Attenuated responses to angiotensin II in follitropin receptor knockout mice, a model of menopause-associated hypertension

Sex Differences in the Immune System in Relation to Hypertension and Vascular Disease

Hypertension is the leading risk factor for cardiovascular disease and mortality worldwide. Despite intensive research into the mechanisms underlying the development of hypertension, it remains difficult to control blood pressure in a large proportion of patients. Young men have a higher prevalence of hypertension compared with age-matched women, and this holds true until approximately the fifth decade of life. Following the onset of menopause, the incidence of hypertension among women begins to surpass that of men. The immune system has been demonstrated to play a role in the pathophysiology of hypertension, and biological sex and sex hormones can affect the function of innate and adaptive immune cell populations. Recent studies in male and female animal models of hypertension have begun to unravel the relationship among sex, immunity, and hypertension. Hypertensive male animals show a bias toward proinflammatory T-cell subsets, including interleukin (IL) 17-producing T_H17 cells, and increased renal infiltration of T cells and inflammatory macrophages. Conversely, premenopausal female animals are largely protected from hypertension, and have a predilection for anti-inflammatory T regulatory cells and production of anti-inflammatory cytokines, such as IL-10. Menopause abrogates female protection from hypertension, which may be due to changes among anti-inflammatory T regulatory cell populations. Since development of novel treatments for hypertension has plateaued, determining the role of sex in the pathophysiology of hypertension may open new therapeutic avenues for both men and women.

Effects of 17β-estradiol on cardiac Na(+)/K(+)-ATPase in high fat diet fed rats

The aim of this study was to investigate in vivo effects of estradiol on Na(+)/K(+)-ATPase activity/expression in high fat (HF) diet fed rats. Adult male Wistar rats were fed normally (Control, n = 7) or with a HF diet (Obese, n = 14) for 10 weeks. After 10 weeks, half of the obese rats were treated with estradiol (Obese + Estradiol, n = 7, 40 μg/kg, i.p.) as a bolus injection and 24 h after treatment all the rats were sacrificed. Estradiol in vivo in obese rats in comparison with obese non-treated rats led to a statistically significant increase in concentration of serum Na(+) (p < 0.05), Na(+)/K(+)-ATPase activity (p < 0.01), expression of α1 (p < 0.01) and α2 (p < 0.05) subunit of Na(+)/K(+)-ATPase, both PI3K subunits p85 (p < 0.01), p110 (p < 0.05), and association of IRS-1 with p85 (p < 0.05), while significantly decrease expression of AT1 (p < 0.05) and Rho A (p < 0.01) proteins. Our results suggest that estradiol in vivo in pathophysiological conditions, such as obesity accompanied with insulin resistance stimulates activity and expression of Na(+)/K(+)-ATPase by a mechanism that involves the participation of IRS-1/PI3K/Akt signaling. In addition, the decreasing level of AT1 and Rho A proteins estradiol probably attenuates the detrimental effect of obesity to decreased IRS-1/PI3K association and consequently reduce Na(+)/K(+)-ATPase activity/expression.

Impact of early life ovariectomy on blood pressure and body composition in a female mouse model of systemic lupus erythematosus

Because of the preponderance of women affected by the chronic autoimmune disease systemic lupus erythematosus (SLE), estrogen is thought to contribute to SLE disease progression. This is supported by evidence from experimental animal models of SLE showing that removal of estrogen in young female mice delays autoantibody production and renal injury and lengthens survival. Blood pressure and changes in body composition are important cardiovascular risk factors that can be regulated by estrogens. Because cardiovascular disease is the leading cause of death in patients with SLE, we used an established female mouse model of SLE (NZBWF1) to test whether early life removal of estrogen impacts the development of hypertension and changes in body composition commonly associated with SLE. Eight-week-old female SLE and control mice (NZW/LacJ) underwent either a sham operation or ovariectomy. Body weight, body composition (fat and lean masses), and renal injury (albuminuria) were monitored until mice reached 34 wk of age, at which time mean arterial pressure was assessed in conscious animals by a carotid catheter. Early life removal of the ovaries delayed the onset of autoantibody production and albuminuria while causing an increase in body weight and fat mass. Blood pressure in the adult was not altered by early life removal of the ovaries. These data suggest that estrogens may have a permissive role for the development of SLE while helping to maintain normal body weight and composition, which is associated with reduced cardiovascular risk.

