Effects of angiotensin blockade in the rostral ventrolateral medulla on maintenance of hypertension induced by chronic L-NAME treatment

The major aim of the present study was to evaluate the role of the angiotensin II receptors located within the rostral ventrolateral medulla (RVLM) in the maintenance of high blood pressure following chronic nitric oxide inhibition. Rats were treated orally with L-NAME (70 mg/kg/day) for 1 week. We inhibited the RVLM neurons using drugs such as Sarthran, Losartan and glycine in urethane-anesthetized rats (1.2 to 1.4 g/kg, i.v.). (1) Bilateral microinjection of Sarthran into the RVLM decreased BP in the hypertensive and normotensive groups, but the depressor effect of the drug was lower in hypertensive than in normotensive rats. (2) The decrease in BP in response to Sarthran in the RVLM compared with glycine was significantly smaller in the hypertensive group, but not in the normotensive group. (3) No change in MAP was observed in response to bilateral microinjection of the Ang AT₁ receptor antagonist Losartan into the RVLM in either group. These results suggest that (1) the endogenous angiotensin receptors of the RVLM are involved in the maintenance of high BP in L-NAME-treated animals and (2) the tonic action of Ang II is not dependent on AT₁ receptors within the RVLM. The possibility of an action via other Ang II receptors remains to be investigated.