High placental expression of FLT1, LEP, PHYHIP and IL3RA - In persons of African ancestry with severe preeclampsia.

INTRODUCTION: Mortality from preeclampsia (PE) and PE-associated morbidities are 3-to 5-fold higher in persons of African ancestry than in those of Asian and European ancestries. METHODS: To elucidate placental contribution to worse PE outcomes in African ancestry pregnancies, we performed bulk RNA sequencing on 50 placentas from persons with severe PE (sPE) of African (n = 9), Asian (n = 18) and European (n = 23) ancestries and 73 normotensive controls of African (n = 10), Asian (n = 15) and European (n = 48) ancestries. RESULTS: Previously described canonical preeclampsia genes, involved in metabolism and hypoxia/angiogenesis including: LEP, HK2, FSTL3, FLT1, ENG, TMEM45A, ARHGEF4 and HTRA1 were upregulated sPE versus normotensive placentas across ancestries. LTF, NPR3 and PHYHIP were higher in African vs. Asian ancestry sPE placentas. Allograft rejection/adaptive immune response genes were upregulated in placentas from African but not in Asian or European ancestry sPE patients; IL3RA was of particular interest because the patient with the highest placental IL3RA expression, a person of African ancestry with sPE, developed postpartum cardiomyopathy, and was the only patient out of 123, that developed this condition. Interestingly, the sPE patients with the highest IL3RA expression among persons of Asian and European ancestries developed unexplained tachycardia peripartum, necessitating echocardiography in the European ancestry patient. The association between elevated placental IL3RA levels and unexplained tachycardia or peripartum cardiomyopathy was found to be significant in the 50 sPE patients (p = .0005). DISCUSSION: High placental upregulation of both canonical preeclampsia and allograft rejection/adaptive immune response genes may contribute to worse PE outcomes in African ancestry sPE patients.

Hemosiderin Accumulation in Liver Decreases Iron Availability in Tachycardia-Induced Porcine Congestive Heart Failure Model.

Despite advances in the management of iron deficiency in heart failure (HF), the mechanisms underlying the effects of treatment remain to be established. Iron distribution and metabolism in HF pathogenesis need to be clarified. We used a porcine tachycardia-induced cardiomyopathy model to find out how HF development influences hepatic and myocardial iron storing, focusing on ferritin, the main iron storage protein. We found that cumulative liver congestion (due to the decrease of heart function) overwhelms its capacity to recycle iron from erythrocytes. As a consequence, iron is trapped in the liver as poorly mobilized hemosiderin. What is more, the ferritin-bound Fe3+ (reflecting bioavailable iron stores), and assembled ferritin (reflecting ability to store iron) are decreased in HF progression in the liver. We demonstrate that while HF pigs show iron deficiency indices, erythropoiesis is enhanced. Renin-angiotensin-aldosterone system activation and hepatic hepcidin suppression might indicate stress erythropoiesisinduced in HF. Furthermore, assembled ferritin increases but ferritin-bound Fe3+ is reduced in myocardium, indicating that a failing heart increases the iron storage reserve but iron deficiency leads to a drop in myocardial iron stores. Together, HF in pigs leads to down-regulated iron bioavailability and reduced hepatic iron storage making iron unavailable for systemic/cardiac needs.

Hemin blunts the depressant effect of chronic nicotine on reflex tachycardia via activation of central NOS/PI3K pathway in female rats.

BACKGROUND: Chronic nicotine administration impairs reflex chronotropic responses that follow arterial baroreceptor unloading in female rats with repleted, but not depleted (ovariectomized, OVX), estrogen (E2). This study investigated whether products of nitric oxide synthase (NOS) and/or heme oxygenase (HO) and related soluble guanylate cyclase (sGC)/phosphatidylinositol 3-kinase (PI3K)/mitogen-activated protein kinases (MAPKs) signaling mediate the E2-sensitive depressant effect of nicotine on reflex tachycardia. METHODS: Baroreflex curves relating reflex tachycardic responses to falls in blood pressure (BP) generated by sodium nitroprusside (SNP) were established in conscious female rats and slopes of the curves were taken as measures of baroreflex sensitivity (BRS). RESULTS: Nicotine (2 mg/kg/day ip, 14 days) reduced BRS in OVX rats treated with E2 but not vehicle. Baroreceptor dysfunction in nicotine-treated OVXE2 rats was abolished after iv treatment with hemin (HO inducer) but not l-arginine (NOS substrate) denoting the importance of reduced availability of carbon monoxide, but not NO, in the nicotine effect. The favorable BRS effect of hemin was abolished after intracisternal (ic) administration of L-NAME (NOS inhibitor) or wortmannin (PI3 K inhibitor). Central circuits of MAPKs do not seem to contribute to the baroreflex facilitatory effect of hemin because the latter was preserved after central inhibition of MAPKERK (PD98059), MAPKp38 (SB203580) or MAPKJNK (SP600125). Likewise, sGC inhibition (ODQ) or E2 receptor blockade (ICI182780) failed to alter the hemin effect. CONCLUSION: The activation of central NOS/PI3K signaling following HO upregulation improves the E2-dependent depressant effect of nicotine on reflex tachycardia.

