Angiotensin II Type 2 Receptor Decreases Ischemia Reperfusion Induced Fluid Leak

Background

Intravascular volume loss from ischemia-reperfusion (IR) injury is a major clinical concern. We hypothesize that angiotensin II decreases IR-mediated microvascular fluid leak via the angiotensin II type 2 receptor in a cAMP dependent manner. We therefore sought to determine hydraulic permeability after IR of venules treated with 1) angiotensin II, 2) angiotensin II and cAMP synthesis inhibitor, and 3) angiotensin II and an angiotensin II type 2 receptor antagonist.

Methods

Rat mesenteric post-capillary venules were micro-cannulated to measure hydraulic permeability (L_p). IR was achieved by placing animals in a 5% oxygen environment and preventing venular flow, after which blood flow was allowed to resume. L_p was measured after IR and treatment with 1) angiotensin II (20 nm), 2) angiotensin II (20 nm) + cAMP synthesis inhibitor (DDA,10uM), and 3) angiotensin II (20 nm) + type 2 receptor antagonist (PD-123319, 300 μm) (n = 6 in each group).

Results

Compared with the seven-fold increase in L_p because of IR alone: 1) angiotensin II attenuated the seven-fold increase by 50% (P < 0.005), 2) cAMP inhibition did not change the effect of angiotensin II on leak, and the type 2 receptor antagonist completely blocked the effects of angiotensin II on IR mediated leak.

Conclusion

Treatment with angiotensin II attenuated increases in hydraulic permeability because of IR by 50%. Inhibition of cAMP synthesis did not change the effect of angiotensin II on IR mediated leak, and angiotensin II type 2 receptor inhibition completely blocked the effects of angiotensin II. These results indicate that angiotensin II decreases IR induced leak via the angiotensin II type 2 receptor in a cAMP independent manner. A better understanding of mediators that reduce intravascular fluid loss from IR-induced microvascular dysfunction may help clinicians treat uncontrolled fluid extravasation that occurs during shock and sepsis.

Key Words: ischemia reperfusion, angiotensin II, AT2 receptor, cAMP, microvascular permeability