Abolition of end-organ damage by antiandrogen treatment in female hypertensive transgenic rats

Effects and clinical implications of sacubitril/valsartan on left ventricular reverse remodeling in patients affected by chronic heart failure: A 24-month follow-up

Background

Compared to angiotensin inhibition, angiotensin-neprilysin "blockade" improves mortality and reduces hospitalizations in patients with heart failure (HF) with reduced ejection fraction (EF). Sacubitril/valsartan is known to influence left ventricular (LV) reverse remodeling with systolic function improvement, although underlying mechanisms remain partially unclear. Our objectives were to evaluate whether sacubitril/valsartan promotes LV remodeling and improves LV ejection fraction (LVEF) (above the 35% threshold by echocardiographic evaluation) and to identify predictors of reverse remodeling in a real-world setting.

Methods

New York Heart Association (NYHA) class II-III patients with EF ≤ 35% were consecutively enrolled. All patients were on optimal medical therapy on the initiation of sacubitril/valsartan therapy. Full clinical and multi-parametric echocardiographic evaluation, electrocardiogram, and laboratory tests were performed at baseline and after 3, 6, 12, and 24 months.

Results

In total, 69 patients were recruited from July 2016 to August 2018. Reverse remodeling was observed in 57.7% (30/52) of patients, occurring within 3, 6, 12, and 24 months in 2, 11, 13, and 4 patients, respectively. Twenty-four (46%) patients showed LVEF improvement above the threshold of 35% during follow-up, occurring in 1, 10, 9, and 4 patients within 3, 6, 12, and 24 months, respectively. Primitive dilated cardiomyopathy and female gender were identified as significant predictors of reverse remodeling. NYHA class was improved in both remodeling and non-remodeling patients.

Conclusion

Sacubitril/valsartan promotes favorable cardiac remodeling and significantly improves LVEF in a significant proportion of HF patients within 24 months, both in NYHA class II and III patients with HF.

Sex differences in cardiovascular actions of the renin-angiotensin system

Cardiovascular disease (CVD) remains a worldwide public health concern despite decades of research and the availability of numerous targeted therapies. While the intrinsic physiological mechanisms regulating cardiovascular function are similar between males and females, marked sex differences have been established in terms of CVD onset, pathophysiology, manifestation, susceptibility, prevalence, treatment responses and outcomes in animal models and clinical populations. Premenopausal females are generally protected from CVD in comparison to men of similar age, with females tending to develop cardiovascular complications later in life following menopause. Emerging evidence suggests this cardioprotection in females is, in part, attributed to sex differences in hormonal regulators, such as the renin-angiotensin system (RAS). To date, research has largely focused on canonical RAS pathways and shown that premenopausal females are protected from cardiovascular derangements produced by activation of angiotensin II pathways. More recently, a vasodilatory arm of the RAS has emerged that is characterized by angiotensin-(1-7) [(Ang-(1-7)], angiotensin-converting enzyme 2 and Mas receptors. Emerging studies provide evidence for a shift towards these cardioprotective Ang-(1-7) pathways in females, with effects modulated by interactions with estrogen. Despite well-established sex differences, female comparison studies on cardiovascular outcomes are lacking at both the preclinical and clinical levels. Furthermore, there are no specific guidelines in place for the treatment of cardiovascular disease in men versus women, including therapies targeting the RAS. This review summarizes current knowledge on sex differences in the cardiovascular actions of the RAS, focusing on interactions with gonadal hormones, emerging data for protective Ang-(1-7) pathways and potential clinical implications for established and novel therapies.

6β-Hydroxytestosterone, a metabolite of testosterone generated by CYP1B1, contributes to vascular changes in angiotensin II-induced hypertension in male mice

Background

Previously, we showed that 6β-hydroxytestosterone (6β-OHT), a cytochrome P450 1B1 (CYP1B1)-derived metabolite of testosterone, contributes to angiotensin II (Ang II)-induced hypertension in male mice. This study was conducted to test the hypothesis that 6β-OHT contributes to increased vascular reactivity, endothelial dysfunction, vascular hypertrophy, and reactive oxygen species production associated with Ang II-induced hypertension.

Methods

Eight- to 10-week-old intact or castrated C57BL/6 J (Cyp1b1^+/+ and Cyp1b1^−/−) mice were anesthetized for implantation of a micro-osmotic pump which delivered Ang II (700 ng/kg/day) or saline for 14 days. Mice were injected with 6β-OHT (15 μg/g b.w every third day), flutamide (8 mg/kg every day), or its vehicle. Blood pressure was measured via tail-cuff. Vascular reactivity, endothelial-dependent and endothelial-independent vasodilation, media to lumen ratio, fibrosis by collagen deposition, and reactive oxygen species production by dihydroethidium staining were determined in the isolated thoracic aorta.

Results

The response of thoracic aorta to phenylephrine and endothelin-1 was increased in Ang II-infused Cyp1b1^+/+ mice compared to intact Cyp1b1^−/− or castrated Cyp1b1^+/+ and Cyp1b1^−/− mice; these effects of Ang II were restored by treatment with 6β-OHT. Ang II infusion caused endothelial dysfunction, as indicated by decreased relaxation of the aorta to acetylcholine in Cyp1b1^+/+ but not Cyp1b1^−/− or castrated Cyp1b1^+/+ and Cyp1b1^−/− mice. 6β-OHT did not alter Ang II-induced endothelial dysfunction in Cyp1b1^+/+ mice but restored it in Cyp1b1^−/− or castrated Cyp1b1^+/+ and Cyp1b1^−/− mice. Ang II infusion increased media to lumen ratio and caused fibrosis and reactive oxygen species production in the aorta of Cyp1b1^+/+ mice. These effects were minimized in the aorta of Cyp1b1^−/− or castrated Cyp1b1^+/+ and Cyp1b1^−/− mice and restored by treatment with 6β-OHT. Treatment with the androgen receptor antagonist flutamide reduced blood pressure and vascular hypertrophy in castrated Ang II-infused mice injected with 6β-OHT.

Conclusions

6β-OHT is required for the action of Ang II to increase vascular reactivity and cause endothelial dysfunction, hypertrophy, and increase in oxygen radical production. The effect of 6β-OHT in mediating Ang II-induced hypertension and associated hypertrophy is dependent on the androgen receptor. Therefore, CYP1B1 could serve as a novel target for the development of therapeutics to treat vascular changes in hypertensive males.