Calcium Dynamics Mediated by the Endoplasmic/Sarcoplasmic Reticulum and Related Diseases.

The flow of intracellular calcium (Ca2+) is critical for the activation and regulation of important biological events that are required in living organisms. As the major Ca2+ repositories inside the cell, the endoplasmic reticulum (ER) and the sarcoplasmic reticulum (SR) of muscle cells are central in maintaining and amplifying the intracellular Ca2+ signal. The morphology of these organelles, along with the distribution of key calcium-binding proteins (CaBPs), regulatory proteins, pumps, and receptors fundamentally impact the local and global differences in Ca2+ release kinetics. In this review, we will discuss the structural and morphological differences between the ER and SR and how they influence localized Ca2+ release, related diseases, and the need for targeted genetically encoded calcium indicators (GECIs) to study these events.

Histopathological and Immunological Characteristics of Tachycardia-Induced Cardiomyopathy.

BACKGROUND: Tachycardiomyopathy or tachycardia-induced cardiomyopathy (TCM) has been known for decades as a reversible form of nonischemic cardiomyopathy. However, its mechanism and properties remain poorly understood. OBJECTIVES: The current study investigated endomyocardial biopsy samples from patients with TCM and compared them with samples from patients with dilated cardiomyopathy (DCM) and inflammatory cardiomyopathy (ICM). METHODS: The study included 189 patients with new-onset heart failure and severely reduced ejection fraction not caused by valvular or ischemic heart disease. Nineteen patients retrospectively fulfilled common criteria of TCM, 79 patients had a diagnosis of DCM, and 91 had a diagnosis of ICM. RESULTS: Patients with TCM, on the basis of clinical criteria, had stronger myocardial expression of major histocompatibility complex class II molecule and enhanced infiltration of CD68+ macrophages compared with patients with DCM. Furthermore, when compared with patients with ICM, the presence of T cells and macrophages was significantly reduced in TCM. Myocardial fibrosis was detected to a significantly lower degree in patients with TCM compared with patients with DCM and ICM. Electron microscopic examination revealed severe structural changes in patients with TCM. A disturbed distribution pattern of mitochondria was predominantly present in TCM. Quantitative assessment of myocyte morphology revealed significantly enhanced myocyte size compared with patients with ICM. Ribonucleic acid expression analysis identified changes in metabolic pathways among the patient groups. CONCLUSIONS: TCM is characterized by changes in cardiomyocyte and mitochondrial morphology accompanied by a macrophage-dominated cardiac inflammation. Thus, further prospective studies are warranted to characterize patients with TCM by endomyocardial biopsy more clearly.

Changes in cardiovascular responses to chemoreflex activation of rats recovered from protein restriction are not related to AT1 receptors.

