Abstract: Objective:To demonstrate the relationship between the changes of lung tissue beta receptors as well as its messenger conduction system and local phospholipaseA₂ activation after hemorrhagic shock and reperfusion injuries （S/R）.Methods:The beta adrenergic receptor and second messenger cAMP and cGMP in rabbit lung tissue after hemorrhagic shock and reperfusion injuries（S/R） were tested by radioreceptor binding assay and radioimmunoassay. The blood pH values and tCO₂ before or after S/R inury also were observed. Results:The number of beta receptor decreased and the receptor affinity increased after S/R injury. Although both cAMP and cGMP were increased, the ratio of cAMP/cGMP was decreased due to the more increase of cGMP than that of cAMP at the same time. Otherwise, beta receptor Bamx was significantly increased and its affinity was decreased by the use of phospholipase A₂ inhibitors chloroquine compounds and antioxidant （TFA） after shock before reperfusion. In addition, cAMP/cGMP after S/R injury was also increased by the use of the above drugs consisting with the increase of beta receptor numbers. Furthermore, following the down regulation of beta receptor and its second messenger, the blood pH value and tCO₂ were decreased, which represented typical acidosis in body but it was attenuated by the above drugs. Conclusion:All those results indicate that the improvement of air exchange and the attenuation of acidosis may be accomplished by the use of phospholipse A₂ inhibitors and antioxdant.