Estrogen receptor beta does not influence ischemic tolerance in the aged female rat heart

A murine model of hypertensive heart disease in older women

We propose a new mouse (C57Bl6/J) model combining several features of heart failure with preserved ejection fraction encountered in older women, including hypertension from Angiotensin II infusion (AngII), menopause, and advanced age. To mimic menopause, we delayed ovariectomy (Ovx) at 12 months of age. We also studied the effects of AngII infusion for 28 days in younger animals and the impact of losing gonadal steroids earlier in life. We observed that AngII effects on heart morphology were different in younger and adult mice (3- and 12-month-old; 20 and 19% increase in heart weight. P < 0.01 for both) than in older animals (24-month-old; 6%; not significant). Ovariectomy at 12 months restored the hypertrophic response to AngII in elderly females (23%, p = 0.0001). We performed a bulk RNA sequencing study of the left ventricle (LV) and left atrial gene expression in elderly animals, controls, and Ovx. AngII modulated (|Log2 fold change| ≥ 1) the LV expression of 170 genes in control females and 179 in Ovx ones, 64 being shared. In the left atrium, AngII modulated 235 genes in control females and 453 in Ovx, 140 shared. We observed many upregulated genes associated with the extracellular matrix regulation in both heart chambers. Many of these upregulated genes were shared between the ventricle and the atrium as well as in control and Ovx animals, namely for the most expressed Ankrd1, Nppb, Col3a1, Col1a1, Ctgf Col8a1, and Cilp. Several circadian clock LV genes were modulated differently by AngII between control and Ovx females (Clock, Arntl, Per2, Cry2, and Ciart). In conclusion, sex hormones, even in elderly female mice, modulate the heart's hypertrophic response to AngII. Our study identifies potential new markers of hypertensive disease in aging female mice and possible disturbances of their cardiac circadian clock.

Biological sex, sex steroids and sex chromosomes contribute to mouse cardiac aging

After menopause, the incidence of cardiovascular disease rapidly rises in women. The disappearing protection provided by sex steroids is a consequence of the development of many risk factors. Preclinical studies are necessary to understand better the effects of ovarian hormones loss cardiac aging. To mimic menopause in mice and study its consequences, we delayed ovariectomy at 12 months and followed animals for 12 months. Using RNA sequencing, we investigated changes in the myocardial exome with aging. In addition, with four-core genotypes (FCG) transgenic mice, we studied sex chromosome effects on cardiac aging. Heart weight increased from 3 to 24 months (males + 35%, females + 29%). In males, 75% of this increase had occurred at 12 months; in females, only 30%. Gonadectomy of mice at 12 months blocked cardiac hypertrophy in both sexes during the second year of life. The dosage of the X chromosomes did not influence cardiac growth in young and older mice. We performed an RNA sequencing study in young and old mice. We identified new highly expressed genes modulated during aging (Bdh, Myot, Cpxm2, and Slc38a1). The myocardial exome in older animals displayed few differences related to the animal's sex or the presence or absence of sex steroids for a year. We show that the morphological evolution of the heart depends on the biological sex via gonadal sex hormone actions. The myocardial exome of old male and female mice is relatively similar. Our study emphasizes the need to consider sex steroid effects in studying cardiac aging.

Periconceptional alcohol alters in vivo heart function in ageing female rat offspring: Possible involvement of oestrogen receptor signalling

NEW FINDINGS

What is the central question of this study? What are the cardiovascular consequences of periconceptual ethanol on offspring throughout the lifespan? What is the main finding and its importance? It is shown for the first time that periconceptional alcohol has sex-specific effects on heart growth, with ageing female offspring exhibiting decreased cardiac output. Altered in vivo cardiac function in ageing female offspring may be linked to changes in cardiac oestrogen receptor expression.

