverse effects of ovarian hormone loss on tissue Doppler-derived LV filling pressures and perivascular fibrosis, and significantly improved myocardial relaxation or mitral annular velocity (e'). Early and late exposures to E2 decreased dihydrobiopterin, but only E2-late yielded significant increases in cardiac nitrite concentrations.

CONCLUSIONS

Although there are some similarities between E2-early and E2-late treatments in relation to preservation of diastolic function and cardiac structure after OVX, the lusitropic potential of E2 is most consistent with late supplementation. The cardioprotective effects of E2-late are independent of blood pressure and may have occurred through regulation of cardiac biopterins and nitric oxide production.

Reduced vasorelaxation to estradiol and G-1 in aged female and adult male rats is associated with GPR30 downregulation

Previously, we reported that chronic activation of the estrogen receptor GPR30 by its selective agonist G-1 decreases blood pressure in ovariectomized hypertensive mRen2.Lewis (mRen2) rats but not intact male littermates. Furthermore, G-1 relaxes female mesenteric resistance arteries via both endothelium-dependent and -independent mechanisms. Because of the lack of a blood pressure-lowering effect by G-1 in males and the potential influence of aging on estrogen receptor expression, we hypothesized that GPR30-dependent vasodilation and receptor expression are altered in males and aged females. Thus, we assessed the response to 17β-estradiol or G-1 in mesenteric arteries obtained from 15-wk-old normotensive Lewis and hypertensive mRen2 females and males as well as 52-wk-old Lewis females. Vasodilation to 17β-estradiol (E₂) and G-1 was significantly attenuated in 15-wk-old Lewis and mRen2 males compared with age-matched females. Pretreatment of male vessels with the nitric oxide synthase inhibitor L-NAME had no significant effect on the estradiol or G-1 response. In aged females, E₂ and G-1 vasorelaxation was also significantly blunted; however, L-NAME essentially abolished the response. Associated with the reduced vascular responses, GPR30 expression in mesenteric arteries was approximately 50% lower in males and aged females compared with young females. We conclude that alterations in GPR30 expression and signaling may contribute to vascular dysfunction in aging females and a greater blood pressure in hypertensive males.

Increased cardiovascular and renal risk is associated with low nephron endowment in aged females: an ovine model of fetal unilateral nephrectomy

Previously we have shown that ovariectomised (OVX) female sheep have reduced renal function and elevated blood pressure from 6 months of age following fetal uninephrectomy (uni-x) at 100 days of gestation (term = 150 days). In the current study we examined if in intact female sheep the onset of decline in renal function and elevation in blood pressure was prevented. Studies were performed at 1 year, 2 and 5 years of age. Following fetal uni-x at 100 days, intact female sheep had ~30% reduction in glomerular filtration rate (GFR) at 1 year, which did not exacerbate with age (P(treatment) = 0.0001, P(age) = 0.7). In contrast renal blood flow was similar between the treatment groups at 1 year of age but had declined in the uni-x animals at 5 years of age (P(treatment × age) = 0.046). Interestingly, intact uni-x sheep did not develop elevations in arterial pressure until 2 years of age. Furthermore, uni-x animals had a similar capacity to respond to a cardiac challenge at 1 year and 2 years of age, however, cardiac functional reserve was significantly reduced compared to sham group at 5 years of age. Uni-x animals exhibited an increase in left ventricular dimensions at 5 years of age compared to the sham animals and compared to 2 years of age (P(treatment)<0.001, P(treatment × age)<0.001). In conclusion, the onset of renal dysfunction preceded the onset of hypertension in intact female uni-x sheep. Furthermore, this study showed that the intact females are protected from the impact of a reduced nephron endowment on cardiovascular health early in life as opposed to our findings in young male sheep and OVX uni-x female sheep. However, with ageing this protection is lost as evidenced by presence of left ventricular hypertrophy and impaired cardiac function in 5 year old uni-x female sheep.

