Gut epithelial apoptosis after severe burn: effects of gut hypoperfusion

Severe cutaneous burn causes transient mesenteric vasoconstriction and altered gut mucosal integrity. We recently showed that burn also increases gut epithelial cell death by apoptosis. The goal of this study was to determine whether changes in gut perfusion after burn contribute to burn-associated gut apoptosis.

We first correlated superior mesenteric artery blood flow with measurement of gut perfusion at the tissue level by laser doppler in four nonburned rats before, during, and after arterial clamping to validate our measurements of gut perfusion. We then characterized gut perfusion sequentially over time after burn; gut perfusion was measured 3 cm from the ligament of Treitz before burn and hourly for 6 hours. A group of control rats underwent the exact same protocol without the burn to exclude effects of anesthesia and laparotomy on tissue perfusion (n = 4). We studied a third group of rats with hypoperfusion of the same duration and magnitude induced mechanically without burn (n = 7). Sections of the proximal gut from all three groups (control without burn, burn, and hypoperfusion without burn) were examined for epithelial apoptosis.

Linear regression analysis demonstrated a strong correlation between superior mesenteric artery blood flow and intestinal tissue perfusion measured by laser doppler under both low and high flow conditions (r = 0.85). Laser doppler measurements of gut perfusion after burn showed deceased gut perfusion that was maximal at 2 hours postburn (p < 0.05), and that persisted for 4 hours (p < 0.05). By 6 hours, gut perfusion returned to baseline. Apoptosis increased significantly in the burn group (2.11 +/- 0.17%) compared with control (0.52 +/- 0.2%) and the mechanically decreased perfusion group (0.51 +/- .03) (p < 0.001).

We conclude that burn-induced gut hypoperfusion is insufficient to cause burn-related increased gut epithelial apoptosis. We speculate that the signal for increased gut epithelial apoptosis is primarily related to proinflammatory mediators induced by the burn wound.