Gender Differences in Cardiac Hypertrophy

Cardiac hypertrophy is an adaptive response to abnormal physiological and pathological stimuli, which can be classified into concentric and eccentric hypertrophy, induced by pressure overload or volume overload, respectively. In both physiological and pathological scenarios, females generally show a more favorable form of hypertrophy compared with their male counterparts. However once established, cardiac hypertrophy is a stronger risk factor for heart failure in females. Pre-menopausal women are better protected against cardiac hypertrophy compared with men, but this protection is abolished following menopause and is partially restored after estrogen replacement therapy. Estrogen exerts its protection by counteracting pro-hypertrophy signaling pathways, whereas androgen mostly plays an opposite role in cardiac hypertrophy. We here summarize the progress in the understanding of sexual dimorphisms in cardiac hypertrophy and highlight recent breakthroughs in the regulatory role of sex hormones and their intricate molecular networks, in order to shed light on gender-oriented therapeutic efficacy for pathological hypertrophy.

Sex differences in the metabolic effects of the renin-angiotensin system

Obesity is a global epidemic that greatly increases risk for developing cardiovascular disease and type II diabetes. Sex differences in the obese phenotype are well established in experimental animal models and clinical populations. While having higher adiposity and obesity prevalence, females are generally protected from obesity-related metabolic and cardiovascular complications. This protection is, at least in part, attributed to sex differences in metabolic effects of hormonal mediators such as the renin-angiotensin system (RAS). Previous literature has predominantly focused on the vasoconstrictor arm of the RAS and shown that, in contrast to male rodent models of obesity and diabetes, females are protected from metabolic and cardiovascular derangements produced by angiotensinogen, renin, and angiotensin II. A vasodilator arm of the RAS has more recently emerged which includes angiotensin-(1-7), angiotensin-converting enzyme 2 (ACE2), mas receptors, and alamandine. While accumulating evidence suggests that activation of components of this counter-regulatory axis produces positive effects on glucose homeostasis, lipid metabolism, and energy balance in male animal models, female comparison studies and clinical data related to metabolic outcomes are lacking. This review will summarize current knowledge of sex differences in metabolic effects of the RAS, focusing on interactions with gonadal hormones and potential clinical implications.

Prenatal androgen exposure causes hypertension and gut microbiota dysbiosis

BACKGROUND

Conditions of excess androgen in women, such as polycystic ovary syndrome (PCOS), often exhibit intergenerational transmission. One way in which the risk for PCOS may be increased in daughters of affected women is through exposure to elevated androgens in utero. Hyperandrogenemic conditions have serious health consequences, including increased risk for hypertension and cardiovascular disease. Recently, gut dysbiosis has been found to induce hypertension in rats, such that blood pressure can be normalized through fecal microbial transplant. Therefore, we hypothesized that the hypertension seen in PCOS has early origins in gut dysbiosis caused by in utero exposure to excess androgen. We investigated this hypothesis with a model of prenatal androgen (PNA) exposure and maternal hyperandrogenemia by single-injection of testosterone cypionate or sesame oil vehicle (VEH) to pregnant dams in late gestation. We then completed a gut microbiota and cardiometabolic profile of the adult female offspring.

RESULTS

The metabolic assessment revealed that adult PNA rats had increased body weight and increased mRNA expression of adipokines: adipocyte binding protein 2, adiponectin, and leptin in inguinal white adipose tissue. Radiotelemetry analysis revealed hypertension with decreased heart rate in PNA animals. The fecal microbiota profile of PNA animals contained higher relative abundance of bacteria associated with steroid hormone synthesis, Nocardiaceae and Clostridiaceae, and lower abundance of Akkermansia, Bacteroides, Lactobacillus, Clostridium. The PNA animals also had an increased relative abundance of bacteria associated with biosynthesis and elongation of unsaturated short chain fatty acids (SCFAs).

CONCLUSIONS

We found that prenatal exposure to excess androgen negatively impacted cardiovascular function by increasing systolic and diastolic blood pressure and decreasing heart rate. Prenatal androgen was also associated with gut microbial dysbiosis and altered abundance of bacteria involved in metabolite production of short chain fatty acids. These results suggest that early-life exposure to hyperandrogenemia in daughters of women with PCOS may lead to long-term alterations in gut microbiota and cardiometabolic function.

Sex-linked differences in the course of chronic kidney disease and congestive heart failure: a study in 5/6 nephrectomized Ren-2 transgenic hypertensive rats with volume overload induced using aorto-caval fistula

The role of hypertension and the renin-angiotensin system (RAS) in sex-related differences in the course of chronic kidney disease (CKD) and congestive heart failure (CHF) remain unclear, especially when the two diseases are combined. In male and female Ren-2 transgenic rats (TGR), a model of hypertension with activation of endogenous RAS, CKD was induced by 5/6 renal mass reduction (5/6 NX) and CHF was elicited by volume overload achieved by creation of an aorto-caval fistula (ACF). The primary aim of the study was to examine long-term CKD- and CHF-related mortality, especially in animals with CKD and CHF combined, with particular interest in the potential sex-related differences. The follow-up period was 23 weeks after the first intervention (5/6 NX). We found, first, that TGR did not exhibit sexual dimorphism in the course of 5/6 NX-induced CKD. Second, in contrast, TGR exhibited important sex-related differences in the course of ACF-induced CHF-related mortality: intact female TGR showed higher survival rate than male TGR. This situation is reversed in the course of combined 5/6 NX-induced CKD and ACF-induced CHF-related mortality: intact female TGR exhibited poorer survival than male TGR. Third, the survival rate in animals with combined 5/6 NX-induced CKD and ACF-induced CHF was significantly worsened as compared with rat groups that were exposed to 'single organ disease'. Collectively, our present results clearly show that CKD aggravates long-term mortality of animals with CHF. In addition, TGR exhibit remarkable sexual dimorphism with respect to CKD- and CHF-related mortality, especially in animals with combined CKD and CHF.

Mechanistic Pathways of Sex Differences in Cardiovascular Disease

Major differences between men and women exist in epidemiology, manifestation, pathophysiology, treatment, and outcome of cardiovascular diseases (CVD), such as coronary artery disease, pressure overload, hypertension, cardiomyopathy, and heart failure. Corresponding sex differences have been studied in a number of animal models, and mechanistic investigations have been undertaken to analyze the observed sex differences. We summarize the biological mechanisms of sex differences in CVD focusing on three main areas, i.e., genetic mechanisms, epigenetic mechanisms, as well as sex hormones and their receptors. We discuss relevant subtypes of sex hormone receptors, as well as genomic and nongenomic, activational and organizational effects of sex hormones. We describe the interaction of sex hormones with intracellular signaling relevant for cardiovascular cells and the cardiovascular system. Sex, sex hormones, and their receptors may affect a number of cellular processes by their synergistic action on multiple targets. We discuss in detail sex differences in organelle function and in biological processes. We conclude that there is a need for a more detailed understanding of sex differences and their underlying mechanisms, which holds the potential to design new drugs that target sex-specific cardiovascular mechanisms and affect phenotypes. The comparison of both sexes may lead to the identification of protective or maladaptive mechanisms in one sex that could serve as a novel therapeutic target in one sex or in both.

