Angiotensin II (Ang II) induces vasodilation, in part, through angiotensin type 2 receptor (AT2R)-induced actions in conditions associated with angiotensin type 1 receptor (AT1R) blockade and AT2R upregulation. Ang II/AT2R-induced vasodilation involves nitric oxide (NO)–cyclic guanosine monophosphate (cGMP)-dependent processes. We previously demonstrated that AT2R-mediated effects involve inhibition of the RhoA/Rho kinase pathway. However, molecular mechanisms underlying this phenomenon are unknown.
In the present in-vivo study we tested the hypothesis that AT2R-elicited vasodilation is associated with nitric oxide synthase (NOS) activation and NO production, and that a cGMP-dependent protein kinase (cGKI), which inactivates RhoA, is upregulated when stroke-prone spontaneously hypertensive rats (SHRSP) are treated with AT1R blockers.
SHRSP and Wistar–Kyoto (WKY) rats were treated with the AT1R blocker valsartan for 14 days. Dilatory responses to Ang II with or without the NOS inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) were performed in norepinephrine-precontracted vessels in the presence of valsartan. Expression of AT2R, endothelial NOS (eNOS) and cGKI was assessed by immunoblotting. NO bioavailability and NAD(P)H oxidase activity were evaluated by chemiluminescence.
Ang II elicited vasodilation in valsartan-treated SHRSP. L-NAME inhibited this effect, indicating a role for NO. eNOS expression and NO concentration were increased twofold by valsartan, only in SHRSP. Expression of cGKI was reduced in SHRSP and restored after valsartan treatment. NAD(P)H oxidase activity was approximately threefold higher in SHRSP versus WKY (P < 0.05) and reduced by valsartan.
Ang II, via AT2R, facilitates vasodilation through NOS/NO-mediated pathways and downregulation of cGKI after chronic AT1R antagonism. These effects may contribute in part to beneficial actions of AT1R blockers in the treatment of hypertension.