Angiotensin II attenuates baroreflexes at nucleus tractus solitarius of rats

Microinjection of angiotensin II (ANG II) into the nucleus tractus solitarius (NTS) has been shown to produce a dose-dependent increase in blood pressure and heart rate. We have tested the effect of subpressor infusions of ANG II (10 ng . kg-1 . min-1) in the NTS on reflex bradycardia after intravenous administration of the vasoconstrictor phenylephrine (1-12 micrograms) in normotensive urethan-anesthetized rats. ANG II within the brain is thought to contribute to the decreased baroreflex sensitivity in spontaneously hypertensive rats (SHR). The sensitivity of the baroreflex was significantly decreased by the infusion of ANG II (1.01 +/- 0.08) compared with control (2.41 +/- 0.51) in the normotensive animals. Baroreflex sensitivity was significantly decreased in SHR (0.40 +/- 0.21) compared with normotensive animals. We conclude that ANG II within the NTS can inhibit the function of baroreceptor reflexes in normotensive animals, suggesting that the endogenous peptide may perform an inhibitory role in the baroreflex arc, and this is further evidence that central ANG II is involved in blood pressure of SHR.