Complement factors C3a and C5a have distinct hemodynamic effects in the rat

Area of Science:

• Immunology
• Pharmacology

Background:

• The effects of C5a infusion in rats are well-documented, including hypotension and neutropenia.
• The comparative effects of C3a in rats remain undefined.
• Understanding C3a receptor (C3aR) activation is crucial for differentiating inflammatory mediator roles.

Purpose of the Study:

• To investigate C3a receptor (C3aR) activation in rats.
• To compare the in vivo effects of C3a and C5a on blood pressure and neutrophils.

Main Methods:

• Utilized recombinant human C3a, a C3aR agonist (WWGKKYRASKLGLAR), and a C3aR antagonist (SB-290157).
• Performed in vitro studies using C3aR-transfected RBL-2H3 cells to assess degranulation.
• Conducted in vivo experiments involving intravenous infusion in rats.

Main Results:

• C3a and WWGKKYRASKLGLAR selectively bound to C3aRs and induced degranulation in vitro, antagonized by SB-290157.
• Intravenous C3a and WWGKKYRASKLGLAR caused a concentration-dependent hypertensive response mediated by prostanoid release.
• C3a infusion led to a transient drop in neutrophils followed by a rise, contrasting with C5a's hypotension and rapid neutropenia.

Conclusions:

• C3aR activation in rats leads to hypertension and distinct neutrophil count changes.
• C3a and C5a exhibit significantly different physiological effects on blood pressure and circulating leukocytes in rats.
• These findings highlight the differential roles of C3a and C5a in inflammatory responses.