Endothelium-dependent, shear-induced vasodilation is rate-sensitive

Area of Science:

• Physiology
• Microcirculation
• Endothelial Function

Background:

• Shear stress is a critical factor regulating vascular tone.
• Endothelium-mediated vasodilation plays a key role in blood flow regulation.
• The relative contributions of shear stress magnitude and rate of change are not fully understood.

Purpose of the Study:

• To quantify the distinct roles of shear stress magnitude and its rate of change in endothelium-mediated arteriolar dilation.
• To investigate the biphasic nature of vasodilation in response to controlled shear stress stimuli.

Main Methods:

• Isolated rat cremaster arterioles were subjected to controlled steps and ramps of shear stress using a feedback system.
• The temporal shear gradient (TSG) was manipulated to vary the rate of shear stress application.
• Both transient and sustained vasodilatory responses were measured.

Main Results:

• Time-dependent, biphasic vasodilations were observed in response to both step and ramp shear stress.
• An initial transient vasodilation peaked rapidly with step shear, while ramp shear produced a lower peak.
• A secondary, sustained vasodilation phase reached a similar steady state for both step and ramp shear.
• Early vasodilation was highly rate-sensitive at high TSGs (>5 dynes/cm²/sec) and magnitude-sensitive at low TSGs (<5 dynes/cm²/sec).

Conclusions:

• Microvascular endothelium mediates two distinct responses to shear stress.
• Rapid shear stress changes (seconds or less) elicit a potent, transient, rate-sensitive vasodilation.
• Slower shear stress changes (longer time scales) elicit a more modest, sustained, magnitude-sensitive vasodilation.