Norepinephrine vascoconstrictor escape in isolated meseneric arteries

Area of Science:

• Vascular pharmacology
• Physiology
• Cardiovascular research

Background:

• Norepinephrine (NE) is a key vasoconstrictor.
• Mesenteric arteries can exhibit
• escape
• from NE's effects, but the mechanism is unclear.

Purpose of the Study:

• Investigate the mechanism of NE-induced vasoconstriction and escape in cat mesenteric arteries.
• Determine the role of ionic composition and electrical activity in this phenomenon.

Main Methods:

• Isolated superfused cat mesenteric arterial rings.
• Administration of norepinephrine (NE) at varying concentrations.
• Manipulation of extracellular ionic solutions (calcium, sodium, chloride substitutions).
• Measurement of isometric force development.

Main Results:

• NE caused initial force increase followed by decline (escape) in 48% of vessels.
• Low calcium abolished phasic contractions and reduced escape.
• Potassium depolarization prevented escape.
• Lithium and iodide/perchlorate substitutions altered peak force and escape.
• Isethionate abolished escape.
• Propranolol had no effect.

Conclusions:

• Escape from NE vasoconstriction in mesenteric arteries is likely due to fading of propagated electrical activity.
• Ionic environment significantly influences NE response and escape.
• The mechanism is independent of beta-adrenergic receptors.