Aging Reduces the Efficacy of Estrogen Substitution to Attenuate Cardiac Hypertrophy in Female Spontaneously Hypertensive Rats

Hearts apart: sex differences in cardiac remodeling in health and disease

Biological sex is an important modifier of physiology and influences pathobiology in many diseases. While heart disease is the number one cause of death worldwide in both men and women, sex differences exist at the organ and cellular scales, affecting clinical presentation, diagnosis, and treatment. In this Review, we highlight baseline sex differences in cardiac structure, function, and cellular signaling and discuss the contribution of sex hormones and chromosomes to these characteristics. The heart is a remarkably plastic organ and rapidly responds to physiological and pathological cues by modifying form and function. The nature and extent of cardiac remodeling in response to these stimuli are often dependent on biological sex. We discuss organ- and molecular-level sex differences in adaptive physiological remodeling and pathological cardiac remodeling from pressure and volume overload, ischemia, and genetic heart disease. Finally, we offer a perspective on key future directions for research into cardiac sex differences.

Combined cardiovascular effects of ovariectomy and high-intensity interval training in female spontaneously hypertensive rats

Hypertensive postmenopausal women are more likely to develop adverse cardiac remodeling and respond less effectively to drug treatment than men. High-intensity interval exercise (HIIE) is a nonpharmacological strategy for the treatment of hypertension; however, the effectiveness in women remains uncertain. This study was designed to evaluate 1) the effects of HIIE training upon morphological and functional markers of cardiovascular health in female SHR and 2) to determine whether the hormonal shift induced by ovariectomy could influence cardiovascular responses to HIIE. Thirty-six SHR were randomly assigned to four groups: ovariectomized sedentary, ovariectomized trained, sham-operated sedentary, and sham-operated trained. The trained rats performed HIIE 5 days/wk for 8 wk. Blood pressure and echocardiographic measurements were performed before and after training in animals. Cardiac response to β-adrenergic stimulation and the expression of calcium regulatory proteins and estrogen receptors in heart samples were assessed. Endothelium-dependent vasorelaxation in response to acetylcholine was evaluated in aortic rings as well as the expression of nitric oxide synthase isoforms (eNOS and P-eNOS) by Western blotting. In both groups of trained SHR, HIIE induced eccentric cardiac remodeling with greater inotropic and chronotropic effects, as well as an increase in SERCA and β1AR expression. However, although the trained rats showed improved endothelial function and expression of eNOS and P-eNOS in the aorta, there was no demonstrated effect on blood pressure. In addition, the responses to HIIE training were not affected by ovariectomy. This work highlights the importance of assessing the cardiovascular efficacy and safety of different exercise modalities in women.NEW & NOTEWORTHY This study reports the effects of high-intensity interval exercise (HIIE) training on cardiac and endothelial function in female hypertensive rats. Despite a lack of effect on blood pressure (BP), HIIE training induces eccentric cardiac remodeling with greater functionals effects. Furthermore, training has beneficial effects on endothelial function. However, ovarian hormones do not seem to modulate cardiac and aortic adaptations to this training modality. All this underlines the need to consider training modalities on the cardiovascular system in women.

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

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

Medroxyprogesterone opposes estradiol-induced renal damage in midlife ovariectomized Long Evans rats

OBJECTIVE

Our laboratory previously published that long-term administration of estradiol (E2) was detrimental to the kidneys of midlife ovariectomized Long Evans rats, contrasting clinical studies in showing that menopausal hormone therapy is associated with decreased albuminuria. However, it is unknown whether this renal benefit was due to estrogen and/or the combination with progestogen. Therefore, the objective of the current study was to determine the impact of medroxyprogesterone (MPA) on E2-mediated renal damage using a rodent model.

METHODS

Female Long Evans retired breeders underwent ovariectomy at 11 months of age and were treated for 40 days with subcutaneous E2, E2+MPA or vehicle at doses mimicking that of menopausal hormone therapy (N = 5-7 per group). Systolic blood pressure was measured along with indices of renal damage and function to investigate the impact of MPA on E2-mediated renal outcomes. Renal estrogen receptor alpha and G protein-coupled estrogen receptor transcript copy numbers were measured in all treatment groups through droplet digital PCR.

