Endothelium-dependent responses in the microcirculation observed in vivo

Area of Science:

• Physiology
• Cardiovascular Research
• Microcirculation Studies

Background:

• Endothelium-dependent responses were first observed 40 years ago in large arteries.
• Research has extensively utilized in vitro methods with conductance vessels.
• The microcirculation's role in organ blood flow has driven in vivo studies of endothelium-dependent dilation.

Purpose of the Study:

• To review in vivo studies of endothelium-dependent dilation and constriction in the microvasculature.
• To explore the various agonists and mediators involved in these responses.
• To discuss the complexities and potential alternative pathways in microvascular endothelium-dependent signaling.

Main Methods:

• Initial in vivo studies used light/dye techniques to selectively damage the endothelium.
• Subsequent research investigated various endothelium-dependent agonists in vivo.
• Studies examined the roles of endothelial nitric oxide synthase, cyclooxygenase, and cytochrome P450 in mediator generation.

Main Results:

• Endothelium-dependent dilation and constriction were unequivocally proven in the microvasculature in vivo.
• Key agonists include acetylcholine, bradykinin, serotonin, and endothelin-1.
• Mediators involve nitric oxide, cyclooxygenase products, cytochrome P450 metabolites, and reactive oxygen species like H2O2.

Conclusions:

• The microcirculation exhibits complex endothelium-dependent responses influenced by multiple pathways.
• Reactive oxygen species play dual roles, potentially inhibiting or mediating dilation.
• Alternative mediators like nitrosothiols may be involved in specific microvascular responses.