The Effects And Mechanisms Of Dexmedetomidine On Postoperative Gastrointestinal Function Recovery

BackgroundPostoperative ileus(POI)is reported as gastrointestinal motility dysfunction accompanied with decreased bowel movements.It follows abdominal surgery or any other surgeries those require general anesthesia.It was reported POI was found from 3 to 32%,and was related to the length of skin cut,the depth of operation and the volume of bleeding.POI is unpathological and temporary.The early clinical manifestations are abdominal pain,distention,nausea and vomiting while delayed eating,delayed flatus and delayed defecation are followed.Then the degree of satisfaction is deceased,the possibility of postoperative infection,pneumonia,anastomotic fistula and other complications is increased.As a result the length of hospital stay is extended,the economic burden on patient and the medical system is increased.There are four aspects for the mechanisms of POI.Firstly,it is abnormal neuromodulation.The autonomic nervous system includes sympathetic and parasympathetic nerves(vagus nerves).Intestinal peristalsis is inhibited by sympathetic excitation while activated by parasympathetic excitation.Sympathetic never activity would be increased by the stress response,anesthesia and postoperative pain.Because a new balance has to establish,parasympathetic excitability is relatively decreased,decreased release of acetylcholine(Ach)is followed,after that intestinal peristalsis is inhibited.At the same time receptors on intestinal smooth muscle are inhibited by the activated sympathetic never,then slow gastrointestinal peristalsis is followed.Secondly,more release of inflammatory factors and other inflammatory mediators.Inflammation is increased by the intestinal turnover.Sleeping macrophages are activated by abdominal surgeries,and are promoted their transfer to intestinal ganglion and mucosa,promotes the release of inflammatory factors and gastrointestinal peristalsis are inhibited.Thirdly,use of opioids.Cardiovascular activity center of medulla oblongata was inhibited by opioids to stimulate the vagus nerve and improve the parasympathetic activity.Heart rate is decreased in cardiovascular system while gastrointestinal peristalsis is inhibited by the relatively hyperactive parasympathetic nerve.Prolonged gastric emptying rate and intestinal transit rate was happened.Finally,surgical trauma.Intestinal manipulation causes intestinal mucosal edema,intestinal bacterial translocation and damage of intestinal mucosal barrier function.The relatively hypoactivity of parasympathetic nerve plays an important role in the formation of POI.Sympathetic and parasympathetic nerve achieve balance by restricting each other.When one of the two goes to positive regulation,the other certainly goes to negative regulation to achieve a new balance.It was reported that use of sympathetic inhibitors or epidural anesthesia could promote postoperative intestinal peristalsis and shorten the first postoperative exhaust time.The mechanism is up-regulated parasympathetic nerve excitability while the inhibited sympathetic nerve excitability to promote postoperative gastrointestinal peristalsis.Dexmedetomidine(DEX)is a highly selective α2 receptor agonists,it has the effects of sedation,analgesia,inhibition of sympathetic hyperactivity,and reduce of inflammatory mediators with little respiratory inhibition.Parasympathetic hyperactivity follow the inhibition of sympathetic hyperactivity to promote bowel movement.Synergistic effect of analgesia by DEX reduces the dosage of opioids.Based on the reported effects of DEX,we hypothesized that DEX could promote postoperative gastrointestinal function.Our research is divided to two steps.Firstly,it is a clinical observation.Previous studies on POI were more based on gastrointestinal surgery,so laparoscopic nephrectomy was chosen to avoid intestinal injury caused by surgical operation as much as possible.Use different dose of DEX to observe the times of first postoperative flatus and defecation,the dose of sufentanil,postoperative pain.Secondly,it is an animal experiment to validate the first step result.Gastric emptying and small intestinal transmit rate were detected to assessment the postoperative gastrointestinal function.