Multiple dilator pathways in skeletal muscle contraction-induced arteriolar dilations

Area of Science:

• Physiology
• Vascular Biology
• Exercise Physiology

Background:

• Muscle contraction is known to induce local and conducted arteriolar dilations.
• The precise signaling pathways mediating these dilations, particularly the roles of nitric oxide (NO), adenosine (Ado) receptors, and ATP-sensitive potassium (K(ATP)) channels, remain incompletely understood.

Purpose of the Study:

• To investigate the involvement of NO, Ado receptors, and K(ATP) channels in arteriolar dilations during muscle contraction.
• To differentiate the roles of these mediators in local versus conducted (upstream) vasodilation.

Main Methods:

• Utilized an in vivo cremaster muscle preparation in anesthetized hamsters.
• Stimulated muscle fibers to induce contraction and measured arteriolar diameter changes at local and upstream sites.
• Administered specific inhibitors: N(omega)-nitro-L-arginine (NO synthase inhibitor), xanthine amine congener (XAC; Ado receptor antagonist), and glibenclamide (Glib; K(ATP) channel inhibitor).

Main Results:

• Muscle contraction induced significant local and upstream arteriolar dilations.
• Local dilation was attenuated by NO synthase inhibition, Ado receptor antagonism, and K(ATP) channel blockade.
• Upstream dilation was significantly attenuated by Ado receptor antagonism and K(ATP) channel blockade, but not by NO synthase inhibition.
• Direct application of glibenclamide to the upstream site attenuated upstream dilation, suggesting a local role of K(ATP) channels at that site.

Conclusions:

• Nitric oxide, adenosine receptors, and K(ATP) channels contribute to local arteriolar dilation initiated by muscle contraction.
• K(ATP) channels and adenosine receptors, but not NO, are crucial for the upstream propagation of this dilation.