RESULTS

Middle-aged female Long Evans rats displayed spontaneous hypertension with similar systolic blood pressures and heart weights between groups. Even though blood pressure was comparable, E2 reduced glomerular filtration rate and increased proteinuria indicating pressure-independent renal damage. Coadministration with MPA prevented E2-induced glomerular filtration rate impairment and proteinuria by promoting renal hypertrophy and preventing renal interstitial fibrosis. Both E2 and E2+MPA reduced renal estrogen receptor alpha (ERα) and increased renal G protein-coupled estrogen receptor mRNA, but neither ERα nor ERß protein was different between groups.

CONCLUSION

MPA was protective against E2-induced renal damage and dysfunction in middle-aged female Long Evans rats. Assessing the impact of hormone therapy on renal outcomes may be an important clinical factor when considering treatment options for postmenopausal women.

Ovariectomy alters lengthening contraction induced heat shock protein expression

Estrogen appears to play a role in minimizing skeletal muscle damage as well as regulating the expression of the protective heat shock proteins (HSPs). To clarify the relationship between estrogen, muscle HSP content, and muscle damage, tibialis anterior (TA) muscles from ovary-intact (OVI; n = 12) and ovariectomized (OVX; 3 weeks, n = 12) female Sprague-Dawley rats were subjected to either 20 or 40 lengthening contractions (LCs). Twenty-four hours after stimulation, TA muscles were removed, processed, and assessed for HSP25 and HSP72 content as well as muscle (damage) morphology. No differences in muscle contractile properties were observed in TA muscles between OVI and OVX animals for peak torque during the LCs. In unstressed TA muscles, the basal expression of HSP72 expression was decreased in OVX animals (P < 0.05) while HSP25 content remained unchanged. Following 20 LCs, HSP25 content was elevated (P < 0.05) in TA muscles from OVX animals but unchanged in muscles from OVI animals. Following 40 LCs, HSP25 content was elevated (P < 0.01) in TA muscles from both OVI and OVX animals while HSP72 content was elevated only in TA muscles from OVI animals (P < 0.05). Taken together, these data suggest the loss of ovarian hormones, such as estrogen, may impair the skeletal muscle cellular stress response thereby rendering muscles more susceptible to certain types of contraction induced damage. Novelty Ovariectomy alters muscle HSP72 content. Muscle contractile measures are maintained following ovariectomy.

Discovery of BAY-298 and BAY-899: Tetrahydro-1,6-naphthyridine-Based, Potent, and Selective Antagonists of the Luteinizing Hormone Receptor Which Reduce Sex Hormone Levels in Vivo

The human luteinizing hormone receptor (hLH-R) is a member of the glycoprotein hormone family of G-protein-coupled receptors (GPCRs), activated by luteinizing hormone (hLH) and essentially involved in the regulation of sex hormone production. Thus, hLH-R represents a valid target for the treatment of sex hormone-dependent cancers and diseases (polycystic ovary syndrome, uterine fibroids, endometriosis) as well as contraception. Screening of the Bayer compound library led to the discovery of tetrahydrothienopyridine derivatives as novel, small-molecule (SMOL) hLH-R inhibitors and to the development of BAY-298, the first nanomolar hLH-R antagonist reducing sex hormone levels in vivo. Further optimization of physicochemical, pharmacokinetic, and safety parameters led to the identification of BAY-899 with an improved in vitro profile and proven efficacy in vivo. BAY-298 and BAY-899 serve as valuable tool compounds to study hLH-R signaling in vitro and to interfere with the production of sex hormones in vivo.

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

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

The Importance of Biological Sex and Estrogen in Rodent Models of Cardiovascular Health and Disease

Nearly one-third of deaths in the United States are caused by cardiovascular disease (CVD) each year. In the past, CVD was thought to mainly affect men, leading to the exclusion of women and female animals from clinical studies and preclinical research. In light of sexual dimorphisms in CVD, a need exists to examine baseline cardiac differences in humans and the animals used to model CVD. In humans, sex differences are apparent at every level of cardiovascular physiology from action potential duration and mitochondrial energetics to cardiac myocyte and whole-heart contractile function. Biological sex is an important modifier of the development of CVD with younger women generally being protected, but this cardioprotection is lost later in life, suggesting a role for estrogen. Although endogenous estrogen is most likely a mediator of the observed functional differences in both health and disease, the signaling mechanisms involved are complex and are not yet fully understood. To investigate how sex modulates CVD development, animal models are essential tools and should be useful in the development of therapeutics. This review will focus on describing the cardiovascular sexual dimorphisms that exist both physiologically and in common animal models of CVD.

