Effect Of Caffeine On Acupuncture-induced Analgesia With The Human Pain Model

Objective:To observe the effect of caffeine on acupuncture-induced analgesia and the expression of adenosine with the human pain model.Methods:The subjects were randomly divided into 0 mg caffeine group,200 mg caffeine group and 400 mg caffeine group. Human pain model was established by potassium ionophoresis method. The three groups were accepted different doses of coffee (containing 0 mg,200 mg and 400 mg of caffeine) intake plus acupuncture on the point of left Zusanli. The change of pain threshold would be measured with Potassium Pain Tester at the time of the baseline,30 minutes after drinking coffee,10, 20,30 minutes during acupuncture and 30 minutes after acupuncture intervention completed, blood samples were collected at the baseline,30 minutes after drinking coffee,30 minutes during acupuncture and 30 minutes after acupuncture intervention completed. The concentration of caffeine and adenosine in plasma were measured by high performance liquid chromatography at the one day after the study. The statistic analysis was perfomed with SPSS21.0. The trial was registered at Clinical Trials.gov(NCT02577770).Results:1. The results of effect of caffeine on the acupuncture-induced analgesia.1) The changes of pain threshold on the point of left Zusanli.The change rate of pain threshold in 0 mg caffeine group was increased 65%, 79%,97%at 10,20,30 minutes during acupuncture, while the change rate of pain threshold recovered to the baseline level at 30 minutes after acupuncture intervention. Compared with the 0 mg caffeine group, the change rate of pain threshold in 200 mg caffeine group and 400 mg caffeine group were reduced at each time point (P<0.05) There were no differences between 200 mg caffeine group and 400 mg caffeine group at each time point (P>0.05)2) The changes of pain threshold on the point of right Zusanli.The change rate of pain threshold in 0 mg caffeine group was increased 74%, 73%,73%at 10,20,30 minutes during acupuncture, while the change rate of pain threshold didn't recovered to the baseline level at 30 minutes after acupuncture intervention. Compared with the 0 mg caffeine group, the change rate of pain threshold in 200 mg caffeine group and 400 mg caffeine group were reduced at each time point(P<0.05); There were no differences between 200 mg caffeine group and 400 mg caffeine group at each time point (P>0.05)3) The changes of pain threshold on the point of left Hegu.The change rate of pain threshold in 0 mg caffeine group was increased 41%, 44%,51% at 10,20,30 minutes during acupuncture, while the change rate of pain threshold recovered to the baseline level at 30 minutes after acupuncture intervention. Compared with the 0 mg caffeine group, the change rate of pain threshold in 200 mg caffeine group and 400 mg caffeine group were reduced at each time point(P<0.05); There were no differences between 200 mg caffeine group and 400 mg caffeine group at each time point (P>0.05)2. The concentration of caffeine in the plasma.The 0 mg caffeine group didn't contain caffeine; the concentration of caffeine in 200 mg caffeine group were 0 ?g/mL,4.48 ?g/mL,5.89 ?g/mL,6.10 ?g/mL at baseline,30 minutes after drinking coffee,30 minutes during acupuncture and 30 minutes after acupuncture intervention; the concentration of caffeine in 400 mg caffeine group were 0 ?g/mL,10.29 ?g/mL,14.18 ?g/mL,13.49 ?g/mL at baseline, 30 minutes after drinking coffee,30 minutes during acupuncture and 30 minutes after acupuncture intervention.3. The changes of adenosine in the plasma.The change rate of adenosine level in 0 mg caffeine group was increased 52% at 30 minutes during acupuncture, compared with the 200 mg caffeine group and 400 mg caffeine group, there was significant difference(P<0.05), while the change rate of adenosine level didn't recovered to the baseline level at 30 minutes after acupuncture intervention, compared with the 400 mg caffeine group, there was significant difference(P<0.05); the change rate of adenosine level in 200 mg caffeine group was reduced 11% at 30 minutes after drinking coffee and increased 6% at 30 minutes during acupuncture, while the change rate of adenosine level recovered to the baseline level at 30 minutes after acupuncture intervention, the change rate of adenosine level in 400 mg caffeine group was gradually reduced, there were no differences between 200 mg caffeine group and 400 mg caffeine group at each time point (P>0.05)Conclusions:1. Caffeine administration prevent antihyperalgesic effect of acupuncture;2. The effect of 200 mg caffeine and 400 mg caffeine on acupuncture-induced analgesia are no differences;3. Adenosine in the plasma may participate in acupuncture-induced analgesia, but the caffeine may affect the release of adenosine during acupuncture-induced analgesia.