ABSTRACT

Alcohol exposure throughout gestation is detrimental to cardiac development and function. Although many women decrease alcohol consumption once aware of a pregnancy, exposure prior to recognition is common. We, therefore, examined the effects of periconceptional alcohol exposure (PC:EtOH) on heart function, and explored mechanisms that may contribute. Female Sprague-Dawley rats received a liquid diet ±12.5% v/v ethanol from 4 days prior to mating until 4 days after mating (PC:EtOH). Cardiac function was assessed via echocardiography, and offspring were culled at multiple time points for assessment of morphometry, isolated heart and aortic ring function, protein and transcriptional changes. PC:EtOH-exposed embryonic day 20 fetuses (but not postnatal offspring) had larger hearts relative to body weight. Ex vivo analysis of hearts at 5-7 months old (mo) indicated no changes in coronary function or cardiac ischaemic tolerance, and apparently improved ventricular compliance in PC:EtOH females (compared to controls). At 12 mo, vascular responses in isolated aortic rings were unaltered by PC:EtOH, whilst echocardiography revealed reduced cardiac output in female but not male PC:EtOH offspring. At 19 mo, left ventricular transcript and protein for type 1 oestrogen receptor (ESR1), HSP90 transcript and plasma oestradiol levels were all elevated in female PC:EtOH exposed offspring. Summarising, PC:EtOH adversely impacts in vivo heart function in mature female offspring, associated with increased ventricular oestrogen-related genes. PC:EtOH may thus influence age-related heart dysfunction in females through modulation of oestrogen signalling.

Nuclear Receptors in Myocardial and Cerebral Ischemia-Mechanisms of Action and Therapeutic Strategies

Nearly 18 million people died from cardiovascular diseases in 2019, of these 85% were due to heart attack and stroke. The available therapies although efficacious, have narrow therapeutic window and long list of contraindications. Therefore, there is still an urgent need to find novel molecular targets that could protect the brain and heart against ischemia without evoking major side effects. Nuclear receptors are one of the promising targets for anti-ischemic drugs. Modulation of estrogen receptors (ERs) and peroxisome proliferator-activated receptors (PPARs) by their ligands is known to exert neuro-, and cardioprotective effects through anti-apoptotic, anti-inflammatory or anti-oxidant action. Recently, it has been shown that the expression of aryl hydrocarbon receptor (AhR) is strongly increased after brain or heart ischemia and evokes an activation of apoptosis or inflammation in injury site. We hypothesize that activation of ERs and PPARs and inhibition of AhR signaling pathways could be a promising strategy to protect the heart and the brain against ischemia. In this Review, we will discuss currently available knowledge on the mechanisms of action of ERs, PPARs and AhR in experimental models of stroke and myocardial infarction and future perspectives to use them as novel targets in cardiovascular diseases.

Estradiol-induced inhibition of endoplasmic reticulum stress normalizes splenic CD4 + T lymphocytes following hemorrhagic shock

The aim is to investigate that 17β-estradiol (E2)/estrogen receptors (ERs) activation normalizes splenic CD4 + T lymphocytes proliferation and cytokine production through inhibition of endoplasmic reticulum stress (ERS) following hemorrhage. The results showed that hemorrhagic shock (hemorrhage through femoral artery, 38–42 mmHg for 90 min followed by resuscitation of 30 min and subsequent observation period of 180 min) decreased the CD4⁺ T lymphocytes proliferation and cytokine production after isolation and incubation with Concanavalin A (5 μg/mL) for 48 h, induced the splenic injury with evidences of missed contours of the white pulp, irregular cellular structure, and typical inflammatory cell infiltration, upregulated the expressions of ERS biomarkers 78 kDa glucose-regulated protein (GRP78) and activating transcription factor 6 (ATF6). Either E2, ER-α agonist propyl pyrazole triol (PPT) or ERS inhibitor 4-Phenylbutyric acid administration normalized these parameters, while ER-β agonist diarylpropionitrile administration had no effect. In contrast, administrations of either ERs antagonist ICI 182,780 or G15 abolished the salutary effects of E2. Likewise, ERS inducer tunicamycin induced an adverse effect similarly to that of hemorrhagic shock in sham rats, and aggravated shock-induced effects, also abolished the beneficial effects of E2 and PPT, respectively. Together, the data suggest that E2 produces salutary effects on CD4⁺ T lymphocytes function, and these effects are mediated by ER-α and GPR30, but not ER-β, and associated with the attenuation of hemorrhagic shock-induced ERS.