Amelioration of renal injury and oxidative stress by the nNOS inhibitor L-VNIO in the salt-sensitive mRen2.Lewis congenic rat

Salt sensitivity is a key risk factor for cardiovascular disease and renal injury. Alterations in renal nitric oxide may contribute to salt-dependent increases in blood pressure and tissue damage. Therefore, we assessed the expression of nitric oxide synthase (NOS) isoforms in the kidney and the effects of nNOS inhibition on renal injury, inflammation, and oxidative stress in the female mRen2.Lewis rat (mRen), a model of salt-sensitive hypertension. We find that a high-salt diet (4% sodium) significantly reduced endothelial NOS mRNA (2.6-fold) and protein (1.5-fold) but increased nNOS mRNA (2.4-fold) and protein (1.9-fold) in the renal cortex of these animals. Immunostaining for nNOS also seemed higher in macula densa and cortical tubules of the rats fed a high-salt diet. Circulating nitrate and nitrite levels were reduced, including the tissue levels of the NOS cofactor tetrahydrobiopterin. Cortical markers of oxidative stress (4HNE, 8-OH-deoxyguanosine) and fibrosis were increased; however, mRNA levels of the NAD(P)H oxidase components NOX4, p22phox, and p47phox were reduced. Chronic treatment with the nNOS inhibitor N-(1-Imino-3-butenyl)-L-ornithine did not influence systolic blood pressure after 4 weeks but significantly attenuated albuminuria, renal fibrosis, inflammation, and indices of oxidative stress. We conclude that an increase in nNOS expression in conjunction with reduced levels of cortical tetrahydrobiopterin may stimulate oxidative stress and renal injury in the salt-sensitive female mRen2.Lewis rat.

Cell therapy with human renal cell cultures containing erythropoietin-positive cells improves chronic kidney injury

New therapeutic strategies for chronic kidney disease (CKD) are necessary to offset the rising incidence of CKD and donor shortage. Erythropoietin (EPO), a cytokine produced by fibroblast-like cells in the kidney, has recently emerged as a renoprotective factor with anti-inflammatory, antioxidant properties. This study (a) determined whether human renal cultures (human primary kidney cells [hPKC]) can be enriched in EPO-positive cells (hPKC(F+)) by using magnetic-bead sorting; (b) characterized hPKC(F+) following cell separation; and (c) established that intrarenal delivery of enriched hPKC(F+) cells would be more beneficial in treatment of renal injury, inflammation, and oxidative stress than unsorted hPKC cultures in a chronic kidney injury model. Fluorescence-activated cell sorting analysis revealed higher expression of EPO (36%) and CD73 (27%) in hPKC(F+) as compared with hPKC. After induction of renal injury, intrarenal delivery of hPKC(F+) or hPKC significantly reduced serum creatinine, interstitial fibrosis in the medulla, and abundance of CD68-positive cells in the cortex and medulla (p < .05). However, only hPKC(F+) attenuated interstitial fibrosis in the renal cortex and decreased urinary albumin (3.5-fold) and urinary tubular injury marker kidney injury molecule 1 (16-fold). hPKC(F+) also significantly reduced levels of renal cortical monocyte chemotactic protein 1 (1.8-fold) and oxidative DNA marker 8-hydroxy-deoxyguanosine (8-OHdG) (2.4-fold). After 12 weeks, we detected few injected cells, which were localized mostly to the cortical interstitium. Although cell therapy with either hPKC(F+) or hPKC improved renal function, the hPKC(F+) subpopulation provides greater renoprotection, perhaps through attenuation of inflammation and oxidative stress. We conclude that hPKC(F+) may be used as components of cell-based therapies for degenerative kidney diseases.

