Area postrema and sympathetic nervous system effects of vasopressin and angiotensin II

1. Precise control over the cardiovascular system requires the integration of both neural and humoral signals related to blood volume and blood pressu re. Humoral signals interact with neural systems, modulating their control over the efferent mechanisms that ultimately determine the level of pressur e and volume. 2. Peptide hormones such as angiotensin (Ang)II and arginine vasopressin (A VP) act through circumventricular organs (CVO) to influence cardiovascular regulation. 3. The area postrema (AP), a CVO in the brainstem, mediates at least some o f the central actions of these peptides, Vasopressin appears to act in the AP to cause sympathoinhihition and a shift in baroreflex control of the sym pathetic nervous system (SNS) to lower pressures. These effects of AVP and the AP appear to be mediated by alpha(2)-adrenoceptor and glutamatergic mec hanisms in the nucleus tractus solitarius. 4. In contrast to AVP AngII has effects in the AP to blunt baroreflex contr ol of heart rate and cause sympathoexcitation. The effects of chronic AngII to increase activity of the SNS may be due to AP-dependent activation of n eurons in the rostral ventrolateral medulla.