Effects of a domain-selective ACE inhibitor in a mouse model of chronic angiotensin II-dependent hypertension

The somatic isozyme of ACE (angiotensin I-converting enzyme) comprises two distinct zinc-dependent catalytic domains with different substrate specificities for angiotensin I (cleaved selectively by the C-domain) and bradykinin (cleaved equally efficiently by both the N- and C-domains). Classical ACEIs (ACE inhibitors) target both domains, with side effects such as cough and angio-oedema being attributed, in part, to N-domain inhibition, probably through bradykinin accumulation. We questioned whether a novel C-domain-selective ACEI (lisW-S) has anti-hypertensive effects without influencing bradykinin status. AngII (angiotensin II)-dependent hypertension was studied in mice that express active human renin in the liver (TtRhRen). Compared with wild-type littermates, TtRhRen mice displayed cardiac hypertrophy and had significantly elevated SBP [systolic BP (blood pressure)] as determined by tail cuff sphygmomanometry (150±3 compared with 112±5 mmHg; P<0.05) and telemetry (163±3 compared with 112±2 mmHg; P<0.01). Treatment with the non-selective ACEI lisinopril (1 mg/kg of body weight per day via an osmotic mini-pump for 2 weeks) reduced SBP (127±3 compared with. 154±6; P<0.05). Similarly, treatment with the C-domain selective ACEI lisW-S (lisinopril-tryptophan; 3.6 mg/kg of body weight per day via an osmotic mini-pump for 2 weeks) reduced BP. Treatment with lisinopril or lisW-S significantly reduced levels of AngII in kidneys (~4-fold; P<0.001). Ang-(2-8) [angiotensin-2-8)] was significantly reduced by lisinopril, but not by lisW-S. Plasma bradykinin levels were significantly increased only in the lisinopril group. These data suggest that C-domain-selective ACEIs reduce BP and AngII levels similarly to classical ACEIs. C-domain-selective ACEIs have the potential to avoid undesirable effects on the bradykinin system common to classic ACEIs and may represent a novel approach to the treatment of hypertension.

Chronic estrogen deficiency causes gastroparesis by altering neuronal nitric oxide synthase function

BACKGROUND

Gastroparesis affects predominantly females; however, the biological basis for this gender bias is completely unknown. Several lines of evidence suggest that nitrergic dependent stomach motility function is reduced in diabetic gastroparesis and that nNOS is estrogen-regulated.

AIMS

The purpose of this study was to investigate whether reduced levels of estradiol-17β (E2) down-regulates tetrahydrobiopterin (BH4, a cofactor for nNOS dimerization and enzyme activity) biosynthesis and therefore nNOS mediated gastric motility would be impaired in a mouse model of chronic estrogen deficiency, follicle stimulating hormone receptor knock-out female mice (FORKO).

METHODS

In-bred 12-week-old female FORKO mice were obtained from our FORKO breeding colony. Gastric emptying was measured in overnight fasting mice. Nitrergic relaxation (AUC/mg tissue) was measured at 2 Hz through electric field stimulation using gastric antrum strips prepared from WT and FORKO mice. Protein expression for nNOSα, BH4 biosynthesis enzymes (GCH-1, DHFR) and estrogen receptors (α, β) were measured in gastric antrum by western blotting. Levels of BH4 and oxidized BH2, B biopterin levels were determined by HPLC.

RESULTS

In FORKO, compared to wild type (WT) stomachs we indentified (1) reduced (%) gastric emptying (64 ± 2.5 vs. 77.6 ± 0.88), (2) greater reduction in nitregic relaxation (-0.13 ± 0.012 vs. -0.28 ± 0.012), (3) increased nNOS dimerization (0.48 ± 0.02 vs. 0.34 ± 0.05), (4) decreased NO release whether measured at 24 h (0.6 ± 0.04 vs. 1.7 ± 0.22, p < 0.05) or at 48 h (3.4 ± 0.26 vs. 5.0 ± 0.15, p < 0.05) of incubation, (5) decreased GCH-1 (1.9 ± 0.06 vs. 2.3 ± 0.04), DHFR (1.8 ± 0.14 vs. 2.4 ± 0.07) and ERα (2.7 ± 0.4 vs. 3.9 ± 0.4) and (6) increased oxidized biopterin levels and decreased ratio of BH4 versus BH2 + B.