Differential regulation of circulating and renal ACE2 and ACE in hypertensive mRen2.Lewis rats with early-onset diabetes

We examined the impact of early diabetes on the circulating and kidney renin-angiotensin system (RAS) in male and female mRen2.Lewis (mRen2) hypertensive rats. Diabetes (DB) was induced by streptozotocin (STZ; 65 mg/kg) at 11 wk of age for 4 wk without insulin replacement. Systolic blood pressures were not increased in DB males or females compared with controls (CON). Circulating angiotensin-converting enzyme 2 (ACE2) increased ninefold (P < 0.05) in DB females and threefold (P < 0.05) in DB males, but circulating ACE and ANG II were higher in the DB groups. Serum C-reactive protein was elevated in DB females but not DB males, and the vascular responses to acetylcholine and estradiol were attenuated in the DB females. Proteinuria, albuminuria, and angiotensinogen excretion increased to a similar extent in both DB females and males. Glomerular VEGF expression also increased to a similar extent in both DB groups. Renal inflammation (CD68(+)cells) increased only in DB females although males exhibited greater inflammation that was not different with DB. Cortical ACE2 did not change in DB females but was reduced (30%) in DB males. Renal neprilysin activity (>75%, P < 0.05) was markedly reduced in the DB females to that in the DB and CON males. ACE activity was significantly lower in both female (75%, P < 0.05) and male (50%; P < 0.05) DB groups, while cortical ANG II and Ang-(1-7) levels were unchanged. In conclusion, female mRen2 rats are not protected from vascular damage, renal inflammation, and kidney injury in early STZ-induced diabetes despite a marked increase in circulating ACE2 and significantly reduced ACE within the kidney.

Activation of GPR30 attenuates diastolic dysfunction and left ventricle remodelling in oophorectomized mRen2.Lewis rats

AIMS

GPR30 is a novel oestrogen receptor expressed in various tissues, including the heart. We determined the role of GPR30 in the maintenance of left ventricular (LV) structure and diastolic function after the surgical loss of ovarian hormones in the female mRen2.Lewis rat, a model emulating the cardiac phenotype of the post-menopausal woman.

METHODS AND RESULTS

Bilateral oophorectomy (OVX) or sham surgery was performed in study rats; the selective GPR30 agonist, G-1 (50 µg/kg/day), or vehicle was given subcutaneously to OVX rats from 13-15 weeks of age. Similar to the cardiac phenotype of sham rats, G-1 preserved diastolic function and structure relative to vehicle-treated OVX littermates independent of changes in blood pressure. G-1 limited the OVX-induced increase in LV filling pressure, LV mass, wall thickness, interstitial collagen deposition, atrial natriuretic factor and brain natriuretic peptide mRNA levels, and cardiac NAD(P)H oxidase 4 (NOX4) expression. In vitro studies showed that G-1 inhibited angiotensin II-induced hypertrophy in H9c2 cardiomyocytes, evidenced by reductions in cell size, protein content per cell, and atrial natriuretic factor mRNA levels. The GPR30 antagonist, G15, inhibited the protective effects of both oestradiol and G-1 on this hypertrophy.

CONCLUSION

These data show that the GPR30 agonist G-1 mitigates the adverse effects of oestrogen loss on LV remodelling and the development of diastolic dysfunction in the study rats. This expands our knowledge of the sex-specific mechanisms underlying diastolic dysfunction and provides a potential therapeutic target for reducing the progression of this cardiovascular disease process in post-menopausal women.

Effects of estrogen on cardiovascular injury in ovariectomized female DahlS.Z-Lepr(fa)/Lepr(fa) rats as a new animal model of metabolic syndrome

