Longitudinal assessment of the effects of oestrogen on blood pressure and cardiovascular autonomic activity in female rats

Gestationally administered RAS modulators reprogram endotoxic cardiovascular and inflammatory profiles in adult male offspring of preeclamptic rats

Previous studies showed that preeclampsia (PE) amplifies cardiovascular dysfunction induced by endotoxemia in adult male, but not female, offspring. Here, we asked if such aggravated endotoxic insult could be nullified by modulators of the renin-angiotensin system (RAS). PE was induced by gestational administration of Nω-nitro-L-arginine methyl ester(L-NAME, a nitric oxide synthase inhibitor). Adult male offspring of PE mothers treated gestationally with angiotensin 1-7 (Ang1-7, angiotensin II-derived vasodilator), losartan (AT1 receptor antagonist), pioglitazone (peroxisome proliferator-activated receptor gamma, PPARγ, agonist), or combined losartan/pioglitazone were instrumented with femoral indwelling catheters and challenged intravenously with a 5-mg/kg dose of lipopolysaccharides (LPS, 5 mg/kg). LPS caused significant decreases in blood pressure (BP) and spectral index of overall heart rate variability and increases in heart rate and left ventricular contractility (dP/dtmax). These effects were mostly reduced to similar magnitudes by individual drug therapies. In offspring born to Ang1-7-treated dams, the spectral index of cardiac sympathovagal balance showed elevated sympathetic dominance in response to LPS. Immunohistochemistry revealed that Ang1-7, but not losartan/pioglitazone, abolished the exaggerated increases in toll-like receptor 4 (TLR-4) expression caused by PE/LPS in heart tissues and neuronal circuits of brainstem rostral ventrolateral medulla (RVLM). By contrast, the losartan/pioglitazone regimen, but not Ang1-7, decreased and increased angiotensin converting enzyme (ACE) and ACE2 expression, respectively. Together, gestational fetal reprogramming of Ang II (depression) and Ang1-7 (activation) arms of RAS effectively counterbalance worsened endotoxic cardiovascular and inflammatory profiles in adult male offspring of PE rats.

Estrogen-mediated mitigation of cardiac oxidative stress in ovariectomized rats is associated with upregulated cardiac circadian clock Per2 and heart-specific miRNAs

AIM

Estrogen (E2) confers cardioprotection in premenopausal women and in models of menopause and its effects, mostly studied in female reproductive organs, vary on a circadian rhythm basis in relation to the circadian clock genes. However, it remains unknown if a similar circadian pattern exists in the female heart in a manner that explains, at least partly, the cardioprotective effect of E2. The aim of the present investigation was to determine if upregulation of the circadian clock Per2 and its regulated heart-specific miRNAs, and redox enzymes contribute to the E2-mediated cardioprotection in ovariectomized rats.

MAIN METHODS

Rats were subjected to ovariectomy (OVX) 2-weeks prior to a 2-week E2 treatment. On the last treatment day, hearts were collected every 4 h. for ex-vivo biochemical measurements. In parallel studies, telemetric mean arterial pressure (MAP) was obtained at the tissue collection times.

KEY FINDINGS

OVX + E2 rats exhibited lower body weight during daytime and MAP during day and night times, and their hearts exhibited: (1) higher Per2 protein abundance, cardioprotective miRNAs (miRNA1, miRNA133a, miRNA208a, miRNA499), mALDH2, and catalase; (2) lower reactive oxygen species, cardio-detrimental miRNA652, carbonyl, MDA and HO-1 levels. The reciprocal Per2/HO-1 relationship was more evident during the daytime and correlated with the upregulated cardioprotective miRNAs in OVX + E2 rats. Finally, cardiac Per2, heart-specific miRNAs and reactive oxygen species levels and redox enzymes activities were similar in normal female and OVX + E2 rats.

SIGNIFICANCE

Enhancement of cardiac Per2, redox enzymes and heart-specific miRNAs likely contribute to E2-mediated mitigation of cardiac oxidative stress in OVX rats.

Estradiol-dependent gene expression profile in the amygdala of young ovariectomized spontaneously hypertensive rats

Estrogen plays a role in cardiovascular functions, emotional health, and energy homeostasis via estrogen receptors expressed in the brain. The comorbid relationship between rising blood pressure, a decline in mood and motivation, and body weight gain after menopause, when estrogen levels drop, suggests that the same brain area(s) contributes to protection from all of these postmenopausal disorders. The amygdala, a major limbic system nucleus known to express high estrogen receptor levels, is involved in the regulation of such physiological and psychological responses. We hypothesized that elevated estrogen levels contribute to premenopausal characteristics by activating specific genes and pathways in the amygdala. We examined the effect of 1-month estradiol treatment on the gene expression profile in the amygdala of ovariectomized young adult female spontaneously hypertensive rats. Estradiol substitution significantly decreased blood pressure, prevented body weight gain, and enhanced the voluntary physical activity of ovariectomized rats. In the amygdala of ovariectomized rats, estradiol treatment downregulated the expression of genes associated with estrogen signaling, cholinergic synapse, dopaminergic synapse, and long-term depression pathways. These findings indicate that the transcriptomic characteristics of the amygdala may be involved in estrogen-dependent regulation of blood pressure, physical activity motivation, and body weight control in young adult female spontaneously hypertensive rats.