CONCLUSION

We conclude that chronic estrogen deficiency negatively modifies the function of both BH4 and nNOS thereby contributing to the development of gastroparesis in a FORKO mouse model.

Potentiation of vascular oxidative stress and nitric oxide-mediated endothelial dysfunction by high-fat diet in a mouse model of estrogen deficiency and hyperandrogenemia

Estrogen deficiency is associated with increased cardiovascular risk due, in part, to hypertension, endothelial dysfunction, obesity, and hypercholesterolemia. Underlying mechanisms for this remain unclear. Here, we investigated whether high-fat intake aggravates vascular dysfunction through oxidative stress and inflammation, which could predispose to cardiovascular injury in conditions of estrogen deficiency, such as menopause. We studied female homozygous follitropin receptor knock out (FORKO) mice, which have hormonal features of clinical menopause and hypertension and wild-type (WT) and heterozygote mice (HTZ), fed a standard or high-fat diet for 4 months. Vascular function and structure were evaluated in arterial segments by pressurized myography. Acetylcholine (ACh)-induced vasodilation was reduced in FORKO vs. WT mice (P < .001). N(varpi)-nitro-l-arginine-methyl-ester inhibited Ach-induced relaxation in all groups on normal chow and in WT and HTZ on high-fat diet (FD) but had no effect in fat-fed FORKO mice. Antioxidant cocktail (superoxide dismutase, catalase, Tempol) increased ACh responses only in high-fat diet FORKO mice (P < .05). Vascular media-to-lumen ratio was increased and reactive oxygen species (ROS) generation, nitrotyrosine formation, and plasma nitrite levels were augmented in fat-fed FORKO vs. FORKO on normal chow. High-fat diet did not influence vascular inflammatory responses in any group. Our data demonstrate that FORKO mice have altered nitric oxide-sensitive vasorelaxation and vascular remodeling, which are aggravated by high-fat diet. Underlying mechanisms for this may involve decreased NO formation and increased generation of ROS and nitrotyrosine. These findings suggest that high-fat intake potentiates vascular damage in estrogen-deficient states, an effect involving increased oxidative stress.

Natriuretic peptide system: a link between fat mass and cardiac hypertrophy and hypertension in fat-fed female rats

The present study was designed to develop an animal model of hypertension and cardiac hypertrophy associated with obesity in female rats. Furthermore, we studied the involvement of the natriuretic peptide system in the mechanisms of these conditions. Obesity was induced in Wistar rats by a high fat diet and ovariectomy. The rats were divided into four groups: ovariectomized or sham-operated with high-fat diet and ovariectomized or sham-operated with control diet. After 24 weeks of diet, rats were killed, and their tissues were removed. Cardiac atrial natriuretic peptide (ANP), clearance receptor (NPr-C) gene expression was determined by PCR. ANP concentrations were measured in plasma. Ovariectomized fat-fed rats (OF) showed increased body weight, visceral fat depot and blood pressure and decreased sodium excretion compared to other groups. Also, these rats showed higher heart-to-body weight and cell diameters of ventricular cardiomyocytes and lower cardiac ANP mRNA and plasma ANP than the control group. The adipocyte and renal NPr-C mRNA of OF rats were higher than the control group. These data showed that combined ovariectomy and high fat diet elicited obesity, hypertension and cardiac hypertrophy. These results suggest that the impairment of the natriuretic peptide system may be one of the mechanisms involved not only in development of hypertension but also in cardiac hypertrophy associated with obesity in ovariectomized rats.

Characterization of an animal model of postmenopausal cardiac hypertrophy and novel mechanisms responsible for cardiac decompensation using ovariectomized pressure-overloaded rats

OBJECTIVE

The development of animal models of cardiovascular disease are critical to define pathophysiological mechanisms and to advance diagnosis and therapy. The lack of a suitable animal model represents a failure to define the mechanisms responsible for postmenopausal myocardial hypertrophy in hypertension and adverse cardiac remodeling.