NEW FINDINGS: What is the central question of this study? In this study, we sought to investigate whether cardiovascular responses to peripheral chemoreflex activation of rats recovered from protein restriction are related to activation of AT1 receptors. What is the main finding and its importance? This study highlights the fact that angiotensinergic mechanisms activated by AT1 receptors do not support increased responses to peripheral chemoreflex activation by KCN in rats recovered from protein restriction. Also, we found that protein restriction led to increased resting ventilation in adult rats, even after recovery. The effects of a low-protein diet followed by recovery on cardiorespiratory responses to peripheral chemoreflex activation were tested before and after systemic angiotensin II type 1 (AT1 ) receptor antagonism. Male Fischer rats were divided into control and recovered (R-PR) groups after weaning. The R-PR rats were fed a low-protein (8%) diet for 35 days and recovered with a normal protein (20%) diet for 70 days. Control rats received a normal protein diet for 105 days (CG105 ). After cannulation surgery, mean arterial pressure, heart rate, respiratory frequency, tidal volume and minute ventilation were acquired using a digital recording system in freely moving rats. The role of angintensin II was evaluated by systemic antagonism of AT1 receptors with losartan (20 mg kg-1 i.v.). The peripheral chemoreflex was elicited by increasing doses of KCN (20-160 µg kg min-1 , i.v.). At baseline, R-PR rats presented increased heart rate and minute ventilation (372 ± 34 beats min-1 and 1.274 ± 377 ml kg-1  min-1 ) compared with CG105 animals (332 ± 22 beats min-1 and 856 ± 112 ml kg-1  min-1 ). Mean arterial pressure was not different between the groups. Pressor and bradycardic responses evoked by KCN (60 µg kg-1 ) were increased in R-PR (+45 ± 13 mmHg and -77 ± 47 beats min-1 ) compared with CG105 rats (+25 ± 17 mmHg and -27 ± 28 beats min-1 ), but no difference was found in the tachypnoeic response. These differences were preserved after losartan. The data suggest that angiotensin II acting on AT1 receptors may not be associated with the increased heart rate, increased minute ventilation and acute cardiovascular responses to peripheral chemoreflex activation in rats that underwent postweaning protein restriction followed by recovery.

Twenty years of vasoplegic syndrome treatment in heart surgery. Methylene blue revised / Vinte anos de tratamento da síndrome vasoplégica em cirurgia cardíaca. Azul de metileno revisado

Objective: This study was conducted to reassess the concepts established over the past 20 years, in particular in the last 5 years, about the use of methylene blue in the treatment of vasoplegic syndrome in cardiac surgery. Methods: A wide literature review was carried out using the data extracted from: MEDLINE, SCOPUS and ISI WEB OF SCIENCE. Results: The reassessed and reaffirmed concepts were 1) MB is safe in the recommended doses (the lethal dose is 40 mg/kg); 2) MB does not cause endothelial dysfunction; 3) The MB effect appears in cases of NO up-regulation; 4) MB is not a vasoconstrictor, by blocking the cGMP pathway it releases the cAMP pathway, facilitating the norepinephrine vasoconstrictor effect; 5) The most used dosage is 2 mg/kg as IV bolus, followed by the same continuous infusion because plasma concentrations sharply decrease in the first 40 minutes; and 6) There is a possible "window of opportunity" for MB's effectiveness. In the last five years, major challenges were: 1) Observations about side effects; 2) The need for prophylactic and therapeutic guidelines, and; 3) The need for the establishment of the MB therapeutic window in humans. Conclusion: MB action to treat vasoplegic syndrome is time-dependent. Therefore, the great challenge is the need, for the establishment the MB therapeutic window in humans. This would be the first step towards a systematic guideline to be followed by possible multicenter studies. .

Objetivo: O presente estudo foi realizado com a finalidade de reavaliar conceitos estabelecidos em 20 anos, com ênfase nos últimos 5 anos, sobre a utilização do azul de metileno no tratamento da síndrome vasoplégica em cirurgia cardíaca. Métodos: Foram considerados dados da literatura utilizando-se três bases de dados (MEDLINE, SCOPUS e ISI Web of Science). Resultados: Os conceitos reavaliados e reafirmados foram: 1) Nas doses recomendadas o AM é seguro (a dose letal é de 40 mg/kg); 2) O AM não causa disfunção endotelial; 3) O efeito do AM só aparece em caso de supra nivelamento do NO; 4) O AM não é um vasoconstritor, pelo bloqueio da via GMPc ele libera a via do AMPc, facilitando o efeito vasoconstritor da norepinefrina; 5) A dosagem mais utilizada é de 2 mg/kg, como bolus EV, seguida de infusão contínua porque as concentrações plasmáticas decaem fortemente nos primeiros 40 minutos, e; 6) Existe uma "janela de oportunidade" precoce para efetividade do AM. Nos últimos cinco anos, os principais desafios foram: 1) Observações de efeitos colaterais; 2) A necessidade de diretrizes, e; 3) A necessidade da determinação de uma janela terapêutica para o uso do AM em humanos. Conclusão: O efeito do AM no tratamento da SV é dependente do tempo, portanto, o grande desafio atual é a necessidade do estabelecimento da janela terapêutica do AM em humanos. Esse seria o primeiro passo para a sistematização de uma diretriz a ser seguida por possíveis estudos multicêntricos. .