α2 receptor inhibitor atipamezole(ATI)was used to antagonize the effect of DEX decrease sympathetic excitability,explore whether DEX promoted postoperative gastrointestinal function through autonomic nerve regulation.3-methyladenine(3-MA)was used to explore whether DEX promoted postoperative gastrointestinal function by reducing inflammatory response,explore the relationship between DEX reducing inflammatory response and phosphatidylinositol-3-kinase/threonine protein kinase B/rapamycin target of rapamycin(PI3K/Akt/mTOR)pathway.Objective1.To investigate the influences of DEX on postoperative intestinal function recovery,postoperative pain,and hemodynamic stability in patients undergoing laparoscopic nephrectomy.2.To explore the influences of DEX on postoperative gastrointestinal function recovery.To investigate the influence of DEX on the autonomic nerve regulation.To investigate the effects and mechanisms of DEX on inflammatory responses.MethodsPart Ⅰ Impact of intravenous dexmedetomidine on postoperative bowel movement recovery after laparoscopic nephrectomyOne hundred and twenty patients who met inclusion criteria and planned to undergo laparoscopic nephrectomy were assigned to group C(normal saline),group D1(maintenance period DEX 0.2 ug/kg/h)and group D2(maintenance period DEX 0.4 ug/kg/h).Before anesthesia induction,DEX(0.5 ug/kg)was given to patients in D1 and D2 groups,while normal saline in C group.When the pneumoperitoneum was done,normal saline in group C,DEX(0.2 ug/kg/h)in group D1 and DEX(0.4 ug/kg/h)in group D2 was intravenously injected respectively and stopped 30 min before the end of the operation.Postoperative control analgesia(PCA)pump was given at the end of the operation.The dosage of DEX was regulated according of the maintenance period.Sufentanil(0.02 ug/kg/h)was added into pump in group C,sufentanil(0.02 ug/kg/h)+ DEX(0.02 ug/kg/h)in group D1 and sufentanil(0.02 ug/kg/h)+ DEX(0.04 ug/kg/h)in group D2.To observe hemodynamics during the surgery at six time points,patient entered the room(T0),5 min after loading dose of test drug(T1),5 min after establishment of pneumoperitoneum(T2),1 h after establishment of pneumoperitoneum(T3),2 h after establishment of pneumoperitoneum(T4),5 min after removal laryngeal mask(T5).MAP and HR were recorded.Recorded postoperative first flatus time,postoperative first defecation time,postoperative first eating time,postoperative numerical rating scale(NRS)at rest(NRSr)and movement(NRSm),sufentanil dosages,rates of postoperative nausea,vomiting,delirium and respiratory depression.Part Ⅱ Effects and mechanisms of dexmedetomidine on postoperative gastrointestinal function recovery of rats1.Animal model and groupingThirty-six rats were randomly divided into six groups,six in each group:control group(CON group),DEX group,intestinal manipulation group(IM group),DEX+IM group,atipamezole+DEX+IM group(ATI+DEX+IM group),3-methyladenine+DEX+IM group(3-MA+DEX+IM group).The effect of DEX on gastrointestinal function is dose-dependent,and the specific dose that is no effect on gastrointestinal function has not been determined.It was reported DEX 80 ug/kg decreased the gastrointestinal function,and DEX 30 ug/kg used in experiment about inflammatory also decreased gastrointestinal function.Therefore,the load(0.5 ug/kg)used in clinical step were converted into rat and to be used in second step.CON group:normal saline was injected through caudal vein.30 min later,methylcellulose and phenol red mixture 1.5ml by gavage.DEX group:DEX(3.0 ug/kg)was injected through caudal vein.30 min later,methylcellulose and phenol red mixture 1.5 ml by gavage.IM group:normal saline was injected through caudal vein.30 min later,intestinal manipulation,as waking up methylcellulose and phenol red mixture 1.5ml was given by gavage.DEX+IM group:DEX(3.0 ug/kg)was injected through caudal vein.30 min later,intestinal manipulation,as waking up methylcellulose and phenol red mixture 1.5 ml was given by gavage.ATI+DEX+IM group:ATI(250 ug/kg)was injected intraperitoneally.30 min later,DEX(3.0 ug/kg)was injected through caudal vein.30 min later,intestinal manipulation,as waking up methylcellulose and phenol red mixture 1.5ml by gavage.3-MA+DEX+IM