METHODS

In this review, we presented a rat model of postmenopausal myocardial hypertrophy, with particular focus on the similarities between the animal model and postmenopausal women regarding myocardial function as well as molecular and subcellular mechanisms. To elucidate the molecular mechanism of left ventricular (LV) hypertrophy and remodeling in postmenopausal women, we analyzed myocardial hypertrophy as well as cardiac function and hypertrophy-related protein expression in ovariectomized (OVX) and pressure overloaded (PO) rats.

RESULTS

The model is characterized by depletion of serum estrogen and increased heart-to-body weight and lung-to-body weight ratios. Moreover, the OVX-PO rats also show increased mean arterial blood pressure, LV end-diastolic pressure, LV developed pressure, and maximal rates of LV contraction and relaxation compared with the OVX group. Importantly, Akt activity was largely attenuated, and both endothelial nitric oxide synthase expression and activity were markedly reduced in the OVX-PO group. Finally, significant increased mortality was observed in the OVX-PO group after chronic isoproterenol administration.

CONCLUSIONS

Our results demonstrate that rats subject to OVX are unable to compensate for hypertrophy partly due to impaired Akt-endothelial nitric oxide synthase signaling along with deteriorated heart function and demonstrated increased mortality. In this review, we discussed the mechanisms of cardiac injury, which could play a critical role in postmenopausal hypertrophy, as well as the characteristics of the OVX-PO female rats as a model to test cardioprotective drugs in postmenopausal women.

17beta-Estradiol induces protein S-nitrosylation in the endothelium

AIMS

Estrogen induces nitric oxide (NO) in the endothelium and appears to protect against inflammation and atherosclerosis. NO can induce post-translational protein modifications such as cysteine S-nitrosylation in the cellular proteins which may exert anti-inflammatory effects. However, whether estrogen can induce protein S-nitrosylation in the endothelium is not known. Given this background, we investigated the role of 17beta-estradiol (E2beta), the major form of estrogen in the body, on endothelial protein S-nitrosylation.

METHODS AND RESULTS

Experiments were performed in human umbilical vein endothelial cells (HUVECs). S-nitrosylation was detected by immunostaining for nitrosocysteine and further confirmed by biotin switch method. Ovariectomized 12-month-old Sprague-Dawley rats with/without estradiol supplementation were used for in vivo validation of findings. We found that physiologically relevant doses of E2beta increased protein S-nitrosylation in HUVECs through estrogen receptor-alpha (ERalpha) and endothelial nitric oxide synthase (eNOS). Interestingly, specific agonists for both ERalpha and ERbeta increased eNOS protein expression, while only the former could activate eNOS through phosphorylation. S-nitrosylation by E2beta prevented angiotensin II-induced upregulation of intercellular cell adhesion molecule-1, suggesting a potential anti-inflammatory mechanism. Finally, we showed that exogenous E2beta could increase endothelial S-nitrosylation in vivo in a rat model.

CONCLUSION

Our results demonstrate for the first time that E2beta increases protein S-nitrosylation in the vascular endothelium, which might be a novel pathway to mediate the protective effects on the vasculature.

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.

Effects of combined AT1 receptor antagonist/NEP inhibitor on vascular remodeling and cardiac fibrosis in SHRSP

BACKGROUND

The association of an angiotensin-converting enzyme inhibitor (ACEI) with a neutral endopeptidase inhibitor (NEPI) has potent blood pressure (BP) lowering action, but is associated with side-effects. We evaluated the effects of combining an angiotensin II type 1 (AT1) receptor blocker (ARB, valsartan) and a NEPI (CGS 25354) in comparison with a dual ACEI/NEPI (CGS 30440) in stroke-prone spontaneously hypertensive rats (SHRSP).