The influence of aging and estradiol to progesterone ratio on rat macrophage phenotypic profile and NO and TNF-α production

The phenotype and function of tissue macrophages substantially depend on the cellular milieu and biological effector molecules, such as steroid hormones, to which they are exposed. Furthermore, in female rats, aging is associated with the altered macrophage functioning and the increased estrogen level is followed by a decrease in that of progesterone. Therefore, the present study aimed to investigate the influence of estradiol/progesterone balance on rat macrophage function and phenotype throughout whole adult lifespan. We ovariectomized rats at the late prepubertal age or at the very end of reproductive lifespan, and examined the expression of ED2 (CD163, a marker of mature resident macrophages related to secretion of inflammatory mediators) on peritoneal macrophages and their ability to produce TNF-α and NO upon LPS-stimulation at different age points. In addition, to delineate direct and indirect effects of estrogen, we assessed the in vitro influence of different concentrations of 17β-estradiol on LPS-induced macrophage TNF-α and NO production. Results showed that: (a) the low frequency of ED2(high) cells amongst peritoneal macrophages of aged rats was accompanied with the reduced TNF-α, but not NO production; (b) estradiol level gradually increased following ovariectomy; (c) macrophage ED2 expression and TNF-α production were dependent on estradiol/progesterone balance and they changed in the same direction; (d) changes in estradiol/progesterone balance differentially affected macrophages TNF-α and NO production; and (e) estradiol exerted pro-inflammatory and anti-inflammatory effects on macrophages in vivo and in vitro, respectively. Overall, our study discloses that estradiol/progesterone balance contributes to the fine-tuning of rat macrophage secretory capacity, and adds to a better understanding of the ovarian steroid hormone role in the regulation of macrophage function, and its significance for the age-associated changes in innate immunity.

The chronic blockade of angiotensin I-converting enzyme eliminates the sex differences of serum cytokine levels of spontaneously hypertensive rats

Sex hormones modulate the action of both cytokines and the renin-angiotensin system. However, the effects of angiotensin I-converting enzyme (ACE) on the proinflammatory and anti-inflammatory cytokine levels in male and female spontaneously hypertensive rats (SHR) are unclear. We determined the relationship between ACE activity, cytokine levels and sex differences in SHR. Female (F) and male (M) SHR were divided into 4 experimental groups each (n = 7): sham + vehicle (SV), sham + enalapril (10 mg/kg body weight by gavage), castrated + vehicle, and castrated + enalapril. Treatment began 21 days after castration and continued for 30 days. Serum cytokine levels (ELISA) and ACE activity (fluorimetry) were measured. Male rats exhibited a higher serum ACE activity than female rats. Castration reduced serum ACE in males but did not affect it in females. Enalapril reduced serum ACE in all groups. IL-10 (FSV = 16.4 ± 1.1 pg/mL; MSV = 12.8 ± 1.2 pg/mL), TNF-α (FSV = 16.6 ± 1.2 pg/mL; MSV = 12.8 ± 1 pg/mL) and IL-6 (FSV = 10.3 ± 0.2 pg/mL; MSV = 7.2 ± 0.2 pg/mL) levels were higher in females than in males. Ovariectomy reduced all cytokine levels and orchiectomy reduced IL-6 but increased IL-10 concentrations in males. Castration eliminated the differences in all inflammatory cytokine levels (IL-6 and TNF-α) between males and females. Enalapril increased IL-10 in all groups and reduced IL-6 in SV rats. In conclusion, serum ACE inhibition by enalapril eliminated the sexual dimorphisms of cytokine levels in SV animals, which suggests that enalapril exerts systemic anti-inflammatory and anti-hypertensive effects.

