Superoxide anions in the paraventricular nucleus mediate cardiac sympathetic afferent reflex in insulin resistance rats.

Abstract

Cardiac sympathetic afferent reflex (CSAR) participates in sympathetic over-excitation. Superoxide anions and angiotensin II (Ang II) mechanisms are associated with sympathetic outflow and CSAR in the paraventricular nucleus (PVN). This study was designed to investigate whether PVN superoxide anions mediate CSAR and Ang II-induced CSAR enhancement response in fructose-induced insulin resistance (IR) rats. CSAR was evaluated with the changes of renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) responses to the epicardial application of capsaicin (CAP) in anaesthetized rats. Compared with Control rats, IR rats showed that CSAR, PVN NAD(P)H oxidase activity, superoxide anions, malondialdehyde (MDA), Ang II and AT1 receptor levels were significantly increased, whereas PVN superoxide dismutase (SOD) and catalase (CAT) activities were decreased. In Control and IR rats, PVN microinjection of superoxide anions scavengers tempol, tiron and PEG-SOD (an analogue of endogenous superoxide dismutase) or inhibition of PVN NAD(P)H oxidase with apocynin caused significant reduction of CSAR, respectively, but DETC (a superoxide dismutase inhibitor) strengthened the CSAR. PVN pre-treatment with tempol abolished, whereas DETC potentiated, Ang II-induced CSAR enhancement response. Moreover, PVN pre-treatment with tempol or losartan prevented superoxide anions increase caused by Ang II in IR rats. PVN superoxide anions mediate CSAR and Ang II-induced CSAR response in IR rats. In IR state, increased NAD(P)H oxidase activity and decreased SOD and CAT activities in the PVN promote superoxide anions increase to involve in CSAR enhancement. Ang II may increase NAD(P)H oxidase activity via AT1 receptor to induce superoxide anion production.