Effect of nitric oxide on rostral ventrolateral medulla modulating cardiac sympathetic afferent reflex in rats with chronic heart failure

Xingya GAO; Rui GUO; Wei WANG; Feng ZHANG; Guoqing ZHU

ABSTRACT

BACKGROUND:

Nitric oxide in the central nervous system is involved in controlling the sympathetic outflow. The authors' recent data show that the reduction of nitric oxide in the rostral ventrolateral medulla (RVLM)enhanced the cardiac sympathetic afferent reflex (CSAR) evoked by stimulating the cardiac sympathetic afferent nerves in rats with chronic heart failure (CHF).

OBJECTIVE:

To further investigate the effect of nitric oxide in the RVLM on modulating the CSAR evoked by epicardial chemical stimulation in rats with CHF.

DESIGN:

Randomized controlled experiment.

SETTING:

Department of Physiology, Nanjing Medical University, and Department of Cellular and Integrative Physiology, University of Nebraska College of Medicine.MATERIALS This study was carried out in the Department of Physiology, Nanjing Medical University from July 2003 to May 2004. A total of 52male Sprague-Dawley rats weighing 360-420 g were used, and were randomly divided into chronic heart failure group and control group with 23 in each group.

METHODS:

The rats were carried out either sham surgery or the left coronary artery ligation. Six to eight weeks later, all rats were anesthetized with α-chloralose and urethane and baroreceptor denervated and vagotomized. The CSAR was evoked by epicardial application of bradykinin (BK, 0.04 μg and 0.4 μg in 2.0 μL) to mimic the effect of chemical stimulation on the heart in the CHF state. The renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP) and heart rate (HR) were recorded at baseline and during elicitation of the CSAR. Cannulae were inserted into the RVLM for microinjections.croinjection of MeTC, a nitric oxide synthase inhibitor, into the RVLM on Effects of epicardial pretreatment with lidocaine on the CSAR in CHF rats.infarction of (30.6±2.0) % of the left ventricular (LV) surface. The systolic arterial pressure, pulse pressure, left ventricle peak systolic pressure and maximum of the first differentiation of left ventricular pressure were decreased and the left ventricular end-diastolic pressure was significantly ininto the RVLM had no significant effects on the CSAR in rats with CHF,of SNAP (50 nmol) into the RVLM inhibited the CSAR in both sham rats ventricle abolished the CSAR evoked by epicardial application ofBK on the same area.

CONCLUSION:

Nitric oxide in the RVLM inhibits the CSAR evoked by epicardial application of BK in normal rats and CHF rats, and the reduction of nitric oxide in the RVLM led to the augmentation of the CSAR in CHF rats.