Estrogen Receptors: Therapeutic Perspectives for the Treatment of Cardiac Dysfunction after Myocardial Infarction

Estrogen receptors (ER) mediate functions beyond their endocrine roles, as modulation of cardiovascular, renal, and immune systems through anti-inflammatory and anti-apoptotic effects, preventing necrosis of cardiomyocytes and endothelial cells, and attenuating cardiac hypertrophy. Estradiol (E2) prevents cardiac dysfunction, increases nitric oxide synthesis, and reduces the proliferation of vascular cells, yielding protective effects, regardless of gender. Such actions are mediated by ER (ER-alpha (ERα), ER-beta (ERβ), or G protein-coupled ER (GPER)) through genomic or non-genomic pathways, which regulate cardiovascular function and prevent tissue remodeling. Despite the extensive knowledge on the cardioprotective effects of estrogen, clinical studies conducted on myocardial infarction (MI) and cardiovascular diseases still include favorable and unfavorable profiles. The purpose of this review is to provide up-to-date information regarding molecular, preclinical, and clinical aspects of cardiovascular E2 effects and ER modulation as a potential therapeutic target for the treatment of MI-induced cardiac dysfunction.

Is Sex a Determinant of COVID-19 Infection? Truth or Myth?

Purpose of Review

Angiotensin-converting enzyme 2 (ACE2), a specific high-affinity angiotensin II-hydrolytic enzyme, is the vector that facilitates cellular entry of SARS-CoV-1 and the novel SARS-CoV-2 coronavirus. SARS-CoV-2, which crossed species barriers to infect humans, is highly contagious and associated with high lethality due to multi-organ failure, mostly in older patients with other co-morbidities.

Recent Findings

Accumulating clinical evidence demonstrates that the intensity of the infection and its complications are more prominent in men. It has been postulated that potential functional modulation of ACE2 by estrogen may explain the sex difference in morbidity and mortality.

Summary

We review here the evidence regarding the role of estrogenic hormones in ACE2 expression and regulation, with the intent of bringing to the forefront potential mechanisms that may explain sex differences in SARS-CoV-2 infection and COVID-19 outcomes, assist in management of COVID-19, and uncover new therapeutic strategies.

Non-genomic Effects of Estrogen on Cell Homeostasis and Remodeling With Special Focus on Cardiac Ischemia/Reperfusion Injury

This review takes into consideration the main mechanisms involved in cellular remodeling following an ischemic injury, with special focus on the possible role played by non-genomic estrogen effects. Sex differences have also been considered. In fact, cardiac ischemic events induce damage to different cellular components of the heart, such as cardiomyocytes, vascular cells, endothelial cells, and cardiac fibroblasts. The ability of the cardiovascular system to counteract an ischemic insult is orchestrated by these cell types and is carried out thanks to a number of complex molecular pathways, including genomic (slow) or non-genomic (fast) effects of estrogen. These pathways are probably responsible for differences observed between the two sexes. Literature suggests that male and female hearts, and, more in general, cardiovascular system cells, show significant differences in many parameters under both physiological and pathological conditions. In particular, many experimental studies dealing with sex differences in the cardiovascular system suggest a higher ability of females to respond to environmental insults in comparison with males. For instance, as cells from females are more effective in counteracting the ischemia/reperfusion injury if compared with males, a role for estrogen in this sex disparity has been hypothesized. However, the possible involvement of estrogen-dependent non-genomic effects on the cardiovascular system is still under debate. Further experimental studies, including sex-specific studies, are needed in order to shed further light on this matter.

