Heart failure and the brain: new perspectives

Paraventricular hypothalamic nucleus: axonal projections to the brainstem

The paraventricular hypothalamic nucleus (PVH) contains many neurons that innervate the brainstem, but information regarding their target sites remains incomplete. Here we labeled neurons in the rat PVH with an anterograde axonal tracer, Phaseolus vulgaris leucoagglutinin (PHAL), and studied their descending projections in reference to specific neuronal subpopulations throughout the brainstem. While many of their target sites were identified previously, numerous new observations were made. Major findings include: 1) In the midbrain, the PVH projects lightly to the ventral tegmental area, Edinger-Westphal nucleus, ventrolateral periaqueductal gray matter, reticular formation, pedunculopontine tegmental nucleus, and dorsal raphe nucleus. 2) In the dorsal pons, the PVH projects heavily to the pre-locus coeruleus, yet very little to the catecholamine neurons in the locus coeruleus, and selectively targets the viscerosensory subregions of the parabrachial nucleus. 3) In the ventral medulla, the superior salivatory nucleus, retrotrapezoid nucleus, compact and external formations of the nucleus ambiguous, A1 and caudal C1 catecholamine neurons, and caudal pressor area receive dense axonal projections, generally exceeding the PVH projection to the rostral C1 region. 4) The medial nucleus of the solitary tract (including A2 noradrenergic and aldosterone-sensitive neurons) receives the most extensive projections of the PVH, substantially more than the dorsal vagal nucleus or area postrema. Our findings suggest that the PVH may modulate a range of homeostatic functions, including cerebral and ocular blood flow, corneal and nasal hydration, ingestive behavior, sodium intake, and glucose metabolism, as well as cardiovascular, gastrointestinal, and respiratory activities.

Silencing nox4 in the paraventricular nucleus improves myocardial infarction-induced cardiac dysfunction by attenuating sympathoexcitation and periinfarct apoptosis

RATIONALE

Myocardial infarction (MI)-induced heart failure is characterized by central nervous system-driven sympathoexcitation and deteriorating cardiac function. The paraventricular nucleus (PVN) of the hypothalamus is a key regulator of sympathetic nerve activity and is implicated in heart failure. Redox signaling in the PVN and other central nervous system sites is a primary mechanism of neuro-cardiovascular regulation, and excessive oxidant production by activation of NADPH oxidases (Noxs) is implicated in some neuro-cardiovascular diseases.

OBJECTIVE

We tested the hypothesis that Nox-mediated redox signaling in the PVN contributes to MI-induced sympathoexcitation and cardiac dysfunction in mice.

METHODS AND RESULTS

Real-time PCR revealed that Nox4 was the most abundantly expressed Nox in PVN under basal conditions. Coronary arterial ligation (MI) caused a selective upregulation of this homolog compared to Nox1 and Nox2. Adenoviral gene transfer of Nox4 (AdsiNox4) to PVN (bilateral) attenuated MI-induced superoxide formation in this brain region (day 14) to the same level as that produced by PVN-targeted gene transfer of cytoplasmic superoxide dismutase (AdCu/ZnSOD). MI mice treated with AdsiNox4 or AdCu/ZnSOD in the PVN showed marked improvement in cardiac function as assessed by echocardiography and left ventricular hemodynamic analysis. This was accompanied by significantly diminished sympathetic outflow and apoptosis in the periinfarct region of the heart.

CONCLUSIONS

These results suggest that MI causes dysregulation of Nox4-mediated redox signaling in the PVN, which leads to sympathetic overactivation and a decline in cardiac function. Targeted inhibition of oxidant signaling in the PVN could provide a novel treatment for MI-induced heart failure.

Cyclic intermittent hypoxia enhances renal sympathetic response to ICV ET-1 in conscious rats

To test the hypothesis that central changes in sympathoregulation might contribute to sympathoexcitation after cyclic intermittent hypoxia (CIH) we exposed male Sprague-Dawley rats to CIH or to room air sham (Sham) for 8h/d for 3 weeks. After completion of the exposure we assessed heart rate, mean arterial pressure and renal sympathetic nerve activity in conscious animals before and after intracerebroventricular (i.c.v.) administration of endothelin-1 (ET-1, 3 pmol). CIH-exposed animals had a significantly greater sympathetic response to ET-1 than did Sham-exposed animals (CIH 137.8+/-15.6% of baseline; Sham 112.2+/-10.0% of baseline; CIH vs. Sham, P=0.0373). This enhanced sympathetic response to i.c.v. ET-1 was associated with greater expression of endothelin receptor A (ETA) protein in the subfornical organs of CIH-exposed relative to Sham-exposed rats. We conclude that 3-week CIH exposure enhances central ET-1 receptor expression and the sympathetic response to i.c.v. ET-1 suggesting central endothelin may contribute to the sympathetic and hemodynamic response to cyclic intermittent hypoxia.

Microglia activation in the hypothalamic PVN following myocardial infarction

Following a myocardial infarction (MI), inflammatory cytokines are elevated in the brain, as well as in plasma, indicating that inflammation is occurring in the brain in addition to the periphery. Microglia are the immune cells in the central nervous system and can produce cytokines when they are activated by an insult or injury. In the present study, we investigated whether MI in rats induces activation of microglia in the brain. We used immunohistochemistry to detect CD11b (clone OX-42) and morphological changes to identify activated microglia. Compared to control rats that had undergone sham surgical procedures, there was a significant increase in activated microglia in the hypothalamic paraventricular nucleus (PVN) following myocardial infarction. Activated microglia were not observed in the ventral hypothalamus, adjacent to the PVN, nor in the cortex, indicating the response was not the result of a generalized inflammatory reaction in the brain. Echocardiography and haemodynamic parameters after myocardial infarction indicated that reduced left ventricular function but congestive heart failure had not developed. In conclusion, microglia are activated in the PVN but not in the adjacent hypothalamus following myocardial infarction. The activated microglia may contribute to the increased local production of pro-inflammatory cytokines observed in the PVN after myocardial infarction and resulting in reduced left ventricular function.

Role of the hypothalamic PVN in the regulation of renal sympathetic nerve activity and blood flow during hyperthermia and in heart failure

The hypothalamic paraventricular nucleus is a key integrative area in the brain involved in influencing sympathetic nerve activity and in the release of hormones or releasing factors that contribute to regulating body fluid homeostasis and endocrine function. The endocrine and hormonal regulatory function of the paraventricular nucleus is well studied, but the regulation of sympathetic nerve activity and blood flow by this region is less clear. Here we review the critical role of the paraventricular nucleus in regulating renal blood blow during hyperthermia and the evidence pointing to an important pathophysiological role of the paraventricular nucleus in the elevated renal sympathetic nerve activity that is a characteristic of heart failure.