Sex and Gender Differences in Risk, Pathophysiology and Complications of Type 2 Diabetes Mellitus

The steep rise of type 2 diabetes mellitus (T2DM) and associated complications go along with mounting evidence of clinically important sex and gender differences. T2DM is more frequently diagnosed at lower age and body mass index in men; however, the most prominent risk factor, which is obesity, is more common in women. Generally, large sex-ratio differences across countries are observed. Diversities in biology, culture, lifestyle, environment, and socioeconomic status impact differences between males and females in predisposition, development, and clinical presentation. Genetic effects and epigenetic mechanisms, nutritional factors and sedentary lifestyle affect risk and complications differently in both sexes. Furthermore, sex hormones have a great impact on energy metabolism, body composition, vascular function, and inflammatory responses. Thus, endocrine imbalances relate to unfavorable cardiometabolic traits, observable in women with androgen excess or men with hypogonadism. Both biological and psychosocial factors are responsible for sex and gender differences in diabetes risk and outcome. Overall, psychosocial stress appears to have greater impact on women rather than on men. In addition, women have greater increases of cardiovascular risk, myocardial infarction, and stroke mortality than men, compared with nondiabetic subjects. However, when dialysis therapy is initiated, mortality is comparable in both males and females. Diabetes appears to attenuate the protective effect of the female sex in the development of cardiac diseases and nephropathy. Endocrine and behavioral factors are involved in gender inequalities and affect the outcome. More research regarding sex-dimorphic pathophysiological mechanisms of T2DM and its complications could contribute to more personalized diabetes care in the future and would thus promote more awareness in terms of sex- and gender-specific risk factors.

Chronic Blockade of the Androgen Receptor Abolishes Age-Dependent Increases in Blood Pressure in Female Growth-Restricted Rats

Intrauterine growth restriction induced via placental insufficiency programs a significant increase in blood pressure at 12 months of age in female growth-restricted rats that is associated with early cessation of estrous cyclicity, indicative of premature reproductive senescence. In addition, female growth-restricted rats at 12 months of age exhibit a significant increase in circulating testosterone with no change in circulating estradiol. Testosterone is positively associated with blood pressure after menopause in women. Thus, we tested the hypothesis that androgen receptor blockade would abolish the significant increase in blood pressure that develops with age in female growth-restricted rats. Mean arterial pressure was measured in animals pretreated with and without the androgen receptor antagonist, flutamide (8 mg/kg/day, SC for 2 weeks). Flutamide abolished the significant increase in blood pressure in growth-restricted rats relative to control at 12 months of age. To examine the mechanism(s) by which androgens contribute to increased blood pressure in growth-restricted rats, blood pressure was assessed in rats untreated or treated with enalapril (250 mg/L for 2 weeks). Enalapril eliminated the increase in blood pressure in growth-restricted relative to vehicle- and flutamide-treated controls. Furthermore, the increase in medullary angiotensin type 1 receptor mRNA expression was abolished in flutamide-treated growth-restricted relative to untreated counterparts and controls; cortical angiotensin-converting enzyme mRNA expression was reduced in flutamide-treated growth-restricted versus untreated counterparts. Thus, these data indicate that androgens, via activation of the renin-angiotensin system, are important mediators of increased blood pressure that develops by 12 months of age in female growth-restricted rats.

Free androgen index as a predictor of blood pressure progression and accelerated vascular aging in menopause

BACKGROUND AND AIMS

We aimed to assess the prognostic value of free androgen index (FAI) and its change over time in arterial stiffness progression, endothelial function and hypertension in postmenopausal women.

METHODS

Postmenopausal women (n = 180) without clinically overt cardiovascular disease or diabetes were consecutively recruited and followed for a median of 29 months. The main outcome measures were changes over time in endothelial function (FMD), reflected waves, localized and systemic (PWV) arterial stiffness and hypertension.

RESULTS

Increased baseline FAI was significantly associated with new onset hypertension (OR for each SD, 2.71, 95% CI 1.14-6.41, p = 0.024), deterioration of pulse wave velocity (PWV) (0.414 m/s per SD), flow-mediated dilation (FMD) (-0.42% per SD), systolic (2.5 mmHg per SD) and pulse pressure progression (2.3 mmHg per SD, p < 0.05 for all). Baseline FAI remained an independent predictor of changes in PWV (p = 0.006), FMD (p = 0.02), peripheral pulse pressure (p = 0.028), transition to new onset hypertension (p = 0.001) and higher BP category (p = 0.012), after adjustment for age, changes in systolic blood pressure, traditional risk factors, vasoactive medication or total testosterone. Baseline FAI improved reclassification for the risk of transition into higher BP category (NRI = 47.5 ± 20.3%, p = 0.02) and abnormal PWV (NRI = 53.4 ± 23.2%, p = 0.021). Similarly, in a subgroup of patients with measured FAI at follow-up, its changes over time predicted changes in PWV, peripheral pulse pressure and hypertension status (p < 0.05 for all).

CONCLUSIONS

In apparently healthy postmenopausal women, FAI could be a novel biomarker superior to total testosterone for accelerated vascular aging and hypertension status.

The usefulness of age and sex to predict all-cause mortality in patients with dilated cardiomyopathy: a single-center cohort study

Objective

Recent studies have shown that sex and age are associated with outcomes in patients with cardiomyopathy. The purpose of this study was to determine the all-cause mortality of dilated cardiomyopathy (DCM) by age and sex.

Methods and results

The patients were divided into non-elderly (age <60 years, n=811) and elderly (age ≥60 years, n=331) groups. No difference in the all-cause mortality rate was observed between elderly and non-elderly patients (27.2% vs 22.2%, log-rank χ²=2.604, P=0.107). Furthermore, no significant difference in mortality was observed between the male and female patients (23.3% vs 24.5%, log-rank χ²=0.707, P=0.400). However, subgroup analysis revealed that elderly male patients exhibited a higher mortality rate than non-elderly male patients (29.4% vs 21.3%, log-rank χ²=5.898, P=0.015), while no difference was observed between the elderly female patients and non-elderly female patients. In the Cox analysis, neither age nor sex was a significant independent predictor of all-cause mortality in patients with DCM.

Conclusion

In conclusion, no significant difference in mortality between male and female patients or between the elderly and non-elderly patients was observed. Only among males was a difference in mortality observed; elderly male patients experienced greater mortality than that of non-elderly male patients. No effect of age or sex on all-cause mortality was observed in patients with DCM.