group:3-MA(30 ug/kg)was injected intraperitoneally.30 min later,DEX(3.0 ug/kg)was injected through caudal vein.30 min later,intestinal as waking up manipulation,methylcellulose and phenol red mixture 1.5ml by gavage.180 min later,isoflurane(5%)to kill the rats,and the chest was opened to confirm death.2.Tissue specimen collection and names of examinationCollected blood to detect catecholamine,Interleukin-1β(IL-1β),IL-6,IL-18 and tumor necrosis factor-α(TNF-α).The gastric emptying rate,small intestine transmit rate,IL-1β,IL-6,IL-18,TNF-α and NLRP3 were measured.The protein expression of phosphatidylinositol-3-kinase(PI3K),threonine protein kinase B(AKT),rapamycin target of rapamycin(mTOR)and its phosphorylation,microtubule-associated protein light chain-3-Ⅰ(LC3-Ⅰ),LC3-Ⅱ,and Beclin-1 were detected.ResultsPart Ⅰ Impact of intravenous dexmedetomidine on postoperative bowel movement recovery after laparoscopic nephrectomy1.Effects of different doses of DEX on postoperative bowel movement recoveryTo determine the effects of DEX on postoperative bowel movement,first postoperative flatus time,defecation time and eating time were accessed.The first flatus time in group D1(41.50±8.24 h)and group D2(38.33±7.60 h)were significantly lower than that in group C(51.31±11.78 h)(P<0.01).The first defecation time in group D1(73.33 ± 19.19 h)and group D2(71.33±19.70 h)were significantly lower than that in group C(92.80±25.51 h)(P<0.01),implying DEX promoted postoperative intestinal function.The first eating time in group D1(44.50 ±8.94 h)and group D2(42.29 ± 7.75 h)were significantly lower than that in group C(54.78 ± 11.58 h)(P<0.01).There was no significant difference between groups D1 and D2(P>0.05).2.Effects of different doses of DEX on postoperative painThe NRSr among three groups were maintained at 0-4.The NRSr of groups D1 and D2 were significantly lower than that in group C at 8 h and 24 h(P<0.05);NRSm among three groups were maintained at 2-6.NRSm in groups D1 and D2 were significantly lower than that in group C at 1 h,2 h,4 h,8 h,12 h,24 h,and 48 h,implying DEX relieved postoperative pain.NRSr and NRSm were not significant differences between groups D1 and D2(P<0.05).3.Effects of different doses of DEX on sufentanilThe dosages of sufentanil among group C(32.58 ± 7.20 ug),group D1(31.63 ±3.28 ug)and group D2(32.75±3.91 ug)were not significant differences(P>0.05).The concentrations of sufentanil in PCA among group C(0.76±0.10 ug/ml),group D1(0.75+0.06 ug/ml)and D2(0.75±0.05 ug/ml)were not significant differences(P>0.05).Within 4 h after surgery,the dosages of sufentanil in group D1 and D2 were lower than that in group C(P<0.05),implying DEX reduced postoperative sufentanil dosages.4.Effects of different doses of DEX on hemodynamicsMAP:they were significantly lower in groups D1 and D2 than that in group C at T1(P<0.05).They were lower at T2,T3,T4 and T5 than T0 in group C.They were lower at T1 and T4 than T0 in groups D1 and D2(P<0.05).HR:they were significantly lower in groups D1 and D2 than that in group C at T1(P<0.05).They were lower at T2,T3 and T4 than T0 in group C.They were lower at T1,T2,T3 and T4 than T0 groups in D1 and D2(P<0.05).5.Effects of different doses of DEX on side effectsNausea,vomiting,delirium and respiratory depression among three groups were not significant differences(P>0.05).Part II Effects and mechanisms of dexmedetomidine on postoperative gastrointestinal function recovery of rats1.Effects of DEX on postoperative gastrointestinal functionTo determine the effects of DEX on postoperative gastrointestinal function,gastric emptying and small intestinal transmit were accessed.Gastric emptying and small intestinal transmit were decreased in IM group compared with CON group(P<0.01).However,treatment with DEX significantly increased gastric emptying and small intestinal transmit(P<0.01),implying DEX promoted the postoperative gastrointestinal function of POI model rats.In addition,treatment with ATI or 3-MA abolished the promoting gastrointestinal function elicited by DEX(P<0.01).The insignificant difference between CON and DEX groups showed that DEX had no effect on normal rats(P>0.05).2.Effects of DEX on autonomic nerve regulationTo determine the effect of DEX on autonomic nerve