Effects Of Mineralocorticoid Receptor In Hypothalamic Paraventricular Nucleus On Sympathoexcitation In Congestive Heart Failure

Despite recent therapeutic advanced, the prognosis for patients with congestiveheart failure (CHF) remains dismal. CHF is the common outcome of a variety ofcardiovascular diseases. Neurohumoral excitation (NHE) is a cardinal manifestationof the CHF syndrome,closely correlated with disease severity and adverse prognosis.Sympathoexcitation is considered a trigger point that promotes the excessive releaseof neurohormones in CHF, where plasma norepinephrine (NE), angiotensin (ANGⅡ),aldosterone, cytokines,etc. were found to be correlated with severity of CHF.However, the mechanisms of sympathoexcitation are still not fully understood. Thehypothalamic paraventricular nucleus (PVN) is a principal central site mediatingneurohumoral responses. PVN is also a critical brain site to regulate extracellularfluid volume and sympathetic drive.The traditional view of aldosterone/mineralocorticoid as a hormone actingprimarily upon receptors in the kidneys and the colon to conserve sodium hasundergone substantial modification in the past two decades, as evidence has emergedfor its involvement in cardiac and vascular fibrosis, central nervous systemmechanisms regulating sodium appetite and sympathetic nerve activity, andexperimental models of hypertension and heart failure. Interest in the role ofaldosterone in cardiovascular diseases was heightened by the Random AldactoneEvaluation Study (RALES), a large clinical trial demonstrating that the addition of asmall oral dose of the mineralocorticoid receptor (MR) antagonist spironolactone (SL)to the regimen of otherwise optimally managed patients with established heart failuredramatically reduced morbidity and mortality. The mechanism(s) accounting for thesebeneficial effects were unknown.Activation of MR in the brain has long been associated with increased saltappetite and sympathetically mediated hypertension. It is therefore reasonable to hypothesize that blocking the activation of brain MR might account, at least inpart, for the salutary influences of MR antagonist in HF.One excitatory mediator that responds to manipulations of brain MR is tumornecrosis factor alpha (TNF--inflammatory cytokine. Plasma levels ofTNF-with ischemia-induced HF also have high circulating levels of TNF-continuous ICV infusion of SL, initiated within24hours of coronary artery ligation,prevents the expected rise in plasma TNF-treatment with the MR agonist in a dose sufficient to induce sodium appetiteincreases plasma TNF-SL. These two studies demonstrated the surprising finding that plasma levels ofpro-inflammatory cytokines are regulated, at least in part, by brain MR.Our recent studies suggest that, in addition to the neurohormones,proinflammatory cytokines (PICs) are upregulated in the PVN and contribute tosympathoexcitation in HF. TNF---6share a common property ofactivating the hypothalamic-pituitary-adrenal axis (HPA) and increasing sympatheticnerve activity. However, the mechanisms by which PICs modulate sympatheticactivity in HF are not clear. A number of excitatory and inhibitory neurotransmittersconverge in the PVN to influence its neuronal activity, including glutamate(Glu),norepinephrine (NE), and gamma-aminobutyric acid (GABA). Glutamate is awell-known excitatory neurotransmitter in the central nervous system and it has beenreported that functional glutamate receptors expressed in the PVN are involved in thecontrol of cardiovascular reflexes. It has also been shown that sympathetichyperactivity in rats with HF is associated with increased extracellular norepinephrine(NE) in the PVN. GABA is a well-known inhibitory neurotransmitter in the centralnervous system and is a dominant inhibitory neurotransmitter within the PVN.Previous work demonstrated a GABA-mediated inhibitory mechanism within thePVN contributing to sympathoexcitation in HF rats. Therefore, we hypothesized thatincreased PICs in the brains of HF rats caused an imbalance in the excitatoryand inhibitory neurotransmitters in the PVN, contributing to increased sympathoexcitation in HF.Part One: Activation of Mineralocorticoid Receptorin Hypothalamic Paraventricular Nucleus Contributes toSympathoexcitation in Congestive Heart FailureAims: To observe the primary hypothesis that mineralocorticoid receptorantagonism would reduce sympathetic activity in rats with HF. Methods:Sprague-Dawly (SD) rats were subjected to coronary artery ligation to induce heartfailure (HF), or sham surgery without ligating the vessel (SHAM). Followed by6weeks treatment with RU28318,30mg/kg per day, orally) or vehicle (drinking water).At the end of the experiment, ensure that in each group there are at least12animalssurvived. After6weeks, left ventricular function parameters, such as left