Adenosine signalling has a protective role in intestinal ischemia and reperfusion injury

Introduction

Gut ischemia and reperfusion (IR), for example in small bowel transplantation or following resuscitation, may result in severe impairment of the intestinal microcirculation. Potential sequelae are mucosal damage, loss of barrier function, bacterial translocation, systemic inflammation, multiple organ failure and death. We hypothesized that extracellular adenosine signalling has a protective role in intestinal IR injury. Using intravital microscopy we investigated the effects of the adenosine receptor agonist NECA (5'-N-ethyl carboxamide adenosine) on leukocyte-endothelial interactions and capillary perfusion in the intestinal microcirculation following intestinal IR.

Methods

Six groups of animals (n = 7 per group) were studied: control (CON), NECA, IR (30 minutes of intestinal ischemia, 2 hours of reperfusion), IR + NECA, IR + NECA + MRS1754 (adenosine A_2B receptor antagonist), IR + NECA + DPCPX (adenosine A₁ receptor antagonist). All substances were administered immediately after declamping of the superior mesenteric artery. Intravital microscopy was performed after 2 hours of reperfusion. Leukocyte adhesion (rolling/firm adherence) and functional capillary density (FCD) were measured offline by blinded investigators.

Results

Following IR we observed a significant increase of leukocyte adherence in the intestinal submucosal venules (for example, V1 venules: CON 20.1 ± 5.8 n/mm², IR 237.8 ± 24.2 n/mm², P < 0.05). Capillary perfusion of the muscular layers of the intestinal wall was reduced (for example, longitudinal muscular layer: CON 112.3 ± 5.3 cm/cm², IR 92.4 ± 8.4 cm/cm²). NECA administration reduced significantly leukocyte adherence (V1 venules: 67.8 ± 6.8 n/mm², P < 0.05) and improved capillary perfusion (longitudinal muscular layer: 113.9 ± 8.3 cm/cm²). Administration of the adenosine A_2B receptor antagonist completely reversed the NECA effects (for example, leukocyte adherence V1 venules: 228.8 ± 33.2 n/mm²), whereas A₁ receptor inhibition only partially abolished the action of NECA (for example, leukocyte adherence V1 venules 124.5 ± 14.5 n/mm²).

Conclusions

The data support the hypothesis, that adenosine signalling is involved in intestinal IR injury. The adenosine A_2B receptors are more important than adenosine A₁ receptors since inhibition of A_2B receptor by MRS1754 completely reversed the effect of the adenosine receptor agonist NECA.