Effects of the angiotensin-(1-7)/Mas/PI3K/Akt/nitric oxide axis and the possible role of atrial natriuretic peptide in an acute atrial tachycardia canine model.

OBJECTIVE: To investigate the effects of the angiotensin-(1-7) signaling pathway and the possible role of atrial natriuretic peptide (ANP) on atrial electrical remodeling in canines with acute atrial tachycardia. METHODS: Forty dogs were randomly assigned to eight groups (five dogs/group): sham, paced control, paced + angiotensin-(1-7), paced + angiotensin-(1-7) + Mas inhibitor, paced + angiotensin-(1-7) + Akt inhibitor, paced + angiotensin-(1-7) + PI3K inhibitor, paced + angiotensin-(1-7) + nitric oxide (NO) inhibitor, and paced + angiotensin-(1-7) + A-71915 (ANP receptor antagonist). Rapid atrial pacing was maintained at 600 bpm for 2 h for all groups, except the sham group, and angiotensin-(1-7) (6 µg kg(-1) h(-1)), Mas inhibitor (5.83 µg kg(-1) h(-1)), Akt inhibitor (2.14 µg kg(-1) h(-1)), PI3K inhibitor (2.86 µg kg(-1) h(-1)), NO synthase inhibitor (180 µg kg(-1)h(-1)), or A-71915 (0.30 µg kg(-1) h(-1)) were administered intravenously. Atrial effective refractory periods, inducibility, and duration of atrial fibrillation (pacing cycle lengths: 300, 250, and 200 ms), and left atrial ANP concentrations were measured. RESULTS: After pacing, the atrial effective refractory periods at the six sites shortened with increased inducibility and duration of atrial fibrillation, which was attenuated by angiotensin-(1-7), and increased ANP concentrations, which was promoted by angiotensin-(1-7) (paced control vs. sham; P < 0.05). All inhibitors and A-71915 blocked the electrophysiological effects of angiotensin-(1-7). ANP secretion induced by angiotensin-(1-7) was also blocked by all inhibitors. CONCLUSION: Angiotensin-(1-7) prevented acute electrical remodeling in canines with acute atrial tachycardia via the angiotensin-(1-7)/Mas/PI3K/Akt/NO signaling pathway. ANP was related to the anti-arrhythmic effects of angiotensin-(1-7).

MicroRNA-1 downregulation increases connexin 43 displacement and induces ventricular tachyarrhythmias in rodent hypertrophic hearts.

Downregulation of the muscle-specific microRNA-1 (miR-1) mediates the induction of pathologic cardiac hypertrophy. Dysfunction of the gap junction protein connexin 43 (Cx43), an established miR-1 target, during cardiac hypertrophy leads to ventricular tachyarrhythmias (VT). However, it is still unknown whether miR-1 and Cx43 are interconnected in the pro-arrhythmic context of hypertrophy. Thus, in this study we investigated whether a reduction in the extent of cardiac hypertrophy could limit the pathological electrical remodeling of Cx43 and the onset of VT by modulating miR-1 levels. Wistar male rats underwent mechanical constriction of the ascending aorta to induce pathologic left ventricular hypertrophy (LVH) and afterwards were randomly assigned to receive 10mg/kg valsartan, VAL (LVH+VAL) delivered in the drinking water or placebo (LVH) for 12 weeks. Sham surgery was performed for control groups. Programmed ventricular stimulation reproducibly induced VT in LVH compared to LVH+VAL group. When compared to sham controls, rats from LVH group showed a significant decrease of miR-1 and an increase of Cx43 expression and its ERK1/2-dependent phosphorylation, which displaces Cx43 from the gap junction. Interestingly, VAL administration to rats with aortic banding significantly reduced cardiac hypertrophy and prevented miR-1 down-regulation and Cx43 up-regulation and phosphorylation. Gain- and loss-of-function experiments in neonatal cardiomyocytes (NCMs) in vitro confirmed that Cx43 is a direct target of miR-1. Accordingly, in vitro angiotensin II stimulation reduced miR-1 levels and increased Cx43 expression and phosphorylation compared to un-stimulated NCMs. Finally, in vivo miR-1 cardiac overexpression by an adenoviral vector intra-myocardial injection reduced Cx43 expression and phosphorylation in mice with isoproterenol-induced LVH. In conclusion, miR-1 regulates Cx43 expression and activity in hypertrophic cardiomyocytes in vitro and in vivo. Treatment of pressure overload-induced myocyte hypertrophy reduces the risk of life-threatening VT by normalizing miR-1 expression levels with the consequent stabilization of Cx43 expression and activity within the gap junction.