METHODS AND RESULTS

Ten-week-old SHRSP were treated with valsartan (10 mg/kg per day), valsartan + CGS 25354 (100 mg/kg per day), CGS 25354, CGS 30440 (10 mg/kg per day) or hydralazine (25 mg/kg per day) for 10 weeks. Mesenteric resistance arteries were studied on a pressurized myograph, whereas cardiac effects were assessed by histology and immunohistochemistry. BP of SHRSP was lowered by combined valsartan/NEPI and ACEI/NEPI slightly more than valsartan, whereas NEPI was ineffective. Valsartan, valsartan/NEPI and ACEI/NEPI normalized resistance artery relaxation responses to acetylcholine, and significantly decreased media/lumen ratio and collagen deposition. All treatments decreased vascular NAD(P)H oxidase-mediated superoxide production. Valsartan/NEPI and ACEI/NEPI decreased media/lumen ratio of intramyocardial coronary arteries, while valsartan alone had no effect. Valsartan/NEPI and ACEI/NEPI increased vascular matrix metalloproteinase-2 activity, and decreased tissue inhibitors of metalloproteinase-2 activity and macrophage infiltration.

CONCLUSION

Combined valsartan/NEPI was almost as effective as a dual ACEI/NEPI in lowering BP and improving vascular remodeling in SHRSP. These findings suggest the potential therapeutic value of combining ARB and NEPI in the treatment of hypertension.

Impairment of the natriuretic peptide system in follitropin receptor knockout mice and reversal by estradiol: implications for obesity-associated hypertension in menopause

Estrogen is considered a major regulator of adipose tissue in females. Estrogen increases circulating levels of atrial natriuretic peptide (ANP), a hormone with renal and cardiovascular effects. The aim of this study was to determine the status of the natriuretic peptide system in female follitropin-receptor knockout (FORKO) mice that could be associated with obesity and hypertension observed in these mutants. Furthermore, estradiol treatment was used to reverse alterations observed. FORKO and wild-type (WT) mice received daily injections of estradiol for 4 d. On the fifth day, blood was collected for determination of plasma ANP levels, and selected tissues were collected for determination of ANP, natriuretic peptide receptor type-A (NPR-A) and type-C (NPR-C) gene expression by RT-PCR and binding of [(125)I]ANP by autoradiography. At 5 months of age, FORKO mice were heavier and had more adipose tissue than WT mice. FORKO mice had lower plasma ANP levels and atrial ANP gene expression and higher renal and adipocyte NPR-C gene expression than WT mice. Estradiol treatment reduced weight gain and increased atrial ANP synthesis as well as decreased ANP clearance NPR-C receptors, resulting in elevation of circulating ANP level. In conclusion, this study shows that FORKO females have an impaired natriuretic peptide system, which may contribute to the susceptibility of FORKO mice to developing age-related hypertension previously shown in these animals. This study establishes a relation between estrogen, adipose tissue, and ANP, which may have important implications in menopausal women.

Cardiac and aortic structural alterations due to surgically-induced menopause associated with renovascular hypertension in rats

Menopause and hypertension independently alter cardiovascular remodelling, but little is known about their effect on left ventricular and aortic wall remodelling. Eight-weeks-old Wistar rats were divided into four groups of six animals each: Sham group, OVX group (ovariectomized rats), 2K1C (two-kidneys, one-clip rats) and OVX + 2K1C group and kept until 19 weeks. Blood pressure (BP) increased 12% in OVX group, 35% in 2K1C and OVX + 2K1C groups compared with sham group. Vaginal cytology showed Sham and 2K1C rats cycling normally, whereas OVX and OVX + 2K1C rats were persistently in dioestrus or proestrus. At euthanasia, left ventricle (LV) and thoracic aorta were removed and analysed (immunohistochemistry and stereology). LV mass/tibia length ratio and cross-sectional area of cardiomyocytes increased in all groups except Sham. The intramyocardial vascularization reduced 30% in comparison with Sham group, with no difference among OVX, 2K1C and OVX + 2K1C groups. The cardiac interstitium increased more than 45% in both 2K1C and OVX + 2K1C groups compared with Sham, but there was no significant difference between Sham and OVX groups. Nuclei number of LV cardiomyocyte diminished in OVX group, followed by 2K1C group and OVX + 2K1C group, with no difference between the 2K1C and the OVX + 2K1C groups. There was positive immunostaining for angiotensin II AT1 receptor in smooth muscle cell layer of aortic tunica media in all groups. These results show that both ovariectomy and renovascular hypertension enhance BP as a single stimulus and therefore produce adverse cardiac remodelling. However, renovascular hypertension exerts a far greater influence than surgically-induced menopause in this parameter.