Brain perivascular macrophages and the sympathetic response to inflammation in rats after myocardial infarction

Inflammation is associated with increased sympathetic drive in cardiovascular diseases. Blood-borne proinflammatory cytokines, markers of inflammation, induce cyclooxygenase 2 (COX-2) activity in perivascular macrophages of the blood-brain barrier. COX-2 generates prostaglandin E(2), which may enter the brain and increase sympathetic nerve activity. We examined the contribution of this mechanism to augmented sympathetic drive in rats after myocardial infarction (MI). Approximately 24 hours after acute MI, rats received an intracerebroventricular injection (1 microL/min over 40 minutes) of clodronate liposomes (MI+CLOD) to eliminate brain perivascular macrophages, liposomes alone, or artificial cerebrospinal fluid. A week later, COX-2 immunoreactivity in perivascular macrophages and COX-2 mRNA and protein had increased in hypothalamic paraventricular nucleus of MI rats treated with artificial cerebrospinal fluid or liposomes alone compared with sham-operated rats. In MI+CLOD rats, neither perivascular macrophages nor COX-2 immunoreactivity was seen in the paraventricular nucleus, and COX-2 mRNA and protein levels were similar to those in sham-operated rats. Prostaglandin E(2) in cerebrospinal fluid, paraventricular nucleus neuronal excitation, and plasma norepinephrine were less in MI+CLOD rats than in MI rats treated with artificial cerebrospinal fluid or liposomes alone but more than in sham-operated rats. Intracerebroventricular CLOD had no effect on interleukin 1beta and tumor necrosis factor-alpha mRNA and protein in the paraventricular nucleus or plasma interleukin-1beta and tumor necrosis factor-alpha, which were increased in MI compared with sham-operated rats. In normal rats, pretreatment with intracerebroventricular CLOD reduced (P<0.05) the renal sympathetic, blood pressure, and heart rate responses to intracarotid artery injection of tumor necrosis factor-alpha (0.5 microg/kg); intracerebroventricular liposomes had no effect. The results suggest that proinflammatory cytokines stimulate sympathetic excitation after MI by inducing COX-2 activity and prostaglandin E(2) production in perivascular macrophages of the blood-brain barrier.

Regulation of central angiotensin type 1 receptors and sympathetic outflow in heart failure

Angiotensin type 1 receptors (AT(1)Rs) play a critical role in a variety of physiological functions and pathophysiological states. They have been strongly implicated in the modulation of sympathetic outflow in the brain. An understanding of the mechanisms by which AT(1)Rs are regulated in a variety of disease states that are characterized by sympathoexcitation is pivotal in development of new strategies for the treatment of these disorders. This review concentrates on several aspects of AT(1)R regulation in the setting of chronic heart failure (CHF). There is now good evidence that AT(1)R expression in neurons is mediated by activation of the transcription factor activator protein 1 (AP-1). This transcription factor and its component proteins are upregulated in the rostral ventrolateral medulla of animals with CHF. Because the increase in AT(1)R expression and transcription factor activation can be blocked by the AT(1)R antagonist losartan, a positive feedback mechanism of AT(1)R expression in CHF is suggested. Oxidative stress has also been implicated in the regulation of receptor expression. Recent data suggest that the newly discovered catabolic enzyme angiotensin-converting enzyme 2 (ACE2) may play a role in the modulation of AT(1)R expression by altering the balance between the octapeptide ANG II and ANG- (1-7). Finally, exercise training reduces both central oxidative stress and AT(1)R expression in animals with CHF. These data strongly suggest that multiple central and peripheral influences dynamically alter AT(1)R expression in CHF.

Apelin gene transfer into the rostral ventrolateral medulla induces chronic blood pressure elevation in normotensive rats

The peripheral apelin system plays a significant role in cardiovascular homeostasis and in the pathophysiology of cardiovascular diseases. However, the central effect of this neurohormonal system in neural control of cardiovascular function remains poorly understood. Thus, this study was undertaken to evaluate the effect of apelin in the rostral ventrolateral medulla (RVLM) on blood pressure, cardiac function, and sympathetic nerve activity. Apelin mRNA and protein levels were detected with real-time RT-PCR and Western blots, respectively. Expression of apelin was significantly enhanced in the RVLM of spontaneously hypertensive rat (SHR) compared with normotensive Wistar-Kyoto (WKY) rats. To study the functional consequence of upregulated apelin expression, apelin was overexpressed by bilateral microinjection of the AAV2-apelin viral vector into the RVLM of WKY rats. Immunofluorescence staining and Western blots demonstrated that microinjection of AAV2-apelin into the RVLM resulted in a significant increase in apelin expression, which was associated with a chronic elevation in blood pressure and cardiac hypertrophy. In addition, direct microinjection of exogenous apelin-13 (200 pmol in 50 nL) into the RVLM caused a 20 mm Hg elevation in blood pressure and a 24% increase in sympathetic nerve activity. The present study is the first to show that apelin expression is enhanced in the RVLM of SHR versus WKY rats and that overexpression of this gene in the RVLM results in chronic blood pressure elevation and cardiac hypertrophy in normotensive rats. Thus, the apelin system in the RVLM may play a very important role in central blood pressure regulation and in the pathogenesis of hypertension.

Stress, depression and cardiovascular dysregulation: a review of neurobiological mechanisms and the integration of research from preclinical disease models

Bidirectional associations between mood disorders and cardiovascular diseases are extensively documented. However, the precise physiological and biochemical mechanisms that underlie such relationships are not well understood. This review focuses on the neurobiological processes and mediators that are common to both mood and cardiovascular disorders. The discussion places an emphasis on the role of exogenous stressors in addition to: (a) neuroendocrine and neurohumoral changes involving dysfunction of the hypothalamic-pituitary-adrenal axis and the activation of the renin-angiotensin-aldosterone system, (b) immune alterations including activation of pro-inflammatory cytokines, (c) autonomic and cardiovascular dysregulation including increased sympathetic drive, withdrawal of parasympathetic tone, cardiac rate and rhythm disturbances, and altered baroreceptor reflex function, (d) central neurotransmitter system dysfunction involving the dopamine, norepinephrine and serotonin systems, and (e) behavioral changes including fatigue and physical inactivity. The review also discusses experimental investigations using preclinical disease models to elucidate the neurobiological mechanisms underlying the link between mood disorders and cardiovascular disease. These include: (a) the chronic mild stress model of depression, (b) a model of congestive heart failure, (c) a model of cardiovascular deconditioning, (d) pharmacological manipulations of body fluid and sodium balance, and (e) pharmacological manipulations of the central serotonergic system. In combination with an extensive human research literature, the investigation of mechanisms underlying mood and cardiovascular regulation using animal models will enhance understanding the association between depression and cardiovascular disease. This will ultimately promote the development of better treatments and interventions for individuals with co-morbid psychological and somatic pathologies.

