Suppression by central adenosine A3 receptors of the cholinergic defense against cardiovascular aberrations of sepsis: role of PI3K/MAPKs/NFκB signaling.

Introduction: Despite the established role of peripheral adenosine receptors in sepsis-induced organ dysfunction, little or no data is available on the interaction of central adenosine receptors with sepsis. The current study tested the hypothesis that central adenosine A3 receptors (A3ARs) modulate the cardiovascular aberrations and neuroinflammation triggered by sepsis and their counteraction by the cholinergic antiinflammatory pathway. Methods: Sepsis was induced by cecal ligation and puncture (CLP) in rats pre-instrumented with femoral and intracisternal (i.c.) catheters for hemodynamic monitoring and central drug administration, respectively. Results: The CLP-induced hypotension, reduction in overall heart rate variability (HRV) and sympathovagal imbalance towards parasympathetic predominance were abolished by i.v. nicotine (100 µg/kg) or i.c. VUF5574 (A3AR antagonist, 2 µg/rat). In addition, the selective A3AR agonist, 3-iodobenzyl-5'-N-methylcarboxamidoadenosine IB-MECA, 4 µg/rat, i.c.) exaggerated the hypotension and cardiac autonomic dysfunction induced by sepsis and opposed the favorable nicotine actions against these septic manifestations. Immunohistochemically, IB-MECA abolished the nicotine-mediated downregulation of NFκB and NOX2 expression in rostral ventrolateral medullary areas (RVLM) of brainstem of septic rats. The inhibitory actions of IB-MECA on nicotine responses disappeared after i.c. administration of PD98059 (MAPK-ERK inhibitor), SP600125 (MAPK-JNK inhibitor) or wortmannin (PI3K inhibitor). Moreover, infliximab (TNFα inhibitor) eliminated the IB-MECA-induced rises in RVLM-NFκB expression and falls in HRV, but not blood pressure. Conclusion: Central PI3K/MAPKs pathway mediates the A3AR counteraction of cholinergic defenses against cardiovascular and neuroinflammatory aberrations in sepsis.

Adenosine A1 receptors of the medullary solitary tract arbitrate the nicotine counteraction of neuroinflammation and cardiovascular dysfunction in septic rats.

The cholinergic pathway plays a crucial role in improving inflammatory end-organ damage. Given the interplay between cholinergic and adenosinergic neurotransmission, we tested the hypothesis that central adenosine A1 receptors (A1ARs) modulate the nicotine counteraction of cardiovascular and inflammatory insults induced by sepsis in rats. Sepsis was induced by cecal ligation and puncture (CLP) 24-h before cardiovascular measurements. Nicotine (25-100 µg/kg i.v.) dose-dependently reversed septic manifestations of hypotension and impaired heart rate variability (HRV) and cardiac sympathovagal balance. Like nicotine, intracisternal (i.c.) administration of N(6)-cyclopentyladenosine (CPA, A1AR agonist) to CLP rats increased indices of HRV and sympathovagal balance. Moreover, greater surges in these parameters were noted upon simultaneous nicotine/CPA administration. The favorable influences of nicotine on blood pressure and HRV in sepsis were diminished after central blockade of A1ARs by i.c. 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX). Molecular studies revealed that (i) septic rises in myocardial and brainstem nucleus of solitary tract (NTS) NFκB expression were abrogated by nicotine and largely reinstated after blockade of A1ARs, and (ii) A1AR expression in the same areas was reduced by DPCPX. It is concluded that myocardial and medullary A1ARs facilitate the cholinergic counteraction of cardiac and neuroinflammation induced by sepsis and interrelated cardiomyopathic and neuropathic hitches.

Possible Ameliorative Effect of Ivabradine on the Autonomic and Left Ventricular Dysfunction Induced by Doxorubicin in Male Rats.

Heart failure is a common adverse effect associated with doxorubicin treatment. The aim of this study is to investigate the effect of ivabradine treatment on doxorubicin-induced heart failure in conscious rats. Rats were treated with doxorubicin (2.5 mg/kg/d) or ivabradine (10 mg/kg/d) alone or along with doxorubicin injections. Changes in heart rate variability (HRV), baroreflex sensitivity, left ventricular (LV) function, serum cardiac troponin T, and cardiac histological features were taken as index parameters for the development of heart failure. Ivabradine significantly reduced the elevated heart rate; normalized the parameters of LV function, dP/dtmax and the relaxation time constant (Tau); reduced the elevated serum level of cardiac troponin T; and minimized the cardiac structural abnormalities in doxorubicin-treated rats. Moreover, ivabradine significantly increased the diminished time domain parameters of HRV, SDNN and rMSSD, and decreased the elevated low frequency power and the low frequency/high frequency while having no effect on the reduced high frequency power. Consistently, ivabradine significantly lowered the elevated baroreflex sensitivity measured by sodium nitroprusside. In conclusion, ivabradine ameliorated the LV dysfunction induced by doxorubicin. Moreover, ivabradine increased the overall HRV and restored the autonomic balance by reducing the sympathetic over activation. Therefore, ivabradine may have a possible therapeutic potential against doxorubicin-induced heart failure.