Caffeine Inhibits Acupuncture-induced Analgesia With Human Acute Pain Model

Objective: To determine the effect of caffeine on acupuncture-induced acute analgesia in human acute pain model.Methods: Enrollment participants were randomly assigned in 3 groups: control group,50 mg caffeine group and 100 mg caffeine group.Human acute pain model was potassium pain model.The participants were consumed 250 ml coffee(containing 0 mg,50 mg and 100 mg caffeine),and then plus acupuncture on the point of left Zusanli(ST36).Outcome measures include: 1)pain threshold(the time point were baseline,30 minutes after coffee,30 minutes after acupuncture,30 minutes after acupuncture intervention completed),2)plasma caffeine levels,3)plasma paraxanthine concentration.The statistic analysis was performed with graphpad 6.0.Results: 1.The effect of lower dose of caffeine on the acupuncture-induced acute analgesia.(1)Comparison of pain threshold at different time within the same groups: Control group: On the acupoint of left Zusanli,left Hegu,and right Zusanli,the change rate of pain threshold increased at 10,20,30 minutes during acupuncture,while it didn't recovered to the baseline level at 30 minutes after acupuncture intervention.50 mg caffeine group and 100 mg caffeine group: left Zusanli,left Hegu,right Zusanli,the change rate of pain threshold decreased all the time after drinking coffee.The results showed that the pain threshold of the control group after acupuncture increased significantly,indicating that acupuncture has acute analgesic effect.The lower dose of caffeine intake reduced the pain threshold,indicating that low-dose caffeine can cause pain,and the pain threshold after acupuncture does not rise,indicating that the analgesic effect of acupuncture was inhibited by caffeine.(2)Comparison of pain threshold among the 3 groups: on the acupoint of left Zusanli,the change rate of pain threshold in 50 mg caffeine group and 100 mg group were reduced at each times compared with control group(P<0.05).But there were no differences between 50 mg caffeine group and 100 mg caffeine group at each time point(P>0.05).The results of right Zusanli and left hegu was the same with the point of left Zusanli.2.The concentration of caffeine in the plasma.The control group didn't contain caffeine.The concentration of caffeine in 50 mg caffeine group was increased after drinking coffee,and the peak concentration of plasm caffeine was 1.3 ?g/mL at 30 minutes after acupuncture intervention.The concentration of caffeine in 100 mg caffeine group reached the peak of 2.45 ?g/mL at 30 minutes after acupuncture intervention.There was significant difference among the three groups.3.The concentration of paraxanthine in the plasma.The concentration of paraxanthine in control group is 0 ?g/mL.The concentration of paraxanthine in 50 mg caffeine group and 100 mg caffeine group began to increase at 30 minutes after drinking coffee.The peak concentration of paraxanthine were 1.62 ug/mL and 1.71 ug/mL respectively.There were no differences between 50 mg caffeine group and 100 mg caffeine group at each time point(p>0.05).Conclusions: 1.Consuming 50 mg and 100 mg Caffeine will inhibit the effect of acute pain relief of acupuncture.However,there is no difference between the two concentration-induced effect.2.The dose of paraxanthine is not related to the concentration of coffee consumed in 50 mg caffeine group and 100 mg caffeine group.