Central mineralocorticoid receptors and cardiovascular disease

The mineralocorticoid receptor (MR) is expressed in many cell types throughout the body, including specific neurons, and mediates diverse functions, many of which are just now being appreciated. MR that pertain to the central modulation of cardiovascular function and health are addressed herein.

Scavenging superoxide selectively in mouse forebrain is associated with improved cardiac function and survival following myocardial infarction

Dysregulation in central nervous system (CNS) signaling that results in chronic sympathetic hyperactivity is now recognized to play a critical role in the pathogenesis of heart failure (HF) following myocardial infarction (MI). We recently demonstrated that adenovirus-mediated gene transfer of cytoplasmic superoxide dismutase (Ad-Cu/ZnSOD) to forebrain circumventricular organs, unique sensory structures that lack a blood-brain barrier and link peripheral blood-borne signals to central nervous system cardiovascular circuits, inhibits both the MI-induced activation of these central signaling pathways and the accompanying sympathoexcitation. Here, we tested the hypothesis that this forebrain-targeted reduction in oxidative stress translates into amelioration of the post-MI decline in myocardial function and increase in mortality. Adult C57BL/6 mice underwent left coronary artery ligation or sham surgery along with forebrain-targeted gene transfer of Ad-Cu/ZnSOD or a control vector. The results demonstrate marked MI-induced increases in superoxide radical formation in one of these forebrain regions, the subfornical organ (SFO). Ad-Cu/ZnSOD targeted to this region abolished the increased superoxide levels and led to significantly improved myocardial function compared with control vector-treated mice. This was accompanied by diminished levels of cardiomyocyte apoptosis in the Ad-Cu/ZnSOD but not the control vector-treated group. These effects of superoxide scavenging with Ad-Cu/ZnSOD in the forebrain paralleled increased post-MI survival rates compared with controls. This suggests that oxidative stress in the SFO plays a critical role in the deterioration of cardiac function following MI and underscores the promise of CNS-targeted antioxidant therapy for the treatment of MI-induced HF.

Mitogen-activated protein kinases mediate upregulation of hypothalamic angiotensin II type 1 receptors in heart failure rats

In heart failure (HF), angiotensin II type 1 receptor (AT(1)-R) expression is upregulated in brain regions regulating sympathetic drive, blood pressure, and body fluid homeostasis. However, the mechanism by which brain AT(1)-R are upregulated in HF remains unknown. The present study examined the hypothesis that the angiotensin II (Ang II)-triggered mitogen-activated protein kinases (MAPKs) p44/42, p38, and c-Jun N-terminal kinase contribute to upregulation of the AT(1)-R in the hypothalamus of rats with HF. AT(1)-R protein, AT(1)-R mRNA, and AT(1)-R immunoreactivity increased in the paraventricular nucleus of hypothalamus and the subfornical organ of rats with ischemia-induced HF compared with sham-operated controls. Phosphorylated p44/42 MAPK, c-Jun N-terminal kinase, and p38 MAPK also increased in paraventricular nucleus and subfornical organ. A 4-week ICV infusion of the AT(1)-R antagonist losartan decreased AT(1)-R protein and phosphorylation of p44/42 MAPK, c-Jun N-terminal kinase, and p38 MAPK in the HF rats. A 4-week ICV infusion of the p44/42 MAPK inhibitor PD98059 or the c-Jun N-terminal kinase inhibitor SP600125 significantly decreased AT(1)-R protein and AT(1)-R immunoreactivity in the paraventricular nucleus and subfornical organ, but the p38 MAPK inhibitor SB203580 did not. Treatment with ICV losartan, PD98059, and SP600125 had no effect on AT(1)-R expression by Western blot in sham-operated rats. In untreated HF rats 4 weeks after coronary ligation, a 3-hour ICV infusion of PD98059, SP600125, or losartan reduced AT(1)-R mRNA in paraventricular nucleus and subfornical organ. These data indicate that MAPK plays an important role in the upregulation of AT(1)-R in the rat forebrain in HF and suggest that Ang II upregulates its own receptor by this mechanism.

The paraventricular nucleus of the hypothalamus - a potential target for integrative treatment of autonomic dysfunction

BACKGROUND

The paraventricular nucleus of the hypothalamus (PVN) has emerged as one of the most important autonomic control centers in the brain, with neurons playing essential roles in controlling stress, metabolism, growth, reproduction, immune and other more traditional autonomic functions (gastrointestinal, renal and cardiovascular).

OBJECTIVES

Traditionally the PVN was viewed as a nucleus in which afferent inputs from other regions were faithfully translated into changes in single specific outputs, whether neuroendocrine or autonomic. Here we present data which suggest that the PVN plays significant and essential roles in integrating multiple sources of afferent input and sculpting an integrated autonomic output by concurrently modifying the excitability of multiple output pathways. In addition, we highlight recent work that suggests that dysfunction of such intranuclear integrative circuitry contributes to the pathology of conditions such as hypertension and congestive heart failure.

CONCLUSIONS

This review highlights data showing that individual afferent inputs (subfornical organ), signaling molecules (orexins, adiponectin), and interneurons (glutamate/GABA), all have the potential to influence (and thus coordinate) multiple PVN output pathways. We also highlight recent studies showing that modifications in this integrated circuitry may play significant roles in the pathology of diseases such as congestive heart failure and hypertension.

