Effects of acupuncture on serotonin, histamine, substance P, and tryptase levels at sensitized points in model rats with knee osteoarthritis

To elucidate the differences in manual acupuncture effectiveness at sensitized points by investigating the mechanisms of local skin action at different sensitization points in rats with knee osteoarthritis (KOA). Forty Sprague–Dawley rats were equally divided into control, model (1 mg of monoiodoacetate into the right knee joint cavity), sham operation, manual acupuncture at right Tianjing acupoint (MAR-SJ 10), and left SJ 10 groups. Safranine-O and fast green staining were used to assess the modeling. The morphological and functional changes in mast cells (MCs) were assessed during acupoint sensitization using toluidine blue and immunofluorescence staining. The levels of serotonin, histamine, substance P (SP), and tryptase at skin acupoints and serum levels of IL-β, IL-6, and TNF-α were detected using ELISA. After 14 days of treatment, the number of MCs and their degranulation rates were statistically higher in the model group than in the control group (both P < .001). After applying acupuncture, the levels of 5-HT, HA, and SP at skin acupoints were lower than those in the model group (all P < .05), and tryptase level was higher (both P < .05). Tryptase level was higher on the skin at the MAL-SJ 10 acupoint than that on the MAR-SJ 10 acupoint ( P = .004). Compared with the model group, the serum levels of IL-1β, IL-6, and TNF-α in the MAR-SJ 10 and MAL-SJ 10 groups were lower (all P < .05). Acupuncture at KOA-sensitized acupoints mitigates joint injury in KOA rats and may bidirectionally regulate local MCs of these acupoints. This finding not only enhances the reference value of sensitizing points in clinical diagnosis and treatment, but also contributes to the understanding of the biological mechanisms underlying acupuncture intervention at sensitizing points.