The effects of estrogen deficiency and aging on myocardial deformation and motion in normotensive female rats

OBJECTIVE

Estrogen deficiency is associated with left ventricular (LV) dysfunction in postmenopausal women and ovariectomized rats. Whether the relationship between estrogen deficiency and LV dysfunction is independent of cardiovascular disease (CVD) risk factors remains uncertain. This study assessed the effects of short-term and long-term estrogen deficiency on cardiac structure and function using conventional and speckle tracking echocardiography, independent of traditional CVD risk factors.

METHODS

Female Sprague-Dawley rats were divided into short-term (6 wks) ovariectomized (n = 9), short-term sham-operated (n = 10), long-term (6 mo) ovariectomized (n = 8), and long-term sham-operated (n = 9) groups. Cardiac geometry, systolic and diastolic function, and myocardial deformation and motion were measured using echocardiography.

RESULTS

Ovariectomy had no effect on conventional echocardiography measures of cardiac structure or function. Compared with short-term, long-term groups had reduced LV internal diameter (false discovery rate [FDR] adjusted P = 0.05) and impaired relaxation (e'; FDR adjusted P = 0.0005) independent of body mass and blood pressure (BP). Global longitudinal strain was impaired in ovariectomized compared with sham-operated rats (FDR adjusted P = 0.05), but not after adjusting for body mass and BP (FDR adjusted P = 0.16). Global longitudinal strain (FDR adjusted P = 0.05), strain rate (FDR adjusted P = 0.002), and velocity (FDR adjusted P = 0.04) were impaired in long-term compared with short-term groups. Global longitudinal strain rate remained impaired after adjustments for body mass and BP (FDR adjusted P = 0.02).

CONCLUSIONS

Estrogen deficiency does not independently cause cardiac remodeling, LV dysfunction, or impaired myocardial deformation. Traditional CVD risk factors accompanying estrogen deficiency may account for cardiac remodeling and dysfunction observed in postmenopausal women.

Cardiac and Brainstem Neuroinflammatory Pathways Account for Androgenic Incitement of Cardiovascular and Autonomic Manifestations in Endotoxic Male Rats

ABSTRACT

Inconsistent reports are available on the role of testosterone in end-organ damage caused by endotoxemia. Here, pharmacologic, surgical, and molecular studies were employed to assess the testosterone modulation of cardiovascular, autonomic, and peripheral and central inflammatory derangements caused by endotoxemia. Studies were performed in conscious male rats preinstrumented with femoral indwelling catheters for the measurement of blood pressure and subjected to castration or pharmacologic interventions that interrupt the biosynthetic cascade of testosterone. Compared with the effects of lipopolysaccharide (10 mg/kg intravenously) in sham operated rats, 2-week castration reduced the lipopolysaccharide-evoked (1) falls in blood pressure, (2) decreases in time- and frequency-domain indices of heart rate variability, (3) shifts in spectral measures of cardiac sympathovagal balance toward parasympathetic dominance, and (4) increases in protein expressions of toll-like receptor-4 and monocyte chemoattractant protein-1 in heart and medullary neurons of the nucleus tractus solitarius and rostral ventrolateral medulla. While the ameliorating actions of castration on endotoxic cardiovascular manifestations were maintained after testosterone replacement, the concomitant inflammatory signals were restored to near-sham levels. The favorable influences of castration on inflammatory and cardiovascular abnormalities of endotoxemia were replicated in intact rats pretreated with degarelix (gonadotropin-releasing hormone receptor blocker) or finasteride (5α-reductase inhibitor) but not formestane (aromatase inhibitor). The data signifies the importance of androgens and its biosynthetic enzymes in cardiovascular and autonomic insults induced by the endotoxic inflammatory response. Clinically, the interruption of testosterone biosynthesis could offer a potential strategy for endotoxemia management.

