Tryptic generation of an angiotensin binding substance

Area of Science:

• Biochemistry
• Endocrinology
• Renal Physiology

Background:

• Renin-angiotensin system (RAS) plays a crucial role in blood pressure regulation.
• Accurate measurement of renin activity is essential for understanding RAS-related disorders.
• Existing radioimmunoassays may be affected by plasma processing methods.

Purpose of the Study:

• To investigate the impact of trypsin treatment on angiotensin I measurement in plasma.
• To identify and characterize a trypsin-generated angiotensin binding substance.
• To reassess renin levels in plasma after accounting for the binding substance.

Main Methods:

• Plasma samples (rat and human) were treated with trypsin.
• A binding substance precursor was isolated and characterized.
• Angiotensin I was added to control and trypsin-treated plasma to assess binding.
• Renin levels were measured using radioimmunoassay before and after trypsin treatment.

Main Results:

• Trypsin treatment generated an angiotensin binding substance, leading to underestimated angiotensin I levels.
• The precursor of the binding substance was converted by trypsin to a 45K form.
• Measured renin levels in trypsin-exposed plasma were approximately twofold higher than in conventional assays.
• This finding suggests a potential explanation for the observed lack of change in inactive renin.

Conclusions:

• Trypsin-induced binding substance formation significantly affects renin activity assays.
• The activation of this binding precursor during renin assays can lead to inaccurate underestimation of active renin.
• This study provides a new perspective on the measurement of inactive renin and its behavior in vivo.