Mast cell degranulation mediates analgesic effects of acupuncture at different stimulation durations in arthritic rats

Background: To understand the effect and mechanism of different acupuncture durations on analgesic effects. Methods: An adjuvant-induced arthritis rat model evaluated the therapeutic effects of acupuncture at the Zusanli acupoint (ST36). A robotic arm provided stable lifting-thrusting stimulation for different durations (2, 5, 10, 20, and 30 min). Mechanical and thermal pain thresholds were measured before and after treatment to assess the analgesic effects. Additionally, tissue sections from ST36 were stained and analyzed to assess mast cell degranulation rates, and in vitro stretching experiments were performed at different stretching times (0–60 min) to measure the release of histamine, 5-hydroxytryptamine, and leukotrienes. Results: Within the 30 min acupuncture duration range set in this study, the pain threshold recovery rate in rats exhibited a steady upward trend as the acupuncture duration gradually increased, reaching its optimal level between 20 and 30 min. The mast cell degranulation rate exhibited a similar time-related trend, reaching 80–90 % at 20–30 min. Correlation analysis revealed a significant positive correlation between the pain threshold recovery rate and mast cell degranulation rate. In the cell-stretching experiment, the release of biochemical mediators was time-dependent. Conclusions: In the adjuvant-induced arthritis rat model, the analgesic effect observed at 20–30 min was superior to that observed at shorter durations, which was associated with the mast cell degranulation rate and release of biochemical mediators in the tissue.