Angiotensin II, sympathetic nerve activity and chronic heart failure.

Sympathetic nerve activity has been reported to be increased in both humans and animals with chronic heart failure. One of the mechanisms believed to be responsible for this phenomenon is increased systemic and cerebral angiotensin II signaling. Plasma angiotensin II is increased in humans and animals with chronic heart failure. The increase in angiotensin II signaling enhances sympathetic nerve activity through actions on both central and peripheral sites during chronic heart failure. Angiotensin II signaling is enhanced in different brain sites such as the paraventricular nucleus, the rostral ventrolateral medulla and the area postrema. Blocking angiotensin II type 1 receptors decreases sympathetic nerve activity and cardiac sympathetic afferent reflex when therapy is administered to the paraventricular nucleus. Injection of an angiotensin receptor blocker into the area postrema activates the sympathoinhibitory baroreflex. In peripheral regions, angiotensin II elevates both norepinephrine release and synthesis and inhibits norepinephrine uptake at nerve endings, which may contribute to the increase in sympathetic nerve activity seen in chronic heart failure. Increased circulating angiotensin II during chronic heart failure may enhance the sympathoexcitatory chemoreflex and inhibit the sympathoinhibitory baroreflex. In addition, increased circulating angiotensin II can directly act on the central nervous system via the subfornical organ and the area postrema to increase sympathetic outflow. Inhibition of angiotensin II formation and its type 1 receptor has been shown to have beneficial effects in chronic heart failure patients.