Alpha(1)-adrenergic-mediated eNOS phosphorylation in intact arteries

Area of Science:

• Vascular Biology
• Cardiovascular Physiology
• Molecular Pharmacology

Background:

• Activation of alpha(1)-adrenergic receptors on arterial smooth muscle induces vasoconstriction.
• A secondary, slow vasodilation follows, mediated by nitric oxide (NO) and potentially involving endothelial cells.
• The precise molecular mechanisms, particularly the role of endothelial nitric oxide synthase (eNOS) phosphorylation, remain unclear.

Purpose of the Study:

• To investigate the role of eNOS phosphorylation at Ser1179 and Thr495 in phenylephrine-induced slow vasodilation.
• To correlate vasomotor responses with changes in eNOS phosphorylation.
• To determine the endothelial dependence of phenylephrine-induced vasodilation.

Main Methods:

• Mouse mesenteric arteries were cannulated, pressurized, and superfused with phenylephrine (PE) or acetylcholine (ACh).
• Vasomotor changes (constriction and dilation) were measured.
• eNOS phosphorylation at Ser1179 and Thr495 was assessed using Western blot analysis.
• Inhibition of NO synthesis (L-NAME) and endothelial denudation were employed.

Main Results:

• Phenylephrine superfusion significantly increased eNOS phosphorylation at Ser1179.
• eNOS phosphorylation at Thr495 showed no significant changes.
• Phenylephrine-induced slow vasodilation was abolished by L-NAME and endothelial denudation, confirming NO and endothelial dependence.
• Increased Ser1179 phosphorylation preceded the slow vasodilation.

Conclusions:

• eNOS phosphorylation at Ser1179 occurs early in response to phenylephrine but does not appear to actively drive the subsequent slow vasodilation.
• The slow vasodilation is nitric oxide-dependent and requires an intact endothelium.
• Phosphorylation at Ser1179 may play a permissive role in eNOS activation, with the precise upstream signaling pathway yet to be elucidated.