Inhibition of programmed necrosis limits infarct size through altered mitochondrial and immune responses in the aged female rat heart

Both advancing age and estrogen loss exacerbate acute myocardial infarction in the female heart. However, the mechanistic underpinnings of age-related differences in cell death after ischemia-reperfusion (I/R) injury in female subjects and reductions in cardioprotective reserve capacity remain largely unexplored. The aim of the present study was to determine the efficacy of programmed necrosis inhibition on infarct size reduction and preservation of left ventricular (LV) function after I/R injury with female aging. Fischer 344 rats were ovariectomized (OVX) at 15 mo and studied at 24 mo (MO OVX) versus adult rats with intact ovaries (6 mo). After in vivo coronary artery ligation (55-min ischemia and 2- or 6-h reperfusion), necrostatin-1 (Nec-1; 3.5 or 5.7 mg/kg) delivered upon reperfusion significantly reduced infarct size by 37% and improved LV function in the MO OVX group ( P < 0.01). Although age-associated elevations in cyclophilin D and mitochondrial acetylation ( P < 0.001) were unaffected by Nec-1, profound reductions in IL-1, IL-6, and TNF-α ( P < 0.05) as well as cardiac immune cell infiltration were observed in MO OVX but not adult rats. We conclude that chronic inflammation and postmenopausal estrogen deficiency conspire to exacerbate acute infarction through a mechanism involving exaggerated mitochondria-mediated programmed necrosis through receptor-interacting protein 1 signaling. Modulatory effects of programmed necrosis inhibition on proinflammatory cytokine production after I/R reveal a potentially important mechanistic target to restore and preserve cardiac function in the OVX aged female heart. NEW & NOTEWORTHY Myocardial infarct size reduction by inhibition of programmed necrosis in aged female subjects suggests a dominant cell death pathway. Alterations in mitochondrial protein levels and acetylation underscore a mitochondria-dependent mechanism, whereas the profound cytokine reduction in aged subjects alone points to a divergent role for immune modulation of programmed necrosis and viable therapeutic target.

Treatment with oestrogen-receptor agonists or oxytocin in conjunction with exercise protects against myocardial infarction in ovariectomized rats

NEW FINDINGS

What is the central question of this study? Could the activation of oxytocin or oestrogen receptors be protective against myocardial injury after ovariectomy? If so, would exercising have an additional ameliorating effect? What is the main finding and its importance? The results revealed that when accompanied by exercise, both oestrogen receptor agonists and oxytocin improved cardiac dysfunction, inhibited the generation of pro-inflammatory cytokines and reduced myocardial injury in ovariectomized female rats, suggesting a new approach for protecting postmenopausal women against ischaemia-induced myocardial injury. To investigate the putative protective effects of oxytocin or oestrogen receptor agonists against myocardial injury of ovariectomized sedentary or exercised rats, female Sprague-Dawley rats assigned to sham-operated control and ovariectomized (OVX) groups were kept sedentary or undertook swimming exercise for 4 weeks and were treated with saline, an oestrogen receptor (ER) β (DPN) or ERα agonist (PPT) or oxytocin. Ovariectomy increased weight gain and anxiety in sedentary rats, whereas exercise prevented weight gain. When accompanied by exercise, both ER agonists and oxytocin inhibited weight gain and anxiety; oxytocin, in the absence or presence of exercise, increased the left ventricular diastolic dimensions and ejection fraction, whereas ER agonists also increased left ventricular diameter when given to exercised rats. Upon the induction of myocardial ischaemia-reperfusion in the OVX rats, plasma creatine kinase-(muscle-brain) was depressed by PPT and oxytocin, whereas DPN, PPT and OT reduced plasminogen activator inhibitor-1 concentrations. The increased tumour necrosis factor-α concentration in OVX rats was also suppressed by exercise or DPN, PPT or oxytocin treatments, whereas the interleukin-6 concentration was diminished by all the treatments when given in conjunction with exercise. Disorganization of cardiac muscle fibres was reduced in all exercised rats. Oestrogen receptor agonists, as well as oxytocin, in conjunction with exercise may be effective new therapeutics to protect against myocardial ischaemia in postmenopausal women.

