Abstract: AIM: To investigate the mechanism of naloxone on mice viral myocarditis caused by coxsackievirus B₃ ( CVB₃ ).METHODS: 120 mice were randomly divided according to experiment protocol and inoculated intraperitoneally with CVB₃ ( 100 ×TCID₅₀ ) 0.1mL.72 h after viral inoculation, 40 of the inoculated mice were given naloxone i.p.2 mg/kg for 21 days.Another 40 inoculated mice were treated with i.p.0.9 % NaCl solution daily and were as CVB3 group.Mice without inoculation ( n =40) were given i.p.0.9 % NaCl solution daily and used as normal controls.Mice were executed, and hearts were collected on Days 5, 7, 14, 21 and 28.The death rate and pathological examination were evaluated.RT-PCR technique and Western Blot technique were used to investigate the changes of expression of κOR mRNA and protein in mice at different time points during VMC with CVB3 infection.RESULTS: On the 5, 7, 14, 21 day after viral infection, the expression of κOR mRNA was dramatically increased in the myocardium of VMC mice( P <0.01).On the 7, 14, 21 day after viral infection, the expression of κOR protein in myocardium of VMC mice was dramatically increased( P <0.05). The death rate in the naloxone group ( 50 %, n =20) was significantly lower than that in the CVB₃ group ( 75 %, n =20);On the 7, 14, 21 day after viral infection, the changes of pathological and expression of κOR mRNA and protein in myocardium of naloxone group were dramatically lower than those in the CVB3 group( P <0.05).CONCLUSION: The up-regulation of κOR gene and protein were observed at different times during VMC.Naloxone can significantly improve the effectiveness in the treatment of VMC by inhibiting the up-regulation of κOR gene and protein.

Key words: κ-opioid receptor;, viral myocarditis, naloxone