Role of CaMKII and ROS in rapid pacing-induced apoptosis.

Tachycardia promotes cell death and cardiac remodeling, leading to congestive heart failure. However, the underlying mechanism of tachycardia- or rapid pacing (RP)-induced cell death remains unknown. Myocyte loss by apoptosis is recognized as a critical factor in the progression to heart failure and simulation of tachycardia by RP has been shown to increase the intracellular levels of at least two potentially proapoptotic molecules, Ca(2+) and reactive oxygen species (ROS). However, whether these molecules mediate tachycardia- or RP-induced cell death has yet to be determined. The aim of this study was to examine the subcellular mechanisms underlying RP-induced apoptosis. For this purpose rat ventricular myocytes were maintained quiescent or paced at 0.5, 5 and 8Hz for 1hr. RP at 5 and 8Hz decreased myocyte viability by 58±3% and 75±6% (n=24), respectively, compared to cells maintained at 0.5Hz, and increased caspase-3 activity and Bax/Bcl-2 ratio, indicative of apoptosis. RP-induced cell death and apoptosis were prevented when pacing protocols were conducted in the presence of either the ROS scavenger, MPG, or nifedipine to reduce Ca(2+) entry or the CaMKII inhibitors, KN93 and AIP. Consistently, myocytes from transgenic mice expressing a CaMKII inhibitory peptide (AC3-I) were protected against RP-induced cell death. Interestingly, tetracaine and carvedilol used to reduce ryanodine receptor (RyR) diastolic Ca(2+) release, and ruthenium red used to prevent Ca(2+) entry into the mitochondria prevented RP-induced cell death, whereas PI3K inhibition with Wortmannin exacerbated pacing-induced cell mortality. We conclude that CaMKII activation and ROS production are involved in RP-induced apoptosis. Particularly, our results suggest that CaMKII-dependent posttranslational modifications of the cardiac ryanodine receptor (RyR) leading to enhanced diastolic Ca(2+) release and mitochondrial Ca(2+) overload could be the underlying mechanism involved. We further show that RP simultaneously activates a protective cascade involving PI3K/AKT signaling which is however, insufficient to completely suppress apoptosis.

Activation of angiotensin-converting enzyme 2/angiotensin-(1-7)/Mas axis attenuates the cardiac reactivity to acute emotional stress.

Recent data indicate the brain angiotensin-converting enzyme/ANG II/AT1 receptor axis enhances emotional stress responses. In this study, we investigated whether its counterregulatory axis, the angiotensin-converting enzyme 2 (ACE2)/ANG-(1-7)/Mas axis, attenuate the cardiovascular responses to acute emotional stress. In conscious male Wistar rats, the tachycardia induced by acute stress (air jet 10 l/min) was attenuated by intravenous injection of ANG-(1-7) [Δ heart rate (HR): saline 136 ± 22 vs. ANG-(1-7) 61 ± 25 beats/min; P < 0.05]. Peripheral injection of the ACE2 activator compound, XNT, abolished the tachycardia induced by acute stress. We found a similar effect after intracerebroventricular injections of either ANG-(1-7) or XNT. Under urethane anesthesia, the tachycardia evoked by the beta-adrenergic agonist was markedly reduced by ANG-(1-7) [ΔHR: saline 100 ± 16 vs. ANG-(1-7) 18 ± 15 beats/min; P < 0.05]. The increase in renal sympathetic nerve activity (RSNA) evoked by isoproterenol was also abolished after the treatment with ANG-(1-7) [ΔRSNA: saline 39% vs. ANG-(1-7) -23%; P < 0.05]. The tachycardia evoked by disinhibition of dorsomedial hypothalamus neurons, a key nucleus for the cardiovascular response to emotional stress, was reduced by ∼45% after intravenous injection of ANG-(1-7). In cardiomyocyte, the incubation with ANG-(1-7) (1 µM) markedly attenuated the increases in beating rate induced by isoproterenol. Our data show that activation of the ACE2/ANG-(1-7)/Mas axis attenuates stress-induced tachycardia. This effect might be either via the central nervous system reducing anxiety level and/or interfering with the positive chronotropy mediated by activation of cardiac ß adrenergic receptors. Therefore, ANG-(1-7) might contribute to reduce the sympathetic load to the heart during situations of emotional stress, reducing the cardiovascular risk.

