Chiropractic Therapy Alleviates Pain Hypersensitivity via the Mast Cell Receptor TRPV1 in PD Model Rats

Objective: This study investigated the antinociceptive effects of chiropractic therapy in a rat model of cold-stimulated primary dysmenorrhea (PD) and explored the mechanism through which it modulates the expression of the transient receptor potential vanilloid 1 (TRPV1) in mast cells (MCs) to ameliorate pain sensitization. Methods: Five groups of rats were used: blank, model, chiropractic, sodium cromoglicate (SCG) + chiropractic, and ibuprofen. Following chiropractic intervention, behavioral responses were observed; serum levels of prostaglandin F2α (PGF2α), prostaglandin E2 (PGE2), cyclooxygenase-2 (COX-2), and arginine vasopressin (AVP) were measured via ELISA; uterine mast cell (MC) expression was detected by toluidine blue staining; and Western blotting and RT–qPCR were employed to quantify TRPV1 protein and mRNA expression, respectively, in the uterus, dorsal root ganglion (DRG), and periaqueductal gray (PAG). Results: Compared with the blank group, the model group exhibited a shortened writhing latency ( P < 0.01). Serum PGF2α, COX-2, and AVP levels were significantly elevated, while PGE2 levels were reduced ( P < 0.01). Uterine MC counts and degranulation increased ( P < 0.01), and TRPV1 protein and mRNA expression in the uterus, DRG, and PAG increased ( P < 0.01). After chiropractic treatment, writhing latency increased ( P < 0.01). Serum PGF2α, COX-2, and AVP levels decreased, whereas PGE2 levels increased ( P < 0.01). Uterine MC counts and degranulation decreased ( P < 0.01, P < 0.05), and TRPV1 protein and mRNA expression in the uterus, DRG, and PAG decreased ( P < 0.01). Conclusion: Chiropractic therapy alleviates pain hypersensitivity in cold-stimulated PD model rats, potentially by modulating uterine MC activation and subsequently downregulating TRPV1 expression in the uterus, DRG, and PAG.