Heterogeneity of endothelial cell function for angiotensin conversion in serial-arranged arterioles

Area of Science:

• Vascular Biology
• Endothelial Cell Function
• Microcirculation Physiology

Background:

• The endothelium plays a crucial role in regulating vascular tone.
• Angiotensin I and II (AI, AII), and norepinephrine (NE) are key vasoconstrictors.
• The specific role of the endothelium in mediating vasoconstriction varies across microvessel orders.

Purpose of the Study:

• To investigate the endothelial cell's involvement in vasoconstriction induced by AI, AII, and NE.
• To determine the differential roles of the endothelium in angiotensin conversion within different microvessel segments.
• To explore the involvement of endothelium-derived relaxing factor (EDRF) and prostaglandin (PG) synthesis in these responses.

Main Methods:

• Studied microvessels from the hamster cheek pouch.
• Utilized light-dye treatment for endothelial impairment.
• Assessed effects of angiotensin-converting enzyme (ACE) inhibition, EDRF blockade, and PG synthesis inhibition.

Main Results:

• In large 2nd-order arterioles, endothelial impairment did not affect AII or NE vasoconstrictor activity or ACE activity.
• In small 4th-order arterioles, endothelial impairment significantly reduced angiotensin conversion but did not alter AII or NE vasoconstrictor responses.
• Endothelial modulation of vasoconstrictor responses via EDRF or PGs was unlikely.

Conclusions:

• The endothelium exhibits differential roles in modulating local angiotensin conversion in distinct arteriolar segments.
• Endothelial cells are critical for angiotensin conversion in smaller arterioles but not larger ones.
• The endothelium does not appear to modulate AII-induced vasoconstriction through EDRF or PG pathways in these microvessels.