Differences in pattern of plasma angiotensinogen in native and nephrectomized rats

Area of Science:

• Biochemistry
• Physiology
• Endocrinology

Background:

• Rat plasma contains two distinct angiotensinogen (Ao) forms, Ao-1 and Ao-2, in varying ratios within individual animals.
• Understanding the differential expression and clearance of these Ao forms is crucial for studying the renin-angiotensin system.

Purpose of the Study:

• To investigate the ratio of Ao-1 to Ao-2 in different rat strains.
• To determine how nephrectomy affects the Ao-1/Ao-2 ratio and total Ao content.
• To compare the kinetic parameters of endogenous plasma renin inactivation for Ao-1 and Ao-2.

Main Methods:

• Separation of Ao-1 and Ao-2 from rat plasma using SP-Sephadex C-50 chromatography.
• Analysis of plasma samples from Wistar, Wistar-Kyoto (WKY), and spontaneously hypertensive rats (SHR) before and after nephrectomy.
• Enzymatic assays to determine kinetic parameters (Km and Vmax) of renin inactivation for both Ao forms.

Main Results:

• Native plasma ratios of Ao-1 to Ao-2 were approximately 2.6:1 (Wistar), 2.4:1 (WKY), and 2.8:1 (SHR).
• Following nephrectomy, these ratios shifted significantly (e.g., to 1.1:1 in Wistar) with substantial increases in total Ao content (4.1-8.2 fold).
• Kinetic analysis showed similar Km and Vmax values for renin inactivation of Ao-1 and Ao-2, indicating comparable substrate affinity and maximal reaction rates.

Conclusions:

• Ao-1 and Ao-2 are likely synthesized in equimolar amounts.
• Ao-2 exhibits a faster clearance rate than Ao-1 in control rats.
• Under stimulated synthesis conditions post-nephrectomy, Ao-2 plasma levels increase more rapidly than the more glycosylated Ao-1.