Influence of exogenous and endogenous estrogen on thermoregulatory responses to mild heat and the interaction with light and dark phases

The present study aimed to determine the influence of estradiol (E2) and the interaction with circadian phases on thermoregulatory responses to mild heat in female rats. Heat loss and production during 3-h exposure to the environment at an ambient temperature of 28-34 °C were assessed by measuring abdominal temperature (Tabd), tail skin temperature, and oxygen consumption in ovariectomized rats with and without E2 replacement (OVX + E2 and OVX, respectively) and in control rats in the proestrus (P) and diestrus (D) phases. In the light phase, Tabd remained unchanged in all groups. Tabd increased in the dark phase, but was lower in the OVX + E2 and P groups than in the OVX and D groups. Oxygen consumption decreased at 34 °C, but to a lesser extent in the OVX + E2 group than in the OVX group. These results suggest that E2 activates thermoregulation in mild heat in the dark phase.

Estrogen-dependent hypersensitivity to diabetes-evoked cardiac autonomic dysregulation: Role of hypothalamic neuroinflammation

AIMS

To investigate if autonomic dysregulation is exacerbated in female rats, subjected to diabetes mellitus (DM), via a paradoxical estrogen (E2)-evoked provocation of neuroinflammation/injury of the hypothalamic paraventricular nucleus (PVN).

MAIN METHODS

We measured cardiac autonomic function and conducted subsequent PVN neurochemical studies, in DM rats, and their respective controls, divided as follows: male, sham operated (SO), ovariectomized (OVX), and OVX with E2 supplementation (OVX/E2).

KEY FINDINGS

Autonomic dysregulation, expressed as sympathetic dominance (higher low frequency, LF, band), only occurred in DM E2-replete (SO and OVX/E2) rats, and was associated with higher neuronal activity (c-Fos) and higher levels of TNFα and phosphorylated death associated protein kinase-3 (p-DAPK3) in the PVN. These proinflammatory molecules likely contributed to the heightened PVN oxidative stress, injury and apoptosis. The PVN of these E2-replete DM rats also exhibited upregulations of estrogen receptors, ERα and ERβ, and proinflammatory adenosine A1 and A2a receptors.

SIGNIFICANCE

The E2-dependent autonomic dysregulation likely predisposes DM female rats and women to hypersensitivity to cardiac dysfunction. Further, upregulations of proinflammatory mediators including adenosine A1 and A2 receptors, TNFα and DAPK3, conceivably explain the paradoxical hypersensitivity of DM females to PVN inflammation/injury and the subsequent autonomic dysregulation in the presence of E2.

Role of Alcohol Oxidative Metabolism in Its Cardiovascular and Autonomic Effects

Several review articles have been published on the neurobehavioral actions of acetaldehyde and other ethanol metabolites as well as in major alcohol-related disorders such as cancer and liver and lung disease. However, very few reviews dealt with the role of alcohol metabolism in the adverse cardiac and autonomic effects of alcohol and their potential underlying mechanisms, particularly in vulnerable populations. In this chapter, following a brief overview of the dose-related favorable and adverse cardiovascular effects of alcohol, we discuss the role of ethanol metabolism in its adverse effects in the brainstem and heart. Notably, current knowledge dismisses a major role for acetaldehyde in the adverse autonomic and cardiac effects of alcohol because of its low tissue level in vivo. Contrary to these findings in men and male rodents, women and hypertensive individuals are more sensitive to the adverse cardiac effects of similar amounts of alcohol. To understand this discrepancy, we discuss the autonomic and cardiac effects of alcohol and its metabolite acetaldehyde in a model of hypertension, the spontaneously hypertensive rat (SHR) and female rats. We present evidence that enhanced catalase activity, which contributes to cardioprotection in hypertension (compensatory) and in the presence of estrogen (inherent), becomes detrimental due to catalase catalysis of alcohol metabolism to acetaldehyde. Noteworthy, studies in SHRs and in estrogen deprived or replete normotensive rats implicate acetaldehyde in triggering oxidative stress in autonomic nuclei and the heart via (i) the Akt/extracellular signal-regulated kinases (ERK)/nitric oxide synthase (NOS) cascade and (ii) estrogen receptor-alpha (ERα) mediation of the higher catalase activity, which generates higher ethanol-derived acetaldehyde in female heart. The latter is supported by the ability of ERα blockade or catalase inhibition to attenuate alcohol-evoked myocardial oxidative stress and dysfunction. More mechanistic studies are needed to further understand the mechanisms of this public health problem.

Essential Role of Ovarian Hormones in Susceptibility to the Consequences of Witnessing Social Defeat in Female Rats

BACKGROUND

Women are at greater risk than men of developing depression and comorbid disorders such as cardiovascular disease. This enhanced risk begins at puberty and ends following menopause, suggesting a role for ovarian hormones in this sensitivity. Here we used a model of psychosocial witness stress in female rats to determine the stress-induced neurobiological adaptations that underlie stress susceptibility in an ovarian hormone-dependent manner.