Expression and complex formation of MMP9, MMP2, NGAL, and TIMP1 in porcine myocardium but not in skeletal muscles in male pigs with tachycardia-induced systolic heart failure.

Matrix metalloproteinases (MMPs) are involved in the remodeling of extracellular matrix in various tissues. Their functioning could be related to the formation of complexes, containing MMP9, MMP2, tissue inhibitor of metalloproteinases type 1 (TIMP1), and neutrophil gelatinase-associated lipocalin (NGAL). Such complexes have not been investigated in either myocardial or skeletal muscles. We examined 20 male pigs with heart failure (HF), and 5 sham-operated animals. There were no differences in the mRNA expression of MMP9, MMP2, TIMP1, and NGAL between diseased and healthy animals, in either left ventricle (LV) myocardium or skeletal muscles. In LV from both diseased and healthy animals, in nonreducing and nondenaturing conditions, we demonstrated the presence of high molecular weight (HMW) complexes (130, 170, and 220 kDa) containing MMP9, TIMP1, and NGAL (also MMP2 in 220 kDa complex) without proteolytic activity, and a proteolytically active 115 kDa MMP9 form together with 72 and 68 kDa bands (proMMP2 and MMP2). Proteolytically active bands were also spontaneously released from HMW complexes. In skeletal muscles from both diseased and healthy animals, in nonreducing and nondenaturing conditions, we found no HMW complexes, and proteolytic activity was associated with the presence of 72 and 68 kDa bands (proMMP2 and MMP2).

Neurons of the A5 region are required for the tachycardia evoked by electrical stimulation of the hypothalamic defence area in anaesthetized rats.

In order to assess the possible interactions between the pontine A5 region and the hypothalamic defence area (HDA), we have examined the pattern of double staining for c-Fos protein immunoreactivity (c-Fos-ir) and tyrosine hydroxylase, throughout the rostrocaudal extent of the A5 region in spontaneously breathing anaesthetized male Sprague-Dawley rats during electrical stimulation of the HDA. Activation of the HDA elicited a selective increase in c-Fos-ir with an ipsilateral predominance in catecholaminergic and non-catecholaminergic A5 somata (P < 0.001 in both cases). A second group of experiments was done to examine the importance of the A5 region in modulating the cardiorespiratory response evoked from the HDA. Cardiorespiratory changes were analysed in response to electrical stimulation of the HDA before and after ipsilateral microinjection of muscimol within the A5 region. Stimulation of the HDA evoked an inspiratory facilitatory response, consisting of an increase in respiratory rate (P < 0.001) due to a decrease in expiratory time (P < 0.01). The respiratory response was accompanied by a pressor response (P < 0.001) and tachycardia (P < 0.001). After muscimol microinjection within the A5 region, pressor and heart rate responses to HDA stimulation were reduced (P < 0.01 and P < 0.001, respectively). The respiratory response persisted unchanged. Finally, to confirm functional interactions between the HDA and the A5 region, extracellular recordings of putative A5 neurones were obtained during HDA stimulation. Seventy-five A5 cells were recorded, 35 of which were affected by the HDA (47%). These results indicate that neurones of the A5 region participate in the cardiovascular response evoked from the HDA. The possible mechanisms involved in these interactions are discussed.

Thyroid hormone is required for hypothalamic neurons regulating cardiovascular functions.

