Is the sympathetic system involved in shock-induced gut and lung injury?

BACKGROUND: β-blockade (BB) has been shown to prevent bone marrow (BM) dysfunction after trauma and hemorrhagic shock (HS). The impact of the sympathetic system and the role of BB on shock-induced distant organ injury is not known. This study will determine if BB has systemic effects and can diminish gut and lung injury after trauma and HS.
METHODS: Male Sprague-Dawley rats were subjected to lung contusion (LC) followed by 45 minute of HS. Animals (n = 6 per group) were then randomized to either receive propranolol (LCHS + BB) immediately after resuscitation or not (LCHS). Gut permeability was evaluated in by diffusion of Mr 4,000 of fluorescein dextran (FD4) from a segment of small bowel into peripheral blood. Villous injury and lung injury were graded histologically by a blinded reader. Plasma-mediated effects of BB were evaluated in vitro by an assessment of BM progenitor growth.
RESULTS: Animals undergoing LCHS had significantly higher plasma levels of FD4 compared with control animals (mean [SEM], 2.8 [0.4] µg/mL vs. 0.8 [0.2] µg/mL). However, animals receiving BB had a significant reduction in plasma FD4 compared with the LCHS group. With the use of BB after LCHS, both ileal and lung injury scores were similar to control. In addition, BM progenitor growth was inhibited by the addition of LCHS plasma, and LCHS + BB plasma showed no inhibition of BM progenitor growth.
CONCLUSION: Propranolol can protect against the detrimental effects of trauma and HS on gut permeability, villous, and lung injury. The effects of BB are likely systemic and appear to be mediated through plasma. BB likely blunts the exaggerated sympathetic response after shock and injury. Propranolol's reduction of both BM dysfunction and distant organ injury further demonstrates the importance of the sympathetic nervous system and its role in potentiating end organ dysfunction after severe trauma.