Although recent clinical trials have found an increased incidence of cardiovascular disease in women on estrogen replacement therapy, the underlying mechanism remains unclear. We have recently characterized DahlS.Z-Lepr(fa)/Lepr(fa) (DS/obese) rats, derived from a cross between Dahl salt-sensitive and Zucker rats, as a new animal model of metabolic syndrome. We have now examined the effects of estrogen replacement on cardiac pathophysiology in ovariectomized female DS/obese (Ovx-DS/obese) rats. Animals subjected to ovariectomy at 7 weeks of age were implanted subcutaneously with a 60-day release pellet containing 0.5 mg of 17β-estradiol (E(2)) or placebo at 8 weeks. Age-matched female homozygous lean littermates (DahlS.Z-Lepr(+)/Lepr(+) or DS/lean rats) of DS/obese rats served as controls. Animals were maintained on a normal diet and were subjected to echocardiography followed by various pathological analyses at 13 weeks of age. Ovx-DS/obese rats manifested hypertension at 7 weeks of age and thereafter and showed left ventricular (LV) fibrosis and diastolic dysfunction at 13 weeks. Treatment with E(2) attenuated hypertension in Ovx-DS/obese rats but had no effect on blood pressure in ovariectomized female DS/lean (Ovx-DS/lean) rats. E(2) treatment exacerbated LV fibrosis and diastolic dysfunction, as well as further increased cardiac oxidative stress and inflammation in Ovx-DS/obese rats, and it elicited similar effects in Ovx-DS/lean rats. E(2) reduced food intake, body weight, and visceral fat content in both Ovx-DS/obese and Ovx-DS/lean rats. E(2) treatment attenuated hypertension and obesity but exacerbated LV fibrosis and diastolic dysfunction in Ovx-DS/obese rats, with these latter effects being associated with increased cardiac oxidative stress and inflammation.

Gender and the renin-angiotensin-aldosterone system

Premenopausal women are protected to some extent from cardiovascular and kidney diseases. Because this protection weakens after menopause, sex hormones are believed to play an important role in the pathogenesis of cardiovascular and kidney diseases. The cardiovascular system and the kidneys are regulated by the renin-angiotensin-aldosterone system (RAAS), which in turn, appears to be regulated by sex hormones. In general, oestrogen increases angiotensinogen levels and decreases renin levels, angiotensin-converting enzyme (ACE) activity, AT(1) receptor density, and aldosterone production. Oestrogen also activates counterparts of the RAAS such as natriuretic peptides, AT(2) receptor density, and angiotensinogen (1-7). Progesterone competes with aldosterone for mineralocorticoid receptor. Less is known about androgens, but testosterone seems to increase renin levels and ACE activity. These effects of sex hormones on the RAAS can explain at least some of the gender differences in cardiovascular and kidney diseases.

Dual ACE-inhibition and AT1 receptor antagonism improves ventricular lusitropy without affecting cardiac fibrosis in the congenic mRen2.Lewis rat

BACKGROUND

Hypertension and left ventricular (LV) hypertrophy often precede diastolic dysfunction and are risk factors for diastolic heart failure. Although pharmacologic inhibition of the renin-angiotensin system (RAS) improves diastolic function and functional capacity in hypertensive patients with LV hypertrophy, the effects of combination therapy with an angiotensin converting enzyme inhibitor (ACEi) and an angiotensin receptor blocker (ARB) are unclear.

METHOD

We assessed the effects of the combined 10-week administration of lisinopril (10 mg/kg/ day, p.o.) and losartan (10 mg/kg/day, p.o.) (LIS/LOS) on diastolic function and LV structure in seven young (5 weeks), prehypertensive congenic mRen2.Lewis male rat, a model of tissue renin overexpression and angiotensin II (Ang II)-dependent hypertension compared to vehicle (VEH) treated (n = 7), age-matched rats.

RESULTS

Systolic blood pressures were 64% lower with the combination therapy (p < 0.001), but there were no differences in heart rate or systolic function between groups. RAS inhibition increased myocardial relaxation, defined by tissue Doppler mitral annular descent (e') by 2.2 fold (p < 0.001). The preserved lusitropy in the LIS/LOS-treated rats was accompanied by a reduction in phospholamban-to-SERCA2 ratio (p < 0.001). Despite lower relative wall thicknesses (VEH: 1.56+/-0.17 versus LIS/LOS: 0.78+/-0.05) and filling pressures, defined by the transmitral Doppler-to-mitral annular descent ratio (E/e', VEH: 28.7+/-1.9 versus LIS/LOS: 17.96+/-1.5), no differences in cardiac collagen were observed.