METHODS

Intact or ovariectomized (OVX) female rats were exposed to five daily 15-minute witness-stress exposures. Witness-stress-evoked burying, behavioral despair, and anhedonia were measured. Cardiovascular telemetry was combined with plasma measurements of inflammation, epinephrine, and corticosterone as indices of cardiovascular dysfunction. Finally, levels of interleukin-1β and corticotropin-releasing factor were assessed in the central amygdala.

RESULTS

Witness stress produced anxiety-like burying, depressive-like anhedonia, and behavioral despair selectively in intact female rats, which was associated with enhanced sympathetic responses during stress, including increased blood pressure, heart rate, and arrhythmias. Moreover, intact female rats exhibited increases in 12-hour resting systolic pressure and heart rate and reductions in heart rate variability. Notably, OVX female rats remained resilient. Moreover, intact, but not OVX, female rats exposed to witness stress exhibited a sensitized cytokine and epinephrine response to stress and distinct increases in levels of corticotropin-releasing factor and interleukin-1β in the central amygdala.

CONCLUSIONS

Together these data suggest that ovarian hormones play a critical role in the behavioral, inflammatory, and cardiovascular susceptibility to social stress in female rats and reveal putative systems that are sensitized to stress in an ovarian hormone-dependent manner.

Renal transplantation increases angiotensin II receptor-mediated vascular contractility associated with changes of epigenetic mechanisms

Hypertension is one of the most common complications following renal transplantation, and it increases the risk of graft loss and other cardiovascular diseases. Previous studies have revealed that the use of angiotensin II (Ang II) blockers for preventing and treating hypertension is closely associated with higher survival following renal transplantation. However, the cellular and molecular mechanisms by which the vascular contractility of the recipient is altered in response to Ang II following renal transplantation have not been fully elucidated. In the present study, using the Fisher‑Lewis rat kidney transplantation model, the blood pressure (BP) of the conscious transplant recipient was measured following the intravenous administration of Ang II. In addition, the mechanisms underlying the Ang II-mediated vascular contractility via the type 1 and type 2 Ang II receptors (AT1R and AT2R, respectively) in large and small-resistance blood vessels were determined in the recipient after renal transplantation. The results showed that renal transplantation significantly increased the Ang II-stimulated BP of the rats. Additionally, ex vivo contractility experiments using aorta and mesenteric arteries revealed that the contractions induced by Ang II were significantly strengthened in the recipient following renal transplantation, and were associated with an increased intracellular Ca2+ concentration. Losartan almost eradicated the Ang II-induced contractions whereas PD-123319 had no apparent effects on the Ang II-induced contractions in the aorta and mesenteric arteries of the recipient. Furthermore, the expression levels of AT1R but not AT2R were significantly increased in the vasculature of the recipient following renal transplantation, which exhibited a close association with selective DNA demethylation detected in the promoter region of the vascular AT1aR gene. These results indicate that changes of recipient vascular AT1R gene expression, occurring through a mechanism involving DNA methylation, increase the vascular contractility in response to Ang II. This may lead to the increased risk of hypertension following renal transplantation.

Cardiovascular Autonomic Responses in the VCD Rat Model of Menopause: Effects of Short- and Long-Term Ovarian Failure

After menopause, hypertension elevates the risk of cardiac diseases, one of the major causes of women's morbidity. The gradual depletion of ovarian follicles in rats, induced by 4-vinylcyclohexene diepoxide (VCD), is a model for studying the physiology of menopause. 4-Vinylcyclohexene diepoxide treatment leads to early ovarian failure (OF) and a hormonal profile comparable to menopause in humans. We have hypothesized that OF can compromise the balance between sympathetic and parasympathetic tones of the cardiovascular system, shifting toward dominance of the former. We aimed to study the autonomic modulation of heart and blood vessels and the cardiovascular reflexes in rats presenting short-term (80 days) or long-term (180 days) OF induced by VCD. Twenty-eight-day-old Wistar rats were submitted to VCD treatment (160 mg/kg, intraperitoneally) or vehicle (control) for 15 consecutive days and experiments were conducted at 80 or 180 days after the onset of treatment. Long-term OF led to an increase in the sympathetic activity to blood vessels and an impairment in the baroreflex control of the heart, evoked by physiological changes in arterial pressure. Despite that, long-term OF did not cause hypertension during the 180 days of exposure. Short-term OF did not cause any deleterious effect on the cardiovascular parameters analyzed. These data indicate that long-term OF does not disrupt the maintenance of arterial pressure homeostasis in rats but worsens the autonomic cardiovascular control. In turn, this can lead to cardiovascular complications, especially when associated with the aging process seen during human menopause.