Responses of cardiac sympathetic nerve activity to changes in circulating volume differ in normal and heart failure sheep

Factors controlling cardiac sympathetic nerve activity (CSNA) in the normal state and those causing the large increase in activity in heart failure (HF) remain unclear. We hypothesized from previous clinical findings that activation of cardiac mechanoreceptors by the increased blood volume in HF may stimulate sympathetic nerve activity (SNA), particularly to the heart via cardiocardiac reflexes. To investigate the effect of volume expansion and depletion on CSNA we have made multiunit recordings of CSNA in conscious normal sheep and sheep paced into HF. In HF sheep (n = 9) compared with normal sheep (n = 9), resting levels of CSNA were significantly higher (34 +/- 5 vs. 93 +/- 2 bursts/100 heart beats, P < 0.05), mean arterial pressure was lower (76 +/- 3 vs. 87 +/- 2 mmHg; P < 0.05), and central venous pressure (CVP) was greater (3.0 +/- 1.0 vs. 0.0 +/- 1.0 mmHg; P < 0.05). In normal sheep (n = 6), hemorrhage (400 ml over 30 min) was associated with a significant increase in CSNA (179 +/- 16%) with a decrease in CVP (2.7 +/- 0.7 mmHg). Volume expansion (400 ml Gelofusine over 30 min) significantly decreased CSNA (35 +/- 12%) and increased CVP (4.7 +/- 1.0 mmHg). In HF sheep (n = 6) the responses of CSNA to both volume expansion and hemorrhage were severely blunted with no significant changes in CSNA or heart rate with either stimulus. In summary, these studies in a large conscious mammal demonstrate that in the normal state directly recorded CSNA increased with volume depletion and decreased with volume loading. In contrast, both of these responses were severely blunted in HF with no significant changes in CSNA during either hemorrhage or volume expansion.

Chronic mild stress impairs cognition in mice: from brain homeostasis to behavior

Exposure to chronic stress in rodents and psychosocial stress in humans has been shown to alter cognitive functions and has been linked to the pathophysiology of mood disorders. The purpose of the present study was to investigate effects and possible mechanisms of a chronic mild stress (CMS) procedure on cognitive behaviors in Swiss albino mice using the object recognition test (ORT) and object location test (OLT). Results showed that CMS exposure impaired cognitive performance and produced amnesia of acquired information in both ORT and OLT. Furthermore, the cognitive impairment was coexistent with increased plasma levels of interleukin-1beta (IL-1beta), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha), as well as with enhanced plasma levels of corticosterone (CORT), corticotrophin-releasing hormone (CRH) and adrenocorticotrophic hormone (ACTH). In addition, severe neuronal cell damage was found, as bromodeoxyuridine (BrdU) positive cells and the expression of brain derived neurotrophic factor (BDNF) in dentate gyrus (DG) of hippocampus were decreased after 5 weeks CMS procedure. Taken together, these findings indicated that CMS exposure-induced impairment of cognitive behaviors might be attributed to the stress-related alterations in brain homeostasis that were reflected in changes in the neuroimmune and neuroendocrine systems as well as in neurogenesis.

Reactive oxygen species in the neuropathogenesis of hypertension

New evidence that has emerged during the past several years clearly demonstrates that reactive oxygen species (ROS) in the brain play a crucial role in blood pressure regulation by serving as signaling molecules within neurons of cardiovascular control regions. In the forebrain, midbrain, and hindbrain, a key role for oxidant stress in the pathogenesis of angiotensin II-dependent and various other models of neurogenic hypertension has also been uncovered. As in the peripheral vasculature, NAD(P)H oxidase appears to be a major enzymatic source of brain ROS, and various homologues of the catalytic subunit of this enzyme appear to be differentially localized to cardiovascular-regulating nuclei in the brain. Recent studies have begun to elucidate the downstream effects of ROS in neurons, and it is now clear that ROS may interact with a number of well-described intracellular signaling pathways involved in neuronal activation. These exciting new discoveries have furthered our understanding of the pathogenesis of neurogenic hypertension and may ultimately lead to the development of new treatments. In this review, we discuss recent evidence in support of a role for brain ROS in the pathogenesis of hypertension and summarize current studies aimed at uncovering the complex mechanisms by which brain ROS regulate blood pressure in both health and cardiovascular disease.

Interaction of AT1 receptors and V1a receptors-mediated effects in the central cardiovascular control during the post-infarct state

Experimental objectives. Because myocardial infarct is associated with overactivation of brain angiotensin II (ANG II) and vasopressin (AVP) V1a receptors we decided to determine whether AT1 and V1a receptors-mediated effects of ANG II and AVP interact in central cardiovascular control during the post-infarct state. Four groups of infarcted and four groups of sham-operated conscious rats entered the study. Results. In the infarcted rats cerebroventricular infusion of AT1 (AT1ANT, losartan) and V1a antagonist {V1aANT,d(CH(2))(5)[Tyr(Me)(2)Ala-NH(2)(9)]VP} and combined infusion of both these compounds performed 4 weeks after induction of the infarct significantly and comparably reduced mean arterial blood pressure (MABP) in comparison to control experiments (artificial cerebrospinal fluid infusion). In the sham rats MABP was not affected by any of the infusions. In control experiments MABP and HR responses to an alarming air jet stress were significantly higher in the infarcted than in the sham rats. Both responses were normalized with the same effectiveness by administration of AT1ANT, V1aANT and AT1ANT+V1aANT. In the sham rats administration of these compounds did not affect MABP and HR responses to stress.

CONCLUSION

The results provide evidence for interaction of AT1 and V1a receptors-mediated effects of ANG II and AVP in the central cardiovascular control during the post-infarct state.

Increased cyclooxygenase-2 expression in hypothalamic paraventricular nucleus in rats with heart failure: role of nuclear factor kappaB

We investigated the role of nuclear factor kappaB (NF-kappaB) in the cytokine-mediated induction of cyclooxygenase-2 activity in the paraventricular nucleus of hypothalamus (PVN), a critical cardiovascular and autonomic center, in rats with heart failure (HF). Sprague-Dawley rats underwent coronary artery ligation to induce HF or sham surgery. HF rats were treated orally for 6 weeks with vehicle (tap water), the NF-kappaB inhibitor pyrrolidine dithiocarbamate (150 mg/kg per day), or the mineralocorticoid receptor antagonist eplerenone (30 mg/kg per day), which has been shown to reduce circulating proinflammatory cytokines in this model. Compared with sham surgery, HF rats had higher (P<0.05) levels of aldosterone, interleukin-1beta and norepinephrine in plasma and prostaglandin E2 in cerebrospinal fluid. In the PVN, NF-kappaB p50 precursor p105 mRNA increased, and mRNA for its inhibitor, IkappaB, decreased (P<0.05). Cyclooxygenase-2 mRNA and protein expression was increased in perivascular cells of the PVN. Both pyrrolidine dithiocarbamate and eplerenone reduced (P<0.05) p105 mRNA and increased IkappaB mRNA in PVN. Both also reduced (P<0.05) cyclooxygenase-2 mRNA and protein expression in PVN, cerebrospinal fluid prostaglandin E2, and plasma norepinephrine. Eplerenone, but not pyrrolidine dithiocarbamate, reduced plasma interleukin-1beta. Pyrrolidine dithiocarbamate and eplerenone had no effect on plasma aldosterone. The results suggest that activation of NF-kappaB is an intermediary step in cytokine-mediated induction of cyclooxygenase-2 in the PVN of HF rats. By enhancing access of prostaglandin E2 to hypothalamic neurons, this mechanism may contribute to augmented sympathetic nerve activity in HF.

