Juniper Publishers Objective: To explore the peripheral mechanism of chrono- acupuncture with respect to purinergic signaling in local acupoints. Methods: The Sprague Dawley (SD) rats were randomly divided into two groups. One group was injected 0.1ml saline as control group. Another group was established by subcutaneous injecting 0.1ml complete Freund’s adjuvant (CFA). After modeling successfully, model rats were randomly divided into model group and acupuncture group based on the basic pain threshold. The basic pain threshold was tested by tail-flick method. The extracellular ATP concentration in local acupoints was detected by high- performance liquid chromatography (HPLC) after acupunctured at different times, which were zeitgeber time 0(ZT0) (7:00), ZT4(11:00), ZT8(15:00), ZT12(19:00), ZT16(23:00), and ZT20(3:00) respectively. Based on the characteristics of the variation of pain threshold and extracellular ATP concentration, the peak phase and valley phase w...