Juxtaglomerular angiotensin II formation

Area of Science:

• Nephrology
• Enzymology
• Physiology

Background:

• Previous research suggested an unidentified enzyme responsible for forming angiotensin II (AII) within the kidney's glomerular region.
• The precise identity and physiological function of this enzyme remained largely uncharacterized.

Purpose of the Study:

• To further characterize the unknown AII-forming enzyme (AFE) and investigate its potential physiological role in the kidney.
• To determine the localization and regulatory factors of AFE activity within renal tissues.

Main Methods:

• AFE activity was measured in various renal tissue preparations, including microdissected glomeruli and cortical/medullary sections.
• The effects of converting enzyme (CE) inhibitors, EDTA, and sodium chloride on AFE activity were assessed.
• Simultaneous measurement of AFE activity and AII immunoreactivity in renal structures and plasma under basal and water-deprived conditions.

Main Results:

• AFE activity was detected in cortical tissue and glomeruli but absent in the renal medulla.
• Specific CE inhibitors (SQ 20881, SQ 14225, DFP) effectively blocked AFE activity.
• AFE activity was not inhibited by EDTA or stimulated by sodium chloride, differentiating it from other known CEs.
• Water deprivation increased AII immunoreactivity in all renal samples but did not alter AFE activity.

Conclusions:

• The study characterizes a novel AII-forming enzyme (AFE) localized to the renal cortex and glomeruli.
• AFE is distinct from other known converting enzymes based on its inhibition profile and lack of response to EDTA or NaCl.
• Despite high local renin activity, AFE does not appear to be the rate-limiting enzyme for AII formation under the investigated conditions, suggesting a complex regulatory system for intrarenal AII production.