The Alleviating Effect Of Dexmedetomidine On Airway Hyperresponsiveness In Mice And Its Mechanism

Background:Airway hyper-responsiveness AHR is a state of abnormal sensitivity of the trachea and bronchus,which is an over-strong and premature response of the airway to a variety of physical,chemical,drug,allergens,exercise and other stimulus factors.Merger of airway hyper-responsiveness in perioperative patients are more sensitive to various stimuli,and easy to cause a variety of respiratory complications,severe cases may appear directly endanger the patient lives the "stillness of the lungs",or severe bronchospasm,secondary hypoxemia,low blood pressure,appear even hypoxic brain damage,heart failure and cardiac arrest.In order to effectively protect the pantient’s "whole airway safety" and life safety during perioperative period,it is an important clinical issue that needs to be solved urgently to clarify the mechanism of airway hyperreaction,and to give effective prevention and treatment measures.Dexmedetomidine(DEX),as a novel highly selective α2 adrenergic receptor agonist,has many effects like sedative,antianxiety,hypnotic,analgesic and sympathetic inhibitory.In recent years,our country has widely in clinical application in patients with general anesthesia surgery preoperative sedation,intraoperative awaken,postoperative analgesia mechanical ventilation and ICU ventilator calm.Recently,some scholars have observed that dexmedetomidine can play a protective role in lung injury through the influence of pulmonary vasoconstriction mechanism,pulmonary vascular ischemia-reperfusion injury and the release of inflammatory cytokines.However,whether dexmedetomidine can alleviate airway hyperresponse caused by airway inflammation and its specific mechanism has not been reported.Therefore,in the field of total airway management,whether dexmedetomidine has a mitigating effect on airway hyperresponse,and whether its mitigating effect is mediated by α2 adrenergic receptors,remains to be further explored and studied.Objectives:1.To establish the mouse airway hyperresponse model,and to observe whether the dexmedetomidine had a alleviating effect on the airway hyperresponse of mice.2.To explore whether dexmedetomidine alleviates airway hyperresponse in mice throughα2 adrenergic receptors.Methods and Results:Part One:The palliative effect of dexmedetomidine on airway hyperreactivity in miceMethods:Twenty-four BALB/c female mice aged 5 to 7 weeks were randomly divided into blank group(K),airway hyper-response group(HDM)and dexmedetomidine treatment group(D),with 8 mice in each group.The airway hyperresponse group and dexmedetomidine treatment group were sensitized with house dust mite extract(HDM)for continuous nasal drops for 5 weeks to establish a model of airway hyperresponse in mice.The dexmedetomidine treatment group received intraperitoneal injection of 25ug/kg dexmedetomidine 5 weeks after nasal drip of HDM for 5 consecutive days.The blank group and the HDM group were given the same amount of normal saline injection.Within 24 h after the last administration,invasive lung function was detected and airway reactivity was detected.Lung lavage was performed on mice to obtain bronchoalveolar lavage fluid(BALF),and the total number of cells in BALF was counted.Lung tissue was fixed with paraformaldehyde,and the pathological changes of lung were observed by HE staining after paraffin section.The eyeball blood of mice was collected and the level of total immunoglobulin E(IgE)in serum was determined by Elisa.Results:Compared with the K group,the airway reactivity,the total number of BALF inflammatory cells and the serum Elisa IgE level were significantly increased in the HDM group(P<0.01).HE staining showed obvious infiltration of inflammatory cells around bronchus and vessels,accompanied by lung injury.Microscopy showed alveolar structural destruction,alveolar wall thickening and edema.After dexmedetomidine treatment,compared with the HDM group,the airway reactivity,the total number of BALF inflammatory cells and the serum Elisa IgE level were significantly decreased in group D(P<0.05).The pathological changes of lung tissue were relieved,only a small amount of exudate and inflammatory cell infiltration could be seen in the interstitium and alveolar space.Part Two:Role of α2 adrenergic receptors in the alleviation of airway hyperresponse by dexmedetomidine in miceMethods:Thirty-two healthy female BALB/c mice were randomly divided into blank group(K),airway hyperresponse group(HDM),dexmedetomidine treatment group(D),yohimbine+dexmedetomidine treatment group(Y),with 8 mice in each group.The establishment method of airway hyperresponse model was the same as that of Part I.Group D was given intraperitoneal injection of dexmedetomidine 25ug/kg for five consecutive days after HDM induced airway hyperresponse.Group Y was given lmg/kg yohimbine intraperitoneally 1 hour before treatment after HDM excitation,and then 25ug/kg dexmedetomidine intraperitoneally.Group K and HDM were given intraperitoneal injection of normal saline,the same amount as dexmedetomidine(0.2 mL).Lung function of mice was measured within 24h after the last dexmedetomidine administration.The lung tissues were fixed with paraformaldehyde,and the pathological changes and goblet cell metaplasia were observed by HE staining and PAS staining.Left lung tissue was paraffin embedded,and immunohistochemistry was conducted to detect lung tissue NF-κB expression after dehydration.The right lung tissue was preserved with liquid nitrogen,and mRNA was extracted.The expression of IL-5 and IL-13 in the lung was determined by PCR.Results:Compared with K group,the airway reactivity,the total number of BALF inflammatory cells and the serum Elisa IgE level were significantly increased in HDM group(P<0.01).HE staining showed obvious infiltration of inflammatory cells around bronchus and blood vessels.PAS staining:there were a lot of goblet cell metaplasia around bronchioles in HDM group.Immunohistochemical staining:there were obvious NF-κB deposition in peribronchiole cells and lung epithelial cells;PCR results showed that the expressions of inflammatory cytokines IL-5 and IL-13 were increased(P<0.01).Compared with HDM group,the airway reactivity of mice in group D was significantly decreased after treatment with dexmedetomidine(P<0.05);The pathological changes of lung tissue,inflammatory cell infiltration and goblet cell metaplasia were relieved.Immunohistochemical staining:Group D NF-κB has a small amount of expression only in peripheral bronchiole cells;PCR results showed that the expression of inflammatory cytokines IL-5 and IL-13 were significantly decreased(P<0.05).Compared with group D,the airway reactivity of group Y was increased after yohimbine blockade(P<0.05).He pathological sections showed obvious pulmonary inflammation in group Y,with a large number of inflammatory cells infiltrating the bronchiole wall and accompanied by significant thickening of the alveolar wall.PAS staining showed obvious goblet cell metaplasia around the bronchiole wall.Immunohisto chemical staining:there are obvious NF-κB deposition in peribronchiole cells and lung epithelial cells;PCR results showed that the expression of inflammatory cytokines IL-5 and IL-13 in lung were increased(P<0.05).Compared with HDM group,there were no significant differences in airway reactivity,lung HE staining and pathological changes of PAS staining in Y group(P>0.05).However,immunohistochemistry detection of lung tissue NF-κB and PCR detection of lung IL-5,IL-13 expression in group Y were lower than HDM group(P<0.05).Conclusions:1.The airway hyperresponse model of BALB/c mice was successfully established by nasal drops of house dust mite extract(HDM)for five consecutive weeks;2.Dexmedetomidine can relieve airway hyperresponse and inflammation in mice;3.As an α2 adrenergic receptor blocker,yohimbine can partially antagonize the alleviating effect of dexmedetomidine on airway hyperresponse and airway inflammation;4.Dexmedetomidine may be partially mediated by α2 adrenergic receptors to alleviate airway hyperresponsitivity and inflammation in mice.