Hemorrhagic shock-induced excessive activation of the sympathetic adrenal medulla system resulted in the intestine continues state of hypoperfusion, which induces intestinal barrier damage. The current study investigated SGB post-processing effect on intestinal barrier function following haemorrhagic shock and found that SGB post-processing significantly improved the long-term survival rate and intestinal barrier function, which was related to the inhibition of autophagy activation.
The stellate ganglion belongs to the sympathetic ganglion, and the electrical activity of its neurons participates in the regulation of the autonomic nervous system. The beneficial effects of SGB are mostly attributed to the inhibition of sympathetic hyperexcitability. The previous study showed that SGB could promote local blood circulation, reduce inflammation, and regulate the nerve-endocrine-immune system's function, which plays a positive role in maintaining the environment's homeostasis. This study found that SGB post-processing dramatically prolonged the survival time and enhanced the survival rate of 72 hours in rats after hemorrhagic shock, suggesting that SGB post-processing is of great significance to the overall intervention hemorrhagic shock.
In severe trauma or shock, the intestine is one of the organs with the earliest hypo-perfusion. Studies have reported that when blood loss occurs but no systemic symptoms or vital signs occur, the small intestine and colon blood flow has decreased by 50%. However, after resuscitation, the intestinal blood perfusion is restored at the latest, making the mesenteric microcirculation in a state of continuous ischemia for a long time during shock resuscitation. In the experiment, we observed the loop blood flow of rats after hemorrhagic shock and found that the intestinal perfusion in the Shock group was significantly reduced, but the intervention of SGB significantly increased the intestinal blood flow in the Shock group. A recent systematic review and meta-analysis of the effect of SGB on the recovery of gastrointestinal function in patients undergoing general anesthesia confirmed the effect of SGB in promoting gastrointestinal recovery after traumatic surgery, which was related to gastrointestinal blood vessels telangiectasis and gastrointestinal motility improvement through the blockage of sympathetic nerves that innervate the gastrointestinal system. The present result suggests that SGB post-processing improves the intestinal blood supply after hemorrhagic shock, which is beneficial for reducing intestinal damage.
When intestinal ischemia and hypoxia occur, gathering many acidic metabolites in the local area directly causes cell metabolism dysfunction and tissue damage and reduces intestinal mucosal epithelial oedema, intraepithelial cell connections rupture, and even cell necrosis. Loss of the top of the mucosa's villi or full-thickness increases intestinal permeability and destroys the intestinal mucosal barrier. Our current work found that SGB postconditioning improved the histomorphology and oedema of intestinal mucosa after hemorrhagic shock. Since intestinal mucosal barrier dysfunction is closely related to increased intestinal permeability, we also tested the plasma concentration of FD4 and the distribution of FD4 in intestinal mucosa and submucosal tissues, and the results showed that SGB postconditioning significantly reduced intestinal mucosal permeability after hemorrhagic shock. These pieces of evidence demonstrated that SGB post-processing relieved intestinal barrier dysfunction after the hemorrhagic shock to a certain extent, which is consistent with the role of SGB pre-treatment[15, 16].
The tight junction (TJ) is mainly a composite structure composed of the transmembrane protein family (occludin and claudin protein) and the peri-membrane protein family (ZO protein)[26, 27], which is the basis for the integrity of the intestinal mucosal barrier structure. The ZO protein connects the Claudin protein, the occludin protein and the actin backbone system together to form a stable tight junction structure. Many studies have confirmed that the expression of tight junction proteins ZO-1, Claudin-1 and occludin are good indicators of intestinal barrier function and permeability function[29, 30]. This study showed that SGB post-processing significantly up-regulated the expressions of ZO-1, Claudin-1 and occludin in shock rats, indicating that SGB post-processing further reduced intestinal barrier dysfunction after hemorrhagic shock.
In generally, autophagy at the physiological level is believed to help maintain the balance between tolerance and defense in the intestine, but excessive autophagy activation has the opposite effect. The mechanism of ischemic intestinal injury may be related to trigger a series of complex cascade reactions, such as ROS burst, mitochondrial calcium overload and neutrophil infiltration, which are all effective activating factors of autophagy and lead to overexpression of autophagy. Our research showed that hemorrhagic shock and resuscitation enhanced the activation of autophagy. On the contrary, SGB post-processing down-regulates autophagy expression in the intestine, which is consistent with the tendency of SGB repairing the intestinal barrier.
On the other hand, we used autophagy inhibitor (3-MA) and activator (RAPA), combined with other intestinal injury evidence, to analyze the effect of autophagy on the intestinal damage caused by haemorrhagic shock and the correlation between SGB post-processing and autophagy. 3-MA has an observably inhibitory effect on the activity of phosphatidylinositol 3-kinase (PI3K), which is an essential component for the recruitment and formation of autophagic vesicles. Therefore, 3-MA blocks the autophagy process and autophagy formation at an early stage in mammals, and has been widely used in the study of autophagy pathophysiology[33–35]. RAPA is a macrolide compound produced by streptomyces hygroscopicus. It targets mammalian target of rapamycin (mTOR) and activates autophagy by inhibiting mTOR phosphorylation. When 3-MA was used to intervene in Shock group, we found that autophagy was inhibited. Simultaneously, 3-MA significantly alleviated intestinal mucosal tissue morphology injury and increased intestinal blood perfusion and reduced intestinal mucosal permeability. These findings indicate that autophagy inhibition by 3-MA is beneficial to lessen the intestinal barrier damage caused by hemorrhagic shock and resuscitation, which is consistent with the effect of SGB post-processing treatment. However, when RAPA was used in the Shock + SGB group, the expression of autophagy was significantly increased. At the same time, the treatment of RAPA significantly offset the beneficial effect of SGB post-processing treatment on the protection of the intestinal barrier. Therefore, it is reasonable to think that SGB post-processing alleviates intestinal barrier dysfunction by inhibiting autophagy. However, our study did not detect the expressions of PI3K and mTOR; then, the role of autophagy-related signaling pathway should be certified in the future.
Since the occurrence of traumatic or hemorrhagic shock is often unpredictable, preventive treatment is impossible. Therefore, we chose to study the therapeutic effect of SGB after hemorrhagic shock in the conscious rats, which is more in line with the actual situation of clinical emergencies. We first verified the effect and mechanism of SGB post-processing on the intestinal injury following hemorrhagic shock. In combination with previous studies on SGB pre-treatment results[15, 16], SGB pre-treatment or post-treatment effectively reduces the intestinal barrier damage after hemorrhagic shock. Still, neither affects blood pressure during acute bleeding.