Thyroid hormone is well known for its profound direct effects on cardiovascular function and metabolism. Recent evidence, however, suggests that the hormone also regulates these systems indirectly through the central nervous system. While some of the molecular mechanisms underlying the hormone's central control of metabolism have been identified, its actions in the central cardiovascular control have remained enigmatic. Here, we describe a previously unknown population of parvalbuminergic neurons in the anterior hypothalamus that requires thyroid hormone receptor signaling for proper development. Specific stereotaxic ablation of these cells in the mouse resulted in hypertension and temperature-dependent tachycardia, indicating a role in the central autonomic control of blood pressure and heart rate. Moreover, the neurons exhibited intrinsic temperature sensitivity in patch-clamping experiments, providing a new connection between cardiovascular function and core temperature. Thus, the data identify what we believe to be a novel hypothalamic cell population potentially important for understanding hypertension and indicate developmental hypothyroidism as an epigenetic risk factor for cardiovascular disorders. Furthermore, the findings may be beneficial for treatment of the recently identified patients that have a mutation in thyroid hormone receptor α1.

A heartfelt response: new thyroid hormone-sensitive neurons in the hypothalamus.

Thyroid hormone is a well-known regulator of metabolic and cardiovascular functions, and signaling through thyroid receptors has differential effects on cells depending on the receptor isoform that they express. In this issue of the JCI, Mittag et al. provide evidence that thyroid hormone receptors are essential for the formation of a population of parvalbuminergic neurons in the anterior hypothalamus, linking, for the first time, impaired thyroid hormone signaling during development to cellular deficits in the hypothalamus. Since this newly discovered cell group is predicted to play a role in regulating cardiovascular function, these findings suggest that developmental hypothyroidism may be the cause of cardiovascular disorders later in life.

Estrogen provokes the depressant effect of chronic nicotine on vagally mediated reflex chronotropism in female rats.

We recently reported that acute nicotine impairs reflex tachycardic activity in estrogen-depleted, but not estrogen-repleted, female rats, suggesting a restraining influence for estrogen against the nicotine effect. In this study, we tested whether the baroreflex-protective effect of estrogen can be replicated when nicotine was administered chronically. We also report on the dose dependence and autonomic modulation of the nicotine-baroreflex interaction. The effects of nicotine (0.5, 1, or 2 mg/kg/day for 14 days) on baroreflex curves relating changes in heart rate to increases [phenylephrine (PE)] or decreases [sodium nitroprusside (SNP)] in blood pressure were evaluated in sham-operated (SO), ovariectomized (OVX), and estrogen-replaced OVX (OVXE(2)) rats. Slopes of the curves were taken as a measure of baroreflex sensitivity (BRS(PE) and BRS(SNP)). In SO rats, both reflex bradycardic and tachycardic responses were attenuated by nicotine in a dose-related fashion. In nicotine-treated rats, blockade of ß-adrenergic (propranolol), but not muscarinic (atropine), receptors caused additional reductions in reflex chronotropic responses, implying that nicotine selectively impairs reflex vagal activity. OVX selectively decreased BRS(PE) but not BRS(SNP) and abolished the nicotine-induced impairment of either response. These effects of OVX were reversed after treatment with estrogen or the estrogen receptor modulator raloxifene. In atropine-treated rats, comparable BRS values were demonstrated in all rat preparations regardless of the estrogen or nicotine milieu. Collectively, the inhibition of vagal activity accounts for the depressant effect of chronic nicotine on baroreflex activity. Furthermore, contrary to nicotine's acute effects, the baroreflex-attenuating effect of chronic nicotine is exacerbated by estrogen.

Tachycardia-induced diastolic dysfunction and resting tone in myocardium from patients with a normal ejection fraction.

OBJECTIVES: The purpose of this study is to evaluate tachycardia-induced relaxation abnormalities in myocardium from patients with a normal ejection fraction. BACKGROUND: Diastolic dysfunction and left ventricular (LV) hypertrophy are closely linked. Tachycardia can induce heart failure symptoms in otherwise asymptomatic patients. To study the effects of tachycardia on myocardial contractility and relaxation, we evaluated the effects of increasing pacing rates in myocardial biopsy samples obtained from patients with a normal ejection fraction. METHODS: LV biopsy samples were obtained during coronary bypass surgery. Myocardial strip preparations were electrically paced at rates from 60 to 180 beats/min. Diastolic resting tone was assessed by cross-bridge deactivation. Calcium transporting systems were functionally examined, and myofilament calcium sensitivity was studied. RESULTS: Incomplete relaxation developed in 7 preparations, with increased diastolic tension development at increasing pacing rates. This was absent in the remaining 7 preparations. Incomplete relaxation was found to be associated with increased LV mass and left atrial volume. Cross-bridge deactivation showed that these preparations also had a significant resting tone. Additional functional analyses suggest that incomplete relaxation is associated with disproportionately elevated cellular calcium loads due to a reduced sarcolemmal calcium extrusion reserve. CONCLUSIONS: Tachycardia-induced incomplete relaxation was associated with increased LV mass and left atrial volumes. We also found a disproportionately increased calcium load at high rates and a substantial resting tone due to diastolic cross-bridge cycling. These observations may play a role in reduced exercise tolerance and tachycardia-induced diastolic dysfunction.

