The physiological role of AT(1) receptors in the ventrolateral medulla

Neurons in the rostral and caudal parts of the ventrolateral medulla (VLM) play a pivotal role in the regulation of sympathetic vasomotor activity and blood pressure. Studies in several species, including humans, have shown t hat these regions contain a high density of AT(1) receptors specifically as sociated with neurons that regulate the sympathetic vasomotor outflow, or t he secretion of vasopressin from the hypothalamus, It is well established t hat specific activation of AT(1) receptors by application of exogenous angi otensin II in the rostral and caudal VLM excites sympathoexcitatory and sym pathoinhibitory neurons, respectively, but the physiological role of these receptors in the normal synaptic regulation of VLM neurons is not known. In this paper we review studies which have defined the effects of specific ac tivation or blockade of these receptors on cardiovascular function, and dis cuss what these findings tell us with regard to the physiological role of A T(1) receptors in the VLM in the tonic and phasic regulation of sympathetic vasomotor activity and blood pressure.