Effects of short-term administration of estradiol on reperfusion arrhythmias in rats of different ages

Little is known about age-related differences in short-term effects of estradiol on ischemia-reperfusion (I/R) insults. The present study was designed to evaluate the effects of short-term treatment with estradiol on reperfusion arrhythmias in isolated hearts of 6-7-week-old and 12-14-month-old female rats. Wistar rats were sham-operated, ovariectomized and treated with vehicle or ovariectomized and treated with 17β-estradiol (E₂; 5 µg·100 g⁻¹·day⁻¹) for 4 days. Hearts were perfused by the Langendorff technique. Reperfusion arrhythmias, i.e., ventricular tachycardia and/or ventricular fibrillation, were induced by 15 min of left coronary artery ligation and 30 min of reperfusion. The duration and incidence of I/R arrhythmias were significantly higher in young rats compared to middle-aged rats (arrhythmia severity index: 9.4 ± 1.0 vs 3.0 ± 0.3 arbitrary units, respectively, P < 0.05). In addition, middle-aged rats showed lower heart rate, systolic tension and coronary flow. Four-day E₂ treatment caused an increase in uterine weight. Although E₂ administration had no significant effect on the duration of I/R arrhythmias in middle-aged rats, it induced a marked reduction in the rhythm disturbances of young rats accompanied by a decrease in heart rate of isolated hearts. Also, this reduction was associated with an increase in QT interval. No significant changes were observed in the QT interval of middle-aged E₂-treated rats. These data demonstrate that short-term estradiol treatment protects against I/R arrhythmias in hearts of young female rats. The anti-arrhythmogenic effect of estradiol might be related to a lengthening of the QT interval.

Stimulation of cardiac apoptosis in ovariectomized hypertensive rats: potential role of the renin-angiotensin system

OBJECTIVES

The mechanisms underlying the increased cardiovascular risk after menopause are poorly understood. Estrogens modulate the cardiac renin-angiotensin system (RAS) and influence cardiac adaptation to afterload. To investigate whether the loss of the natural inhibition of the RAS by estrogen may be linked to an increase of cardiac apoptosis, we studied 17β-estradiol (E2) and/or angiotensin-converting enzyme (ACE) inhibitor treatment effects on cardiomyocyte survival in ovariectomized spontaneously hypertensive rats (SHRs).

METHODS

Five groups of female SHRs were evaluated for 8 weeks. One group served as nonovariectomized control; the other four groups underwent bilateral ovariectomy and were randomized to receive 60-day-release pellets containing placebo or 0.5 mg of E2, the ACE inhibitor ramipril at the dosage of 2.5 mg/kg per day, or the combination of the two treatments.

RESULTS

Ovariectomy increased cardiomyocyte apoptosis and induced proapoptotic changes of Bcl-2 and Bax genes and proteins. These modifications were associated with an upregulation of ACE and angiotensin II type 1 (AT1) receptor genes. Ramipril was as effective as E2 in preventing cardiac apoptosis and in restoring cardiac brain natriuretic peptide in association with reduced cardiac ACE and AT1 receptor gene expression. In contrast to the ramipril treatment, the favorable effect of E2 on cardiac apoptosis occurred independently from changes in SBP. No synergistic effect was observed when the two treatments were combined.

CONCLUSION

These data show that ovariectomy stimulates myocardium apoptosis by a mechanism involving Bax and Bcl-2 genes. The antiapoptotic effect of E2 and ACE inhibitor treatment was linked to a downregulation of cardiac RAS.

Ovariectomy does not affect the cardiac sympathovagal balance of female SHR but estradiol does

The low incidence of cardiovascular diseases, including hypertension, in premenopausal women has led to the conclusion that ovarian hormones may have a protective effect on the cardiovascular system. We evaluated the effects of ovariectomy and/or estradiol on sympathovagal balance and heart rate variability (HRV) in female spontaneously hypertensive rats (SHR) with tachycardia and compared them to Wistar rats (12 weeks old; N = 8-12). Ovariectomy (OVX) and/or estradiol (10 µg/kg) did not affect basal arterial pressure in either rat strain, but estradiol increased basal heart rate (HR) in OVX SHR (454 ± 18 vs 377 ± 9 bpm). HR changes elicited by methylatropine and propranolol were used to evaluate the sympathovagal balance. Ovariectomy did not affect the cardiac sympathovagal balance of any group, while estradiol increased sympathetic tone in OVX SHR (120 ± 8 vs 56 ± 10 bpm) and sham-operated Wistar rats (57 ± 7 vs 28 ± 4 bpm), and decreased the parasympathetic tone only in OVX SHR (26 ± 7 vs 37 ± 5 bpm). HRV was studied in the frequency domain (Fast Fourier Transformation). Spectra of HR series were examined at low frequency (LF: 0.2-0.75 Hz) and high frequency (HF: 0.75-3 Hz) bands. The power of LF, as well as the LF/HF ratio, was not affected by ovariectomy, but estradiol increased both LF (29 ± 4 vs 18 ± 3 nu in Wistar sham-operated, 26 ± 5 vs 15 ± 3 nu in Wistar OVX, 50 ± 3 vs 38 ± 4 nu in SHR sham-operated, and 51 ± 3 vs 42 ± 3 nu in SHR OVX) and LF/HF (0.48 ± 0.08 vs 0.23 ± 0.03 nu in Wistar sham-operated, 0.41 ± 0.14 vs 0.19 ± 0.05 nu in Wistar OVX, 0.98 ± 0.11 vs 0.63 ± 0.11 nu in SHR sham-operated, and 1.10 ± 0.11 vs 0.78 ± 0.1 nu in SHR OVX). Thus, we suggest that ovariectomy did not affect the cardiac sympathovagal balance of SHR or Wistar rats, while estradiol increased the sympathetic modulation of HR.