Genetic ablation of angiotensinogen in the subfornical organ of the brain prevents the central angiotensinergic pressor response

The subfornical organ (SFO) of the brain has long been considered a critical integrating center for the cardiovascular actions of the renin-angiotensin system (RAS). Early reports of angiotensin II (Ang II) immunoreactivity in the SFO and its neural projections to downstream cardiovascular nuclei raised the possibility that Ang II is produced locally and functions as a putative neurotransmitter in these circuits. However, evidence of functionally significant de novo synthesis of Ang II in the SFO has been lacking. Here, implementing spatiotemporally restricted gene ablation by way of the Cre recombinase/loxP system, we provide the first direct evidence that the local RAS in the SFO has a critical role in blood pressure regulation. Using a transgenic mouse harboring an angiotensinogen (AGT) gene modified for Cre-mediated deletion (hAGT(flox)), in combination with gene transfer of an adenovirus encoding Cre targeted to the SFO, we show that deletion of the Ang II substrate in this brain region nearly abolishes the pressor and bradycardic effects of renin infused in the CNS. Immunohistochemical analyses verified intense and restricted expression of Cre in the SFO, which paralleled the decrease in AGT expression selectively in this site. Further physiological studies confirmed the integrity of central angiotensinergic and nonangiotensinergic cardiovascular response systems in the Cre-treated mice. In addition to establishing that AGT expression in the SFO and its local conversion to Ang II has a profound effect on blood pressure, this study provides proof-of-principle of the utility of this approach for dissecting the brain RAS and other complex systems in CNS cardiovascular circuits.

Novel effect of mineralocorticoid receptor antagonism to reduce proinflammatory cytokines and hypothalamic activation in rats with ischemia-induced heart failure

Blocking brain mineralocorticoid receptors (MRs) reduces the high circulating levels of tumor necrosis factor (TNF)-alpha in heart failure (HF) rats. TNF-alpha and other proinflammatory cytokines activate neurons in the paraventricular nucleus (PVN) of hypothalamus, including corticotropin-releasing hormone (CRH) neurons, by inducing cyclooxygenase (COX)-2 activity and synthesis of prostaglandin E2 by perivascular cells of the cerebral vasculature. We tested the hypothesis that systemic treatment with a MR antagonist would reduce hypothalamic COX-2 expression and PVN neuronal activation in HF rats. Rats underwent coronary ligation to induce HF, confirmed by echocardiography, or sham surgery, followed by 6 weeks treatment with eplerenone (30 mg/kg per day, orally) or vehicle (drinking water). Eplerenone-treated HF rats had lower plasma TNF-alpha, interleukin (IL)-1beta and IL-6, less COX-2 staining of small blood vessels penetrating PVN, fewer PVN neurons expressing Fra-like activity (indicating chronic neuronal activation), and fewer PVN neurons staining for TNF-alpha, IL-1beta, and CRH than vehicle-treated HF rats. COX-2 and CRH protein expression in hypothalamus were 1.7- and 1.9-fold higher, respectively, in HF+vehicle versus sham+vehicle rats; these increases were attenuated (26% and 25%, respectively) in HF+eplerenone rats. Eplerenone-treated HF rats had less prostaglandin E2 in cerebrospinal fluid, lower plasma norepinephrine levels, lower left ventricular end-diastolic pressure, and lower right ventricle/body weight and lung/body weight ratios, but no improvement in left ventricular function. Treatment of HF rats with anticytokine agents, etanercept or pentoxifylline, produced very similar results. This study reveals a previously unrecognized effect of MR antagonism to minimize cytokine-induced central neural excitation in rats with HF.

NADPH oxidases of the brain: distribution, regulation, and function

The NADPH oxidase is a multi-subunit enzyme that catalyzes the reduction of molecular oxygen to form superoxide (O(2)(-)). While classically linked to the respiratory burst in neutrophils, recent evidence now shows that O(2)(-) (and associated reactive oxygen species, ROS) generated by NADPH oxidase in nonphagocytic cells serves myriad functions in health and disease. An entire new family of NADPH Oxidase (Nox) homologues has emerged, which vary widely in cell and tissue distribution, as well as in function and regulation. A major concept in redox signaling is that while NADPH oxidase-derived ROS are necessary for normal cellular function, excessive oxidative stress can contribute to pathological disease. This certainly is true in the central nervous system (CNS), where normal NADPH oxidase function appears to be required for processes such as neuronal signaling, memory, and central cardiovascular homeostasis, but overproduction of ROS contributes to neurotoxicity, neurodegeneration, and cardiovascular diseases. Despite implications of NADPH oxidase in normal and pathological CNS processes, still relatively little is known about the mechanisms involved. This paper summarizes the evidence for NADPH oxidase distribution, regulation, and function in the CNS, emphasizing the diversity of Nox isoforms and their new and emerging role in neuro-cardiovascular function. In addition, perspectives for future research and novel therapeutic targets are offered.

Cytoglobin is a stress-responsive hemoprotein expressed in the developing and adult brain

Cytoglobin (Cygb) is a novel tissue hemoprotein relatively similar to myoglobin (Mb). Because Cygb shares several structural features with Mb, we hypothesized that Cygb functions in the modulation of oxygen and nitric oxide metabolism or in scavenging free radicals within a cell. In the present study we examined the spatial and temporal expression pattern of Cygb during murine embryogenesis. Using in situ hybridization, RT-PCR, and Northern blot analyses, limited Cygb expression was observed during embryogenesis compared with Mb expression. Cygb expression was primarily restricted to the central nervous system and neural crest derivatives during the latter stages of development. In the adult mouse, Cygb is expressed in distinct regions of the brain as compared with neuroglobin (Ngb), another globin protein, and these regions are responsive to oxidative stress (i.e., hippocampus, thalamus, and hypothalamus). In contrast to Ngb, Cygb expression in the brain is induced in response to chronic hypoxia (10% oxygen). These results support the hypothesis that Cygb is an oxygen-responsive tissue hemoglobin expressed in distinct regions of thenormoxic and hypoxic brain and may play a key role in the response of the brain to ahypoxic insult.