CONCLUSION

We conclude that the lusitropic benefit of early dual RAS blockade may be due to improved vascular hemodynamics and/or cardiac calcium handling rather than effects on extracellular matrix reduction.

Estradiol increases angiotensin II type 1 receptor in hearts of ovariectomized rats

We tested the hypothesis that 17beta-estradiol (E(2)) has dual effects on the heart, increasing levels of proteins thought to have beneficial cardiovascular effects (e.g. endothelial nitric oxide (NO) synthase (eNOS)) as well as those thought to have detrimental cardiovascular effects (e.g. type 1 angiotensin II (AngII) receptor (AT(1)R)). Ovariectomized Wistar rats consuming a high-sodium diet received one of four treatments (n=7 per group): group 1, placebo pellets; group 2, E(2) (0 x 5 mg/pellet, 21-day release); group 3, NOS inhibitor, N(omega)-nitro-L-arginine-methyl-ester (L-NAME; 40 mg/kg per day for 14 days) plus Ang II (0 x 225 mg/kg per day on days 11-14); group 4, E(2) plus L-NAME/Ang II. E(2) increased cardiac levels of estrogen receptors ESR1 and ESR2, an ESR-associated membrane protein caveolin-3, eNOS, and phosphorylated (p)eNOS, thus, exerting potentially beneficial cardiovascular effects on NO. However, E(2) also increased cardiac levels of proteins associated with cardiovascular injury and inflammation including, AT(1)R, protein kinase C delta (PRKCD), phosphorylated PRKC, and phosphorylated extracellular signal regulated kinase (pMAPK)3/1, plasminogen activator inhibitor-1 (PAI-1), osteopontin and ED-1, a monocyte/macrophage-specific protein. E(2) treatment led to similar protein changes in the hearts of L-NAME/Ang II-treated rats except that the increase in peNOS was prevented, and L-NAME/Ang II and E(2) had additive effects in increasing cardiac PRKCD and PAI-1. Thus, the highest levels of cardiac PAI-1 and PRKCD occurred in L-NAME/Ang II-treated rats receiving E(2). In summary, E(2) treatment increased cardiac expression of AT(1)R as well as the expression of pro-inflammatory and prothrombotic factors.

Differential effects of sex steroids in young and aged female mRen2.Lewis rats: a model of estrogen and salt-sensitive hypertension

BACKGROUND

Male-female differences in the expression of hypertension and in end-organ damage are evident in both experimental models and human subjects, with males exhibiting a more rapid onset of cardiovascular disease and mortality than do females. The basis for these male-female differences is probably the balance of the complex effects of sex steroids (androgens, estrogen, progesterone) and their metabolites on the multiple regulatory systems that influence blood pressure (BP). A key target of estrogen and other steroids is likely to be the different components of the renin-angiotensin-aldosterone system (RAAS).

OBJECTIVE

The aim of this study was to review the current experimental evidence on the protective effects of estrogen in hypertensive models.

METHODS

The search terms estrogen , renin-aangiotensin-aldosterone system, renin receptor, salt-sensitivity, endorgan damage, hypertension, kidney, mRen2. Lewis, and injury markers were used to identify relevant publications in the PubMed database (restricted to the English language) from January 1990 to October 2007.

RESULTS

In a new congenic model that expresses the mouse renin 2 gene (mRen2. Lewis), estrogen depletion (via ovariectomy [OVX ]) in young rats was found to have a marked stimulatory effect on the progression of increased BP and cardiac dysfunction. Moreover, estrogen depletion exacerbated salt-sensitive hypertension and the extent of salt-induced cardiac and renal injury in young mRen2. Lewis rats, which probably reflected the inability to appropriately regulate various components of the RAAS. However, OVX in aged mRen2. Lewis rats conveyed renal protective effects from a high-salt diet compared with intact hypertensive littermates (64 weeks), and these effects were independent of changes in BP.