Ovariectomy in aged versus young rats augments matrix metalloproteinase-mediated vasoconstriction in mesenteric arteries

OBJECTIVE

Ovarian deficiency is known to undermine vasoprotective mechanisms and accelerate cardiovascular disease in postmenopausal women. In a rat model of menopause (aged ovariectomized [Ovx] rats), we recently revealed a vasoconstrictor pathway mediated by matrix metalloproteinases (MMPs) via cleavage of big endothelin-1 (ET-1). However, the specific impact of aging and/or Ovx on this pathway remains unknown. We hypothesized that aging exacerbates MMP-mediated vasoconstriction in an ovary-deficient state.

METHODS

Young and aged female Sprague-Dawley rats, either intact or Ovx, were assessed for MMP-dependent vasoreactivity. Dose responses to big ET-1 in the absence or presence of an MMP inhibitor (GM6001) were tested on small mesenteric arteries using a pressure myograph system. MMP levels in the vascular tissue were measured by gelatin zymography.

RESULTS

Both young Ovx and aged Ovx animals demonstrated a similar increase in the vasoconstriction to big ET-1 compared with the age-matched intact groups. MMP inhibition attenuated big ET-1 response in both Ovx groups and aged controls, but this effect was more pronounced in aged Ovx arteries (area under the curve reduction, 3.8 +/- 0.6 units in aged Ovx rats vs 1.5 +/- 0.5 units in young Ovx rats or 1.8 +/- 0.6 units in aged intact rats; P < 0.05). MMP-2 activity in the vascular tissue increased with age and was further augmented by Ovx.

CONCLUSIONS

Regardless of age, ovarian loss increases vascular reactivity to big ET-1, which is mediated, in part, by MMP. Superimposed with advancing age, ovarian deficiency further increases the proconstrictor role of MMP, which corresponds with higher MMP-2 levels in the aging vessel wall. MMP-mediated vasoconstriction may be a mechanism contributing to vascular dysfunction in postmenopausal women.

Estrogen improves TIMP-MMP balance and collagen distribution in volume-overloaded hearts of ovariectomized females

Our previous studies demonstrate that 17beta-estradiol limits chronic volume overload-induced hypertrophy and improves heart function in ovariectomized rats. One possible cardioprotective mechanism involves the interaction between estrogen, estrogen receptors, and proteins of the extracellular matrix (ECM). The impact of estrogen deficiency and replacement on left ventricular (LV) hypertrophy and ECM protein expression was studied using five female rat groups: intact sham-operated, ovariectomized sham-operated, intact with volume overload, ovariectomized with volume overload, and ovariectomized with volume overload treated with estrogen. After 8 wk, LV protein extracts were evaluated by Western blot analysis for matrix metalloproteinase-2 (MMP-2) and MMP-9, MT1-MMP, tissue inhibitors of MMPs (TIMP)-1, TIMP-2, TIMP-3 and TIMP-4, collagens type I and III, and estrogen receptor alpha and beta expression. MMP proteolytic activity was assessed by zymography. All volume-overloaded groups exhibited LV hypertrophy, which was associated with a loss of interstitial collagen and perivascular fibrosis. After 8 wk of volume overload, 70% of ovariectomized rats developed heart failure, in contrast to only one intact rat. A downregulation of MMP-2, estrogen receptor-alpha (ERalpha), and ERbeta, and upregulation of MMP-9 and MT1-MMP were found in the volume-overloaded hearts of ovariectomized rats. Estrogen treatment improved TIMP-2/MMP-2 and TIMP-1/MMP-9 protein balance, restored ERalpha expression, and prevented MMP-9 activation, perivascular collagen accumulation and development of heart failure. However, estrogen did not fully restore ERbeta expression and did not prevent the increase of MMP-9 expression or loss of interstitial collagen. These results support that estrogen limits undesirable ECM remodeling and LV dilation, in part, through modulation of ECM protein expression in volume-overloaded hearts of ovariectomized rats.

