Differential effects of sarcolemmal and mitochondrial K(ATP) channels activated by 17 beta-estradiol on reperfusion arrhythmias and infarct sizes in canine hearts

17β-Oestradiol facilitates M2 macrophage skewing and ameliorates arrhythmias in ovariectomized female infarcted rats

Epidemiological studies have suggested a lower incidence of arrhythmia‐induced sudden cardiac death in women than in men. 17β‐oestradiol (E2) has been reported to have a post‐myocardial infarction antiarrhythmic effect, although the mechanisms have yet to be elucidated. We investigated whether E2‐mediated antioxidation regulates macrophage polarization and affects cardiac sympathetic reinnervation in rats after MI. Ovariectomized Wistar rats were randomly assigned to placebo pellets, E2 treatment, or E2 treatment +3‐morpholinosydnonimine (a peroxynitrite generator) and followed for 4 weeks. The infarct sizes were similar among the infarcted groups. At Day 3 after infarction, post‐infarction was associated with increased superoxide levels, which were inhibited by administering E2. E2 significantly increased myocardial IL‐10 levels and the percentage of regulatory M2 macrophages compared with the ovariectomized infarcted alone group as assessed by immunohistochemical staining, Western blot and RT‐PCR. Nerve growth factor colocalized with both M1 and M2 macrophages at the magnitude significantly higher in M1 compared with M2. At Day 28 after infarction, E2 was associated with attenuated myocardial norepinephrine levels and sympathetic hyperinnervation. These effects of E2 were functionally translated in inhibiting fatal arrhythmias. The beneficial effect of E2 on macrophage polarization and sympathetic hyperinnervation was abolished by 3‐morpholinosydnonimine. Our results indicated that E2 polarized macrophages into the M2 phenotype by inhibiting the superoxide pathway, leading to attenuated nerve growth factor‐induced sympathetic hyperinnervation after myocardial infarction.

Uridine treatment prevents myocardial injury in rat models of acute ischemia and ischemia/reperfusion by activating the mitochondrial ATP-dependent potassium channel

The effect of uridine on the myocardial ischemic and reperfusion injury was investigated. A possible mechanism of its cardioprotective action was established. Two rat models were used: (1) acute myocardial ischemia induced by occlusion of the left coronary artery for 60 min; and (2) myocardial ischemia/reperfusion with 30-min ischemia and 120-min reperfusion. In both models, treatment with uridine (30 mg/kg) prevented a decrease in cell energy supply and in the activity of the antioxidant system, as well as an increase in the level of lipid hydroperoxides and diene conjugates. This led to a reduction of the necrosis zone in the myocardium and disturbances in the heart rhythm. The blocker of the mitochondrial ATP-dependent potassium (mitoKATP) channel 5-hydroxydecanoate limited the positive effects of uridine. The data indicate that the cardioprotective action of uridine may be related to the activation of the mitoKATP channel. Intravenously injected uridine was more rapidly eliminated from the blood in hypoxia than in normoxia, and the level of the mitoKATP channel activator UDP in the myocardium after uridine administration increased. The results suggest that the use of uridine can be a potentially effective approach to the management of cardiovascular diseases.

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.

Involvement of sex hormonal regulation of K+ channels in electrophysiological and contractile functions of muscle tissues

Sex hormones, such as testosterone, progesterone, and 17β-estradiol, control various physiological functions. This review focuses on the sex hormonal regulation of K⁺ channels and the effects of such regulation on electrophysiological and contractile functions of muscles. In the cardiac tissue, testosterone and progesterone shorten action potential, and estrogen lengthens QT interval, a marker of increased risk of ventricular tachyarrhythmias. We have shown that testosterone and progesterone in physiological concentration activate KCNQ1 channels via membrane-delimited sex hormone receptor/eNOS pathways to shorten the action potential duration. Mitochondrial K⁺ channels are also involved in the protection of cardiac muscle. Testosterone and 17β-estradiol directly activate mitochondrial inner membrane K⁺ channels (Ca²⁺ activated K⁺ channel (K_Ca channel) and ATP-sensitive K⁺ channel (K_ATP channel)) that are involved in ischemic preconditioning and cardiac protection. During pregnancy, uterine blood flow increases to support fetal growth and development. It has been reported that 17β-estradiol directly activates large-conductance Ca²⁺-activated K⁺ channel (BK_Ca channel) attenuating arterial contraction. Furthermore, 17β-estradiol increases expression of BK_Ca channel β1 subunit which enhances BK_Ca channel activity by DNA demethylation. These findings are useful for understanding the mechanisms of sex or generation-dependent differences in the physiological and pathological functions of muscles, and the mechanisms of drug actions.

Editor's Choice- Reperfusion cardiac arrhythmias and their relation to reperfusion-induced cell death

Reperfusion does not only salvage ischaemic myocardium but can also cause additional cell death which is called lethal reperfusion injury. The time of reperfusion is often accompanied by ventricular arrhythmias, i.e. reperfusion arrhythmias. While both conditions are seen as separate processes, recent research has shown that reperfusion arrhythmias are related to larger infarct size. The pathophysiology of fatal reperfusion injury revolves around intracellular calcium overload and reactive oxidative species inducing apoptosis by opening of the mitochondrial protein transition pore. The pathophysiological basis for reperfusion arrhythmias is the same intracellular calcium overload as that causing fatal reperfusion injury. Therefore both conditions should not be seen as separate entities but as one and the same process resulting in two different visible effects. Reperfusion arrhythmias could therefore be seen as a potential marker for fatal reperfusion injury.

Sexual dimorphism of cardiovascular ischemia susceptibility is mediated by heme oxygenase

We investigated the gender differences in heme-oxygenase (HO) enzyme, which produces endogenous vascular protective carbon monoxide (CO). We studied (1) the activity and expression of HO enzymes in the left ventricle (LV) and aorta, (2) basal increase in basal blood pressure provoked by arginine vasopressine (AVP) in vivo, (3) the heart perfusion induced by AVP, (4) the ST segment depression provoked by adrenaline and 30 seconds later phentolamine, and (5) the aorta ring contraction induced by AVP in female and male Wistar rats. We found that HO activity and the expression of HO-1 and HO-2 were increased in female rat aorta and LV. We demonstrated that the basal blood pressure and administration of AVP provoked blood pressure response are increased in the males; the female myocardium was less sensitive towards angina. Both differences could be aggravated by the inhibition of HO. The aorta rings were more susceptible towards vasoconstriction by AVP in males; isolated heart perfusion decrease was higher in males. The HO inhibition aggravated the heart perfusion in both sexes. In conclusion, the increased HO activity and expression in females might play a role in the sexual dimorphism of cardiovascular ischemia susceptibility during the reproductive age.

Neuroprotective effects of 17β-estradiol associate with KATP in rat brain

Previous studies have indicated that estrogen protects the brain from ischemic damage and regulates K(ATP) channel activity; the present study was designed to address the involvement of K(ATP) channels in the neuroprotective effects of estrogen in focal cerebral ischemia: in experiment 1, K(ATP) mRNA and protein in the cortices of rats were compared among groups of ovariectomized rats (Ovx-1), Sham-operated rats (Sham-1), and ovariectomized rats administered 17β-estradiol (Estr-1). In experiment 2, neurobehavioral scores and infarct volume of rats were evaluated after middle cerebral artery occlusion in ovariectomized rats (Ovx-2), Sham-operated rats (Sham-2), ovariectomized female rats administered 17β-estradiol (Estr-2), and ovariectomized rats administered both 17β-estradiol and stereotactic injections of glibenclamide (Estr+G). Our results showed that the Kir6.2 and SUR1 mRNA and protein levels in the brain cortices of female ovariectomized rats were lower than those in Sham rats. However, the expression levels of Kir6.2 and SUR1 in brain cortices of ovariectomized rats recovered after supplementation with 17β-estradiol. The protective effects of 17β-estradiol were abolished by glibenclamide, a K(ATP) channel blocker. This indicates that estradiol significantly upregulates the expression of K(ATP) channel subunits and channel activity in the brain cortices of ovariectomized rats. This regulation is associated with the neuroprotective effects of estradiol.

