|dc.description.abstract||Background: Ang II plays a major role in cardiovascular regulation. Recently, it has
become apparent that vascular superoxide anion may play an important role in
hypertension development. Treatment with antisense NAD(P)H oxidase or SOD
decreased BP in Ang II-infused rats. Wang et al recently reported mice which lack one of
the subunits of NAD(P)H oxidase developed hypertension at a much lower extent when
compared to the wild type animals infused with Ang II, indicating that superoxide anion
contributes to elevation in BP in the Ang II-infused hypertensive model. In the Ang
II-infused hypertensive model, altered reactivity of blood vessels is often associated with
the elevation of systolic blood pressure. We have observed abnormal tension
development and impaired endothelium-dependent relaxation in the isolated aorta of Ang
II-infused and DOCA-salt hypertensive rats. Recently, several other cellular signal
molecules, including ERK1I2 and PI3K, have been determined to play important roles in
the regulation of smooth muscle contraction and relaxation. ERKl/2 and PI3K pathways
are also reported to contribute to Ang II induced cell growth, hypertrophy, remodeling
and contraction. Moreover, these signaling pathways have shown ROS-sensitive
properties. Therefore, the aim of the present study is to investigate the roles of ERKl12
and PI3K in vascular oxidative stress, spontaneous tone and impaired endothelium
relaxation in Ang II-infused hypertensive model.
Hypothesis: We hypothesize that the activation of ERKl12 and PI3K are elevated in response to an Ang II infusion for 6 days. The elevated activation of phospho-ERKl/2
and PI3K mediated the increased level of vascular superoxide anion, the abnormal
vascular contraction and impaired endothelium-dependent vascular relaxation in Ang
II-infused hypertensive rats.
Methods: Vascular superoxide anion level is measured by lucigenin chemiluminescence.
Spontaneous tone and ACh-induced endothelium-dependent relaxation was measured by
isometric tension recording in organ chamber. The activity of ERK pathway will be
measured by its Western blot of phosphorylation of ERK. PI3K activity was evaluated
indirectly by Western blot of the phosphorylation of PDKl, a downstream protein of
PI3K signaling pathway. The role of each pathway was also addressed via comparing the
responses to the specific inhibitors.
Results: Superoxide anion was markedly increased in the isolated thoracic aorta from
Ang II-infused rats. There was spontaneous tone developed in rings from Ang II-induced
hypertensive but not sham-operated normotensive rats. ACh-induced
endothelium-dependent relaxation function is impaired in Ang II-infused hypertensive
rats. Superoxide dismutase and NAD(P)H oxidase inhibitor, apocynin, inhibited the
abnormal spontaneous tone and ameliorated impaired endothelium-dependent relaxation.
The expression of phopho-ERKII2 was enhanced in Ang II-infused rats, indicating the
activity of ERK1I2 could be increased. MEK1I2 inhibitors, PD98059 and U126, but not
their inactive analogues, SB203580 and U124, significantly reduced the vascular
superoxide anion in aortas from Ang II-infused rats. The MEK1I2 inhibitors reduced the
spontaneous tone and improved the impaired endothelium-dependent relaxation in aorta
of hypertension. These findings supported the role of ERKII2 signaling pathway in
vascular oxidative stress, spontaneous tone and impaired endothelium-dependent
relaxation in Ang II-infused hypertensive rats.
The amount of phospho-PDK, a downstream protein of PI3K was increased in Ang II rats
indicating the activity of PI3K activity was elevated. Strikingly, PI3K significantly
inhibited the increase of superoxide anion level, abnormal spontaneous tone and restored
endothelium-dependent relaxation in Ang II-infused hypertensive rats. These findings
indicated the important role of PI3K in Ang II-infused hypertensive rats.
Conclusion: ERKII2 and PI3K signaling pathways are sustained activated in Ang
II-infused hypertensive rats. The activated ERKII2 and PI3K mediate the increase of
vascular superoxide anion level, vascular abnormal spontaneous tone and impaired