Development of progressive albuminuria in male Munich Wistar Frömter rats is androgen dependent

Munich Wistar Frömter (MWF) rats develop spontaneous albuminuria that is linked to autosomal genetic loci and inherit a nephron deficit in both female and male animals, respectively. However, albuminuria and kidney damage are clearly more pronounced in males. Here we tested whether androgens and the androgen receptor influence albuminuria in male MWF. We first demonstrated in a pilot study that orchiectomy (Ox) of male MWF led to a significant suppression of urinary albumin excretion (UAE), while continuous testosterone supplementation in MWF Ox led to UAE levels similar to sham-operated (Sham) MWF rats. Subsequently, we performed a comparative main study between male MWF and normal Wistar rats to evaluate the effect of the androgen receptor on UAE development in adult animals up to the age of 18 wk. MWF Sham developed a marked increase in UAE compared with Wistar Sham (48.30 ± 6.16 vs. 0.42 ± 0.08 mg/24 h, P < 0.0001). UAE was significantly lower in MWF Ox compared with MWF Sham (-55%, P < 0.0001). In MWF Ox animals supplemented with testosterone and treated with the androgen receptor antagonist flutamide (OxTF) UAE at 18 wk was even lower compared with MWF Ox (-71%, P < 0.01) and similar to age-matched female MWF. The mRNA expression of renal tubular injury markers Kim1 and NGAL was increased in MWF Sham compared with Wistar Sham (P < 0.0008, respectively) and expression decreased significantly in MWF OxTF (P < 0.0004, respectively). Thus, the sexual dimorphism in albuminuria development in MWF can be attributed to testosterone and the androgen receptor in male rats.

Sex-dependent differences in renal angiotensinogen as an early marker of diabetic nephropathy

AIM

The renal renin-angiotensin system (RAS) has been implicated in the pathogenesis of diabetic nephropathy. The aim of this study was to investigate sex differences in renal renin-angiotensin system (RAS) and the roles of androgens in diabetes-associated renal injury.

METHODS

Renal injury and fibrosis were studied in streptozotocin-induced diabetic rats by albuminuria and by gene expression of collagen I and fibronectin. RAS was investigated by analysing the plasma angiotensinogen (AOGEN) and renin activity (PRA) and their renal gene expression. Also, a group of diabetic rats was treated with the anti-androgen flutamide.

RESULTS

Albuminuria was significantly lower in diabetic females than in males (1.2 [0.8-1.5] versus 4.4 [2.2-6.1] mg/24 h, data are median [IQR] values, P < 0.05). Renal AOGEN mRNA levels were increased by diabetes in males (8.1 ± 0.8% in diabetes versus 0.8 ± 0.2% in control, P < 0.001) but not in females (1.0 ± 0.1% in diabetes versus 0.8 ± 0.1% in control, P > 0.05), as were collagen I and fibronectin mRNAs. Furthermore, AOGEN mRNA levels were strongly correlated with albuminuria (Spearman r = 0.64, 95% [CI] 0.36-0.81, P < 0.0001). Diabetes decreased PRA, renal renin mRNA and plasma AOGEN in both females and males. Anti-androgen treatment decreased albuminuria only in diabetic males without affecting the endocrine or renal RAS.

CONCLUSIONS

These data indicate that renal but not hepatic AOGEN or renin is positively associated with diabetic albuminuria and contribute to the sex-dependent differences in renal injury. Androgens may contribute to albuminuria in male independently of the RAS.

Prenatal testosterone exposure induces hypertension in adult females via androgen receptor-dependent protein kinase Cδ-mediated mechanism

Prenatal exposure to excess testosterone induces hyperandrogenism in adult females and predisposes them to hypertension. We tested whether androgens induce hypertension through transcriptional regulation and signaling of protein kinase C (PKC) in the mesenteric arteries. Pregnant Sprague-Dawley rats were injected with vehicle or testosterone propionate (0.5 mg/kg per day from gestation days 15 to 19, SC) and their 6-month-old adult female offspring were examined. Plasma testosterone levels (0.84±0.04 versus 0.42±0.09 ng/mL) and blood pressures (111.6±1.3 versus 104.5±2.4 mm Hg) were significantly higher in prenatal testosterone-exposed rats compared with controls. This was accompanied with enhanced expression of PKCδ mRNA (1.5-fold) and protein (1.7-fold) in the mesenteric arteries of prenatal testosterone-exposed rats. In addition, mesenteric artery contractile responses to PKC activator, phorbol-12,13-dibutyrate, was significantly greater in prenatal testosterone-exposed rats. Treatment with androgen receptor antagonist flutamide (10 mg/kg, SC, BID for 10 days) significantly attenuated hypertension, PKCδ expression, and the exaggerated vasoconstriction in prenatal testosterone-exposed rats. In vitro exposure of testosterone to cultured mesenteric artery smooth muscle cells dose dependently upregulated PKCδ expression. Analysis of PKCδ gene revealed a putative androgen responsive element in the promoter upstream to the transcription start site and an enhancer element in intron-1. Chromatin immunoprecipitation assays showed that androgen receptors bind to these elements in response to testosterone stimulation. Furthermore, luciferase reporter assays showed that the enhancer element is highly responsive to androgens and treatment with flutamide reverses reporter activity. Our studies identified a novel androgen-mediated mechanism for the control of PKCδ expression via transcriptional regulation that controls vasoconstriction and blood pressure.

Prenatal testosterone exposure leads to hypertension that is gonadal hormone-dependent in adult rat male and female offspring

Prenatal testosterone exposure impacts postnatal reproductive and endocrine function, leading to alterations in sex steroid levels. Because gonadal steroids are key regulators of cardiovascular function, it is possible that alteration in sex steroid hormones may contribute to development of hypertension in prenatally testosterone-exposed adults. The objectives of this study were to evaluate whether prenatal testosterone exposure leads to development of hypertension in adult males and females and to assess the influence of gonadal hormones on arterial pressure in these animals. Offspring of pregnant rats treated with testosterone propionate or its vehicle (controls) were examined. Subsets of male and female offspring were gonadectomized at 7 wk of age, and some offspring from age 7 to 24 wk received hormone replacement, while others did not. Testosterone exposure during prenatal life significantly increased arterial pressure in both male and female adult offspring; however, the effect was greater in males. Prenatal androgen-exposed males and females had more circulating testosterone during adult life, with no change in estradiol levels. Gonadectomy prevented hyperandrogenism and also reversed hypertension in these rats. Testosterone replacement in orchiectomized males restored hypertension, while estradiol replacement in ovariectomized females was without effect. Steroidal changes were associated with defective expression of gonadal steroidogenic genes, with Star, Sf1, and Hsd17b1 upregulation in testes. In ovaries, Star and Cyp11a1 genes were upregulated, while Cyp19 was downregulated. This study showed that prenatal testosterone exposure led to development of gonad-dependent hypertension during adult life. Defective steroidogenesis may contribute in part to the observed steroidal changes.