Activity of mitochondrial ATP-dependent potassium channel in animals with different resistance to hypoxia before and after the course of hypoxic training

Activity of mitochondrial ATP-dependent potassium channel in rats with high genetically determined resistance to hypoxia was higher than in sensitive animals. Adaptation of low resistant rats to hypoxia was accompanied by activation of the channel, facilitation of potassium recycling in mitochondria, and a decrease in the rate of H2O2 formation. Our results indicate that mitochondrial ATP-dependent potassium channel plays an important role in the delayed mechanisms of animal's adaptation to hypoxia.

Concentration-dependent effects of the soy phytoestrogen genistein on the proteome of cultured cardiomyocytes

The soy-derived phytoestrogen genistein (GEN) has received attention for its potential benefits on the cardiovascular system by providing direct protection to cardiomyocytes against pathophysiological stresses. Here, we employed a proteomic approach to study the concentration-dependent effects of GEN treatments on cardiomyocytes. Cultured HL-1 cardiomyocytes were treated with low (1μM) and high (50μM) concentrations of GEN. Proteins were pre-fractionated by sequential hydrophilic/hydrophobic extraction and both protein fractions from each treatment group were separated by 2D gel electrophoresis (2DE). Overall, approximately 2,700 spots were visualized on the 2D gels. Thirty-nine and 99 spots changed in volume relative to controls (p<0.05) following the low- and high-concentration GEN treatments, respectively. From these spots, 25 and 62 protein species were identified by ESI-MS/MS and Mascot database searching, respectively. Identified proteins were further categorized according to their functions and possible links to cardioprotection were discussed. MetaCore gene ontology analysis suggested that 1μM GEN significantly impacted the anti-apoptosis process, and that both the low and high concentrations of GEN influenced the glucose catabolic process and regulation of ATPase activity. This proteomics study provides the first global insight into the molecular events triggered by GEN treatment in cardiomyocytes.

Mitochondria are sources of metabolic sink and arrhythmias

Mitochondria have long been recognized for their central role in energy transduction and apoptosis. More recently, extensive work in multiple laboratories around the world has significantly extended the role of cardiac mitochondria from relatively static arbitrators of cell death and survival pathways to highly dynamic organelles that form interactive functional networks across cardiomyocytes. These coupled networks were shown to strongly affect cardiomyocyte responses to oxidative stress by modulating cell signaling pathways that strongly impact physiological properties. Of particular importance is the role of mitochondria in modulating key electrophysiological and calcium cycling properties in cardiomyocytes, either directly through activation of a myriad of mitochondrial ion channels or indirectly by affecting cell signaling cascades, ATP levels, and the over-all redox state of the cardiomyocyte. This important recognition has ushered a renewed interest in understanding, at a more fundamental level, the exact role that cardiac metabolism, in general and mitochondria, in particular, play in both health and disease. In this article, we provide an overview of recent advances in our growing understanding of the fundamental role that cardiac mitochondria play in the genesis of lethal arrhythmias.

Functioning of the mitochondrial ATP-dependent potassium channel in rats varying in their resistance to hypoxia. Involvement of the channel in the process of animal's adaptation to hypoxia

The mechanism of tissue protection from ischemic damage by activation of the mitochondrial ATP-dependent K(+) channel (mitoK(ATP)) remains unexplored. In this work, we have measured, using various approaches, the ATP-dependent mitochondrial K(+) transport in rats that differed in their resistance to hypoxia. The transport was found to be faster in the hypoxia-resistant rats as compared to that in the hypoxia-sensitive animals. Adaptation of animals to the intermittent normobaric hypoxia increased the rate of transport. At the same time, the intramitochondrial concentration of K(+) in the hypoxia-sensitive rats was higher than that in the resistant and adapted animals. This indicates that adaptation to hypoxia stimulates not only the influx of potassium into mitochondria, but also K(+)/H(+) exchange. When mitoK(ATP) was blocked, the rate of the mitochondrial H(2)O(2) production was found to be significantly higher in the hypoxia-resistant rats than that in the hypoxia-sensitive animals. The natural flavonoid-containing adaptogen Extralife, which has an evident antihypoxic effect, increased the rate of the mitochondrial ATP-dependent K(+) transport in vitro and increased the in vivo tolerance of hypoxia-sensitive rats to acute hypoxia 5-fold. The involvement of the mitochondrial K(+) transport in the mechanism of cell adaptation to hypoxia is discussed.

Cardiac mitochondria and arrhythmias

Despite a high prevalence of sudden cardiac death throughout the world, the mechanisms that lead to ventricular arrhythmias are not fully understood. Over the last 20 years, a growing body of evidence indicates that cardiac mitochondria are involved in the genesis of arrhythmia. In this review, we have attempted to describe the role that mitochondria play in altering the heart's electrical function by introducing heterogeneity into the cardiac action potential. Specifically, we have focused on how the energetic status of the mitochondrial network can alter sarcolemmal potassium fluxes through ATP-sensitive potassium channels, creating a 'metabolic sink' for depolarizing wave-fronts and introducing conditions that favour catastrophic arrhythmia. Mechanisms by which mitochondria depolarize under conditions of oxidative stress are characterized, and the contributions of several mitochondrial ion channels to mitochondrial depolarization are presented. The inner membrane anion channel in particular opens upstream of other inner membrane channels during metabolic stress, and may be an effective target to prevent the metabolic oscillations that create action potential lability. Finally, we discuss therapeutic strategies that prevent arrhythmias by preserving mitochondrial membrane potential in the face of oxidative stress, supporting the notion that treatments aimed at cardiac mitochondria have significant potential in attenuating electrical dysfunction in the heart.

Cardioprotective effects of long-term treatment with raloxifene, a selective estrogen receptor modulator, on myocardial ischemia/reperfusion injury in ovariectomized rats

OBJECTIVE

The aim of this study was to investigate the beneficial effect of long-term treatment with raloxifene (RAL), a selective estrogen receptor modulator, on myocardial ischemia/reperfusion (MI/R) injury in ovariectomized (Ovx) rats.

METHODS

Ovariectomy was performed in female Sprague-Dawley rats 8 weeks old. Ovx rats were treated with RAL 1 or 5 mg/kg (gavage, once daily) or 17beta-estradiol (E2; 50 microg/kg SC, three times a week) for 8 weeks. The cardioprotective effect of RAL was evaluated in an open-chest anesthetized rat model of MI/R, which was induced by 40-minute left coronary artery occlusion and 100-minute reperfusion.

RESULTS

Long-term treatment with RAL 1 mg/kg significantly suppressed the duration of ventricular tachycardia elicited by MI. After MI/R, the levels of plasma creatine kinase-MB fraction and lactate dehydrogenase in Ovx rats were significantly higher than those in the sham group, which were significantly reduced by long-term treatment with RAL 1 mg/kg or E2. Neutrophil myeloperoxidase activity in ischemic myocardium markedly increased in the Ovx group, whereas long-term treatment with RAL 1 or 5 mg/kg or E2 significantly suppressed the elevation of myeloperoxidase activity. After MI/R, the protein expression of phosphorylated inhibitory kappaBalpha and caspase-3 in ischemic myocardium pronouncedly increased in the Ovx group and was attenuated by long-term treatment with RAL 1 mg/kg or E2.

CONCLUSIONS

Long-term treatment with RAL can reduce the severity of MI-induced arrhythmias and attenuate MI/R-induced damages and apoptosis in Ovx rats. This cardioprotective effect of RAL may be associated with inhibition of neutrophil infiltration and suppression of nuclear factor-kappaB activation.

