The Relationship Between Histamine And Histamine H₁ Receptor And Inflammatory Response In Rats With Ventilator-induced Lung Injury

Objective Mechanical ventilation is widely used in clinic as a means of ventilation management in general anesthesia patients,critical patients and a therapeutic means of lung diseases.At present,the outcome of lung injury caused by mechanical ventilation has been widely recognized and valued.How to reduce and avoid the side injury caused by this necessary medical means is an urgent problem to be solved.In addition to the tissue injury caused by mechanical factors,biological injury such as inflammatory reaction plays an important role in the process of ventilator-induced lung injury（VILI）.Inflammatory response is regulated by many systems including immune system,which has complex links and involves a wide range.The role of histamine and its receptor in a variety of inflammatory diseases has been widely studied.The purpose of this study is to observe the relationship between histamine and histamine H₁receptor and early inflammatory response in the lungs of VILI,and to provide a new scientific basis for the study of lung protective measures during mechanical ventilation.Methods 56 clean-grade healthy male Sprague-Dawley rats,aged 9-10 weeks and weighing 250-300 g,were divided into seven groups（n=8）using a random number table method:Control group（group C）,Normal V_T group（group NV）,High V_T group（group HV）and Saline control group（group S）,Premedication with lemastatin group（group Cle1-3）.After anesthesia,tracheotomy was inserted into endotracheal intubation in all group.The rats were retained spontaneous breathing in group C.The rats were mechanically ventilated with the tidal volume（V_T）of 8 ml/kg,respiratory rate（RR）40 breaths/min,inspiratory/expiratory（I/E）ratio 1:1,and inspired oxygen fraction（FiO₂）ratio 21%in group NV.The rats were mechanically ventilated with the V_T of 40 ml/kg,RR 40 breaths/min,I/E ratio 1:1,and FiO₂ 21%in group HV.30 min before anesthesia,Group S was intramuscular injected with 1.8ml/kg of normal saline,Group Cle 1-3 were respectively intramuscular injected with clemastine at 0.45 mg/kg,0.9 mg/kg and 1.8 mg/kg（the concentrations were 0.25,0.5 and 1 mg/ml respectively）,and then the rats in group S and group Cle 1-3 were mechanically ventilated with the same ventilator settings as group HV.After anesthesia,in group C,group NV and group HV,carotid artery was separated and blood gas was collected for analysis.After ventilation for 4 hours,the arterial blood was taken again for blood gas analysis.The rats were sacrificed by neck amputation at 4 h of ventilation,the left lung bronchoalveolar lavage fluid（BALF）was centrifuged immediately.The supernatant was collected for determination of concentrations of interleukin-6（IL-6）,tumor necrosis factor-alpha（TNF-α）and histamine in BALF by enzyme-linked immunosorbent assay（ELISA）.After centrifugation,precipitation cells was dyed by EOS staining,and eosinophils（EOS）were counted.The right anterior lobe of lung was stained with HE to observe the morphological changes of lung tissues by microscopic examination.The wet mass/dry mass（W/D）ratio of the right lung tissue was measured.Some middle lobes of right lung were stained with immunohistochemistry to observe the expression of H₁ receptor.In group S,group Cle 1-3,the rats were sacrificed by neck amputation at4 h of ventilation,the left lung BALF was centrifuged immediately.The supernatant was collected for determination of concentrations of IL-6,TNF-αand albumin in BALF by ELISA.After centrifugation,precipitation cells was dyed by EOS staining,and EOS were counted.The wet mass/dry mass（W/D）ratio of the right lung tissue was measured.Results There was no significant difference in Pa O₂/FiO₂ between group C,NV and HV.After 4 hours ventilation,compared with group C,Pa O₂/FiO₂ in NV group had no significant difference,but Pa O2/FiO2 in HV group decreased（P<0.05）.Compared with group C,the lung injury score of NV group increased（P<0.05）,compared with NV group,the lung injury score of HV group increased（P<0.05）.The W/D ratio of lung tissue increased in HV group（P<0.05）.The lung tissue damage of rats in high tidal volume mechanical ventilation group was serious.After 4hours ventilation,comparison of IL-6,TNF-αconcentration and EOS count in BALF:compared with group C,TNF-αand EOS in BALF increased in NV group（P<0.05）,compared with NV group,the concentrations of IL-6,TNF-αand EOS in BALF increased in HV group（P<0.05）.After 4 hours ventilation,the expression of histamine and H₁ receptor in lung:compared with group C,there was no significant difference in the concentration of histamine in BALF and the expression of H₁receptor in lung tissue of NV group,compared with NV group,the concentration of histamine in BALF increased（P<0.05）and the expression level of H₁ receptor in lung tissue increased of HV group（P<0.05）.Rats pretreated with H₁ receptor antagonists:After ventilation,compared with S group,the concentrations of IL-6,TNF-α,EOS,W/D ratio and albumin in BALF decreased in Cle1-3 group（P<0.05）.Compared with different doses of H₁ receptor antagonists,the concentrations of IL-6and TNF-αin BALF of Cle1-3 group decreased in turn（P<0.05）,there was no significant difference between EOS count in BALF and W/D ratio of lung tissue in Cle1-3 group.Conclusion The expression of histamine and histamine H₁ receptor in the lungs of rats with VILI was increased by high tidal volume,which was consistent with the change trend of inflammatory response in the lungs.Blocking H₁ receptor can reduce the inflammatory response in the lungs of VILI and may be helpful in protect the lung in VILI.