Age and ischemia differentially impact mitochondrial ultrastructure and function in a novel model of age-associated estrogen deficiency in the female rat heart

Altered mitochondrial respiration, morphology, and quality control collectively contribute to mitochondrial dysfunction in the aged heart. Because myocardial infarction remains the leading cause of death in aged women, the present study utilized a novel rodent model to recapitulate human menopause to interrogate the combination of age and estrogen deficiency on mitochondrial ultrastructure and function with cardiac ischemia/reperfusion (I/R) injury. Female F344 rats were ovariectomized (OVX) at 15 months and studied at 24 months (MO OVX; n = 40) vs adult ovary intact (6 months; n = 41). Temporal declines in estrogen concomitant with increased visceral adipose tissue were observed in MO OVX vs adult. Following in vivo coronary artery ligation or sham surgery, state 3 mitochondrial respiration was selectively reduced by age in subsarcolemmal mitochondria (SSM) and by I/R in interfibrillar mitochondria (IFM); left ventricular maximum dP/dt was reduced in MO OVX (p < 0.05). Elevated cyclophilin D and exacerbated I/R-induced mitochondrial acetylation in MO OVX suggest permeability transition pore involvement and reduced protection vs adult (p < 0.05). Mitochondrial morphology by TEM revealed an altered time course of autophagy coordinate with attenuated Drp1 and LC3BII protein levels with age-associated estrogen loss (p < 0.05). Here, reductions in both SSM and IFM function may play an additive role in enhanced susceptibility to regional I/R injury in aged estrogen-deficient female hearts. Moreover, novel insight into altered cardiac mitochondrial quality control garnered here begins to unravel the potentially important regulatory role of mitochondrial dynamics on sustaining respiratory function in the aged female heart.

Estrogenic Impact on Cardiac Ischemic/Reperfusion Injury

The increase in cardiovascular disease and metabolic syndrome incidence following the onset of menopause has highlighted the role of estrogen as a cardiometabolic protective agent. Specifically regarding the heart, estrogen induced an improvement in cardiac function, preserved calcium homeostasis, and inhibited the mitochondrial apoptotic pathway. The beneficial effects of estrogen in relation to cardiac ischemia/reperfusion (I/R) injury, such as reduced infarction and ameliorated post-ischemic recovery, have also been shown. Nevertheless, controversial findings exist and estrogen therapy is reported to be related to a higher rate of thromboembolic events and atrial fibrillation in post-menopausal women. Therefore, greater clarification is needed to evaluate the exact potential of estrogen use in cases of cardiac I/R injury. This article reviews the effects of estrogen, in both acute and chronic treatment, and collates the studies with regard to their in vivo, in vitro, or clinical trial settings in cases of cardiac I/R injury and myocardial infarction.

G-protein-coupled estrogen receptor as a new therapeutic target for treating coronary artery disease

Coronary heart disease (CHD) continues to be the greatest mortality risk factor in the developed world. Estrogens are recognized to have great therapeutic potential to treat CHD and other cardiovascular diseases; however, a significant array of potentially debilitating side effects continues to limit their use. Moreover, recent clinical trials have indicated that long-term postmenopausal estrogen therapy may actually be detrimental to cardiovascular health. An exciting new development is the finding that the more recently discovered G-protein-coupled estrogen receptor (GPER) is expressed in coronary arteries-both in coronary endothelium and in smooth muscle within the vascular wall. Accumulating evidence indicates that GPER activation dilates coronary arteries and can also inhibit the proliferation and migration of coronary smooth muscle cells. Thus, selective GPER activation has the potential to increase coronary blood flow and possibly limit the debilitating consequences of coronary atherosclerotic disease. This review will highlight what is currently known regarding the impact of GPER activation on coronary arteries and the potential signaling mechanisms stimulated by GPER agonists in these vessels. A thorough understanding of GPER function in coronary arteries may promote the development of new therapies that would help alleviate CHD, while limiting the potentially dangerous side effects of estrogen therapy.