PKC-permitted elevation of sarcolemmal KATP concentration may explain female-specific resistance to myocardial infarction

The female myocardium, relative to that of the male, exhibits sustained resistance to ischaemic tissue injury, a phenomenon termed sex-specific cardioprotection (SSC). SSC is dependent upon the sarcolemmal K(ATP) channel (sarcK(ATP)), and protein kinase C (PKC). Here we investigate whether PKC-mediated regulation of sarcK(ATP) concentration can explain this endogenous form of protection. Hearts from male (M) and female (F) rats were Langendorff-perfused for 30 min prior to either regional ischaemia-reperfusion (I/R), or global ischaemia (GISC). For both protocols, pre-ischaemic blockade of PKC was achieved by chelerythrine (Chel) in male (M + C) and female (F + C) hearts. Additional female hearts underwent sarcK(ATP) antagonism during I/R by HMR-1098 (HMR), either alone or in combination with Chel (HMR + Chel). GISC hearts were fractionated to assess cellular distribution of PKC and sarcK(ATP). Sex-specific infarct resistance was apparent under control I/R (F, 23 +/- 3% vs. M, 36 +/- 4%, P < 0.05) and abolished by Chel (F + C, 36 +/- 3%). Female infarct resistance was susceptible to sarcK(ATP) blockade (Control, 16 +/- 2% vs. HMR, 27 +/- 3%), and PKC blockade had no additional effect (HMR + Chel, 26 +/- 2%). The prevalence of Kir6.2 and SUR2 was higher in the sarcolemmal fractions of females (Kir6.2: F, 1.24 +/- 0.07 vs. M, 1.02 +/- 0.06; SUR2: F, 3.16 +/- 0.22 vs. M, 2.45 +/- 0.09; ratio units), but normalized by Chel (Kir6.2: F, 1.06 +/- 0.07 vs. M, 0.99 +/- 0.06; SUR2: F, 2.99 +/- 0.09 vs. M, 2.82 +/- 0.22, M; ratio units). Phosphorylation of sarcolemmal PKC was reduced by Chel (p-PKC/PKC: control, 0.43 +/- 0.02; Chel, 0.29 +/- 0.01; P < 0.01). We conclude that PKC-mediated regulation of sarcK(ATP) may account for the physiologically sustainable dependence of SSC upon both PKC and sarcK(ATP), and that this regulation involves PKC-permitted enrichment of the female sarcolemma with sarcK(ATP). As such, the PKC-sarcK(ATP) axis may represent a target for sustainable prophylactic induction of cardioprotection.

Effect of ATP-sensitive potassium channel agonists on sympathetic hyperinnervation in postinfarcted rat hearts

Although the acute administration of ATP-sensitive potassium (KATP) channel agonists provides a neuroprotection, it is unclear whether similar benefits are found by modulating sympathetic innervation in chronic settings after myocardial infarction. We assessed whether KATP channel agonists can attenuate the sprouting of cardiac sympathetic nerves after infarction. Male Wistar rats after ligating coronary artery were randomized to either saline, nicorandil, pinacidil, glibenclamide, or a combination of 1) nicorandil and glibenclamide or 2) pinacidil and glibenclamide for 4 wk. To elucidate the role of mitochondrial KATP channels in modulating nerve growth factor, 5-hydroxydecanoate was assessed in an in vitro model. The measurement of myocardial norepinephrine levels revealed a significant elevation in saline-treated infarcted rats compared with sham-operated rats, consistent with excessive sympathetic innervation. Excessive sympathetic innervation was blunted after giving the rats either nicorandil or pinacidil, compared with saline, as assessed by the immunohistochemical analysis of tyrosine hydroxylase, growth associated protein-43, and neurofilament and Western blot analysis and real-time quantitative RT-PCR of nerve growth factor. The arrhythmic scores during programmed stimulation in the saline- or glibenclamide-treated infarcted rats were significantly higher than those of rats treated with KATP channel agonists. In contrast, the beneficial effects of nicorandil and pinacidil were abolished by administering either glibenclamide or 5-hydroxydecanoate. The sympathetic hyperinnervation after infarction is attenuated by the activation of mitochondrial KATP channels. The chronic use of mitochondrial KATP channel agonists after infarction may attenuate the arrhythmogenic response to programmed electrical stimulation.

Estrogen protects the heart from ischemia-reperfusion injury via COX-2-derived PGI2

There is an accumulating body of data to suggest that estrogen mediates its cardioprotective effects via cyclooxygenase activation and synthesis of prostaglandins (PG), specifically PGI2. We hypothesized that inhibition of COX-2 would prevent estrogen's cardioprotective effects after myocardial ischemia-reperfusion. Acute treatment with 17beta-estradiol (E2; 20 microg/rabbit) increased COX-2 protein expression and activity in the myocardium. To determine the effects of COX-2 inhibition on infarct size after E2 treatment, New Zealand white rabbits were anesthetized and administered the COX-2 inhibitor nimesulide (5 mg/kg) or vehicle intravenously 30 minutes before an intravenous injection of E2. Thirty minutes after estrogen treatment, the coronary artery was occluded for 30 minutes followed by 4 hours of reperfusion. E2 significantly decreased infarct size as a percent of area at risk when compared to vehicle (18.9 +/- 3.1 versus 47.0 +/- 4.1; P < 0.001). Pretreatment with nimesulide nullified the infarct size sparing effect of E2 (55.8 +/- 5.6). Treatment with the PGI2 receptor antagonist RO3244794 also abolished the protective effects of E2 (45.3 +/- 4.5). The results indicate that estrogen protects the myocardium from ischemia-reperfusion injury through increased production of COX-2-derived PGI2. The data indicate that selective COX-2 inhibitors might counteract the potential cytoprotective effects of estrogen in premenopausal or postmenopausal women.

Estrogen-mediated protection in myocardial ischemia-reperfusion injury

Before menopause, a woman has a relatively low risk for developing cardiovascular disease. After menopause, however, the risk increases nearly twofold and cardiovascular disease remains the number one cause of death among women. Observational trials and studies in animal models of cardiovascular disease suggested that females have reduced injury after myocardial ischemia and reperfusion injury. However, two large clinical trials, the women's health initiative (WHI) and the heart estrogen and progestin replacement study (HERS), found an increase in cardiovascular incidences in women taking hormone replacement therapy. The discrepancy between these data highlights the need for further research on the mechanism of estrogen in the cardiovascular system. Animal studies have demonstrated protective effects by endogenous estrogen (gender differences) and also by the administration of exogenous estrogen. In vivo studies suggest a possible anti-inflammatory mechanism of estrogen. Exogenous estrogen has been shown to have anti-oxidant activities. Pre-treatment with estrogen prior to myocardial ischemia and reperfusion causes a decrease in neutrophil infiltration into the irreversibly injured myocardium, decrease in C-reactive protein expression, and deposition of the membrane attack complex. This review will summarize the protection afforded by estrogen as well as discuss several possible mechanisms of protection for exogenous estrogen administration.

