Angiotensin II metabolism by tissues from developing rats

Area of Science:

• Biochemistry
• Physiology
• Pharmacology

Background:

• Angiotensin II (AII) is a key peptide hormone regulating blood pressure.
• Understanding AII degradation is crucial for comprehending its physiological effects and developing related therapeutics.
• Previous studies have explored AII metabolism, but age-related differences, particularly in renal tissue, require further investigation.

Purpose of the Study:

• To investigate the age-dependent metabolism of angiotensin II (AII) in rat plasma, liver, and kidney.
• To characterize the degradation products and kinetics of AII hydrolysis in different tissues and age groups.
• To determine if age influences the rate and pathways of AII breakdown.

Main Methods:

• Incubation of radiolabeled Asp1-125I-Tyr4-angiotensin II (125I-AII) with rat plasma, liver homogenates, and kidney homogenates from rats of different ages.
• Analysis of degradation products using electrophoresis and peptide mapping.
• Quantification of 125I-tyrosine accumulation as a measure of AII hydrolysis.
• Determination of half-life (t1/2) for 125I-AII disappearance.

Main Results:

• 125I-AII was degraded in plasma, liver, and kidney homogenates, yielding 125I-tyrosine and peptide fragments (amino-terminus tetrapeptide, carboxy-terminus hexapeptide).
• AII degradation in plasma and liver homogenates showed no significant age-related changes in half-life.
• Kidney homogenates exhibited a significant, age-dependent increase in AII degradation rate, with half-life decreasing from 8.3 min in 2-week-old rats to 2.8 min in 8-week-old adult rats.
• The increased renal metabolism of AII correlated with a two-fold increase in 125I-tyrosine release in older rats.

Conclusions:

• Renal metabolism of angiotensin II is significantly influenced by age, accelerating substantially from postnatal development to adulthood.
• Plasma and liver angiotensin II degradation rates are not significantly affected by age within the studied period.
• The findings highlight the importance of age as a factor in renal angiotensin II processing and suggest potential implications for age-related cardiovascular regulation.