Background— In a recent study, we demonstrated that an increase in oxidative stress in the rostral ventrolateral medulla plays a critical role in the sympathoexcitation observed in chronic heart failure (CHF). Growing evidence indicates that exercise training evokes an antioxidative effect in CHF. In the present study, we therefore hypothesized that long-term exercise exerts its beneficial effect on autonomic activity in CHF via central antioxidative mechanisms. Methods and Results— Experiments were performed on New Zealand White rabbits. All rabbits were instrumented to measure mean arterial pressure, heart rate, and renal sympathetic nerve activity and to test baroreflex sensitivity. Exercise training significantly decreased baseline renal sympathetic nerve activity (65.8±5.2% to 41.3±3.9% of Max [where “Max” is the maximum renal sympathetic nerve activity induced by a 50-mL puff of smoke directed to the external nares of the rabbit], P <0.05) and increased the maximal gain of the baroreflex curves for heart rate (2.2±0.2 to 4.6±0.7 bpm per mm Hg, P <0.01) and renal sympathetic nerve activity (1.9±0.2% to 4.5±0.4% of Max per mm Hg, P <0.01) in CHF rabbits. Exercise training increased expression of CuZn superoxide dismutase (0.3±0.1 to 1.5±0.3 [ratio of CuZn superoxide dismutase to tubulin], P <0.01) and decreased NAD(P)H oxidase subunit gp91 ^phox protein expression (1.9±0.2 to 1.2±0.1 [ratio of gp91 ^phox to tubulin], P <0.05) in the rostral ventrolateral medulla of CHF rabbits. Central overexpression of CuZn superoxide dismutase dose-dependently decreased baseline renal sympathetic nerve activity (control, 68.5±7.1% of Max; 10 ¹⁰ particles of adenovirus, 53.2±4.4% of Max; and 10 ¹¹ particles of adenovirus, 33.7±3.5% of Max; P <0.05) in CHF rabbits. Conclusions— These results suggest that an upregulation in central antioxidative mechanisms and suppressed central prooxidant mechanisms may contribute to the exercise training–induced beneficial effects on autonomic activity in CHF.

Upregulation of angiotensin II type 1 receptors (AT ₁ R) in the rostral ventrolateral medulla (RVLM) contributes to the sympathoexcitation in the chronic heart failure (CHF). However, the role of angiotensin II type 2 receptor (AT ₂ R) is not clear. In this study, we measured AT ₁ R and AT ₂ R protein expression in the RVLM and determined their effects on renal sympathetic nerve activity, blood pressure, and heart rate in anesthetized sham and CHF rats. We found that (1) although AT ₁ R expression in the RVLM was upregulated, the AT ₂ R was significantly downregulated (CHF: 0.06±0.02 versus sham: 0.15±0.02, P <0.05); (2) simultaneously stimulating RVLM AT ₁ R and AT ₂ R by angiotensin II evoked sympathoexcitation, hypertension, and tachycardia in both sham and CHF rats with greater responses in CHF; (3) stimulating RVLM AT1R with angiotensin II plus the specific AT ₂ R antagonist PD123319 induced a larger sympathoexcitatory response than simultaneously stimulating AT ₁ R and AT ₂ R in sham rats, but not in CHF; (4) activating RVLM AT ₂ R with CGP42112 induced a sympathoinhibition, hypotension, and bradycardia only in sham rats (renal sympathetic nerve activity: 36.4±5.1% of baseline versus 102±3.9% of baseline in artificial cerebrospinal fluid, P <0.05); (5) pretreatment with 5,8,11,14-eicosatetraynoic acid, a general inhibitor of arachidonic acid metabolism, into the RVLM attenuates the CGP42112-induced sympathoinhibition. These results suggest that AT ₂ R in the RVLM exhibits an inhibitory effect on sympathetic outflow, which is, at least partially, mediated by an arachidonic acid metabolic pathway. These data implicate a downregulation in the AT ₂ R as a contributory factor in the sympathoexcitation in CHF.