Persistent beneficial effect of postconditioning against infarct size: role of mitochondrial K(ATP) channels during reperfusion

This study tested the hypothesis that inhibition of myocardial injury and modulation of mitochondrial dysfunction by postconditioning (Postcon) after 24 h of reperfusion is associated with activation of K(ATP) channels. Thirty dogs undergoing 60 min of ischemia and 24 h of reperfusion (R) were randomly divided into four groups:

CONTROL

no intervention at R; Postcon: three cycles of 30 s R alternating with 30 s re-occlusion were applied at R; 5-hydroxydecanoate (5-HD): the mitochondrial K(ATP) channel blocker was infused 5 min before Postcon; HMR1098: the sarcolemmal K(ATP) channel blocker was administered 5 min before Postcon. After 24 h of R, infarct size was smaller in Postcon relative to CONTROL (27 +/- 4%* Vs. 39 +/- 2% of area at risk), consistent with a reduction in CK activity (66 +/- 7* Vs. 105 +/- 7 IU/g). The infarct-sparing effect of Postcon was blocked by 5-HD (48 +/- 5%(dagger)), but was not altered by HMR1098 (29 +/- 3%*), consistent with the change in CK activity (102 +/- 8(dagger) in 5-HD and 71 +/- 6* IU/g in HMR1098). In H9c2 cells exposed to 8 h hypoxia and 3 h of reoxygenation, Postcon up-regulated expression of mito-K(ATP) channel Kir6.1 protein, maintained mitochondrial membrane potential and inhibited mitochondrial permeability transition pore (mPTP) opening evidenced by preserved fluorescent TMRE and calcein staining. The protective effects were blocked by 5-HD, but not by HMR1098. These data suggest that in a clinically relevant model of ischemia-reperfusion (1) Postcon reduces infarct size and decreases CK activity after prolonged reperfusion; (2) protection by Postcon is achieved by opening mitochondrial K(ATP) channels and inhibiting mPTP opening. *P < 0.05 Vs. CONTROL; P < 0.05 Vs. Postcon.

Estradiol abolishes reduction in cell death by the opioid agonist Met5-enkephalin after oxygen glucose deprivation in isolated cardiomyocytes from both sexes

There is evidence for differences in the response to the treatment of cardiovascular disease in men and women. In addition, there are conflicting results regarding the effectiveness of pharmacologically induced protection or ischemic preconditioning in females. We investigated whether the ability of Met5-enkephalin (ME) to reduce cell death after oxygen-glucose deprivation (OGD) is influenced by the presence of 17β-estradiol (E2) in a nitric oxide (NO)- and estrogen receptor-dependent manner. On postnatal day 7 to 8, murine cardiomyocytes from wild-type or inducible NO synthase (iNOS) knockout mice were separated by sex, isolated by collagenase digestion, cultured for 24 h, and subjected to 90 min OGD and 180 min reoxygenation at 37°C ( n = 4 to 5 replicates). Cell cultures were incubated in E2 for 15 min or 24 h before OGD. ME was used to increase cell survival. Cell death was assessed by propidium iodide. More than 300 cells were examined for each treatment. Data are presented as means ± SE. As a result, in both sexes, ME-induced cell survival was lost in the presence of E2, and the ability of ME to improve cell survival was restored after treatment with the estrogen receptor antagonist ICI-182780. Furthermore, iNOS was necessary for ME to increase cell survival following OGD in vitro. We conclude that ME-induced reduction in cell death is abolished by E2 in a sex-independent manner via activation of estrogen receptors, and this interaction is dependent on iNOS.

Ovarian steroids stimulate adenosine triphosphate-sensitive potassium (KATP) channel subunit gene expression and confer responsiveness of the gonadotropin-releasing hormone pulse generator to KATP channel modulation

The ATP-sensitive potassium (K(ATP)) channels couple intracellular metabolism to membrane potential. They are composed of Kir6.x and sulfonylurea receptor (SUR) subunits and are expressed in hypothalamic neurons that project to GnRH neurons. However, their roles in regulating GnRH secretion have not been determined. The present study first tested whether K(ATP) channels regulate pulsatile GnRH secretion, as indirectly reflected by pulsatile LH secretion. Ovariectomized rats received sc capsules containing oil, 17beta-estradiol (E(2)), progesterone (P), or E(2)+P at 24 h before blood sampling. Infusion of the K(ATP) channel blocker tolbutamide into the third ventricle resulted in increased LH pulse frequency in animals treated with E(2)+P but was without effect in all other groups. Coinfusion of tulbutamide and the K(ATP) channel opener diazoxide blocked this effect, whereas diazoxide alone suppressed LH. Effects of steroids on Kir6.2 and SUR1 mRNA expression were then evaluated. After 24hr treatment, E(2)+P produced a modest but significant increase in Kir6.2 expression in the preoptic area (POA), which was reversed by P receptor antagonism with RU486. Neither SUR1 in the POA nor both subunits in the mediobasal hypothalamus were altered by any steroid treatment. After 8 d treatment, Kir6.2 mRNA levels were again enhanced by E(2)+P but to a greater extent in the POA. Our findings demonstrate that 1) blockade of preoptic/hypothalamic K(ATP) channels produces an acceleration of the GnRH pulse generator in a steroid-dependent manner and 2) E(2)+P stimulate Kir6.2 gene expression in the POA. These observations are consistent with the hypothesis that the negative feedback actions of ovarian steroids on the GnRH pulse generator are mediated, in part, by their ability to up-regulate K(ATP) channel subunit expression in the POA.

Physiological concentration of 17beta-estradiol on sympathetic reinnervation in ovariectomized infarcted rats

17beta-Estradiol (E2) has been shown to exert antiarrhythmic effect after myocardial infarction; however, the mechanisms remain unclear. This study was performed to determine whether E2 exerts beneficial effects through attenuated sympathetic hyperreinnervation after infarction. Two weeks after ovariectomy, female Wistar rats were assigned to coronary artery ligation or sham operation. Twenty-four hours after coronary ligation, rats underwent one of five treatments: 1) sc vehicle treatment (control), 2) sc E2 treatment, 3) sc E2 treatment + tamoxifen (a potent estrogen receptor antagonist), 4) bosentan (an endothelin receptor blocker), or 5) sc E2 treatment + bosentan and followed for 4 wk. Myocardial endothelin-1 and norepinephrine levels at the remote zone revealed a significant elevation in control infarcted rats, compared with sham-operated rats, which is consistent with sympathetic hyperinnervation after infarction. Sympathetic hyperinnervation was blunted after giving the rats either E2 or bosentan, assessed by immunohistochemical analysis of tyrosine hydroxylase, growth-associated protein 43 and neurofilament, and Western blotting and real-time quantitative RT-PCR of nerve growth factor. Arrhythmic scores during programmed stimulation in E2-treated infarcted rats were significantly lower than in control-infarcted rats. Addition of bosentan did not have additional beneficial effects, compared with rats treated with E2 alone. The beneficial effect of E2 on sympathetic hyperinnervation was abolished by tamoxifen. Our data indicated that E2 has a role for sympathetic hyperinnervation after infarction, probably through an endothelin-1-depedent pathway. Chronic administration of E2 after infarction may attenuate the arrhythmogenic response to programmed electrical stimulation.

A gender-independent proarrhythmic action of 17β-estradiol in anaesthetized rabbits

Women are at increased risk of having drug-induced arrhythmias such as torsade de pointes but less susceptible to arrhythmias associated with myocardial ischaemia. We have shown previously that 17beta-estradiol had greater antiarrhythmic activity in female rats than in male rats subject to myocardial ischaemia. The aim of this work was to investigate the effects of acute administration of 17beta-estradiol in both sexes in an established in vivo model of drug-induced arrhythmias. In alpha(1)-adrenoceptor-stimulated, pentobarbital-anaesthetized rabbits, 17beta-estradiol (100, 300 or 1000 ng/kg bolus followed by 10, 30 or 100 ng/kg/min infusion) tended to increase the incidence of torsade de pointes, induced by clofilium, in both sexes: from 50% in controls to 80%, 70% and 80% in females; from 40% in controls to 60%, 70% and 80% in males with increasing doses of 17beta-estradiol (n=10 per group). The total duration of all episodes of torsade de pointes was increased significantly by the highest dose of 17beta-estradiol compared to vehicle in both female and male rabbits: from 9+/-4 s to 93+/-26 s in females; from 26+/-14 s to 96+/-20 s in males. There were no baseline differences between the sexes in heart rate, QTc interval or epicardial monophasic action potential duration. The proarrhythmic effect of acute administration of 17beta-estradiol in the alpha(1)-adrenoceptor-stimulated anaesthetized rabbit model was independent of gender. This indicates that the underlying mechanism differs from that involved in the gender-selective reduction of ischaemia-induced arrhythmias by 17beta-estradiol.