A single pill to treat postmenopausal hypertension? Not yet

Postmenopausal women make up one of the fastest growing populations in the United States. Women typically have a higher incidence of cardiovascular disease following menopause. One of the major risk factors for cardiovascular disease is hypertension, and after menopause, blood pressure (BP) increases progressively in women. Also after menopause, the progression of renal disease increases in women compared with aged matched men. However, the mechanism(s) responsible for the post-menopausal increase in BP and renal injury are yet to be elucidated. Moreover the best therapeutic options to treat postmenopausal hypertension in women are not clear. Hypertension in postmenopausal women are usually associated with other cardiovascular risk factors, such as dyslipidemias, visceral obesity and endothelial dysfunction. Recently it became apparent that in a large number of hypertensive postmenopausal women, their BP is not well controlled with conventional antihypertensive medications. A clear understanding of the complex pathogenesis of postmenopausal hypertension is needed in order to offer the best therapeutic options for these women.

Sex and gender differences in myocardial hypertrophy and heart failure

Cardiovascular disease is the most common cause of death in men and women worldwide. Men develop most, but not all, cardiovascular diseases at an earlier age while the number of affected women significantly increases with higher age. Heart failure (HF) is a common cause of cardiovascular death and carries a poor prognosis in both genders. Risk factors and myocardial adaptations in HF in men and women are different. Female hearts develop a more favorable physiological form of myocardial remodeling than male hearts. This may be related to sex hormones, estrogens and testosterone. A clinical study for gender differences in human aortic stenosis supports the hypotheses. HF management differs between both sexes, with underdiagnosis and undertreatment and less use of invasive therapies in women. Nevertheless, women frequently have better outcomes than men. Gender research will contribute directly to patient-oriented benefit by suggesting clinical protocols.

Testosterone increases: sodium reabsorption, blood pressure, and renal pathology in female spontaneously hypertensive rats on a high sodium diet

Estrogen (E) and testosterone (T) are important in the sexually dimorphic pattern of blood pressure (BP) development. The goal was to examine the effects of endogenous E and exogenous T in the development of hypertension in female spontaneously hypertensive rats (SHR) on a high sodium diet. Female SHR (N = 27, 5-week) were divided into four groups: (1) control (n = 8), (2) ovariectomized (OVX, n = 26), (3) testosterone implants with intact ovaries (T, n = 6), and (4) ovariectomized + testosterone implants (OVX+T, n = 7). T was given immediately after OVX and replaced every two weeks and they were fed a 3% NaCl diet. BP was measured weekly and plasma norepinephrine (NE) analyzed by HPLC. OVX+T females exhibited the greatest elevation in BP (190 ± 4.0 mmHg) compared to controls at 15 weeks of age (140 ± 3.4 mmHg, P < .001) and a pattern of hypertension development similar to that of male SHR. Females with T treatment showed evidence of glomerulosclerosis. In conclusion, T accelerated the development of hypertension similar to the BP pattern observed in males; the presence of ovaries attenuated the T induced increase in BP; T increased renal sodium reabsorption, and T increased glomerulosclerosis.

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.

Increased blood pressure and water intake in transgenic mice expressing rat tonin in the brain

Tonin is a serine proteinase of the kallikrein family that can produce angiotensin II directly from angiotensinogen. To clarify the importance of this enzyme for central nervous control of the cardiovascular system, we generated transgenic mice, TGM(rTon), that express rat tonin in astrocytes. These mice present high levels of tonin mRNA and activity specifically in the brain. As a consequence, TGM(rTon) develop increased blood pressure and water intake. Lisinopril, an ACE inhibitor, is less hypotensive for transgenic mice than for control animals. The AT(1) receptor antagonist candesartan equally lowers blood pressure in transgenic and in control mice. Plasma angiotensin II, but not angiotensin I, is increased in TGM(rTon) compared to the wild type, suggesting release of the peptide from the brain into the circulation. However, AT(1) receptors are desensitized in this transgenic model, as demonstrated by a blunted pressor response to intravenous application of angiotensin II. In conclusion, tonin in the brain may represent an alternative pathway for angiotensin II generation with effects on the cardiovascular system.

Physiology of Kidney Renin

The protease renin is the key enzyme of the renin-angiotensin-aldosterone cascade, which is relevant under both physiological and pathophysiological settings. The kidney is the only organ capable of releasing enzymatically active renin. Although the characteristic juxtaglomerular position is the best known site of renin generation, renin-producing cells in the kidney can vary in number and localization. (Pro)renin gene transcription in these cells is controlled by a number of transcription factors, among which CREB is the best characterized. Pro-renin is stored in vesicles, activated to renin, and then released upon demand. The release of renin is under the control of the cAMP (stimulatory) and Ca2+(inhibitory) signaling pathways. Meanwhile, a great number of intrarenally generated or systemically acting factors have been identified that control the renin secretion directly at the level of renin-producing cells, by activating either of the signaling pathways mentioned above. The broad spectrum of biological actions of (pro)renin is mediated by receptors for (pro)renin, angiotensin II and angiotensin-( 1 – 7 ).

Sex, diabetes and the kidney

The incidence and the rate of progression of nondiabetic renal disease is generally greater in men compared with age-matched women, suggesting that the female sex is protective and/or that the male sex is a risk factor for the development and progression of nondiabetic renal disease. In diabetes, even though the male sex still appears to be a risk factor, this relationship is not as strong as it is in nondiabetic renal disease. Experimental evidence suggests that both estrogens and androgens play an important role in the pathophysiology of renal disease. Thus one of the potential mechanisms for the absence of a clear sex difference in the setting of diabetes may be alterations in sex hormone levels. Indeed, studies suggest that diabetes is a state of an imbalance in sex hormone levels; however, whether these changes correlate with the decline in renal function associated with diabetes is unclear. Furthermore, diabetic renal disease rarely develops before puberty, and the onset of puberty accelerates microalbuminuria, supporting the idea of the involvement of sex hormones in the development and progression of the disease. However, other than a handful of experimental studies indicating that treatment with or removal of sex hormones alters the course of diabetic renal disease, very few studies have actually directly examined the correlation between sex hormones and the disease development and progression. Further studies are necessary to determine the precise contribution of sex hormones in the pathophysiology of diabetic renal disease to develop novel and potentially sex-specific therapeutic treatments.

