Nephrectomy, converting enzyme inhibition, and angiotensin peptides

Area of Science:

• Physiology
• Biochemistry
• Endocrinology

Background:

• The renin-angiotensin-aldosterone system (RAAS) regulates blood pressure and fluid balance.
• Angiotensin II (Ang II) is a key peptide in the RAAS, primarily formed by angiotensin-converting enzyme (ACE).
• The precise contributions of kidney-derived renin and ACE to circulating and tissue Ang II levels remain incompletely understood.

Purpose of the Study:

• To elucidate the roles of kidney-derived renin and ACE in regulating Ang II peptide levels.
• To investigate alternative pathways for Ang II formation in the absence of kidney renin.

Main Methods:

• Measurement of angiotensin peptides (Ang-(1-7), Ang II, Ang-(1-9), Ang I) in plasma and various tissues.
• Utilized Sprague-Dawley rats subjected to control conditions, ramipril (ACE inhibitor) administration, nephrectomy (24h and 48h), and combined nephrectomy and ramipril treatment.

Main Results:

• Ramipril significantly reduced Ang II levels in plasma and most tissues, confirming ACE's major role in Ang II formation.
• Nephrectomy drastically decreased plasma renin and increased plasma angiotensinogen, while reducing tissue Ang II, highlighting kidney renin's importance.
• Ang II persisted in anephric rats, suggesting renin-independent formation, potentially amplified by increased angiotensinogen.

Conclusions:

• Kidney-derived renin and ACE are critical for maintaining Ang II levels.
• Ang II can be synthesized via pathways independent of kidney renin, particularly in anephric states.
• ACE inhibition may not fully suppress Ang II in all tissues when kidney renin is absent, indicating non-ACE-dependent pathways.