Sex influences the susceptibility to reperfusion-induced sustained ventricular tachycardia and β-adrenergic receptor blockade in conscious rats

Reperfusion after a brief period of cardiac ischemia can lead to potentially lethal arrhythmias. Importantly, there are sex-related differences in cardiac physiology and in the types and severity of cardiac arrhythmias. Therefore, we tested the hypothesis that gonadal hormones influence the susceptibility to reperfusion-induced sustained ventricular tachycardia (VT), as well as the response to β-adrenergic receptor blockade. Male and female intact and gonadectomized rats were instrumented, and arterial pressure, temperature, ECG, and cardiac output were recorded. In addition, a snare was placed around the left main coronary artery. Tension was applied to the snare for determination of susceptibility to sustained VT produced by 3 min of occlusion and reperfusion of the left main coronary artery in conscious rats. Reperfusion culminated in sustained VT in 77% (10 of 13 susceptible) of female rats and 56% (9 of 16 susceptible) of male rats ( P > 0.05, male vs. female). β-Adrenergic receptor blockade prevented sustained VT in females only [1 of 9 susceptible females (11%) vs. 6 of 9 susceptible males (67%), P < 0.05]. Ovariectomy did not significantly reduce the susceptibility to reperfusion arrhythmias [5 of 9 susceptible (56%)]. In sharp contrast, orchidectomy significantly increased the susceptibility to reperfusion arrhythmias [9 of 9 susceptible (100%)]. Finally, β-adrenergic receptor blockade prevented sustained VT in ovariectomized females [0 of 4 susceptible (0%)] and orchidectomized males [0 of 7 susceptible (0%)], but the protective effect of β-blockade was due to a reduction in heart rate in males only. Thus gonadal hormones influence the susceptibility to reperfusion-induced arrhythmias, as well as the effects and mechanisms of β-adrenergic receptor blockade.

Medroxyprogesterone acetate prevents the cardioprotective and anti-inflammatory effects of 17β-estradiol in an in vivo model of myocardial ischemia and reperfusion

Previous studies demonstrated the protective effects of estrogen administration in models of cardiovascular disease. However, there is a discrepancy between these data and those from the recent clinical trials with hormone replacement therapy in menopausal women. One possible explanation for the divergent results is the addition of progestin to the hormone regimen in the Women's Health Initiative and the Heart and Estrogen/Progestin Replacement Study trials. The aim of the present study was to examine the effects of a combination of 17β-estradiol (E2, 20 μg) and medroxyprogesterone acetate (MPA, 80 μg) on infarct size in New Zealand White rabbits. Infarct size as a percentage of the area at risk was significantly reduced by administration of E2 30 min before induction of myocardial ischemia compared with vehicle (19.5 ± 3.1 vs. 55.7 ± 2.6%, P < 0.001). However, E2 + MPA failed to elicit a reduction in infarct size (52.5 ± 4.6%), and MPA had no effect (50.8 ± 2.6%). E2 also reduced serum levels of cardiac troponin I, immune complex deposition in myocardial tissue, activation of the complement system, and lipid peroxidation. All these effects were reversed by MPA. The results suggest that MPA antagonizes the infarct-sparing effects of E2, possibly through modulation of the immune response after ischemia and reperfusion.

The Pathway-Selective Estrogen Receptor Ligand WAY-169916 Reduces Infarct Size After Myocardial Ischemia and Reperfusion by an Estrogen Receptor Dependent Mechanism

Previous studies have shown that estrogen treatment protects the heart from reperfusion injury. The adverse effects of long-term estrogen treatment limit its clinical use and emphasize the need for the development of specific pharmacological interventions such as pathway-selective estrogen receptor (ER) ligands. Pathway-selective ER ligands are compounds that retain estrogen's anti-inflammatory ability, but they are devoid of conventional estrogenic action. In the present study, the pathway-selective ER ligand WAY-169916 was assessed for its cardioprotective potential in an in vivo model of ischemia-reperfusion injury. Anesthetized, ovariectomized rabbits were administered WAY-169916 (1 mg/kg), 17beta-estradiol (E2; 20 microg/rabbit), or vehicle intravenously 30 minutes before a 30-minute occlusion and 4 hours of reperfusion. Acute treatment with either WAY-169916 or E2 resulted in a decrease in infarct size, expressed as a percent of area at risk (WAY-169916, 21.2 +/- 3.3; P < 0.001 and E2, 18.8 +/- 1.7; P < 0.001) compared with vehicle 59.4 +/- 5.4). Pretreatment with estrogen receptor antagonist ICI 182,780 significantly limited the infarct size sparing effect of both WAY-169916 and E2 when expressed as a percent of the risk region (WAY 169916, 47.4 +/- 4.4; E2, 53.01 +/- 5.0). The results demonstrate that WAY-169916 protects the heart against ischemia-reperfusion injury through an ER-dependent mechanism.

Age- and gender-related differences in mitochondrial oxygen consumption and calcium with cardioplegia and diazoxide

BACKGROUND

We have recently shown that the cardioprotection afforded by cardioplegia is affected by age and gender and is less effective in the aged female rabbit heart compared with the aged male rabbit heart. We hypothesized that these differences were due to age and gender-specific modulation of mitochondrial oxygen consumption and mitochondrial free matrix calcium ([Ca2+](Mito)) content occurring during early reperfusion.

METHODS

To test this hypothesis, 104 male and female rabbit hearts, mature (15 to 20 weeks) and aged (>32 months), were subjected to Langendorff perfusion. Control hearts were perfused for 75 minutes. Global ischemia hearts were underwent 30 minutes of equilibrium, 30 minutes of global ischemia, and 15 minutes of reperfusion. Cardioplegia (potassium/magnesium) +/- diazoxide was infused 5 minutes before global ischemia. Mitochondria were isolated from left ventricular tissue and used for the measurement of oxygen consumption and [Ca2+](Mito).

RESULTS

Mitochondrial oxygen consumption was significantly increased in the mature and aged female hearts in all treatment groups (p < 0.001 versus male). Cardioplegia +/- diazoxide modulated mitochondrial oxygen consumption, but these effects were significantly decreased in the aged heart and in the female heart (p < 0.001 each versus male). Cardioplegia (potassium/magnesium) significantly decreased [Ca2+](Mito) (p < 0.001 versus global ischemia) in aged but not mature hearts. The addition of diazoxide to potassium/magnesium significantly decreased [Ca2+](Mito) in mature and aged males (p < 0.001 versus potassium/magnesium) but not in females.

CONCLUSIONS

These results demonstrate that mitochondrial oxygen consumption and [Ca2+](Mito) are modulated by age and gender and play an important role in the differences observed between mature and aged male and female response to global ischemia and the cardioprotection afforded by cardioplegia +/- diazoxide.