Oxidative stress and autonomic dysregulation contribute to the acute time-dependent myocardial depressant effect of ethanol in conscious female rats

BACKGROUND

The molecular mechanisms of the acute hypotensive and indirectly assessed cardiac depressant effect of ethanol (EtOH)-evoked myocardial depression and hypotension in female rats are not known. We tested the hypothesis that a time-dependent myocardial depression caused by EtOH is initiated by its direct and indirect (cardiac vagal dominance) effects and is exacerbated by gradual development of oxidative stress.

METHODS

In conscious female rats, we directly measured left ventricular developed pressure (LVDP), the maximal rise of ventricular pressure over time (dP/dtmax ), blood pressure (BP), heart rate (HR), and sympathovagal activity following intragastric EtOH (1 g/kg) or water over 90 minutes. Catalytic activity of acetaldehyde (ACA)-generating (alcohol dehydrogenase [ADH] and catalase) and eliminating aldehyde dehydrogenase [ALDH2] enzymes along with mediators of oxidative stress were measured in myocardial tissues collected at 30, 60, or 90 minutes after EtOH or water.

RESULTS

EtOH reduced myocardial function (LVDP and dP/dtmax ) within 5 to 10 minutes before the steady fall in BP in conscious proestrus rats. Further, EtOH shifted the sympathovagal balance, analyzed by spectral analysis of high frequency and low frequency of interbeat intervals, toward vagal dominance. Prior vagal blockade (atropine) or antioxidant (tempol) treatment attenuated EtOH-evoked myocardial depression and hypotension. Ex vivo studies revealed time-dependent: (i) enhancement of ADH, but not ALDH2 activity (indicative of elevated ACA levels), (ii) increases in phosphorylated Akt and ERK1/2, NADPH-oxidase activity, reactive oxygen species, malondialdehyde, and 4-hydroxy-2-nonenal-modified proteins. These molecular responses along with reduced myocardial catalase activity were most evident at 90 minutes post-EtOH when the reductions in cardiac function and BP reached their nadir.

CONCLUSIONS

Vagal dominance and time-dependent myocardial oxidative stress along with the accumulation of cardiotoxic aldehydes mediate EtOH-evoked myocardial dysfunction and hypotension in conscious proestrus female rats.

Endothelial and neuronal nitric oxide synthases variably modulate the oestrogen-mediated control of blood pressure and cardiovascular autonomic control

1. We have shown previously that long-term oestrogen (E2) replacement lowers blood pressure (BP) and improves cardiovascular autonomic control in ovariectomized (OVX) rats. In the present study, we investigated whether constitutive and/or inducible (i) nitric oxide synthase (NOS) modulate these E2 effects. 2. We evaluated changes in BP, myocardial contractility index (dP/dtmax ) and power spectral indices of haemodynamic variability following selective inhibition of endothelial (e) NOS with N(5)-(1-iminoethyl)-L-ornithine (L-NIO), neuronal (n) NOS with N(ω)-propyl-L-arginine (NPLA) or iNOS with 1400W in telemetered OVX rats treated for 16 weeks with (OVXE2) or without (control; OVXC) E2. 3. The OVXE2 rats exhibited: (i) reduced BP and increased dP/dtmax ; (ii) cardiac parasympathetic dominance, as reflected by the reduced low-frequency (LF; 0.25-0.75 Hz)/high-frequency (HF; 0.75-3 Hz) ratio of interbeat intervals (IBI(LF/HF)); and (iii) reduced LF oscillations of systolic BP, suggesting a reduced vasomotor sympathetic tone. Inhibition of eNOS (L-NIO; 20 mg/kg, i.p.) elicited a shorter-lived pressor response in OVXE2 than OVXC, rats along with reductions in dP/dtmax and increases in the spectral index of spontaneous baroreflex sensitivity (index α). Treatment with 1 mg/kg, i.p., NPLA reduced BP and increased the IBI(LF/HF) ratio in OVXE2 but not OVXC rats. The iNOS inhibitor 1400W (5 mg/kg, i.p.) caused no haemodynamic changes in OVXC or OVXE2 rats. 4. Overall, constitutive NOS isoforms exert restraining tonic modulatory BP effects that encompass eNOS-mediated reductions and nNOS-mediated elevations in BP in OVXE2 rats. Baroreflex facilitation and dP/dtmax reductions may account for the shorter pressor action of L-NIO in E2-treated, compared with untreated, OVX rats.