The sympathetic control of blood pressure

Hypertension - the chronic elevation of blood pressure - is a major human health problem. In most cases, the root cause of the disease remains unknown, but there is mounting evidence that many forms of hypertension are initiated and maintained by an elevated sympathetic tone. This review examines how the sympathetic tone to cardiovascular organs is generated, and discusses how elevated sympathetic tone can contribute to hypertension.

Fractal rigidity by enhanced sympatho-vagal antagonism in heartbeat interval dynamics elicited by central application of corticotropin-releasing factor in mice

The dynamics of heartbeat interval fluctuations were studied in awake unrestrained mice following intracerebroventricular application of the neuropeptide corticotropin-releasing factor (CRF). The cardiac time series derived from telemetric ECG monitoring were analyzed by non-parametric techniques of nonlinear signal processing: delay-vector variance (DVV) analysis, higher-order variability (HOV) analysis, empirical mode decomposition (EMD), multiscale embedding-space decomposition (MESD), multiexponent multifractal (MEMF) analysis. The analyses support the conjecture that cardiac dynamics of normal control mice has both deterministic and stochastic elements, is nonstationary, nonlinear, and exerts multifractal properties. Central application of CRF results in bradycardia and increased variability of the beat-to-beat fluctuations. The altered dynamical properties elicited by CRF reflect a significant loss of intrinsic structural complexity of cardiac control which is due to central neuroautonomic hyperexcitation, i.e., enhanced sympatho-vagal antagonism. The change in dynamical complexity is characterized by an effect referred to as fractal rigidity, leading to a significant impairment of adaptability to extrinsic challenges in a fluctuating environment. The impact of dynamical neurocardiopathy as a major precipiting factor for the propensity of cardiac arrhythmias or sudden cardiac death by unchecked central CRF release in significant acute life events in man is critically discussed.

Water deprivation activates a glutamatergic projection from the hypothalamic paraventricular nucleus to the rostral ventrolateral medulla

Elevated sympathetic outflow contributes to the maintenance of blood pressure in water-deprived rats. The neural circuitry underlying this response may involve activation of a pathway from the hypothalamic paraventricular nucleus (PVH) to the rostral ventrolateral medulla (RVLM). We sought to determine whether the PVH-RVLM projection activated by water deprivation is glutamatergic and/or contains vasopressin- or oxytocin-neurophysins. Vesicular glutamate transporter 2 (VGLUT2) mRNA was detected by in situ hybridization in the majority of PVH neurons retrogradely labeled from the ipsilateral RVLM with cholera toxin subunit B (CTB; 85% on average, with regional differences). Very few RVLM-projecting PVH neurons were immunoreactive for oxytocin- or vasopressin-associated neurophysin. Injection of biotinylated dextran amine (BDA) into the PVH produced clusters of BDA-positive nerve terminals within the ipsilateral RVLM that were immunoreactive (ir) for the VGLUT2 protein. Some of these terminals made close appositions with tyrosine-hydroxylase-ir dendrites (presumptive C1 cells). In water-deprived rats (n=4), numerous VGLUT2 mRNA-positive PVH neurons retrogradely labeled from the ipsilateral RVLM with CTB were c-Fos-ir (16-40%, depending on PVH region). In marked contrast, few glutamatergic, RVLM-projecting PVH neurons were c-Fos-ir in control rats (n=3; 0-3%, depending on PVH region). Most (94% +/- 4%) RVLM-projecting PVH neurons activated by water deprivation contained VGLUT2 mRNA. In summary, most PVH neurons that innervate the RVLM are glutamatergic, and this population includes the neurons that are activated by water deprivation. One mechanism by which water deprivation may increase the sympathetic outflow is activation of a glutamatergic pathway from the PVH to the RVLM.

Enhanced involvement of brain vasopressin V1 receptors in cardiovascular responses to stress in rats with myocardial infarction

Stress is one of the factors provoking cardiovascular complications. The purpose of the study was to explore the role of vasopressin (VP) in central control of arterial blood pressure and heart rate under resting conditions and during stimulation by an alarming stress (air jet stress) in myocardial infarct-induced cardiac failure. Six groups of male Sprague Dawley (SD) rats were subjected either to sham surgery (sham rats) or to ligation of a left coronary artery (infarcted rats). After 5 weeks both infarcted and sham rats were subjected either to intracerebroventricular infusion of artificial cerebrospinal fluid (aCSF) (sham aCSF and infarcted aCSF), [Arg8]-VP (sham VP and infarcted VP) or VP V1a receptor antagonist (d(CH2)5[Tyr(Me)2Ala-]VP, sham V1ANT and infarcted V1ANT). Air jet stress elicited significantly greater increases in mean arterial blood pressure (MABP) and heart rate in the infarcted aCSF than in the sham aCSF rats. Intracerebroventricular infusion of V1ANT significantly reduced resting MABP and MABP and heart rate increases in response to stress in the infarcted but not in the sham rats. Intracerebroventricular infusion of VP elicited a significant increase in resting MABP in the infarcted VP but not in the sham VP rats. The results provide evidence for enhanced engagement of the brain V1 VP receptors in regulation of resting MABP and in generation of exaggerated cardiovascular responses to air jet stress during the post-infarct state.

Paraventricular nucleus, stress response, and cardiovascular disease

The paraventricular nucleus of the hypothalamus (PVN) is a complex effector structure that initiates endocrine and autonomic responses to stress. It receives inputs from visceral receptors, circulating hormones such as angiotensin II, and limbic circuits and contains neurons that release vasopressin, activate the adrenocortical axis, and activate preganglionic sympathetic or parasympathetic outflows. The neurochemical control of the different subgroups of PVN neurons is complex. The PVN has been implicated in the pathophysiology of congestive heart failure and the metabolic syndrome.

Efficacy of aldosterone receptor antagonism in heart failure: potential mechanisms

Results of the Randomized Aldactone Evaluation Study and the Eplerenone Post-acute Myocardial Infarction Heart Failure Efficacy and Survival Study indicate aldosterone receptor antagonism, together with angiotensin-converting enzyme inhibition and loop diuretics, is a most effective strategy in reducing risk for all-cause and cardiovascular-related mortality and morbidity in patients with symptomatic heart failure. Responsible mechanisms are likely multifactoral. As a circulating hormone, aldosterone has well-known endocrine properties that contribute to the pathophysiology of congestive heart failure. This includes Na+ resorption at the expense of K+ excretion in such tissues as kidneys, colon, sweat, and salivary glands. Mg2+ excretion at these sites is likewise enhanced by aldosterone, whereas adrenal aldosterone secretion is regulated by extracellular Mg2+. Other endocrine actions of aldosterone receptor-ligand binding include: a reduction in biologically active cytosolic-free Mg2+, with intracellular Ca2+ loading in nonepithelial cells such as peripheral blood mononuclear cells; its influence on endothelial cell function; and its central actions, including the choroid plexus, activity of the hypothalamic paraventricular nucleus, and autonomic nervous system. De novo generation of aldosterone within the cardiovasculature is recognized and findings suggest its auto/paracrine properties contribute to tissue repair. Each of these actions is interrupted by aldosterone receptor antagonism and therefore may contribute to its salutary response in heart failure.