Background: Chronic heart failure (CHF) is associated with redox imbalance. Downregulation of Nrf2 (nuclear factor [erythroid-derived 2]-like 2) plays important roles in disrupting myocardial redox homeostasis and mediating sympathetic nerve activity in the setting of CHF. However, it is unclear if circulating extracellular vesicles (EVs) elicit sympathetic excitation in CHF by disrupting central redox homeostasis. We tested the hypothesis that cardiac-derived EVs circulate to the presympathetic rostral ventrolateral medulla and contribute to oxidative stress and sympathetic excitation via EV-enriched microRNA-mediated Nrf2 downregulation. Methods: Data were collected on rats with CHF post–myocardial infarction (MI) and on human subjects with ischemic CHF. EVs were isolated from tissue and plasma, and we determined the miRNAs cargo that related to targeting Nrf2 translation. We tracked the distribution of cardiac-derived EVs using in vitro labeled circulating EVs and cardiac-specific membrane GFP ⁺ transgenic mice. Finally, we tested the impact of exogenously loading of antagomirs to specific Nrf2-related miRNAs on CHF-EV–induced pathophysiological phenotypes in normal rats (eg, sympathetic and cardiac function). Results: Nrf2 downregulation in CHF rats was associated with an upregulation of Nrf2-targeting miRNAs, which were abundant in cardiac-derived and circulating EVs from rats and humans. EVs isolated from the brain of CHF rats were also enriched with Nrf2-targeting miRNAs and cardiac-specific miRNAs. Cardiac-derived EVs were taken up by neurons in the rostral ventrolateral medulla. The administration of cardiac-derived and circulating EVs from CHF rats into the rostral ventrolateral medulla of normal rats evoked an increase in renal sympathetic nerve activity and plasma norepinephrine compared with Sham-operated rats, which were attenuated by exogenously preloading CHF-EVs with antagomirs to Nrf2-targeting miRNAs. Conclusions: Cardiac microRNA-enriched EVs from animals with CHF can mediate crosstalk between the heart and the brain in the regulation of sympathetic outflow by targeting the Nrf2/antioxidant signaling pathway. This new endocrine signaling pathway regulating sympathetic outflow in CHF may be exploited for novel therapeutics.

Background. We have previously documented the finding that central angiotensin type 2 receptors (AT2R) negatively modulate sympathetic outflow and arter

Central angiotensin II plays a critical role in the regulation of cardiovascular function and autonomic activity, in part, via angiotensin type 1 receptors in the rostral ventrolateral medulla (RVLM). Increasing evidence indicates that angiotensin II can also act on angiotensin type 2 receptors (AT ₂ Rs) to exert antagonistic effects. In the current study we determined the effects of overexpression of AT ₂ R in the RVLM on sodium and water excretion and on blood pressure in conscious rats. The overexpression of AT ₂ R was induced by bilateral microinjection of the AT ₂ R adenovirus (Ad5-SYN-AT2R-IRES-EGFP, 2.5×10 ⁶ infection units in 0.5 μL; Ad5-SYN-EGFP as the control, 2.5×10 ⁶ infection units in 0.5 μL) into the RVLM of rats. Immunofluorescence staining showed that microinjection of AT ₂ R adenovirus into the RVLM evoked local overexpression. Significant overexpression of AT ₂ R in the RVLM began at 24 hours and was sustained up to 12 days after microinjection. Overexpression of AT ₂ R in the RVLM significantly decreased the nocturnal arterial blood pressure and increased the 24-hour urine excretion at days 2, 3, and 4 after gene delivery compared with the control rats. These alterations were abolished by the microinfusion of captopril into the RVLM and were enhanced by angiotensin II infusion. Overexpression of AT ₂ R in the RVLM also significantly decreased the urine concentration of noradrenaline and 24-hour noradrenaline excretion (1.1±0.5 μg in control rats and 2.4±0.5 μg in AT ₂ R rats; P <0.05). These results suggest that overexpression of AT ₂ R in the RVLM induced a diuresis that may be mediated, in part, by sympathoinhibition.