Low-dose estrogen is as effective as high-dose treatment in rats with postmenopausal hypertension

: This study was conducted to test the hypothesis that 17β-estradiol therapy improves redox balance by decreasing reactive oxygen species production and increasing nitric oxide (NO) bioavailability, favoring Akt pathway activation and resulting in a better autonomic vascular control. Ovariectomized female Wistar rats were divided into 4 groups: (1) vehicle (VL) and animals treated with a pellet of 17β-estradiol for 21 days; (2) low dose (LE; 0.05 mg); (3) medium dose (ME; 0.2 mg); and (4) high dose (HE; 0.5 mg). Arterial pressure and its sympathetic nervous system modulation were evaluated by spectral analysis. Nitric oxide synthase and NADPH oxidase (Nox) activities, H2O2 concentration, redox status (GSH/GSSG), protein expression of Trx-1 and p-Akt/Akt were evaluated in the aorta, whereas NO metabolites were measured in the serum. Estrogen-treated groups showed a significant decrease in arterial pressure and sympathetic vascular drive. Redox status was significantly improved and NADPH oxidase and H2O2 were decreased in all estrogen-treated groups. Estrogen also induced an enhancement in NO metabolites, nitric oxide synthase activity, and Akt phosphorylation. This study demonstrated that estrogen treatment to ovariectomized rats induced cardioprotection, which was evidenced by reduced blood pressure variability and vascular sympathetic drive. These effects were associated with an improved redox balance and Akt activation, resulting in an enhanced NO bioavailability.

The influence of age and weight status on cardiac autonomic control in healthy children: a review

Heart rate variability (HRV) analyses can provide a non-invasive evaluation of cardiac autonomic activity. How autonomic control normally develops in childhood and how this is affected by obesity remain incompletely understood. In this review we examine the evidence that childhood age and weight status influence autonomic control of the heart as assessed using HRV. Electronic databases (Pubmed, EMBASE and Cochrane Library) were searched for studies examining HRV in healthy children from birth to 18 years who adhered to the Task Force (1996) guidelines. Twenty-four studies met our inclusion criteria. Seven examined childhood age and HRV. A reduction in 24-hour LF:HF was reported from birth to infancy (1 year), while overall HRV (SDNN) showed a marked and progressive increase. From infancy to early-to-late childhood (from 12 months to 15 years) LF:HF ratio was reported to decline further albeit at a slower rate, while RMSSD and SDNN increased. Twenty studies examined the effects of weight status and body composition on HRV. In a majority of studies, obese children exhibited reductions in RMSSD (n = 8/13), pNN50% (n = 7/9) and HF power (n = 14/18), no difference was reported for LF (n = 10/18), while LF:HF ratio was elevated (n = 10/15). HRV changes during childhood are consistent with a marked and progressive increase in cardiac parasympathetic activity relative to sympathetic activity. Obesity disrupts the normal maturation of cardiac autonomic control.

The effect of hormone therapy on mean blood pressure and visit-to-visit blood pressure variability in postmenopausal women: results from the Women's Health Initiative randomized controlled trials

OBJECTIVES

Mean and visit-to-visit variability (VVV) of blood pressure (BP) are associated with an increased cardiovascular disease risk. We examined the effect of hormone therapy on mean and VVV of BP in postmenopausal women from the Women's Health Initiative (WHI) randomized controlled trials.

METHODS

BP was measured at baseline and annually in the two WHI hormone therapy trials, in which 10 739 and 16 608 postmenopausal women were randomized to conjugated equine estrogens (CEEs, 0.625 mg/day) or placebo, and CEEs and medroxyprogesterone acetate (MPA, 2.5 mg/day) or placebo, respectively.

RESULTS

At the first annual visit (year 1), mean SBP was 1.04 mmHg [95% confidence interval (CI) 0.58, 1.50] and 1.35 mmHg (95% CI 0.99, 1.72) higher in the CEEs and CEEs and MPA arms, respectively, compared with the corresponding placebos. These effects remained stable after year 1. CEEs also increased the VVV of SBP (ratio of VVV in CEEs vs. placebo, 1.03; P < 0.001), whereas CEEs and MPA did not (ratio of VVV in CEEs and MPA vs. placebo, 1.01; P = 0.20). After accounting for study drug adherence, the effects of CEEs and CEEs and MPA on mean SBP increased at year 1, and the differences in the CEEs and CEEs and MPA arms vs. placebos also continued to increase after year 1. Further, both CEEs and CEEs and MPA significantly increased the VVV of SBP (ratio of VVV in CEEs vs. placebo, 1.04; P < 0.001; ratio of VVV in CEEs and MPA vs. placebo, 1.05; P < 0.001).

CONCLUSION

Among postmenopausal women, CEEs and CEEs and MPA at conventional doses increased mean and VVV of SBP.