Neuroendocrine and cytokine profile of chronic mild stress-induced anhedonia

A bidirectional relationship exists between depression and cardiovascular disease. Patients with major depression are more likely to develop cardiac events, and patients with myocardial infarction and heart failure are more likely to develop depression. A feature common to both clinical syndromes is activation of proinflammatory cytokines and stress hormones, including the hypothalamic-pituitary-adrenal axis and the renin-angiotensin-aldosterone system. In the present study we examined the hypothesis that exposure to chronic mild stress (CMS), an experimental model of depression that induces anhedonia in rats, is sufficient to activate the production of proinflammatory cytokines and stress hormones that are detrimental to the heart and vascular system. Four weeks of exposure of male, Sprague-Dawley rats to mild unpredictable environmental stressors resulted in anhedonia which was operationally defined as a reduction in sucrose intake without a concomitant effect on water intake. Humoral assays indicated increased plasma levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), plasma renin activity, aldosterone, and corticosterone in the CMS exposed rats. Tissue TNF-alpha and IL-1beta were increased in the hypothalamus, and TNF-alpha was increased in the pituitary gland. These humoral responses to CMS, associated with anhedonia as an index of depression in the rat, are likely to be associated with neurohumoral mechanisms that may contribute to adverse cardiac events. The findings provide a basis for examining more directly the interactions among the central, endocrine, and immune systems in depression associated with heart disease.

Acute coronary syndromes and heart failure may reflect maladaptations of trauma physiology that was shaped during pre-modern evolution

We hypothesize that the pathophysiology of many cardiovascular diseases reflects a maladaptation of the triad of trauma response: adrenergia, inflammation, and coagulation. During biologic evolution, trauma has likely been a prevailing factor in natural selection. Components of the trauma triad act to limit hemorrhage, defend wounds against microorganisms, and initiate reconstruction. Response pathways that enable survival after trauma confer obvious adaptive advantages especially if the individual goes on to reproduce. Modern humans have shaped their own ecologic environment in such a way that the incidence of trauma has waned and previously unseen pathologies have emerged. Manifestations of modern diet, changing lifestyles, and extended lifespan have suddenly created new pathologic challenges to our prehistoric physiologic system. During our evolutionary heritage, endothelial injury and end-organ hypoxia were likely exclusively associated with physical trauma and the responses of the trauma triad were appropriate. Today, endothelial injury is more often precipitated by distinctly modern stressors such as hypertension, smoking, diabetes, and dyslipidemia. The once-adaptive trauma response can maladaptively initiate dangerous, self-propelling cycles of adrenergia, inflammation, and coagulation. Acute coronary syndromes perhaps best exemplify this phenomenon. Congestive heart failure, which often ensues, can similarly be seen as a maladaptation of the trauma triad. Whereas end-organ hypoxia was once commonly associated with trauma, now hypoxia is more often attributable to distinctly modern stressors such as pump failure. The fluid conservation and inflammation that results from the trauma triad was clearly adaptive in our prehistoric past, but in congestive heart failure the response is maladaptive, engendering self-propelling exacerbations of pump failure and vascular disease. Our maladaptive trauma response hypothesis portends new diagnostic and therapeutic paradigms for cardiovascular diseases and has ramifications for many other conditions such as stroke, venous thrombosis, vasculitis, aortic disease, arterial disease, pulmonary embolism, and restenosis.

Angiotensin II Receptor mRNA Expression and Vasoconstriction in Human Coronary Arteries: Effects of Heart Failure and Age

Angiotensin II is a potent vasoconstrictor that is implicated in the pathogenesis of hypertension, heart failure and atherosclerosis. In the present study, angiotensin II receptor mRNA expression levels were quantified by real-time polymerase chain reaction and the vasocontractile responses to angiotensin II were characterised by in vitro pharmacology in endothelium-denuded human coronary arteries. Angiotensin II type 1 (AT(1)) and type 2 (AT(2)) receptor mRNA expression levels were significantly down-regulated in arteries from patients with heart failure as compared to controls. The angiotensin II-induced vasoconstriction diminished with increasing age in patients with heart failure (r(2)=0.31, P<0.05). Also, the AT(1) receptor mRNA expression levels decreased with increasing age in patients with heart failure (r(2)=0.74, P<0.05), while no such correlation could be shown in the control group (r(2)=0.04, P=n.s.). The AT(2) receptor mRNA expression levels did not correlate with age in patients with heart failure or controls. In conclusion, the diminished angiotensin II vasoconstriction with age in heart failure patients is most likely due to a lower density of AT(1) receptors and may result from a longer period of exposure to heart failure in older patients.

Effect of stress induced by electrical stimulation of the hypothalamus on the electrical stability of the heart in rabbits

The influence of stress on cardiac electrical stability (CES) and chaotic dynamics of the electrical activity of the heart was studied in acute and chronic experiments in rabbits. Stress was caused by 2-3 h daily immobilization of the animals with electrical stimulation of emotiogenic centers of the hypothalamus through implanted electrodes. CES was estimated by the thresholds for ventricular arrhythmia: paroxysmal ventricular tachycardia, repeated ventricular extrasystoles and ventricular fibrillation (VF). The results showed: (i) CES in stressed rabbits was decreased significantly compared with controls; (ii) the level of chaos at the onset of VF in stressed rabbits was increased significantly compared with controls; (iii) heart rate of stressed rabbits was significantly greater than in controls; (iv) changes in CES parameters depended on whether stress was acute or chronic; (v) acute stress promoted transition of spontaneously reversible VF into spontaneously irreversible VF. Thus, stress increased the degree of disorganization of heart electrical activity and also decreased its electrical stability. The experiments indicate that stress is a destabilizing factor influencing the reversibility of heart rate disorders. The probability of such reversibility depends on whether stress is acute or chronic: acute stress is more likely to lead to irreversible spontaneous VF.

