In the practice of traditional Chinese medicine, endometriosis is believed to be caused by blood stasis and is characterised by dysmenorrhea, which is difficult to control. Shixiao San (SXS) has a long history of use in the treatment of gynaecological diseases. The prescriptions composed of SXS include Typhae Pollen and Faeces Trogopterori, both of which have anti-inflammatory activity. In addition, Typhae Pollen can be used to treat many kinds of blood stasis diseases.
The purpose of the present study was to investigate the effect of SXS on pain relief in rats with endometriosis and to preliminarily explore its mechanism of action in alleviating pain.
Ten rats received sham operation as the Sham group, and 30 endometriosis model rats were randomly divided into three groups: the Model, Shixiao San-Low (SXS-L), and Shixiao San-High (SXS-H) groups. The rats were administered the appropriate treatment via intragastric gavage for 4 weeks. The thermal radiation pain and mechanical pain thresholds of the rats were measured every 7 days after treatment. Finally, the distribution density of nerve fibres in endometrial tissue, the inflammatory infiltration of the dorsal root ganglion (DRG), the expression of TRPV1 in the DRG, and the expression of IL-1β, TNF-α, and IL-6 in ectopic tissue were measured.
After SXS treatment, the growth of ectopic tissue in rats with endometriosis was significantly suppressed, their thermal radiation pain and mechanical pain thresholds increased, the density of nerve fibres and the expression of inflammatory factors in ectopic tissues reduced, and inflammatory cells infiltration in the DRG of the animals alleviated. Meanwhile, the expression of TRPV1 in the DRG was downregulated in rats with endometriosis.
SXS could possibly inhibit the development of endometriosis and relieve pain in patients with endometriosis by reducing inflammatory responses in ectopic tissue and the DRG.

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