Electroacupuncture at ST36 Alleviates Visceral Hypersensitivity by Suppressing Eosinophil-Induced TRPV1 Expression on Duodenum.

BACKGROUND AND AIMS: Electroacupuncture (EA) has been reported to have a therapeutic potential for visceral hypersensitivity. Recent studies have highlighted the crucial role of the duodenum in visceral hypersensitivity, suggesting it as a potential therapeutic target. This study investigates how EA regulates visceral hypersensitivity in the duodenum. METHOD: We established a visceral hypersensitivity model in rats by intragastric administration of iodoacetamide. Various parameters were evaluated, including electromyographic recordings in vivo, mesentery afferent nerve spontaneous discharge, mechanical sensitivity, and chemical sensitivity. Western blotting and immunofluorescence were employed to detect the protein expression of nociceptor transient receptor potential vanilloid 1 (TRPV1) and to assess eosinophil infiltration by labeling eosinophil major basic protein (EMBP). We examined whether the effect of EA was mediated by TRPV1, using the agonist capsaicin and the antagonist SB366791. Eosinophils were counted, and their activation and degranulation status were assessed. We explored the impact of eosinophils on the neuron fibers of the intestine. RESULTS: EA decreased firing of visceral afferent action potentials including spontaneous, mechanosensitive and chemosensitive mesentery afferent discharge, and attenuated visceromotor electromyographic activity. The above effects of EA were reversed by intraperitoneal injection or in vitro enteric nerve administration of TRPV1 agonist capsaicin. EA substantially reduced the area of neuron fibers and the TRPV1 expression. Furthermore, in vitro experiments using primary cell cultures indicated that eosinophils' degranulation with different doses could stimulate neuron fibers. EA at ST36 was found to reduce both the number of duodenal eosinophil-positive cells and the levels of their degranulation products. CONCLUSION: These results suggested that EA at ST36 alleviates visceral hypersensitivity by inhibiting eosinophils degranulation and TRPV1 expression in the duodenum.