Autonomic Cardiovascular Damage during Post-menopause: the Role of Physical Training

Menopause is part of the aging process and is characterized by the natural cessation of menstruation; during this time, the production of ovarian hormones, especially estrogen, is sharply reduced. This reduction can cause symptoms and disorders that affect most women and can interfere with their quality of life. Women are also more susceptible to cardiovascular diseases during this period, considering that these ovarian hormones would be associated with a protective effect on the cardiovascular system, by acting at various levels, contributing to the body homeostasis. Among several effects on the cardiovascular system, the ovarian hormones seem to play an important role in the autonomic control of heart rate and blood pressure. A reduction in ovarian hormones causes an autonomic imbalance and increases the risk of cardiovascular diseases. In fact, this increased risk is justified by the key role the autonomic nervous system plays in all cardiac regulatory mechanisms, exerting a tonic and reflexive influence on the main variables of the cardiovascular system. The autonomic system controls various cardiovascular parameters, such as the modulation of heart rate and blood pressure, myocardial contractility and venous capacitance, directly participating in the regulation of cardiac output. Over the years, the standard treatment for menopause symptoms and disorders has been hormone replacement therapy (HRT). However, many studies have indicated the risks of HRT, which justify the need for new non-pharmacological therapies. To this end, physical training, mainly aerobic, has been applied with excellent results on the cardiovascular autonomic nervous system, as it reduces the risk of cardiac diseases and improves the survival rate with direct beneficial effects on the quality of life of these women during the aging process.

Sex differences in mechanisms of cardiac excitation-contraction coupling

The incidence and expression of cardiovascular diseases differs between the sexes. This is not surprising, as cardiac physiology differs between men and women. Clinical and basic science investigations have shown important sex differences in cardiac structure and function. The pervasiveness of sex differences suggests that such differences must be fundamental, likely operating at a cellular level. Indeed, studies have shown that isolated ventricular myocytes from female animals have smaller and slower contractions and underlying calcium transients compared to males. Recent evidence suggests that this arises from sex differences in components of the cardiac excitation–contraction coupling pathway, the sequence of events linking myocyte depolarization to calcium release from the sarcoplasmic reticulum and subsequent contraction. The concept that sex hormones may regulate intracellular calcium at the level of the cardiomyocyte is important, as levels of these hormones decline in both men and women as the incidence of cardiovascular disease rises. This review focuses on the impact of sex on cardiac contraction, in particular at the cellular level, and highlights specific components of the excitation–contraction coupling pathway that differ between the sexes. Understanding sex hormone regulation of calcium homeostasis in the heart may reveal new avenues for therapeutic strategies to treat cardiac dysfunction and cardiovascular diseases.

Aerobic physical training has little effect on cardiovascular autonomic control in aging rats subjected to early menopause

We investigated and compared the effects of physiological menopause (PM) and early menopause (EM) and the adaptations promoted by physical training on the cardiovascular autonomic control of aged rats. Female Wistar rats (N=72) were assigned to 3 groups: control (22 weeks old rats, undergoing sham surgery in the 10th week of life), PM (82 weeks old rats, undergoing sham surgery in the 10th week of life) and EM (82 weeks old rats, undergoing ovariectomy in the 10th week of life). In each group, half of the rats were subjected to swimming training over a period of 10 weeks. Sedentary PM and EM groups had higher basal mean arterial pressure (MAP) and heart rate (HR) and lower intrinsic HR compared to the sedentary control group. Physical training reduced MAP in PM group. All trained groups had lower basal HR; however, only control and PM-trained groups showed decreased intrinsic HR. The assessment of cardiac autonomic balance showed that PM and EM sedentary groups exhibited sympathetic predominance compared to control group. After physical training, only EM group presented sympathetic predominance. HR variability (pulse interval) was similar among all sedentary groups. However, control and PM-trained groups showed lower power in low frequency band (LF; 0.2-0.75 Hz) and higher power in high frequency band (HF; 0.75-3.0 Hz). The analysis of systolic arterial pressure variability revealed that PM and EM sedentary groups had higher LF power. However, PM group showed lower LF power following physical training. Finally, PM and EM groups had a reduction in spontaneous baroreflex sensitivity, that was attenuated by physical training. The overall results suggest that PM or EM promotes similar negative effects on MAP, HR and cardiovascular autonomic control. However, unlike the PM group, physical training was not able to mitigate all negative effects of EM on cardiovascular autonomic control.

