Angiotensin formation in the isolated rat hindlimb

Area of Science:

• Physiology
• Cardiovascular Science
• Biochemistry

Background:

• The renin-angiotensin system (RAS) plays a crucial role in regulating blood pressure and fluid balance.
• While the systemic RAS is well-studied, the existence and function of a local vascular RAS remain areas of investigation.

Purpose of the Study:

• To investigate the local vascular generation of angiotensin in isolated perfused rat hindquarters.
• To elucidate the roles of renin and angiotensin-converting enzyme (ACE) in this vascular system.

Main Methods:

• Isolated perfused rat hindquarters model.
• High-performance liquid chromatography (HPLC) and radioimmunoassay for angiotensin quantification.
• Pharmacological inhibition of renin and ACE using specific inhibitors (H-142 and captopril).
• Perfusion with renin substrate, Angiotensin I (Ang I), and Angiotensin II (Ang II).

Main Results:

• Spontaneous release of Ang I and Ang II was detected in the hindlimb perfusate.
• Angiotensin converting enzyme (ACE) inhibition abolished Ang II release and increased Ang I levels.
• Renin perfusion induced angiotensin release and vasoconstriction, effects blocked by renin inhibitor H-142.
• ACE inhibition prevented Ang II formation and vasoconstriction but increased Ang I levels.
• Ang I was significantly converted to Ang II within the hindlimb vasculature, a process inhibited by ACE inhibitors.

Conclusions:

• The data provide strong evidence for a functional vascular renin-angiotensin system.
• The vascular system possesses the enzymatic machinery to generate and metabolize angiotensin locally.
• This local system may contribute to vascular tone regulation independently of the systemic RAS.