Isoproterenol induces vascular oxidative stress and endothelial dysfunction via a Giα-coupled ß2-adrenoceptor signaling pathway.

OBJECTIVE: Sustained ß-adrenergic stimulation is a hallmark of sympathetic hyperactivity in cardiovascular diseases. It is associated with oxidative stress and altered vasoconstrictor tone. This study investigated the ß-adrenoceptor subtype and the signaling pathways implicated in the vascular effects of ß-adrenoceptor overactivation. METHODS AND RESULTS: Mice lacking the ß1- or ß2-adrenoceptor subtype (ß1KO, ß2KO) and wild-type (WT) were treated with isoproterenol (ISO, 15 µg.g(-1) x day(-1), 7 days). ISO significantly enhanced the maximal vasoconstrictor response (Emax) of the aorta to phenylephrine in WT (+34%) and ß1KO mice (+35%) but not in ß2KO mice. The nitric oxide synthase (NOS) inhibitor L-NAME abolished the differences in phenylephrine response between the groups, suggesting that ISO impaired basal NO availability in the aorta of WT and ß1KO mice. Superoxide dismutase (SOD), pertussis toxin (PTx) or PD 98,059 (p-ERK 1/2 inhibitor) incubation reversed the hypercontractility of aortic rings from ISO-treated WT mice; aortic contraction of ISO-treated ß2KO mice was not altered. Immunoblotting revealed increased aortic expression of Giα-3 protein (+50%) and phosphorylated ERK1/2 (+90%) and decreased eNOS dimer/monomer ratio in ISO-treated WT mice. ISO enhanced the fluorescence response to dihydroethidium (+100%) in aortas from WT mice, indicating oxidative stress that was normalized by SOD, PTx and L-NAME. The ISO effects were abolished in ß2KO mice. CONCLUSIONS: The ß2-adrenoceptor/Giα signaling pathway is implicated in the enhanced vasoconstrictor response and eNOS uncoupling-mediated oxidative stress due to ISO treatment. Thus, long-term ß2-AR activation might results in endothelial dysfunction.

Increased vascular contractility and oxidative stress in ß2-adrenoceptor knockout mice: the role of NADPH oxidase.

BACKGROUND/AIMS: ß(2)-adrenoceptor (ß(2)-AR) activation induces smooth muscle relaxation and endothelium-derived nitric oxide (NO) release. However, whether endogenous basal ß(2)-AR activity controls vascular redox status and NO bioavailability is unclear. Thus, we aimed to evaluate vascular reactivity in mice lacking functional ß(2)-AR (ß(2)KO), focusing on the role of NO and superoxide anion. METHODS AND RESULTS: Isolated thoracic aortas from ß(2)KO and wild-type mice (WT) were studied. ß(2)KO aortas exhibited an enhanced contractile response to phenylephrine compared to WT. Endothelial removal and L-NAME incubation increased phenylephrine-induced contraction, abolishing the differences between ß(2)KO and WT mice. Basal NO availability was reduced in aortas from ß(2)KO mice. Incubation of ß(2)KO aortas with superoxide dismutase or NADPH inhibitor apocynin restored the enhanced contractile response to phenylephrine to WT levels. ß(2)KO aortas exhibited oxidative stress detected by enhanced dihydroethidium fluorescence, which was normalized by apocynin. Protein expression of eNOS was reduced, while p47(phox) expression was enhanced in ß(2)KO aortas. CONCLUSIONS: The present results demonstrate for the first time that enhanced NADPH-derived superoxide anion production is associated with reduced NO bioavailability in aortas of ß(2)KO mice. This study extends the knowledge of the relevance of the endogenous activity of ß(2)-AR to the maintenance of the vascular physiology.