Organ Selective Regulation of Sympathetic Outflow by the Brain Angiotensin System

Angiotensin II (Ang II) has actions on the sympathetic nervous system both as a circulating hormone acting on the circumventricular organs and also as a neurotransmitter/ neuromodulator acting within the brain. Administration of Ang II into the cerebral ventricles has diverse effects on sympathetic nerve activity (SNA), causing an increase in cardiac and splanchnic and a decrease in renal SNA. Similar contrasting effects on cardiac and renal SNA are seen with administration of hypertonic saline, which is thought to act centrally through angiotensinergic pathways. In heart failure there is compelling evidence that central angiotensinergic mechanisms contribute to the increases in cardiac and renal SNA, which have numerous detrimental effects. Although there is evidence that Ang II regulates sympathetic activity, and contributes to excess SNA in disease, the exact sites in the brain at which Ang II acts to selectively control SNA to individual organs are not well defined.