Role of angiotensin II Type 1A receptors in cardiovascular reactivity and neuronal activation after aversive stress in mice.

We determined whether genetic deficiency of angiotensin II Type 1A (AT(1A)) receptors in mice results in altered neuronal responsiveness and reduced cardiovascular reactivity to stress. Telemetry devices were used to measure mean arterial pressure, heart rate, and activity. Before stress, lower resting mean arterial pressure was recorded in AT(1A)(-/-) (85+/-2 mm Hg) than in AT(1A)(+/+) (112+/-2 mm Hg) mice; heart rate was not different between groups. Cage-switch stress for 90 minutes elevated blood pressure by +24+/-2 mm Hg in AT(1A)(+/+) and +17+/-2 mm Hg in AT(1A)(-/-) mice (P<0.01), and heart rate increased by +203+/-9 bpm in AT(1A)(+/+) and +121+/-9 bpm in AT(1A)(-/-) mice (P<0.001). Locomotor activation was less in AT(1A)(-/-) (3.0+/-0.4 U) than in AT(1A)(+/+) animals (6.0+/-0.4 U), but differences in blood pressure and heart rate persisted during nonactive periods. In contrast to wild-type mice, spontaneous baroreflex sensitivity was not inhibited by stress in AT(1A)(-/-) mice. After cage-switch stress, c-Fos immunoreactivity was less in the paraventricular (P<0.001) and dorsomedial (P=0.001) nuclei of the hypothalamus and rostral ventrolateral medulla (P<0.001) in AT(1A)(-/-) compared with AT(1A)(+/+) mice. Conversely, greater c-Fos immunoreactivity was observed in the medial nucleus of the amygdala, caudal ventrolateral medulla, and nucleus of the solitary tract (P<0.001) of AT(1A)(-/-) compared with AT(1A)(+/+) mice. Greater activation of the amygdala suggests that AT(1A) receptors normally inhibit the degree of stress-induced anxiety, whereas the lesser activation of the hypothalamus and rostral ventrolateral medulla suggests that AT(1A) receptors play a key role in autonomic cardiovascular reactions to acute aversive stress, as well as for stress-induced inhibition of the baroreflex.

Exercise and tachycardia increase NADPH oxidase and ryanodine receptor-2 activity: possible role in cardioprotection.

AIM: Our objective was to investigate in cardiac muscle the contribution of NADPH oxidase to (a) ryanodine receptor-2 (RyR2) S-glutathionylation and (b) the preconditioning effects of exercise and tachycardia on infarct size following coronary artery occlusion. METHODS AND RESULTS: We measured NADPH oxidase activity, RyR2 S-glutathionylation, and calcium release kinetics in sarcoplasmic reticulum (SR) vesicles isolated from dog ventricular muscle after exercise and tachycardia, plus or minus prior administration of the NADPH oxidase inhibitor apocynin. In ventricular muscle sections, we studied the colocalization of NADPH oxidase and RyR2 by confocal microscopy using fluorescent antibodies. We determined the effect of apocynin on the infarct size produced by occlusion of the descendent anterior coronary artery in animals preconditioned by exercise or tachycardia. Exercise and tachycardia increased NADPH oxidase activity, RyR2 S-glutathionylation, and calcium release rates in isolated SR vesicles. Cardiac muscle sections displayed significant colocalization of NADPH oxidase and RyR2, suggesting direct and specific effects of reactive oxygen species (ROS) produced by NADPH oxidase on RyR2 activation. The NADPH oxidase inhibitor apocynin prevented the increase in RyR2 S-glutathionylation, reduced calcium release activity, and completely prevented the protective effects of exercise and tachycardia on infarct size. CONCLUSIONS: The loss of cardioprotection induced by the NADPH oxidase inhibitor suggests that ROS generated by this enzyme are important mediators of the preconditioning response, which presumably involves NADPH oxidase-induced RyR2 S-glutathionylation.