CONCLUSION

These studies in hypertensive mRen2. Lewis rats underscored the influence of ovarian hormones on BP and tissue injury, as well as the plasticity of this response, apparently due to age and salt status.

Cardiac hypertrophy is associated with altered thioredoxin and ASK-1 signaling in a mouse model of menopause

Oxidative stress is implicated in menopause-associated hypertension and cardiovascular disease. The role of antioxidants in this process is unclear. We questioned whether the downregulation of thioredoxin (TRX) is associated with oxidative stress and the development of hypertension and target-organ damage (cardiac hypertrophy) in a menopause model. TRX is an endogenous antioxidant that also interacts with signaling molecules, such as apoptosis signal-regulated kinase 1 (ASK-1), independently of its antioxidant function. Aged female wild-type (WT) and follitropin receptor knockout (FORKO) mice (20-24 wk), with hormonal imbalances, were studied. Mice were infused with ANG II (400 ng x kg(-1) x min(-1); 14 days). Systolic blood pressure was increased by ANG II in WT (166+/-8 vs. 121+/-5 mmHg) and FORKO (176+/-7 vs. 115+/-5 mmHg; P<0.0001; n=9/group) mice. In ANG II-infused FORKO mice, cardiac mass was increased by 42% (P<0.001). This was associated with increased collagen content and augmented ERK1/2 phosphorylation (2-fold). Cardiac TRX expression and activity were decreased by ANG II in FORKO but not in WT (P<0.01) mice. ASK-1 expression, cleaved caspase III content, and Bax/Bcl-2 content were increased in ANG II-infused FORKO (P<0.05). ANG II had no effect on cardiac NAD(P)H oxidase activity or on O(2)(*-) levels in WT or FORKO. Cardiac ANG II type 1 receptor expression was similar in FORKO and WT. These findings indicate that in female FORKO, ANG II-induced cardiac hypertrophy and fibrosis are associated with the TRX downregulation and upregulation of ASK-1/caspase signaling. Our data suggest that in a model of menopause, protective actions of TRX may be blunted, which could contribute to cardiac remodeling independently of oxidative stress and hypertension.

Sex differences in circulating and renal angiotensins of hypertensive mRen(2). Lewis but not normotensive Lewis rats

Sex differences in blood pressure are evident in experimental models and human subjects, yet the mechanisms underlying this disparity remain equivocal. The current study sought to define the extent of male-female differences in the circulating and tissue renin-angiotensin aldosterone systems (RAASs) of congenic mRen(2). Lewis and control Lewis rats. Male congenics exhibited higher systolic blood pressure than females [200 +/- 4 vs. 146 +/- 7 mmHg, P < 0.01] or Lewis males and females [113 +/- 2 vs. 112 +/- 2 mmHg, P > 0.05]. Plasma ANG II levels were twofold higher in male congenics [47 +/- 3 vs. 19 +/- 3 pM, P < 0.01] and fivefold higher than in male or female Lewis rats [6 +/- 1 vs. 6 +/- 1 pM]. ANG I levels were also highest in the males; however, plasma ANG-(1-7) was higher in female congenics. Male congenics exhibited greater circulating renin and angiotensin-converting enzyme (ACE) activities, as well as angiotensinogen, than female littermates. Renal cortical and medullary ANG II levels were also higher in the male congenics versus all the other groups; ANG I was lower in the males. Cortical ACE2 activity was higher in male congenics, yet neprilysin activity and protein were greater in the females, which may contribute to reduced renal levels of ANG II. These data reveal that sex differences in both the circulating and renal RAAS are apparent primarily in the hypertensive group. The enhanced activity of the RAAS in male congenics may contribute to the higher pressure and tissue injury evident in the strain.