Enhanced resistance artery sensitivity to agonists under isobaric compared with isometric conditions

Area of Science:

• Physiology
• Vascular Biology
• Pharmacology

Background:

• Vascular resistance arteries exhibit myogenic tone, a property that influences their response to vasoactive stimuli.
• Understanding this interaction is crucial for comprehending blood pressure regulation.

Purpose of the Study:

• To compare the responsiveness of rabbit mesenteric resistance arteries to agonists under isometric and isobaric conditions.
• To investigate the role of pressure-induced myogenic tone and membrane potential in vascular reactivity.

Main Methods:

• Rabbit mesenteric resistance arteries were studied under both pressurized (isobaric) and non-pressurized (isometric) conditions.
• Vascular diameter changes and force generation were measured in response to various vasoactive agents (norepinephrine, histamine, angiotensin II).
• Vascular smooth muscle cell membrane potential was manipulated using partial depolarization with KCl.

Main Results:

• Pressurized arteries exhibited spontaneous myogenic tone, reducing diameter, and were more sensitive to norepinephrine and histamine than isometrically mounted arteries.
• Angiotensin II produced a sustained response only in pressurized vessels.
• Reducing pressure abolished myogenic tone and decreased sensitivity to norepinephrine.
• Partial depolarization of isometrically mounted arteries mimicked the increased sensitivity observed in pressurized vessels, revealing responses to angiotensin II.

Conclusions:

• Pressure-induced myogenic tone fundamentally interacts with and enhances the sensitivity of resistance arteries to vasoactive stimuli.
• Vascular smooth muscle cell membrane potential plays a pivotal role in determining the reactivity of the resistance vasculature.
• These findings highlight the importance of considering physiological pressure conditions when studying vascular responses.