Mutation of the Follicle-Stimulating Hormone Receptor Gene 5′-Untranslated Region Associated With Female Hypertension

Inactivating mutations in the follicle-stimulating hormone receptor (FSHR) gene have been reported to cause hereditary hypergonadotropic ovarian failure. It has been found recently that the FSHR knockout mouse exhibits hypertension. The aim of the present study was to investigate the association between polymorphisms in the human FSHR gene and essential hypertension (EH) by using single nucleotide polymorphisms (SNPs). We selected 5 SNPs in the gene (rs1394205, rs2055571, rs11692782, rs1007541, and rs2268361) and performed 2 genetic case-control studies in different populations. A confirmative case-control study was performed using 1035 EH patients and 1058 age-matched controls. Transcriptional activities were measured with a luciferase assay system. The first case-control study found that the A allele of rs1394205 was significantly higher in EH females (P=0.010). In addition, in the confirmative case-control study, there was a significant difference for this SNP between female normotensive subjects (44.5%) and EH patients (50.7%) (P=0.043). Multiple logistic regression analysis in female subjects also revealed a significant association of subjects with the A allele of rs1394205 with EH (P=0.033), with the odds ratio calculated as 1.68 (95% CI: 1.04 to 2.73). Transcriptional activity of the A allele was 56+/-8% (mean+/-SD) of that observed for the G-type allele (P=0.001). Serum estradiol levels were significantly lower in patients with the A/A genotype than in patients without the A/A genotype (P=0.004). The SNP in the 5'-untranslated region of the FSHR gene affects levels of transcriptional activity and is a susceptibility mutation of EH in women.

Angiotensin II induces vascular dysfunction without exacerbating blood pressure elevation in a mouse model of menopause-associated hypertension

BACKGROUND

Follitropin-receptor knockout (FORKO) mice are estrogen-deficient, hyperandrogenic and exhibit features of menopause and elevated blood pressure (BP). Because the renin-angiotensin system has been implicated in menopause-associated hypertension, we questioned whether angiotensin II (Ang II) challenge would further increase BP in FORKO mice and whether this is associated with cardiovascular remodeling and inflammation.

RESULTS

Ang II (400 ng/kg per min) increased BP, assessed by radiotelemetry, similarly in female FORKO and wild-type (WT) mice. Acetylcholine-induced vasodilation was attenuated and Ang II-induced contraction was enhanced in FORKO mice (P < 0.05). This was associated with increased expression of vascular Ang type 1 receptors (AT1R) and estrogen receptor alpha (ERalpha). Vascular structure (media/lumen ratio) was similar in both groups. Abundance of gp91, nitrotyrosine formation and superoxide production, indices of inflammation and cardiac collagen content were increased in Ang II-treated FORKO compared to Ang II-treated WT mice (P < 0.05).

CONCLUSIONS

Thus, in FORKO mice Ang II exacerbates endothelial dysfunction, augments contractility, increases oxidative stress, and promotes cardiac fibrosis without worsening vascular remodeling or BP elevation compared to Ang II-treated WT controls. Our findings suggest that in FORKO mice Ang II may be more important in influencing vascular tone and endothelial function, possibly through oxidative stress and altered ERalpha signaling, than in arterial remodeling and BP elevation.

Early obesity and age-related mimicry of metabolic syndrome in female mice with sex hormonal imbalances

OBJECTIVE

To investigate the relationship of early obesity to metabolic syndrome during sex hormonal imbalances in mutant female mice at different ages.

RESEARCH METHODS AND PROCEDURES

Hormonal imbalances, accumulation and nature of adipose tissue, food intake, glucose tolerance, and expression of candidate genes and markers of inflammation were studied by comparing wild-type, null, and haploinsufficient follitropin receptor knockout female mice at different ages.