Estrogen and the female heart

Estrogen has a plethora of effects in the cardiovascular system. Studies of estrogen and the heart span human clinical trials and basic cell and molecular investigations. Greater understanding of cell and molecular responses to estrogens can provide further insights into the findings of clinical studies. Differences in expression and cellular/intracellular distribution of the two main receptors, estrogen receptor (ER) α and β, are thought to account for the specificity and differences in responses to estrogen. Much remains to be learned in this area, but cellular distribution within the cardiovascular system is becoming clearer. Identification of GPER as a third ER has introduced further complexity to the system. 17β-estradiol (E2), the most potent human estrogen, clearly has protective properties activating a signaling cascade leading to cellular protection and also influencing expression of the protective heat shock proteins (HSP). E2 protects the heart from ischemic injury in basic studies, but the picture is more involved in the whole organism and clinical studies. Here the complexity of E2's widespread effects comes into play and makes interpretation of findings more challenging. Estrogen loss occurs primarily with aging, but few studies have used aged models despite clear evidence of differences between the response to estrogen deficiency in adult and aged animals. Thus more work is needed focusing on the effects of aging vs. estrogen loss on the cardiovascular system.

Sex and sex hormones in cardiac stress--mechanistic insights

Important sex differences in the onset and characteristics of cardiovascular disease are evident, yet the mechanistic details remain unresolved. Men are more susceptible to cardiovascular disease earlier in life, though younger women who have a cardiovascular event are more likely to experience adverse outcomes. Emerging evidence is prompting a re-examination of the conventional view that estrogen is protective and testosterone a liability. The heart expresses both androgen and estrogen receptors and is functionally responsive to circulating sex steroids. New evidence of cardiac aromatase expression indicates local estrogen production may also exert autocrine/paracrine actions in the heart. Cardiomyocyte contractility studies suggest testosterone and estrogen have contrasting inotropic actions, and modulate Ca(2+) handling and transient characteristics. Experimentally, sex differences are also evident in cardiac stress responses. Female hearts are generally less susceptible to acute ischemic damage and associated arrhythmias, and generally are more resistant to stress-induced hypertrophy and heart failure, attributed to the cardioprotective actions of estrogen. However, more recent data show that testosterone can also improve acute post-ischemic outcomes and facilitate myocardial function and survival in chronic post-infarction. The myocardial actions of sex steroids are complex and context dependent. A greater mechanistic understanding of the specific actions of systemic/local sex steroids in different cardiovascular disease states has potential to lead to the development of cardiac therapies targeted specifically for men and women.

Age-related differences in cardiac ischemia-reperfusion injury: effects of estrogen deficiency

Despite conflicting evidence for the efficacy of hormone replacement therapy in cardioprotection of postmenopausal women, numerous studies have demonstrated reductions in ischemia/reperfusion (I/R) injury following chronic or acute exogenous estradiol (E2) administration in adult male and female, gonad-intact and gonadectomized animals. It has become clear that ovariectomized adult animals may not accurately represent the combined effects of age and E2 deficiency on reductions in ischemic tolerance seen in the postmenopausal female. E2 is known to regulate the transcription of several cardioprotective genes. Acute, non-genomic E2 signaling can also activate many of the same signaling pathways recruited in cardioprotection. Alterations in cardioprotective gene expression or cardioprotective signal transduction are therefore likely to result within the context of aging and E2 deficiency and may help explain the reduced ischemic tolerance and loss of cardioprotection in the senescent female heart. Quantification of the mitochondrial proteome as it adapts to advancing age and E2 deficiency may also represent a key experimental approach to uncover proteins associated with disruptions in cardiac signaling contributing to age-associated declines in ischemic tolerance. These alterations have important ramifications for understanding the increased morbidity and mortality due to ischemic cardiovascular disease seen in postmenopausal females. Functional perturbations that occur in mitochondrial respiration and Ca(2+) sensitivity with age-associated E2 deficiency may also allow for the identification of alternative therapeutic targets for reducing I/R injury and treatment of the leading cause of death in postmenopausal women.