ventricularend-diastolic pressure (LVEDP) and maximum change in pressure over time (±dp/dtmax) were determined by hemodynamic measurements. The right ventricular-to-bodyweight (RV/BW) and lung-to-body weight (lung/BW) ratios were calculated asindices of pulmonary congestion and right ventricular remodeling, two indices of theseverity of HF. The renal sympathetic nerve activity (RSNA) was recorded and theplasma NE level was measured using an ELISA kit, two indices of the severity ofsympathetic nervous excitation. ELISA techniques was also used to measure TNF-ALDO levels in plasma and PGE2level in CSF. Immunohistochemical studies wereperformed to assess the expression of TNF--2, and CRH in PVN. Results:RU28318treated HF rats had lower plasma TNF--2staining of PVNneurons, and fewer PVN neurons staining for TNF--treatedHF rats. RU28318.-treated HF rats had less prostaglandin E2in cerebrospinal fluid,lower RSNA and plasma norepinephrine levels, lower left ventricular end-diastolicpressure,and lower right ventricle/body weight and lung/body weight ratios, but noimprovement in left ventricular function. Conclusion: This study demonstrates thatmineralocorticoid receptor antagonism would reduce sympathetic activity andcytokine stress peripherally and centrally Part Two: Brain Mineralocorticoid Receptor InducesSympathetic Drive by Increasing Circulating ProinflammatoryCytokines in Congestive Heart FailureAims: To examined the potential impact of oral administration of a selective MRantagonist, RU28318, on blood-borne cytokines and on cytokine-driven central neuralmechanisms that may contribute to the progression of heart failure. Methods:Sprague-Dawly (SD) rats were underwent coronary ligation to induce HF, or shamsurgery. Followed by6weeks treatment with RU28318,30mg/kg per day, orally orvehicle (drinking water), as in Part One. Another set of rats were treated withanticytokine agents infliximab (INF,30mg/kg daily, in drinking water) to determinewhether the cytokine lowering effect of MR antagonism is sufficient to account forthe observed responses to RU28318. Combined MR antagonism and cytokineinhibition to determine whether it would produce additive or facilitative responses. Atthe end of the experiment, ensure that in each group there are at least12animalssurvived. After6weeks, left ventricular function parameters were determined byhemodynamic measurements. RV/BW and lung/BW ratios were calculated, the RSNAwas recorded. The plasma NE, PIC, ALDO level and concentration of PIC in PVNwas measured using ELISA techniques. Immunohistochemical studies wereperformed to assess the expression of TNF---2, and CRH in PVN.Western blot was used to measure COX-2and CRH protein expression. Results:Treatment of HF rats with anticytokine agents, infliximab, or combined MRantagonist and cytokine inhibition produced very similar results. Conclusion: Thisstudy reveals an effect of MR antagonism to minimize cytokine-induced centralneural excitation in rats with HF. Part Three: Effect of Tumour Necrosis Factor-to Attenuate Neurotransmitters Imbalancedin Congestive Heart FailureAims: Blocking brain tumour necrosis factor-(TNF-neurotransmitters imbalanced in congestive heart failure (HF). we explored thepossible roles of brain proinflammatory cytokines (PIC) on modulatingneurotansmitters in the exaggerated sympathetic activity in HF. Methods:Sprague-Dawley rats were underwent coronary ligation to induce HF or SHAMcontrol. And then, they were treated for4-weeks with a continuousintracerebroventricular (ICV) infusion of the TNF-infliximab (INF,10g/h), or vehicle. Another set of HF and SHAM rats were treated withintraperitoneal (ip) infusion of a similar dose of INF. After4weeks, LVEDP and±dp/dtmaxwere measured by hemodynamic measurements. The RV/BW and lung/BWratios were calculated. The RSNA was recorded. Plasma and tissue inflammatorycytokine levels were measured using ELISA techniques. The concentrations of NEand the rate-limiting enzymes of glutamate and GABA, respectively, TH and GAD67,and circulating catecholamine levels were measured using HPLC withelectrochemical detection. Immunohistochemical labelling was performed to identifyTH, GAD67and nNOS in PVN. Results: HF rats had higher levels of glutamate, NE,and TH, and lower levels of GABA, nNOS, and67-kDa isoform of glutamatedecarboxylase (GAD67) in the PVN when compared with SHAM rats. Plasmacytokines, NE, epinephrine, angiotensin and renal sympathetic nerve activity(RSNA) were also increased in HF rats. The same ICV treatments also attenuated theincreased RSNA in HF rats. IP treatment with similar doses of INF did not affectglutamate, NE, TH, GABA, nNOS, and GAD67in the PVN and had no effect onRSNA of HF rats. Conclusion: These findings indicate that brain PICs induceneurotransmitters imbalanced and contribute to the increased sympathetic drive inHF.