regulation,catecholamine concentration was accessed.It was increased in IM group compared with CON group(P<0.01).However,treatment with DEX significantly decreased catecholamine concentration(P<0.01),implying DEX inhibited sympathetic activity.In addition,treatment with ATI or 3-MA abolished the inhibiting sympathetic activity elicited by DEX(P<0.05).The insignificant difference between CON and DEX groups showed that DEX had no effect on normal rats(P>0.05).3.Effects of DEX on inflammatory responses3.1 Effects of DEX on IL-1β,IL-6,IL-18 and TNF-αTo determine the effect of DEX on inflammatory reactions,changes of IL-1β,IL-6,IL-18,TNF-α were tested.It was found higher in IM group than in CON group(P<0.01).However,their concentrations were significantly decreased after the treatment of DEX(P<0.01),implying DEX decreased inflammatory reactions.In addition,treatment with ATI or 3-MA abolished the decreasing inflammatory reactions elicited by DEX(P<0.05).The insignificant difference between CON and DEX groups showed that DEX had no effect on normal rats(P>0.05).3.2 Effects of DEX on NLRP3By further evaluating the inflammatory responses of intestine,we found intestinal manipulation was significantly increased expression of NLRP3,which was downregulated by DEX(P<0.01).Moreover,ATI and 3-MA could reverse the effect of DEX(P<0.05).The insignificant difference between CON and DEX groups showed that DEX had no effect on normal rats(P>0.05).4.Effects of DEX on PI3K/AKT/mTOR pathway related proteinsTo verify the correlation between the PI3K/AKT/mTOR pathway and the pharmacological effects of DEX,we examined expression of PI3K,phosphorylated PI3K(p-PI3K),AKT,p-AKR,mTOR,p-mTOR.The western blot results showed that established POI model,expression of p-PI3K/PI3K,p-AKT/AKT and p-mTOR/mTOR were significantly higher(P<0.01).However,DEX reversed the effect of intestinal manipulation,and ATI and 3-MA could block the effect of DEX(P<0.01).The insignificant difference between CON and DEX groups showed that DEX had no effect on normal rats(P>0.05).5.Effects of DEX on autophagy-related proteinsTo verify the effect of DEX on autophagy relative protein,we accessed the autophagy-related proteins microtubule-associated protein light chain 3-Ⅰ(LC3-Ⅰ),beclin-1.Our results showed that intestinal manipulation decreased the expression of LC3-Ⅱ and Beclin-1(P<0.01).With DEX intervention,the LC3-Ⅱ/LC3-Ⅰ ratio and expression of Beclin-1 were significantly increased(P<0.01).Morever,ATI and 3-MA could reverse the effects of DEX,as they reduced the LC3-Ⅱ/LC3-Ⅰ ratio and expression of Beclin-1(P<0.05).The insignificant difference between CON and DEX groups showed that DEX had no effect on normal rats(P>0.05).Conclusion1.Postoperative infusion of DEX at maintenance period 0.4 ug/kg/h shorten first postoperative flatus time,defecation time and eating time,facilitates bowel movements with stable hemodynamics,relieves pain and decreases the doses of opioids.2.Postoperative gastrointestinal function is facilitated by infusion of DEX in rats.The first mechanism is regulation of autonomic nerve system,sympathetic activity is inhibited by DEX,relatively leading to hyperfunction of parasympathetic nerve.The second mechanism is inflammatory response was reduced by DEX through inhibiting α2AR/PI3K/AKT/mTOR pathway.Innovation and significance1.It is the first time to observe the effects of DEX on postoperative intestinal function in patients undergoing laparoscopic nephrectomy avoiding the influence of gut damage.2.It was the first time to observe the effects of DEX on postoperative intestinal function by adding DEX into PCA.3.It was verified that the effects of DEX on postoperative gastrointestinal function recovery in rats.4.It was verified that the effects of DEX on autonomic nerve regulation.5.It was clarified that the effects of DEX on inflammatory responses through PI3K/AKT/mTOR pathway to promote postoperative gastrointestinal function recovery.Limitations1.It has not been further proved that DEX promotes postoperative gastrointestinal function through central system or peripheral system.2.It has not been further verified that whether autophagy participates in the process of DEX promoting postoperative gastrointestinal unction recovery.