RENAL SYMPATHETIC BAROREFLEX EFFECTS OF ANGIOTENSIN-II INFUSIONS INTOTHE ROSTRAL VENTROLATERAL MEDULLA OF THE RABBIT

1. The effects of local infusion of angiotensin II (AII) into the rost ral ventrolateral medulla (RVLM) pressor area on the renal sympathetic baroreflex were compared with the excitatory amino acid glutamate in urethane anaesthetized rabbits with chronically implanted renal nerve electrodes. Baroreflex blood pressure-renal nerve activity curves were obtained by intravenous infusion of phenylephrine and nitroprusside b efore and after treatments. 2. Infusion of 4 pmol/min of All into the RVLM increased blood pressure by 12 +/- 2 mmHg and transiently increas ed resting sympathetic nerve activity. The renal sympathetic barorefle x curves were shifted to the right. The upper plateau of the sympathet ic reflex increased by 29 +/- 8% (n = 6, P < 0.025). 3. Infusions of g lutamate into the RVLM, at a dose which was equipressor to that of All , also increased resting renal sympathetic nerve activity. In contrast to AII, this increase was maintained throughout the infusion. Glutama te shifted the reflex curve to the right and increased the upper plate au of the sympathetic reflex by 44 +/- 5% without affecting the lower plateau. 4. These results support the suggestion that AII can act at t he level of the RVLM pressor area to facilitate baroreflex control of renal sympathetic activity in a similar fashion to that produced by fo urth ventricular administration. 5. Thus the RVLM is a likely candidat e site for modulation of the renal sympathetic baroreflex. The similar ity of the actions of All to those of glutamate suggest that it may di rectly excite sympathetic vasomotor cells in this region.