Differential vascular sensitivity to luminally and adventitially applied endothelin-1

Area of Science:

• Vascular biology
• Cardiovascular physiology
• Endocrinology

Background:

• Endothelin-1 (ET-1) is a potent vasoconstrictor secreted into the vascular lumen.
• Its role as a circulating pressor substance requires investigation of its direct effects on vascular smooth muscle.

Purpose of the Study:

• To determine if luminal ET-1 can directly stimulate smooth muscle in isolated vascular segments.
• To assess the barrier function of the endothelium against circulating ET-1.

Main Methods:

• Isolated rabbit femoral arteries and veins were perfused separately on luminal and adventitial surfaces.
• Vasomotor responses to luminally administered ET-1 (1 nM) were measured in segments with and without endothelium.
• Endothelium-derived relaxing factor (EDRF) and prostacyclin (PGI2) release were assessed.

Main Results:

• Luminal ET-1 induced significant vasoconstriction in vascular segments lacking endothelium.
• No significant vasomotor response was observed in segments with intact endothelium.
• ET-1 stimulation did not lead to detectable EDRF release, with only a slight increase in PGI2 release.

Conclusions:

• The vascular endothelium forms a significant barrier to circulating ET-1 (up to 1 nM) in intact vessels.
• This barrier limits the direct pressor effects of ET-1 on vascular smooth muscle.
• Endothelial barrier function to ET-1 has no functionally significant impact on endothelial autacoid release.