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.

Glomerular hypertrophy precedes albuminuria and segmental loss of podoplanin in podocytes in Munich-Wistar-Frömter rats

Focal segmental glomerulosclerosis (FSGS) is a common cause of end-stage renal disease. Albuminuria is a risk factor for FSGS and is influenced by environmental, genetic, and sex-specific factors. Podocytes play a central role in the development of albuminuria, but the precise relationship between early glomerular and podocyte-associated damage and albuminuria is unclear. Furthermore, experimental findings demonstrate a sex difference in development of albuminuria and FSGS. We investigated the early glomerular changes in male Munich-Wistar-Frömter (MWF) rats, which spontaneously develop albuminuria, and male albuminuria-resistant spontaneously hypertensive rats (SHR). In addition, since female MWF rats are protected from overt proteinuria and progressive renal disease, we compared the phenotypic changes in podocytes during early development of albuminuria in male and female MWF rats. In male MWF rats, glomerular hypertrophy preceded the onset of albuminuria and was greater than in male SHR. Albuminuria developed starting at 6 wk of age and coincided with focal and segmental loss of podoplanin, increased expression of desmin, entrapment of albumin in affected podocytes, and focal and segmental foot process effacement at the ultrastructural level. Other podocyte-associated molecules, such as nephrin and zonula occludens 1, were unaffected. Early glomerular hypertrophy and podocyte damage did not differ between male and female MWF rats. Our data show for the first time that albuminuria in male and female MWF rats is preceded by glomerular hypertrophy and accompanied by focal and segmental loss of podoplanin when FSGS was not yet present.

Sex and sex hormones influence the development of albuminuria and renal macrophage infiltration in spontaneously hypertensive rats

There is a sex difference in hypertensive renal injury, with men experiencing greater severity and a more rapid progression of renal disease than women; however, the molecular mechanisms protecting against renal injury in women are unknown. The goal of this study was to determine whether sex hormones modulate blood pressure and the progression of albuminuria during the developmental phase of hypertension in male and female spontaneously hypertensive rats (SHR). Studies were also performed to examine how sex and sex hormones influence two major risk factors for albuminuria, overactivation of the renin-angiotensin system and oxidative stress. Blood pressure was measured by telemetry in gonad-intact and gonadectomized male and female SHR. Microalbumin excretion, measured over time, and macrophage infiltration were used to assess renal health. Male SHR had significantly higher blood pressures than female SHR, and gonadectomy decreased blood pressures in males with no effect in females. Male SHR displayed a gonad-sensitive increase in albuminuria over time, and female SHR had a gonad-sensitive suppression in macrophage infiltration. Female SHR had greater plasma ANG II levels and similar levels of renal cortical ANG II vs. levels shown in males but less AT(1)-receptor protein expression in the renal cortex. Female SHR also had a gonad-sensitive decrease in renal oxidative stress. Therefore, the renal protection afforded to female SHR is associated with lower blood pressure, decreased macrophage infiltration, and decreased levels of oxidative stress.

Methods in the evaluation of cardiovascular renin angiotensin aldosterone activation and oxidative stress

Renin angiotensin aldosterone system (RAAS) activation plays an essential role in the development of cardiovascular disease (CVD). Multiple pathophysiologic processes are able to activate RAAS, among which hypertension, obesity, diabetes mellitus 2, and chronic kidney disease deserve special attention, because they are the main contributors to CVD. Adding to the well-known effects of RAAS overactivity on the vasculature and water and electrolyte balance, current evidence links abnormal activation of the RAAS to increased production of reactive oxygen species (ROS) and oxidative stress. This association is mediated at least partially through interaction of angiotensin II (Ang II) with its receptor angiotensin receptor 1 (AT1R) in cardiovascular tissue, and subsequent activation of the nicotinamide adenine dinucleotide phosphate (NADPH) enzymatic complex, which finally leads to increased ROS production. This resulting state of enhanced oxidative stress contributes largely to generalized atherosclerosis and finally to CVD. The generation of animal models of increased RAAS and Ang II expression, in particular the Ren2 rodent model, provides important opportunities to better characterize the relationship between this system and the production of ROS. This chapter describes methods to evaluate, characterize, and quantify the activity of the RAAS and NADPH oxidase, as well as the production of ROS production in animal model of RAAS.

Gonadal steroids, salt-sensitivity and renal function

PURPOSE OF REVIEW

The aim of this article is to discuss the impact of male and female sex hormones on renal function and to develop the concept that salt-sensitivity of renal function behaves independently of the systemic blood pressure response to salt and may contribute to renal sex-specific differences.

RECENT FINDINGS

Men exhibit a more rapid age-related decline in renal function than women and some renal diseases are clearly sex dependent. Recent studies have shown that gonadal steroids have an important influence on sodium handling and renal hemodynamics that may offer a key for understanding the sexual dimorphism of the renal function. It has been found that androgens increase proximal sodium reabsorption and intraglomerular pressure by modulating afferent and efferent arteriolar tonus via angiotensin II, endothelin and oxidative stress. In contrast, female sex hormones lead to a renal vasodilation and decrease filtration fraction.

SUMMARY

Some newly discovered mechanisms triggering the salt-sensitivity of the renal function and the interaction between gonadal steroids and components of the renin cascade may play an important role in the dimorphism of renal response to salt.

The Effect of Flutamide on Systemic and Renal Hemodynamics in Zucker Diabetic Rats: Paradoxic Renal Vasodilator Response to Endothelin-1 and TXA2 Receptor Activation in Female Sex

BACKGROUND

There is increasing evidence that endogenous sex hormones regulate vascular reactivity, and testosterone may contribute to the worse prognosis for renal disease in men. Male Zucker diabetic rats exhibit improved renal hemodynamic responses after castration. It is, however, unclear whether endogenous testosterone affects renal and systemic microcirculatory responses in the female sex, especially in type 2 diabetes.

AIM

To test the hypothesis that endogenous testosterone in the female Zucker diabetic rat exerts a pathophysiologically relevant modulation of endothelial and renal microvascular function.

METHODS

Female Zucker diabetic rats (FZDR) aged 5-6 weeks and from the same litter were divided into 2 groups (n = 6-8 each). The experimental group received the androgen receptor blocker flutamide, dissolved in alcohol and added to their drinking water (500 mL) at 20 mg/rat/week. The control FZDR received only the alcohol vehicle added to the same volume of drinking water. Both FZDR groups were treated for 3 months before undergoing the hemodynamic studies. A sex comparison control group of male Zucker diabetic rats (MZDR), also aged 5-6 weeks, was studied, following same protocol. Mean arterial pressure (MAP) and renal cortical blood flow (RCF) response to phenylephrine, acetylcholine, TXA2-mimetic U46619, endothelin-1 (ET-1), angiotensin II, and L-NG-nitro arginine methyl ester were studied. Furthermore, the role of protein kinase C in the responses was assessed using phorbol-12,13 dibutyrate 10(-4) M. The impact of flutamide on body weights and blood glucose of the rats were also determined.