Blockade of electron transport before ischemia protects mitochondria and decreases myocardial injury during reperfusion in aged rat hearts

Myocardial injury is increased in the aged heart following ischemia and reperfusion (I-R) in both humans and experimental models. Hearts from aged 24-month-old Fischer 344 rats sustain greater cell death and decreased contractile recovery after I-R compared with 6-month-old adult controls. Cardiac mitochondria incur damage during I-R contributing to cell death. Aged rats have a defect in complex III of the mitochondrial electron transport chain (ETC) localized to the interfibrillar population of cardiac mitochondria (IFM), situated in the interior of the cardiomyocyte among the myofibrils. The defect involves the quinol oxidation site (Qo) and increases the production of reactive oxygen species (ROS) in the baseline state. Ischemia further decreases complex III activity via functional inactivation of the iron-sulfur subunit. We studied the contribution of ischemia-induced defects in complex III with the increased cardiac injury in the aged heart. The reversible blockade of the ETC proximal to complex III during ischemia using amobarbital protects mitochondria against ischemic damage, removing the ischemia component of mitochondrial dysfunction. Reperfusion of the aged heart in the absence of ischemic mitochondrial damage decreases net ROS production from mitochondria and reduces cell death. Thus, even despite the persistence of the age-related defects in electron transport, protection against ischemic damage to mitochondria can reduce injury in the aged heart. The direct therapeutic targeting of mitochondria protects against ischemic damage and decreases cardiac injury during reperfusion in the high risk elderly heart.

Age and ovariectomy abolish beneficial effects of female sex on rat ventricular myocytes exposed to simulated ischemia and reperfusion

Sex differences in responses to myocardial ischemia have been described, but whether cardiomyocyte function is influenced by sex in the setting of ischemia and reperfusion has not been elucidated. This study compared contractions and intracellular Ca²⁺ in isolated ventricular myocytes exposed to ischemia and reperfusion. Cells were isolated from anesthetized 3-month-old male and female Fischer 344 rats, paced at 4 Hz (37°C), exposed to simulated ischemia (20 mins) and reperfused. Cell shortening (edge detector) and intracellular Ca²⁺ (fura-2) were measured simultaneously. Cell viability was assessed with Trypan blue. Ischemia reduced peak contractions and increased Ca²⁺ levels equally in myocytes from both sexes. However, contraction amplitudes were reduced in reperfusion in male myocytes, while contractions recovered to exceed control levels in females (62.6±5.1 vs. 140.1±15.8%; p<0.05). Only 60% of male myocytes excluded trypan blue dye after ischemia and reperfusion, while all female cardiomyocytes excluded the dye (p<0.05). Parallel experiments were conducted in myocytes from ∼24-month-old female rats or 5–6-month-old rats that had an ovariectomy at 3–4 weeks of age. Beneficial effects of female sex on myocyte viability and contractile dysfunction in reperfusion were abolished in cells from 24-month-old females. Aged female myocytes also exhibited elevated intracellular Ca²⁺ and alternans in ischemia. Cells from ovariectomized rats displayed increased Ca²⁺ transients and spontaneous activity in ischemia compared to sham-operated controls. None of the myocytes from ovariectomized rats were viable after 15 minutes of ischemia, while 75% of sham cells remained viable at end of reperfusion (p<0.05). These findings demonstrate that cardiomyocytes from young adult females are more resistant to ischemia and reperfusion injury than cells from males. Age and OVX abolish these beneficial effects and induce Ca²⁺ dysregulation at the level of the cardiomyocyte. Thus, beneficial effects of estrogen in ischemia and reperfusion are mediated, in part, by effects on cardiomyocytes.