Angiotensin II receptor binding and the baroreflex pathway.

Angiotensin II (Ang II) acts centrally to modulate autonomic activity and cardiovascular function. Using in vitro autoradiography we have determined the distribution of putative receptors for ANG II in brain regions associated with the baroreflex pathway. Ang II receptor binding sites were observed in the nucleus of the solitary tract (NTS), the dorsal motor nucleus of vagus, the rostral and caudal ventrolateral medulla and intermediolateral cell column of the spinal cord. Receptor binding sites were also observed in the nodose ganglion and in association with nerve fibres in the heart. Nodose ganglionectomy and vagal ligation studies revealed that Ang II receptor binding sites are produced in the nodose ganglion and transported in the vagus nerve to terminals of vagal afferent neurones. In the NTS these presynaptic receptors could mediate the known baroreflex inhibitory action of Ang II by inhibition of neurotransmitter release. In the cat, Ang II receptors were sharply localized in the rostral ventrolateral medulla to the subretrofacial nucleus. Microinjection of Ang II (10-50 pmoles) into this region induced a sympathetically-mediated pressor response. Together these results demonstrate several regions within the baroreflex arc which contain Ang II receptors, at which Ang II may modulate cardiovascular control and autonomic function.