Effect of pravastatin on left ventricular mass in the two-kidney, one-clip hypertensive rats

We have demonstrated that myocardial ATP-sensitive potassium (KATP) channels are implicated in the development of cardiac hypertrophy in hyperlipidemic rabbits. We investigated the effect of pravastatin on development of ventricular hypertrophy in male normolipidemic Wistar rats with two-kidney, one-clip (2K1C) hypertension and whether the attenuated hypertrophic effect was via activation of KATPchannels. Twenty-four hours after the left renal artery was clipped, rats were treated with one of the following therapies for 8 wk: vehicle, nicorandil (an agonist of KATPchannels), pravastatin, glibenclamide (an antagonist of KATPchannels), hydralazine, nicorandil plus glibenclamide, or pravastatin plus glibenclamide. Systolic blood pressure, relative left ventricular (LV) weight, and cardiomyocyte sizes significantly increased in vehicle-treated 2K1C rats compared with those in sham-operated rats. Treatment with either nicorandil or pravastatin significantly attenuated LV hypertrophy/body weight compared with the vehicle, which was further confirmed by downregulation of LV atrial natriuretic peptide mRNA. Nicorandil-induced effects were abolished by administering glibenclamide. Similarly, pravastatin-induced beneficial effects were reversed by the addition of glibenclamide, implicating KATPchannels as the relevant target. A dissociation between the effects of blood pressure and cardiac structure was noted because pravastatin and hydralazine reduced arterial pressure similarly. These results suggest a crucial role of cardiac KATPchannel system in the development of ventricular hypertrophy in the 2K1C hypertensive rats. Pravastatin is endowed with cardiac antihypertrophic properties probably through activation of KATPchannels, independent of lipid and hemodynamic changes.

Pharmacological postconditioning with the phytoestrogen genistein

Estrogens are known to activate the phosphatidyl-inosityl 3-kinase (PI3K)/Akt pathway, which is central in the cardioprotection afforded by ischemic postconditioning. Therefore, our goal was to investigate whether a phytoestrogen, genistein, could induce a pharmacological postconditioning and to investigate potential mechanisms. We used low doses of genistein in order to avoid tyrosine kinases inhibition. Thus, pentobarbital-anesthetized rabbits underwent a coronary artery occlusion followed by 4 h of reperfusion. Prior to reperfusion, they randomly received an i.v. injection of either saline (Control), 100 or 1000 microg/kg of genistein (Geni(100) and Geni(1000), respectively), and 10 or 100 microg/kg of 17beta-estradiol (17beta(10) and 17beta(100), respectively). Infarct size (IS, % area at risk) was significantly reduced in Gen(100), Gen(1000) and 17beta(100) but not in 17beta(10) (6+/-2, 16+/-5, 12+/-3 and 29+/-7%, respectively) vs. Control (35+/-4%). A significant decrease in the percentage of TUNEL-positive nuclei within infarcted area was observed in Gen(100) and 17beta(100) vs. Controls. The estrogen receptor antagonist fulvestrant (1 mg/kg i.v.) and the PI3K inhibitor wortmaninn (0.6 mg/kg) abolished the cardioprotective effect of genistein. Western blots also demonstrated an increase in Akt posphorylation in Gen(100). In the same group, in vitro mitochondrial swelling studies demonstrated a significant inhibition of calcium-induced opening of mitochondrial transition pore vs. Controls. In conclusion, genistein exerts pharmacological postconditioning with a similar potency as 17beta-estradiol through a pathway involving activation of the estrogen receptor, of PI3K/Akt and mitochondrial preservation. Therefore, genistein should not be only considered as an inhibitor of tyrosine kinase but also as a cardioprotective estrogen.

Effects of pravastatin on ventricular remodeling by activation of myocardial KATP channels in infarcted rats: role of 70-kDa S6 kinase

Reactive cardiomyocyte hypertrophy after myocardial infarction is an important risk factor for arrhythmias. Myocardial ATP-sensitive potassium (K(ATP)) channels have been implicated in attenuating cardiac hypertrophy by inhibition of 70-kDa S6 kinase. We investigated the effect of pravastatin on ventricular hypertrophy during remodeling after myocardial infarction and whether the attenuated hypertrophic effect was via activation of myocardial K(ATP) channels. Twenty-four hours after ligation of the anterior descending artery, male Wistar rats were randomized to either vehicle, nicorandil (an agonist of K(ATP) channels), pravastatin, glibenclamide (an antagonist of K(ATP) channels), or a combination of nicorandil and glibenclamide or pravastatin and glibenclamide for 4 weeks. Infarct size and mortality were similar among the infarcted groups. Cardiomyocyte sizes isolated by enzymatic dissociation after infarction significantly increased at the border zone in vehicle-treated infarcted rats compared with sham-operated rats. Rats in the nicorandil- and pravastatin-treated groups significantly attenuated cardiomyocyte hypertrophy, as compared with the vehicle-treated group. Arrhythmic scores during programmed stimulation mirrored those of cardiomyocyte hypertrophy. Increased 70-kDa S6 kinase mRNA expression in cardiac remodeling was confirmed by reverse transcription-polymerase chain reaction, consistent with the results of immunohistochemistry and Western blot for the phosphorylation of 70-kDa S6 kinase. Nicorandil-induced effects were abolished by administering glibenclamide. Similarly, the beneficial effects of pravastatin were abolished by administering glibenclamide, implicating K(ATP) channels as the relevant target. Activation of K(ATP) channels by pravastatin administration can attenuate ventricular remodeling through a S6 kinase-dependent pathway after infarction.

Neuronal differentiation of PC12 cells abolishes the expression of membrane androgen receptors

Sex steroids affect adrenal chromaffin cell function. In the present work, we have examined the expression and functional significance of membrane androgen receptor sites in normal rat adrenal chromaffin cells and in the PC12 rat pheochromocytoma cell line which can differentiate to either a neuronal or to an epithelial phenotype and expresses membrane estrogen receptor sites. Our data are as follows: (a) no cytosolic androgen receptors were found in both normal chromaffin and PC12 cells; (b) both types of chromaffin cells expressed high affinity membrane testosterone binding sites; (c) activation of these sites increased cytosolic Ca(2+), decreased catecholamine secretion and induced apoptosis; (d) NGF-induced neuronal differentiation of PC12 cells resulted in the suppression of the number of membrane testosterone sites. In conclusion, our data provide evidence for the existence of specific membrane testosterone receptors on adrenal chromaffin cells via which androgens, (some of them originating in the cortex) modulate their function. Neuronal differentiation of chromaffin cells results in a significant attenuation of these effects, via suppression of the expression of membrane androgen receptors suggesting, that the latter are specific for epithelioid chromaffin cells.

Greater antiarrhythmic activity of acute 17beta-estradiol in female than male anaesthetized rats: correlation with Ca2+ channel blockade

BACKGROUND AND PURPOSE

Female sex hormones may protect pre-menopausal women from sudden cardiac death. We therefore investigated the effects of the main female sex hormone, 17beta-estradiol, on ischaemia-induced cardiac arrhythmias and on the L-type Ca2+ current (ICaL).

EXPERIMENTAL APPROACH

In vivo experiments were performed in pentobarbital-anaesthetized rats subjected to acute coronary artery occlusion. ICaL was measured by the whole-cell patch-clamp technique, in rat isolated ventricular myocytes.

KEY RESULTS

Acute intravenous administration of 17beta-estradiol as a bolus dose followed by a continuous infusion, commencing 10 min before coronary artery occlusion, had dose-dependent antiarrhythmic activity. In female rats 300 ng kg(-1) + 30 ng kg(-1) min(-1) 17beta-estradiol significantly reduced the number of ventricular premature beats (VPBs) and the incidence of ventricular fibrillation (VF). A ten fold higher dose of 17beta-estradiol was required to cause similar effects in male rats. In vitro 17beta-estradiol reduced peak ICaL in a concentration-dependent manner. The EC50 was ten-fold higher in male myocytes (0.66 microM) than in females (0.06 microM).

CONCLUSIONS AND IMPLICATIONS

These results indicate that 17beta-estradiol has marked dose-dependent antiarrhythmic activity that is greater in female rats than in males. A similar differential potency in blocking ICaL in myocytes from female and male rats can account for this effect. This provides an explanation for the antiarrhythmic activity of 17beta-estradiol and gender-selective protection against sudden cardiac death.

