Superoxide anions in the paraventricular nucleus mediate the enhanced cardiac sympathetic afferent reflex and sympathetic activity in renovascular hypertensive rats

Abstract

An enhanced cardiac sympathetic afferent reflex (CSAR) is involved in the sympathetic activation in renovascular hypertension. The present study was designed to determine the role of superoxide anions in the paraventricular nucleus (PVN) in mediating the enhanced CSAR and sympathetic activity in renovascular hypertension in the two-kidney, one-clip (2K1C) model. Sinoaortic denervation and vagotomy were carried out, and renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded under anesthesia. The CSAR was evaluated by the response of RSNA to the epicardial application of capsaicin. Superoxide anion levels and NAD(P)H oxidase activity in the PVN increased in 2K1C rats and were much higher in 2K1C rats than in sham-operated (sham) rats after the epicardial application of capsaicin or PVN microinjection of ANG II. In both 2K1C and sham rats, PVN microinjection of the superoxide anion scavenger tempol or the NAD(P)H oxidase inhibitor apocynin abolished the CSAR, whereas the SOD inhibitor diethyldithiocarbamic acid (DETC) potentiated the CSAR. Tempol and apocynin decreased but DETC increased baseline RSNA and MAP. ANG II in the PVN caused larger responses of the CSAR, baseline RSNA, and baseline MAP in 2K1C rats than in sham rats. The effects of ANG II were abolished by pretreatment with tempol or apocynin in both 2K1C and sham rats and augmented by DETC in the PVN in 2K1C rats. These results indicate that superoxide anions in the PVN mediate the CSAR and the effects of ANG II in the PVN. Increased superoxide anions in the PVN contribute to the enhanced CSAR and sympathetic activity in renovascular hypertension.