Nitric oxide-mediated arteriolar dilation after endothelial deformation

Area of Science:

• Vascular Biology
• Endothelial Function
• Physiology

Background:

• Arteriolar constriction is often followed by dilation.
• The role of endothelial cells in this post-constriction response is not fully understood.
• Nitric oxide (NO) is a key regulator of vascular tone.

Purpose of the Study:

• To investigate the hypothesis that mechanical deformation of the endothelium during arteriolar constriction stimulates nitric oxide (NO) release.
• To elucidate the role of NO in modulating arteriolar diameter changes.
• To determine if endothelial cell deformation itself can induce NO production.

Main Methods:

• Isolated rat mesenteric arterioles were subjected to agonist-induced constrictions (phenylephrine, U-46619, KCl) and pressure changes.
• Nitric oxide synthase inhibition (L-NNA) and endothelial denudation were used to assess NO's role.
• Cultured mesenteric arteriolar endothelial cells (EC) were stimulated with agonists and subjected to mechanical deformation.
• Nitrite production, an indicator of NO release, was measured using a fluorometric assay.

Main Results:

• Agonist-induced constrictions were followed by potent dilations, which were reduced by L-NNA or EC removal.
• Increased extraluminal pressure causing diameter reduction led to post-pressure dilation, diminished by L-NNA or EC removal.
• Cultured EC released NO in response to acetylcholine but not PE, U-46619, or KCl.
• Mechanical deformation of cultured EC significantly increased NO release.

Conclusions:

• Endothelial cell deformation during arteriolar constriction elicits nitric oxide (NO) release.
• This NO release acts as a mechanism to modulate and limit arteriolar constriction.
• Mechanical forces on endothelial cells are a significant factor in regulating vascular tone.