Estrogen, aging and the cardiovascular system

Estrogen is a powerful hormone with pleiotropic effects. Estrogens have potent antioxidant effects and are able to reduce inflammation, induce vasorelaxation and alter gene expression in both the vasculature and the heart. Estrogen treatment of cultured cardiac myocytes and endothelial cells rapidly activates NFkappaB, induces heat-shock protein (HSP)-72, a potent intracellular protective protein, and protects cells from simulated ischemia. In in vivo models, estrogens protect against ischemia and trauma/hemorrhage. Estrogens may decrease the expression of soluble epoxide hydrolase, which has deleterious effects on the cardiovascular system through metabolism of epoxyeicosatrienoic acids. Natural (endogenous) estrogens in premenopausal women appear to protect against cardiovascular disease and yet controlled clinical trials have not indicated a benefit from estrogen replacement postmenopause. Much remains to be understood in regards to the many properties of this powerful hormone and how changes in this hormone interact with aging-associated changes. The unexpected negative results of trials of estrogen replacement postmenopause probably arise from our lack of understanding of the many effects of this hormone.

Preventive effects of raloxifene, a selective estrogen receptor modulator, on monocrotaline-induced pulmonary hypertension in intact and ovariectomized female rats

We investigated whether the chronic treatment with raloxifene, a selective estrogen receptor modulator, prevents the development of monocrotaline-induced pulmonary hypertension in ovary-intact and ovariectomized female rats. Four weeks after a single subcutaneous injection of monocrotaline (60 mg/kg), right ventricular systolic pressure, right ventricle-to-left ventricle plus septal weight ratio, pulmonary arterial medial thickening and endothelin-1 levels in right ventricular tissue increased significantly in both female rats, compared with saline-treated control rats. These monocrotaline-induced alterations were much greater in ovariectomized rats than the changes in intact females. Daily oral administration of raloxifene (10 mg/kg/day for 4 weeks) significantly attenuated the increase in right ventricular systolic pressure to the same levels in both groups of animals, but raloxifene suppressed the increases in right ventricle-to-left ventricle plus septal weight ratio and pulmonary arterial medial thickness more efficiently in ovariectomized females than the case with intact females. In addition, raloxifene completely suppressed the increase in right ventricular endothelin-1 levels in ovariectomized rats, but not in intact females. These data suggest that chronic treatment with raloxifene effectively prevents the development of monocrotaline-induced pulmonary hypertension in ovariectomized female rats than in intact females, at least in part, by suppressing right ventricular endothelin-1 overproduction.

Contribution of endothelin A receptors in endothelin 1-dependent natriuresis in female rats

Renal medullary endothelin B receptors contribute to blood pressure regulation by facilitating salt excretion. Premenopausal females have relatively less hypertension than males; therefore, we examined whether there is a sex difference in the natriuretic response to renal medullary infusion of endothelin peptides in the rat. All of the experiments were conducted in anesthetized wild-type (wt) or endothelin B-deficient (sl/sl) rats. Infusion of endothelin 1 (ET-1) significantly increased sodium excretion (U(Na)V) in female, but not male, wt rats (Delta U(Na)V: 0.41+/-0.07 versus -0.04+/-0.06 micromol/min, respectively). The endothelin B receptor agonist sarafotoxin 6c produced similar increases in U(Na)V in both male (Delta 0.58+/-0.15 micromol/min) and female (Delta 0.67+/-0.18 micromol/min) wt rats. Surprisingly, ET-1 markedly increased U(Na)V in female (Delta 0.70+/-0.11 micromol/min) but not male sl/sl rats (Delta 0.00+/-0.05 micromol/min). ET-1 had no effect on medullary blood flow in females, although medullary blood flow was significantly reduced to a similar extent in males of both strains. These results suggest that the lack of a natriuretic response to ET-1 in male rats is because of reductions in medullary blood flow. Treatment with ABT-627, an endothelin A receptor antagonist, or N(G)-propyl-L-arginine, an NO synthase 1 inhibitor, prevented the increase in U(Na)V observed in female rats. Gonadectomy eliminated the sex difference in the U(Na)V and medullary blood flow response to ET-1. These findings demonstrate that there is no sex difference in endothelin B-dependent natriuresis, and the endothelin A receptor contributes to ET-1-dependent natriuresis in female rats, an effect that requires NO synthase 1. These findings provide a possible mechanism for why premenopausal women are more resistant to salt-dependent hypertension.