RESULTS

Flutamide-treated FZDR had a significant reduction in body weight/adiposity to 432 +/- 44 g, compared to controls at 553 +/- 37 g (P = 0.045), and random blood glucose concentration of 185 +/- 44 g/dL, compared to the control FZDR at 475 +/- 34 g/dL (P = 0.002). Vehicle-treated FZDR (n = 6-8), exhibited little or no systemic or renal response to any of the agonists. By contrast, flutamide treatment of FZDR (n = 5-7) caused a normalization of the dose-dependent MAP and RCF pressor response to phenylephrine [P < 0.005, analysis of variance (ANOVA)] and the vasodilator response to acetylcholine (P <. 0.01, ANOVA). Flutamide-treated FZDR showed enhanced pressor response to U46619 (P = 0.024, ANOVA), ET-1, and angiotensin II (P < 0.03, ANOVA). Surprisingly, the augmented systemic pressor action of U46619 and ET-1 was accompanied by a renal vasodilator action, with paradoxic RCF increases to U46619 (P < 0.003, ANOVA) and to ET-1 (P < 0.001, ANOVA) only in flutamide-treated FZDR. By contrast, flutamide-treated MZDR exhibited no significant change in body weight and an attenuation of the vasoconstrictor responses and enhanced nitric oxide-mediated dilatation compared with male controls. However, no specific effect on ET-1 or TXA2 receptor-mediated renal perfusion was discernible. Both L-NG-nitro arginine methyl ester and the protein kinase C agonist phorbol-12,13 dibutyrate [10(-4)M] significantly increased MAP and reduced RCF (P < 0.03) in the experimental FZDR compared with their controls.

CONCLUSION

Flutamide administration to FZDR resulted in the reversal of abnormal systemic and renal alpha-1-mediated vasoconstriction and enhanced nitric oxide-mediated vasodilation. Flutamide caused a paradoxic but specific increase in renal perfusion during ET-1 and TXA2 receptor activation, which could be renoprotective in females. The salutary effects of flutamide on vascular reactivity in the FZDR may be mediated by a protein kinase C-dependent mechanism. These results are compatible with the notion that endogenous testosterone may regulate systemic and renal microcirculation in the female sex and in the type 2 diabetic state.

Gender differences in renal nuclear receptors and aryl hydrocarbon receptor in 5/6 nephrectomized rats

This study was aimed at delineating molecular pathways essential in gender-different pathogenesis of chronic kidney diseases (CKD). Renal transcripts of nuclear receptors and metabolic enzymes in male and female kidneys from 5/6 nephrectomized (Nx) rats 7 weeks post-Nx were examined using branched DNA signal amplification assay. Nx-males had marked kidney injury coupled with anemia and malnutrition. Nx-females had moderate renal injury, and were free of albuminuria, anemia, and malnutrition. Nx-males had systemic and renal inflammation, which were largely absent in Nx-females. Blood 17beta-estradiol, testosterone, and corticosterone did not change, whereas urinary testosterone decreased in both genders. Compared to males, female kidneys had higher androgen receptor (AR) and aryl hydrocarbon receptor (AhR) but lower estrogen receptor alpha (ERalpha). Compared to Nx-males, female remnant kidneys had less decreases in ERalpha and peroxisome proliferator-activated receptor alpha (PPARalpha), had no induction of AR and decrease of acyl-CoA oxidase, whereas had induction of cytochrome P450 4a1 (Cyp4a1) but decrease of AhR. Renal protein expression of a 52-kDa isoform of Wilm's tumor 1 (WT1), transcription factor critical in nephrogenesis, decreased dramatically in Nx-males but largely preserved in Nx-females. In conclusion, gender divergences in basal expression and alteration of ERalpha, AR, AhR, WT1, and PPARalpha/Cyp4a1 during CKD may explain gender differences in CKD progression and outcome of renal transplantation.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

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.

Antihypertensive effects of flutamide in rats that are exposed to a low-protein diet in utero

OBJECTIVE

We investigated whether gestational age of in utero low-protein diet played a role in the subsequent development of adult hypertension and whether it is gender dependent and examined whether flutamide (a specific, nonsteroidal competitive antagonist of the androgen receptor) reduces blood pressure in rat offspring that are exposed to in utero low-protein diet (6%).

STUDY DESIGN

Pregnant rats were fed either with 20% protein (control) or 6% protein (low-protein diet) from day 1 or day 12 of gestation. Fetoplacental weights and mortality rates of pups were assessed. Systolic blood pressure, mean arterial blood pressure, and circulatory hormone levels in offspring were determined. In addition, male and female hypertensive offspring were treated with flutamide, and their blood pressure was monitored.

RESULTS

After delivery, pup weights were reduced, and pup mortality rates increased in the low-protein diet-day 1 group. Systolic blood pressure and mean arterial blood pressure were elevated in low-protein diet-day 1 males and females and low-protein diet-day 2 males. Significant (P < .05) reduction in blood pressure was achieved with flutamide in low-protein diet-day 1 females. Serum estradiol levels were decreased (P < .05) in low-protein diet-day 1 females; flutamide attenuated this effect.

CONCLUSION

The day of in utero insult by low-protein diet is critical in the induction of adult hypertension; the severity is gender dependent. Flutamide was found to protect against hypertension only in females.

Abrogation of oxidative stress improves insulin sensitivity in the Ren-2 rat model of tissue angiotensin II overexpression