Effects of low-dose ketanserin on atherosclerosis in rats and rabbits

The present study was designed to test the hypothesis that a small dose of ketanserin, which enhances baroreflex activity, prevents the early lesions of atherosclerosis. In experiment 1, baroreflex sensitivity (BRS) was measured in 31 spontaneously hypertensive rats (SHRs) in a conscious state using a computerized blood pressure monitoring system. Four weeks later, the rats were administered vitamin D3 and fed a high-cholesterol diet for 8 weeks to induce atherosclerosis. Then their hearts and aortae were removed for pathological examination. A negative correlation was found between BRS and the scores of coronary (r = -0.460, P < 0.01) and aortic atherosclerosis (r = -0.448, P < 0.05) in SHR. In experiment 2, SHRs were divided into 3 groups (n = 10 in each group) and received a dose of ketanserin of 0.3, 1.0, and 3.0 mg/kg (i.g.), respectively. At the smallest dose (0.3 mg/kg), ketanserin did not lower blood pressure but enhanced BRS. In experiment 3, SHRs were administered vitamin D3, fed a high-cholesterol diet, and simultaneously treated with low-dose ketanserin. The atherosclerosis scores of the treatment group were significantly lower than those of the control group (coronary score: 0.90 ± 0.14 vs. 1.76 ± 0.27, P < 0.05; aortic scores: 1.00 ± 0.39 vs. 2.18 ± 0.41, P < 0.05). In experiment 4, male New Zealand White rabbits were fed a high-cholesterol diet and treated with low-dose ketanserin at the same time. The atherosclerosis scores of the treatment group were significantly lower than those of the control group (aortic scores: 0.26 ± 0.20 vs. 0.60 ± 0.31, P < 0.05). In conclusion, the present study demonstrated, for the first time, that low-dose ketanserin prevented the development of atherosclerosis independent of its blood pressure lowering action in SHRs and New Zealand White rabbits at least in part via enhancement of arterial baroreflex function.

Novel strategies and targets for the management of hypertension

Hypertension, as the sole or comorbid component of a constellation of disorders of the cardiovascular (CV) system, is present in over 90% of all patients with CV disease and affects nearly 74 million individuals in the United States. The number of medications available to treat hypertension has dramatically increased during the past 3 decades to some 50 medications as new targets involved in the normal regulation of blood pressure have been identified, resulting in the development of new agents in those classes with improved therapeutic profiles (e.g., renin-angiotensin-aldosterone system; RAAS). Despite these new agents, hypertension is not adequately managed in approximately 30% of patients, who are compliant with prescriptive therapeutics, suggesting that new agents and/or strategies to manage hypertension are still needed. Some of the newest classes of agents have targeted other components of the RAS, for example, the selective renin inhibitors, but recent advances in vascular biology have provided novel potential targets that may provide avenues for new agent development. These newer targets include downstream signaling participants in pathways involved in contraction, growth, hypertrophy, and relaxation. However, perhaps the most unique approach to the management of hypertension is a shift in strategy of using existing agents with respect to the time of day at which the agent is taken. This new strategy, termed "chronotherapy," has shown considerable promise in effectively managing hypertensive patients. Therefore, there remains great potential for future development of safe and effective agents and strategies to manage a disorder of the CV system of epidemic proportion.

Effect of 17beta-oestradiol replacement on vascular responsiveness in ovariectomized diabetic rats

1. Women with functional ovaries exhibit a gender advantage in terms of the prevalence of cardiovascular diseases. However, whether this gender bias pertains in diabetes is unknown. 2. The aim of the present study was to examine the effects of 17beta-oestradiol (E2) on vascular responsiveness in normal and diabetic ovariectomized (OVX) rats. Aged-matched female rats were divided into four groups as follows: (i) OVX; (ii) OVX + E2 treated; (iii) diabetic OVX; and (iv) diabetic OVX + E2 treated. Bilateral ovariectomy was performed and streptozotocin was used to induce experimental diabetes. Rats were treated with 1 mg/kg per day, p.o., E2 for 8 weeks. 3. Although E2 treatment had no effect on blood glucose levels in normal and diabetic OVX rats, it significantly reduced systolic blood pressure and prevented diabetes-induced loss of bodyweight gain. 4. In segments of the thoracic aorta, concentration-dependent vasoconstrictor responses to KCl and phenylephrine were significantly attenuated following E2 treatment in both the normal and diabetic groups. The sarcoplasmic/endoplasmic reticulum calcium ATPase inhibitor thapsigargin (10(-6) mol/L) and the Ca(2+) channel blocker nifedipine (10(-6) mol/L) inhibited the transient vasoconstriction to PE in all groups. The constrictor effect of PE was increased by the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME; 10(-6) mol/L), but was reduced by superoxide dismutase (SOD; 100 U/mL) and the cyclo-oxygenase inhibitor indomethacin (10(-6) mol/L) in all groups. Responses to acetylcholine (ACh; 10(-6) mol/L) demonstrated reduced endothelium-dependent relaxation in non-E2-treated groups. Relaxation responses to ACh were increased by 100 U/mL SOD and 10(-6) mol/L indomethacin, but were reduced by 10(-6) mol/L l-NAME in all groups. There were no differences among the four groups in terms of relaxation responses to sodium nitroprusside (10(-11) to 10(-6) mol/L). 5. In conclusion, the results of the present study suggest that oestrogen treatment has beneficial effects on vascular function in both diabetic and non-diabetic OVX rats due to Ca(2+) regulation and anti-oxidation.