Estrogen effects on MMP-13 and MMP-14 regulation of left ventricular mass in Dahl salt-induced hypertension

BACKGROUND

Female Dahl salt-sensitive (DS) rats fed a low-salt diet develop hypertension at 6 months of age. Ovariectomy at 2 months of age accelerates the development of hypertension, and estrogen replacement delays it. Although acute pressure overload induces structural changes in the left ventricle (LV) further effects of gradual hypertension on LV remodeling have not been examined in the DS rat model.

OBJECTIVE

The purpose of this study was to test the hypothesis that aging and estrogen loss in hypertensive DS rats are accompanied by changes in LV remodeling.

METHODS

Four groups of DS rats were examined: young intact, middle-aged (MA) intact, MA ovariectomized (MA-OVX), and MA-OVX with 17beta-eestradiol (E(2)) supplementation (MA-OVX+E(2)). Myocardial matrix metalloproteinases (MMPs),tissue inhibitors of metalloproteinases (TIMPs),and extracellular matrix (ECM) proteins were assessed by immunoblotting.

RESULTS

Each of the 4 groups comprised 6 animals. Mean (SEM) LV mass was significantly greater in the MA-intact and the MA-OVX groups (1257 [31] mg and 1199 [25] mg, respectively; both, P < 0.05) compared with the young-intact group (697 [6] mg). LV mass in the MA-OVX+E(2) group was significantly lower compared with the MA-intact and MA-OVX groups (both, P < 0.05), suggesting that estrogen may attenuate LV remodeling. Fibronectin and collagen III and IV concentrations increased significantly in the MA-intact and MA-OOVX groups (all, P < 0.05),indicating increased fibrosis. Multiple MMPs also increased in the MA-intact an nd MA-OVX rats, including MMP-3, -7, -99, -113, and -114, and all TIMPs. In contrast, estrogen attenuated fibrosis by increasing MMP-8 concentrations and increasing collagen III fragments. From good-fit regression modeling, MMP-13 and MMP-14 concentrations correlated positively with LV mass for the MA-intact and MA-OVX groups, respectively.

CONCLUSIONS

Gradual hypertension stimulated ECM turnover by increasing both MMP/TIMP production and ECM degradation. Estrogen loss or gain resulted in a shift in MMP profiles, suggesting that MMP-13 and MMP-14 may be differentially regulated in postmenopausal hypertension.

Ventilation and phrenic output following high cervical spinal hemisection in male vs. female rats

Female sex hormones influence the neural control of breathing and may impact neurologic recovery from spinal cord injury. We hypothesized that respiratory recovery after C2 spinal hemisection (C2HS) differs between males and females and is blunted by prior ovariectomy (OVX) in females. Inspiratory tidal volume (VT), frequency (fR), and ventilation (VE) were quantified during quiet breathing (baseline) and 7% CO2 challenge before and after C2HS in unanesthetized adult rats via plethysmography. Baseline breathing was similarly altered in all rats (reduced VT, elevated fR) but during hypercapnia females had relatively higher VT (i.e. compared to pre-injury) than male or OVX rats (p<0.05). Phrenic neurograms recorded in anesthetized rats indicated that normalized burst amplitude recorded ipsilateral to C2HS (i.e. the crossed phrenic phenomenon) is greater in females during respiratory challenge (p<0.05 vs. male and OVX). We conclude that sex differences in recovery of VT and phrenic output are present at 2 weeks post-C2HS. These differences are consistent with the hypothesis that ovarian sex hormones influence respiratory recovery after cervical spinal cord injury.