Heart estrogen receptor alpha: distinct membrane and nuclear distribution patterns and regulation by estrogen

Estrogen receptor alpha (ERalpha) is present in the heart consistent with estrogen-induced modulation of cardiac function by genomic and non-genomic mechanisms, and with estrogen-mediated cardioprotective effects. We show that, in heart from adult male rats, ERalpha is detected mainly as two distinct isoforms: (i) a approximately 66 kDa isoform with the expected mass of the classical full-length ERalpha and (ii) an additional isoform of approximately 45 kDa. Differential centrifugation separated the 66 kDa isoform into the cytosolic fraction; while the 45 kDa isoform was enriched in the membrane fraction. High-resolution confocal studies show that ERalpha is distributed in the nucleus, cytosol, and various membranes including the plasmalemma. Notoriously, ERalpha labeling was very prominent in T-tubular membranes defined by alpha-actinin staining and the intercalated disks. In the T-tubules, ERalpha degree of association to alpha-actinin depends on the distribution pattern of the receptor along the T-tubules; association is high when ERalpha pattern is "continuous," while it is low when the receptor has a discontinuous "granular" distribution. Nuclear ERalpha has a distinct trabecular distribution and it is excluded from the heterochromatin, consistent with an active transcription factor. Treatment with estrogen ( approximately 4 h) produced an overall decrease in both nuclear and non-nuclear ERalpha levels and made more evident discrete ERalpha nuclear puncta uncovering cellular mechanism(s) of short term action of estrogen in the heart. The results indicate that the levels of the cardiac ERalpha isoforms are downregulated by estrogen and are differentially distributed: the full-length ERalpha is mainly compartmentalized in the cytosol and nucleus, while the 45 kDa isoform is mainly present in membrane structures. The membrane localization of ERalpha may support the rapid effects of estrogens on heart function.

Age- and gender-related differences in ischemia/reperfusion injury and cardioprotection: effects of diazoxide

BACKGROUND

Recent studies have demonstrated that aging is associated with reduced tolerance to ischemia and that the aged (not senescent) female heart has greater susceptibility to ischemia as compared with the aged male heart. Previously, we have shown that ischemia can be modulated with cardioplegia in the male heart; however, efficacy in the female heart was unknown.

METHODS

In this study, male and female mature (15 to 20 weeks) aged (>32 months) rabbit hearts (n = 134) were subjected to Langendorff perfusion. Control hearts were perfused for 180 minutes. Global ischemia hearts received 30 minutes of equilibrium, 30 minutes of global ischemia, and 120 minutes of reperfusion. Cardioplegia +/- diazoxide was infused separately, 5 minutes before global ischemia.

RESULTS

Global ischemia significantly decreased postischemic functional recovery and significantly increased infarct size in the mature and aged male and female heart (p < 0.05 versus control). The effects of global ischemia were significantly exacerbated (p < 0.05) in the aged heart as compared with the mature heart. Cardioplegia +/- diazoxide significantly increased postischemic functional recovery and significantly decreased infarct size in mature male and female hearts, but these effects were significantly decreased in the aged heart (p < 0.05) and in the aged female as compared with the aged male heart.

CONCLUSIONS

Postischemic functional recovery and infarct size are affected by age but not by gender. The cardioprotection afforded by cardioplegia is affected by age and gender with a strong age-by-gender interaction for end-diastolic pressure and infarct size. Our results indicate that currently optimized cardioplegia protocols effective in the male heart are not as efficacious in the aged female heart.

The cardioprotective effect of uridine and uridine-5'-monophosphate: the role of the mitochondrial ATP-dependent potassium channel

The activity of mitochondrial ATP-dependent potassium channel (mitoKATP) of rat heart and liver mitochondria was shown to decrease during aging. This partially explains the increase of risk of ischemia at a mature age since mitoKATP activation provides cardioprotection. We demonstrated that uridine-5'-diphosphate (UDP) possesses the property to activate mitoKATP. At a concentration of 30 microM, it reactivated mitoKATP in mitochondria, and 5-hydroxydecanoate (5-HD) eliminated this effect. In experimental animals, UDP precursors uridine and uridine-5'-monophosphate (UMP) (both 30 mg/kg, administered intravenously 5 min before coronary occlusion) decreased the myocardium ischemic alteration index (1.9 and 3.5 times, respectively) and the T-wave amplitude within 60 min after occlusion. Both effects were inhibited by Glibenclamide (Glib) and 5-HD. UMP and uridine decreased the number of premature ventricular beats 5.6 and 1.9 times and the duration of ventricular tachycardia 9.4 and 4.1 times, respectively. Glib and 5-HD inhibited the anti-arrhythmic parameters, 5-HD being less effective. Uridine and UMP decreased the duration of fibrillation 10.8 and 3.6 times, respectively, and this effect was not abolished by Glib and 5-HD. Thus, uridine and UMP, which are the precursors of UDP in the cell, possess cardioprotective properties. MitoKATP prevents mainly ischemic injuries and partially rhythm disorders.

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

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

Activation of estrogen receptor-alpha protects the in vivo rabbit heart from ischemia-reperfusion injury

The estrogen receptor (ER) mediates estrogenic activity in a variety of organs, including those in the reproductive, cardiovascular, immune, and central nervous systems. Experimental studies have demonstrated that 17beta-estradiol (E2) protects the heart from ischemia-reperfusion injury. Two estrogen receptors, ER alpha and ER beta, mediate the actions of estrogen; however, it is not certain which ER mediates the cardioprotective effects of E2. In the present study, the ER-selective agonists 4,4',4''-[4-propyl-(1H)-pyrazole-1,3,5-triyl]tris-phenol (PPT; ER alpha) and 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN; ER beta) were assessed for their cardioprotective potential in an in vivo rabbit model of ischemia-reperfusion injury. Anesthetized female rabbits were administered PPT (3 mg/kg), DPN (3 mg/kg), E2 (20 microg/rabbit), or vehicle intravenously 30 min before a 30-min occlusion of the left anterior descending coronary artery followed by 4 h of reperfusion. Acute treatment with E2 (17.7 +/- 2.9%; P < 0.001) and PPT (18.1 +/- 2.9%; P < 0.001), but not DPN (45.3 +/- 2.4%) significantly decreased infarct size as a percent of area at risk compared with vehicle (45.3 +/- 2.4%). Coadministration of PPT or E2 with the ER antagonist ICI-182,780 limited the infarct size-sparing effect of the compounds (43.8 +/- 6.6% and 40.6 +/- 5.7% respectively, expressed as a percentage of risk region). PPT reduced the release of cardiac-specific troponin-I and reduced the tissue deposition of the membrane attack complex and C-reactive protein similar to that of E2. The results indicate that activation of ER alpha, but not ER beta, is required for the observed cardioprotective effects of E2.

Mitochondrial dysfunction in cardiovascular disease

Whereas the pathogenesis of atherosclerosis has been intensively studied and described, the underlying events that initiate cardiovascular disease are not yet fully understood. A substantial number of studies suggest that altered levels of oxidative and nitrosoxidative stress within the cardiovascular environment are essential in the development of cardiovascular disease; however, the impact of such changes on the subcellular or organellar components and their functions that are relevant to cardiovascular disease inception are less understood. In this regard, studies are beginning to show that mitochondria not only appear susceptible to damage mediated by increased oxidative and nitrosoxidative stress, but also play significant roles in the regulation of cardiovascular cell function. In addition, accumulating evidence suggests that a common theme among cardiovascular disease development and cardiovascular disease risk factors is increased mitochondrial damage and dysfunction. This review discusses aspects relating mitochondrial damage and function to cardiovascular disease risk factors and disease development.