To evaluate the role of renin-angiotensin system (RAS)-mediated oxidative stress in insulin resistance (IR), we compared the effects of the angiotensin II (ANG II) receptor blocker (ARB) valsartan and a superoxide dismutase (SOD) mimetic, tempol, on whole body glucose tolerance and soleus muscle insulin-stimulated glucose uptake in transgenic hypertensive TG(mREN-2)27 (Ren-2) rats. Ren-2 rats and Sprague-Dawley (SD) controls were given valsartan (30 mg/kg) or tempol (1 mmol/l) in their drinking water for 21 days. IR was measured by glucose tolerance testing (1 g/kg glucose ip). IR index (AUC(glucose) x AUC(insulin)) was significantly higher in the Ren-2 animals compared with SD controls (30.5 +/- 7.0 x 10(6) arbitrary units in Ren-2 vs. 10.2 +/- 2.4 x 10(6) in SD, P < 0.01). Both valsartan and tempol treatment normalized Ren-2 IR index. Compared with SD controls (100%), there was a significant increase in superoxide anion production (measured by lucigenin-enhanced chemiluminescence) in soleus muscles of Ren-2 rats (133 +/- 15%). However, superoxide production was reduced in both valsartan- and tempol-treated (85 +/- 22% and 59 +/- 12%, respectively) Ren-2 rats. Insulin (INS)-mediated 2-deoxyglucose (2-DG) uptake (%SD basal levels) was substantially lower in Ren-2 rat soleus muscle compared with SD (Ren-2 + INS = 110 +/- 3% vs. SD + INS = 206 +/- 12%, P < 0.05). However, Ren-2 rats treated with valsartan or tempol exhibited a significant increase in insulin-mediated 2-DG uptake compared with untreated transgenic animals. Improvements in skeletal muscle insulin-dependent glucose uptake and whole body IR in rats overexpressing ANG II by ARB or SOD mimetic indicate that oxidative stress plays an important role in ANG II-mediated insulin resistance.

Sex hormone regulation of systemic endothelial and renal microvascular reactivity in type-2 diabetes: studies in gonadectomized and sham-operated Zucker diabetic rats

BACKGROUND

Male Zucker diabetic rats exhibit a more severe endotheliopathy in comparison with their female diabetic litter mates. The plasma concentrations of both thromboxanes and endothelins are elevated in diabetes, and the receptor cross-talk between TXA(2) and ET-1 receptors may be enhanced in type-2 diabetic Zucker rats.

AIMS

To determine the role of the endogenous sex steroid hormones, testosterone and estradiol on the systemic and renal microvascular reactivity to ET-1, thromboxane-mimetic U46619, ET-TXA(2) receptor interaction, and the nitric oxide vasodilator system in Zucker hypertensive-diabetic rats.

METHODS

Male and female Zucker rats aged 8-10 weeks were each divided into two groups. The male rats were castrated or underwent a sham operation. The female rats were spayed (bilateral ovariectomy and hysterectomy) or had a sham operation. All rats were studied 4-6 weeks after the gonadectomy or sham operations. Blood glucose and insulin as well as plasma concentrations of testosterone and estradiol were determined. Haemodynamic studies were undertaken with determination of the dose-response curve for mean arterial pressure (MAP), renal cortical flow (RCF) and renal medullary blood flow (MBF) in response to ET-1 and U46619, and the effect of interdiction of the ET-TXA(2) interaction with ET-antagonists BQ610 and BQ788. The role of endogenous NO was assessed by its response to graded acetylcholine doses and to a L-NG-nitro-arginine methyl ester (L-NAME) infusion.

RESULTS

Castrated male rats had a significantly lower blood glucose concentration (295 +/- 33 mg dL(-1)) compared with their sham-controls (481 +/- 40 mg dL(-1)), P = 0.008. Mean arterial pressure tended to be lower in the castrated rats. Gonadectomy reduced the plasma testosterone and estradiol concentrations. Castration abolished the hypotensive action of U46619 compared with sham-operated male rats (P < 0.0001, anova). Conversely, the pressor action of U46619 seen in the sham-operated female rats was reversed to a profound hypotensive action in the spayed rats (P < 0.001, anova). The change in MAP after U46619 was inversely correlated to the plasma testosterone concentration (r = -0.73, P = 0.027). The paradoxical hypotensive response elicited by ET-1 in the Zucker diabetic rats of both sexes was abolished by castration only (P < 0.005, anova). Castration caused a significant (P = 0.011) augmentation of the vasodilator response to acetylcholine, while spaying caused a slight attenuation. Castration, but not spaying, resulted in significant increases in MBF after U46619 (P = 0.003, anova), ET-1 (P = 0.005, anova) and acetylcholine (P = 0.053, anova). The ET-(B) antagonist BQ788 augmented the U46619-induced rise in MAP in castrated male rats, and also abolished the U46619-induced increase in MBF (P < 0.01 anova). L-NAME (25 mg kg(-1)) increased MAP and decreased MBF in the gonadectomized and sham-operated rats, except for the castrated male Zucker rats, where it significantly increased MBF (+90 +/- 31 PU) (P = 0.0004, anova) despite the increase in MAP.

CONCLUSIONS

Testosterone and estradiol regulate systemic and microvascular reactivity to TXA(2) receptor stimulation in type-2 diabetic Zucker rats. The impact of testosterone on blood glucose concentration, blood pressure, and the systemic and renal microcirculatory response to ET-1 and NO, as well as the endothelin-thromboxane receptor cross talk, is greater, and opposite to that of estradiol. The effects of testosterone withdrawal may at least in part be mediated by the ET-B receptor subtype and NO generation. Androgen blockade should be investigated further for the reversal or delay of hypertensive-diabetic endotheliopathy.

Estrogen or the AT1 antagonist olmesartan reverses the development of profound hypertension in the congenic mRen2. Lewis rat

The influence of estrogen on the regulation of cardiovascular function remains a controversial and complex area of investigation. We assessed the effects of estrogen depletion in the congenic mRen(2). Lewis rat, established from the back-cross of the original (mRen2)-27 transgenic onto the Lewis inbred strain. Ovariectomy of heterozygous mRen(2). Lewis at 4 to 5 weeks resulted in a progressive increase in blood pressure compared with the sham surgery congenics at weeks 6 to 11. At 11 weeks, the ovariectomized mRen(2). Lewis (OVX) systolic blood pressure averaged 195+/-3.7 mm Hg versus 141+/-4.0 mm Hg for sham. Plasma Angiotensin (Ang) II, serum ACE activity, plasma renin concentration, as well as urinary excretion of Ang II, 8-isoprostane F2alpha, and endothelin-1 were elevated; however, renal mRNA levels of eNOS were suppressed after ovariectomy. Estrogen replacement reduced blood pressure below both the sham and OVX by 11 weeks (125+/-2.9 mm Hg, n=7, P<0.01 versus OVX and sham). Moreover, the AT1 receptor antagonist olmesartan (CS866; week 12 to 16) essentially normalized blood pressure to 113+/-5.4 mm Hg (n=6, P<0.01 versus OVX and sham). The attenuation of the hypertension was still evident 7 weeks after complete withdrawal of treatment (124+/-4.1 mm Hg at week 23). In summary, the OVX mRen.2. Lewis exhibited a rapid and sustained increase in blood pressure. Estrogen or olmesartan lowered pressure by a similar extent. We conclude that the ovary exerts considerable influence on the regulation of the blood pressure in the mRen2. Lewis strain, possibly by limiting activation of the renin-angiotensin system.