RESULTS

Follitropin receptor deletion in mice produced null females that are infertile and haploinsufficient mice that undergo accelerated biological aging. Both types of mutants with sex hormonal imbalances have central obesity without hyperphagia, but circulating leptin is elevated. Adipocyte hyperplasia and hypertrophy is attributed to elevated peroxisome proliferator-activated receptor gamma expression. Adiponectin protein levels increase in fat tissue and plasma. Only mutants but not controls acquire age-dependent decline in glucose tolerance with high insulin and altered pancreatic beta cells. Changes in inflammation markers, decreased muscle insulin receptor phosphorylation, and increase of the enzyme protein tyrosine phosphatase 1B indicate insulin resistance.

DISCUSSION

In this animal model, the chronological appearance of early obesity induced by hormonal imbalances culminates in characteristics that are attributable to metabolic syndrome, including cardiovascular abnormalities. Dissection of the depot-specific alterations and defining molecular interrelationships could help in developing targeted remedies and resolving complications and controversies related to health benefits and adversities of current hormone replacement therapy.

Sex dimorphism in cardiac pathophysiology: experimental findings, hormonal mechanisms, and molecular mechanisms

The higher cardiovascular risk in men and post-menopausal women implies a protective action of estrogen. A large number of experimental studies have provided strong support to this concept. However, the recent clinical trials with negative outcomes regarding hormone replacement therapy call for "post hoc" reassessment of existing information, models, and research strategies as well as a summary of recent findings. Sex steroid hormones, in particular estrogen, regulate numerous processes that are related to the development and progression of cardiovascular disease through a variety of signaling pathways. Use of genetically modified models has resulted in interesting information on diverse actions mediated by steroid receptors. By focusing on experimental findings, we have reviewed hormonal, cellular, and signaling mechanisms responsible for sex dimorphism and actions of hormone replacement therapy and addressed current limitations and future directions of experimental research.

What have we learned about gonadotropin function from gonadotropin subunit and receptor knockout mice?

A number of biochemical and physiological studies elucidated the roles of pituitary and placental glycoprotein hormones. Advances in the past two decades in manipulating the mouse genome by random or site-specific mutagenesis have heralded a new dimension to our understanding of the biology of gonadotropins. It is now possible to model many human reproductive disorders involving gonadotropins/gonadotropin-signaling in the mouse. Mutant mice selectively lacking either FSH or LH or their cognate receptors have been generated. The gonadotropin ligand and the corresponding receptor knockout mice mostly phenocopy each other. Analyses with these genetic models confirmed earlier physiological studies; in addition they also revealed novel roles for gonadotropins previously unrecognized. While FSH action seems dispensable for male but not female fertility, absence of LH causes infertility in both the sexes. While Sertoli cell number and germ cell carrying capacity of the Sertoli cells in compromised in FSH mutants, both somatic and germ cell lineages are affected in the LH mutants resulting in complete male infertility. FSH mutant females demonstrate a preantral stage block in folliculogenesis and FSH alone is not sufficient to promote full folliculogenesis in the absence of LH. Pre-ovulatory stage follicles do not form and most of the follicles undergo apoptosis in the absence of LH. Many extra-gonadal phenotypes have been described for the receptor knockout mice and whether these bear any resemblances to those in patients with similar inactivating mutations in the receptors for FSH and LH remains an open question. Thus the in vivo models will continue to have a significant impact in understanding gonadotropin physiology and pathophysiology and serve as novel genetic tools to study signaling mechanisms in the gonads.

Novel mechanisms responsible for postmenopausal hypertension

Blood pressure increases in many women after menopause. Hypertension is one of the major risk factors for cardiovascular disease. However, the mechanisms responsible for the postmenopausal increase in blood pressure are yet to be elucidated. Various humoral systems have been proposed to play a role in postmenopausal hypertension, such as changes in estrogen/androgen ratios, increases in endothelin and oxidative stress, and activation of the renin-angiotensin system (RAS). In addition, obesity, type II diabetes, and activation of the sympathetic nervous system are common in postmenopausal women and may also play important roles. However, progress in elucidating the mechanisms responsible for postmenopausal hypertension has been hampered by the lack of a suitable animal model. The aging female spontaneously hypertensive rat (SHR) exhibits many of the characteristics found in postmenopausal women. In this review, some of the possible mechanisms that could play a role in postmenopausal hypertension are discussed, as well as the characteristics of the aged female SHR as a model to study.