Effect of pravastatin on left ventricular mass by activation of myocardial K ATP channels in hypercholesterolemic rabbits

Epidemiological studies showed that hypercholesterolemia was associated with a higher left ventricular mass. Myocardial ATP-sensitive potassium (K(ATP)) channels have been implicated in the development of cardiac hypertrophy. We investigated the effect of pravastatin on hypercholesterolemia-induced ventricular hypertrophy and whether the attenuated hypertrophic effect was via activation of myocardial K(ATP) channels. In this study, we evaluated the hemodynamic, biochemical, and morphological responses to pravastatin in cholesterol-fed (1%) rabbits. Male New Zealand White rabbits were randomized to either vehicle, nicorandil (an agonist of K(ATP) channels), pravastatin, glibenclamide (an antagonist of K(ATP) channels), or a combination of nicorandil and glibenclamide or pravastatin and glibenclamide for 8 weeks. The left ventricular weight and left ventricular myocyte sizes increased 8 weeks after cholesterol-feeding in comparison to that in normocholesterolemic rabbits. Pravastatin administration significantly decreased the left ventricular weight by 12% and cardiomyocyte cell areas by 30%. Hyperlipidemic rabbits in the nicorandil- and pravastatin-treated groups significantly attenuated cardiomyocyte hypertrophy, as compared with the vehicle-treated group (3162 +/- 277 microm(2), 3372 +/- 228 microm(2) versus 4388 +/- 163 microm(2) in the vehicle group, both P < 0.0001, respectively). Nicorandil-induced effects were abolished by administering glibenclamide. Similarly, pravastatin-induced beneficial effects were reversed by the addition of glibenclamide, implicating K(ATP) channels as the relevant target. The results of the present study suggest a pathogenetic role of K(ATP) channels in hypercholesterolemia-induced ventricular hypertrophy. The antihypertropic effects of pravastatin may be related to activation of K(ATP) channels, and result in an amelioration of cardiomyocyte hypertrophy development by an atherogenic diet.

SEX DIFFERENCES IN THE MYOCARDIAL INFLAMMATORY RESPONSE TO ACUTE INJURY

Hemorrhage, trauma, ischemia/reperfusion, burn, and sepsis each lead to cardiac dysfunction. These insults lead to an inflammatory cascade, which plays an important role in this process. Gender has been shown to influence the inflammatory response, as well as outcomes after acute injury. The mechanisms by which gender affects the inflammatory response to and the outcome of acute injury are being actively investigated. We searched PubMed for articles in the English language by using the search words sex, gender, estrogen, testosterone, inflammation, acute injury, ischemia reperfusion, sepsis, trauma, and burns. These were used in various combinations. We read the abstracts of the relevant titles to confirm their relevance, and the full articles were then extracted. References from extracted articles were checked for any additional relevant articles. This review will examine evidence for gender differences in the outcome to acute injury, explain the myocardial inflammatory response to acute injury, and elucidate the various mechanisms by which gender affects the myocardial response to acute injury.

17Beta-estradiol as a receptor-mediated cardioprotective agent

Cardiac tissue that undergoes an ischemic episode exhibits irreversible alterations that become more extensive upon reperfusion. Estrogen treatment has been reported to protect against reperfusion injury, but the mechanism remains unknown. The cardioprotective effects of 17beta-estradiol, a biologically active form of the hormone, and 17alpha-estradiol were assessed in an in vivo occlusion-reperfusion model. Anesthetized, ovariectomized rabbits were administered 17beta-estradiol (20 microg), 17alpha-estradiol (1 mg), or vehicle intravenously 30 min before a 30-min occlusion of the left anterior descending (LAD) coronary artery followed by 4 h of reperfusion. Infarct size as a percentage of area at risk decreased in the 17beta-estradiol-treated group (18.8 +/- 1.7) compared with 17alpha-estradiol (41.9 +/- 4.8; P < 0.01) or vehicle groups (48 +/- 5.5; P < 0.001). Similar results were obtained when infarct size was expressed as a percentage of total left ventricle. The second objective of the study was to assess fulvestrant (Faslodex, ICI 182,780), an estrogen receptor antagonist, for its effects on infarct size in ovariectomized female rabbits treated with 17beta-estradiol. ICI 182,780 was administered intravenously 1 h before the administration of 17beta-estradiol (20 microg) or vehicle. The hearts were subjected to 30-min LAD coronary artery occlusion and 4 h of reperfusion. Pretreatment with ICI 182,780 significantly limited the infarct size sparing effect of 17beta-estradiol when expressed as a percentage of the risk region (53.0 +/- 5.0). The results indicate that 17beta-estradiol protects the heart against ischemia-reperfusion injury and that the observed cardioprotection is mediated by the estrogen receptor.

Impairment of myocardial protection in type 2 diabetic patients

Diabetic patients are more prone to develop postinfarction complications. It remained unclear whether diabetes mellitus- or sulfonylureas-associated changes of ATP-sensitive potassium (K(ATP)) channels, an integral player in ischemic preconditioning, are responsible for the increased mortality. The purpose of this study was to determine the impact of diabetes mellitus per se and different sulfonylurea administration on cardioprotective effects in diabetic patients undergoing coronary angioplasty. Myocardial ischemia after coronary angioplasty was evaluated in 20 nondiabetic and 23 diabetic patients chronically taking either glibenclamide or glimepiride. Nondiabetic patients treated with glimepiride significantly lowered the ischemic burden assessed by an ST-segment shift, chest pain score, and myocardial lactate extraction ratios compared with the glibenclamide-treated patients, implying that acute administration of glimepiride did not abolish cardioprotection. In the diabetic glibenclamide-treated group, the reduction in the ST-segment shift afforded by nicorandil in the first inflation (-58% vs. the first inflation in the glibenclamide group alone) was similar to that afforded by preconditioning (-59% during the second vs. the first inflation). In glimepiride-treated groups, the magnitude of attenuated lactate production was less in diabetes than that in nondiabetes at the second inflation, suggesting that diabetes mellitus per se plays a role in determining lactate production. Our results show that both diabetes mellitus and sulfonylureas can act in synergism to inhibit activation of K(ATP) channels in patients undergoing coronary angioplasty. The degree of inhibition assessed by metabolic and electrocardiographic parameters is less severe during treatment with glimepiride than with glibenclamide. Restitution of a preconditioning response in glimepiride-treated patients may be the potential beneficial mechanism.

Differential role of K(ATP) channels activated by conjugated estrogens in the regulation of myocardial and coronary protective effects

BACKGROUND

We have demonstrated that estrogen can reduce myocardial injury in ischemia-reperfusion via activation of ATP-sensitive potassium (K(ATP)) channels. We sought to determine whether the protective effect of estrogen extends to epicardial coronary artery with attenuated vasoconstriction in patients after angioplasty by activation of such channels.

METHODS AND RESULTS

The study was designed to prospectively investigate 41 consecutive patients scheduled for elective coronary angioplasty. Pretreatment with estrogen limited myocardial ischemia during coronary occlusion and attenuated postangioplasty coronary vasoconstriction at the dilated and distal segments. An inhibitor of K(ATP) channels, glibenclamide, did not affect coronary vasomotor response, although it abolished the beneficial effect of estrogen on myocardial ischemia. Patients to whom estrogen was administered after the second balloon deflation experienced a similar magnitude of myocardial ischemia as controls but showed significantly attenuated vasoconstriction compared with controls (P=0.0001). Endothelin-1 levels from the great cardiac vein rose significantly from 1.9+/-0.4 to 3.1+/-0.6 pg/mL (P=0.001) 15 minutes after angioplasty in the control group; this was attenuated after estrogen was administered. Significant correlation was found between the changes in coronary vasomotion of the dilated segment and endothelin-1 levels (r=0.65, P<0.0001).

CONCLUSIONS

These results demonstrate that estrogen is protective against both myocardial ischemia and coronary vasoconstriction through different mechanisms. The myocardial effect of estrogen was abolished by glibenclamide, which suggests that the cardioprotective effect of estrogen may result from activation of K(ATP) channels. In contrast, estrogen-induced attenuated vasoconstriction is associated with an attenuated release of endothelin-1, independent of K(ATP) activation.