Ligand-dependent activation of ER{beta} lowers blood pressure and attenuates cardiac hypertrophy in ovariectomized spontaneously hypertensive rats

AIMS

The biological effects of oestrogens are mediated by two different oestrogen receptor (ER) subtypes, ERalpha and ERbeta, which might play different, redundant, or opposing roles in cardiovascular disease. Previously, we have shown that the selective ERalpha agonist 16alpha-LE2 improves vascular relaxation, attenuates cardiac hypertrophy, and increases cardiac output without lowering elevated blood pressure in spontaneously hypertensive rats (SHR). Because ERbeta-deficient mice exhibit elevated blood pressure and since the ERbeta agonist 8beta-VE2 attenuated hypertension in aldosterone-salt-treated rats, we have now tested the hypothesis that the isotype-selective ERbeta agonist 8beta-VE2 might be capable of lowering elevated blood pressure in ovariectomized SHR.

METHODS AND RESULTS

Treatment of ovariectomized SHR with 8beta-VE2 for 12 weeks conferred no uterotrophic effects but lowered elevated systolic blood pressure (-38 +/- 5 mmHg, n = 31, P < 0.001 vs. placebo) as well as peripheral vascular resistance (-31.3 +/- 4.6%, P < 0.001 vs. placebo). 8beta-VE2 enhanced aortic ERbeta expression (+75.7 +/- 7.1%, P < 0.01 vs. placebo), improved NO-dependent vasorelaxation, augmented phosphorylation of the vasodilator-stimulated phosphoprotein in isolated aortic rings (P < 0.05 vs. placebo), increased cardiac output (+20.4 +/- 2.5%, P < 0.01 vs. placebo), and attenuated cardiac hypertrophy (-22.2 +/- 3.2%, p < 0.01 vs. placebo). 8beta-VE2, in contrast to oestradiol, did not enhance cardiac alpha-myosin heavy chain expression.

CONCLUSION

Ligand-dependent activation of ERbeta confers blood pressure lowering effects in SHR that are superior to those of 17beta-estradiol or the ERalpha agonist 16alpha-LE2 and attenuates cardiac hypertrophy primarily by a reduction of cardiac afterload without promoting uterine growth.

Specific adaptations of estrogen receptor alpha and beta transcripts in liver and heart after endurance training in rats

Estrogens exert their biological roles mainly through estrogen receptors (ER) that function as ligand-activated transcription factors. ER content in a cell is regulated by many factors and is decisive for estrogen action. The purpose of the present study was to investigate the influence of an 8-wk endurance training program on ER expression in the liver, right atrium (RA), and left ventricle (LV) of intact and ovariectomized (Ovx) rats. We measured ERalpha and ERbeta mRNA content by reverse transcription-polymerase chain reaction (RT-PCR). We found an important increase in ERalpha mRNA levels in the liver (300%; P < 0.01) and in ERbeta mRNA levels in the RA (200%; P < 0.05), and a marked decrease in ERalpha (80%; P < 0.01) and ERbeta (40%; P < 0.05) transcripts content in the LV of intact rats after endurance training. On the other hand, ERalpha mRNA levels were depressed by 50% (P < 0.01) in the liver, and increased by 60% (P < 0.01) in LV of Ovx rats after exercise training. These results first indicate that endurance training is associated with modifications of ER transcripts levels in the liver, LV, and RA of female rats. More specifically, these effects are tissue and isoform-specific and the direction of the response (increase or decrease) is different in intact and Ovx rats. It is suggested that some of the adaptations to endurance training in liver and heart may be mediated by an ER-dependent mechanism.

Actions of estrogen and estrogen receptors in nonclassical target tissues

Hormonal effects on classical endocrine target organs such as the female reproductive tract, mammary gland, ovary, and neuroendocrine system have been thoroughly studied, with significant advancements in our understanding of estrogen actions and disease conditions from both cell culture as well as new experimental animal models. Knowledge of the highly appreciated effects of estrogen in nonclassical endocrine organ systems, arising from epidemiological and clinical findings in the cardiovascular, immune, GI tract, and liver, is only now becoming clarified from the development and use of knock-out or transgenic animal models for the study of both estrogen and ER activities. There are considerable epidemiological data showing that premenopausal females (Barrett-Connor 1997; Crabbe et al. 2003) have reduced risk for cardiovascular disease. However, a recent large clinical trial failed to show cardioprotection for postmenopausal females on estrogen-progestin replacement (Rossouw et al. 2002). In fact, the Women's Health Initiative Study showed increased cardiovascular risk for females taking an estrogen-progestin combination. These studies suggest that we need a better understanding of the mechanisms responsible for cardioprotection in females.