Genetic targeting of the brain renin-angiotensin system in transgenic rats: Impact on stress-induced renin release

The advance of genetic technologies to permit tissue-specific targeted gene manipulation allowed the development of transgenic models with alterations of the renin-angiotensin (RAS) solely in the brain. We have used such methodology to develop a transgenic rat with a brain specific alteration of the RAS [TGR(ASrAOGEN)], in order to elucidate a causative role for the brain RAS and its relevance in different pathophysiological processes. The TGR(ASrAOGEN) rats have decreased levels of angiotensinogen (AOGEN) throughout the brain because of an antisense inhibition of the astroglial AOGEN synthesis. In this review we aimed at summarizing the experience obtained from utilizing the TGR(ASrAOGEN) rat model to study the brain RAS and present novel results providing evidence for the involvement of this system in stress-induced renin release.

Brain mineralocorticoid receptors: orchestrators of hypertension and end-organ disease

PURPOSE OF REVIEW

'New' tasks have been discovered for aldosterone and its receptor, the mineralocorticoid receptor, within both epithelial tissues of vectorial ion and water transport, such as the kidney, and non-epithelial organs, including the brain, heart and vessels. Promising results of clinical trials using low doses of mineralocorticoid receptor antagonists to forestall end-organ disease is resulting in an increase in their use, yet the biology of the mineralocorticoid receptor is far from clear.

RECENT FINDINGS

Mineralocorticoid receptors within the kidney, heart and blood vessels mediate direct effects of aldosterone, including tissue inflammation, hypertrophy and fibrosis, that are independent of blood pressure. Activation, by aldosterone, of mineralocorticoid receptors in the brain increases central sympathetic nervous system drive to the periphery, thereby producing hypertension through multiple mechanisms, and increases levels of proinflammatory cytokines in both the circulation and peripheral tissues. Blocking of the mineralocorticoid receptor of the forebrain lowers the levels of peripheral tissue cytokines, including those induced by ischemic injury in the heart. Aldosterone is produced within the heart, blood vessels and brain, potentially liberating regulation of local concentrations of the steroid from peripheral mechanisms of control. A conundrum yet to be explained is the ligand-dependent functional specificity of the mineralocorticoid receptor in some non-epithelial tissues, which may be crucial to our understanding the end-organ pathophysiology of hypertension.

SUMMARY

New technology is rapidly adding layers of complexity to, rather than simplifying, our understanding of the facile terms 'hemodynamic homeostasis' and 'end-organ' disease, but within this new knowledge lies the promise of better, more precise treatment of hypertension and its sequelae.

Redox signaling in central neural regulation of cardiovascular function

One of the most prominent concepts to emerge in cardiovascular research over the past decade, especially in areas focused on angiotensin II (AngII), is that reactive oxygen species (ROS) are critical signaling molecules in a wide range of cellular processes. Many of the physiological effects of AngII are mediated by ROS, and alterations in AngII-mediated redox mechanisms are implicated in cardiovascular diseases such as hypertension and atherosclerosis. Although most investigations to date have focused on the vasculature as a key player, the nervous system has recently begun to gain attention in this field. Accumulating evidence suggests that ROS have important effects on central neural mechanisms involved in blood pressure regulation, volume homeostasis, and autonomic function, particularly those that involve AngII signaling. Furthermore, oxidant stress in the central nervous system is implicated in the neuro-dysregulation associated with some forms of hypertension and heart failure. The main objective of this review is to discuss the recent progress and prospects for this new field of central redox signaling in cardiovascular regulation, while also addressing the molecular tools that have spurred it forward.

Alteration of NMDA NR1 receptors within the paraventricular nucleus of hypothalamus in rats with heart failure

One of the pathophysiological characteristics of chronic heart failure (HF) is elevated sympathetic drive, which is a major factor contributing to the morbidity and mortality of HF. Resent evidence points to a central mechanism that contributes to the sympathetic abnormality in HF. The paraventricular nucleus (PVN) of the hypothalamus is an important site that integrates sympathetic nerve activity. Studies have shown that glutamate elicits excitatory effects on neurons in the PVN through the NMDA receptor. The goal of the present study was to examine the role of NMDA receptors in the altered sympathetic nerve activation during HF. The left coronary ligation-induced heart failure model in the rat was used. In alpha-chloralose and urethane anesthetized rats, microinjection of NMDA into the PVN (50 to 200 pmol) produced dose-dependent increases in renal sympathetic nerve discharge (RSND), arterial blood pressure (BP), and heart rate (HR). This response to NMDA was significantly potentiated (27+/-7%) in HF compared with sham rats. On the other hand, microinjection of the NMDA receptor antagonist AP-5 (4 to 16 nmol) into the PVN caused significant decreases in RSND, BP, and HR only in rats with HF but very slight changes in sham rats. Furthermore, using microdialysis and HPLC in combination with electrochemical detection techniques, we found that the glutamate level in the PVN was not increased significantly in HF compared with sham rats. However, using RT-PCR, Western blot, and immunofluorescence techniques, it was found that NMDA NR1 subunit mRNA expression and protein level in the PVN were significantly increased in HF compared with sham rats. These data suggest that the increased glutamatergic activity on sympathetic regulation, due to the upregulation of NMDA NR1 receptor subunits within the PVN may contribute to the elevated sympathoexcitation during HF.

Increased peripheral resistance in heart failure: new evidence suggests an alteration in vascular smooth muscle function

Increased peripheral resistance is a hallmark of chronic heart failure and has been primarily attributed to neurohumoral pathways involving both the renin-angiotensin and sympathetic nervous systems. The increased resistance is thought to serve as a compensatory mechanism to help maintain perfusion to the vital organs by sustaining blood pressure in the fate of a failing heart. Local mechanisms, and in particular endothelial dysfunction, have also been shown to be important contributors in regulating arterial resistance and vascular remodeling in this disease. In this issue of the British Journal of Pharmacology, Gschwend et al. (2003) present new data suggesting that in the absence of a functional endothelium, myogenic constriction of small pressurized mesenteric arteries, an intrinsic property of vascular smooth muscle cells, is enhanced in a coronary artery ligation-induced myocardial infarction model of congestive heart failure (CHF) in the rat. The increased myogenic tone appears to be tightly linked to angiotensin II type 1 receptors (AT(1)). The possibility that CHF-induced stimulation of myogenic constriction is due to the local release of preformed angiotensin II or constitutive upregulation of the AT(1) receptor signaling pathways are discussed along with other potential cellular and molecular mechanisms previously suggested to play a role in myogenic reactivity.