Objective To observe changes of mast cells(MCs) number and morphology

and substance P(SP) expression in Evans blue(EB) extravasated region around acupoint "Pishu"(BL 20) and "Weishu"(BL 21) after acute gastric mucosal injury(AGMI) so as to investigate the mechanism underlying visceral problems-induced acupoint activation.Methods Thirty adult Wistar rats were randomly divided into normal control(n=15) and AGMI groups(n=15).AGMI model was duplicated by perfusing the rats with 0.5 mol/L HCl(1 mL/100 g) after fasting for 20 h.Five hours after AGMI

the rats were treated by tail-intravenous injection of EB dye(5 mg/100 g

50 mg/mL in normal saline) for inducing dye-plasma extravasation in the skin around BL 20

BL 21 regions

etc.at the back.The rats of the normal control group were treated with tail-intravenous injection of 0.9% NaCl.The skin and subcutaneous tissues(2 mm×2 mm) of extravasated EB dye points(BL 20 or BL 21 region) and those 2 mm lateral to the extravasated EB dye points in the model group and the corresponding points in the normal control group were sampled(followed by fixing them in 4% paraformaldehyde)

sectioned and stained by toluidine blue(for labeling MCs).The expression of SP in the extravasated EB dye skin and subcutaneous tissues was detected by immunohistochemistry(n=5) and western blot(n=5) respectively.The number of MCs in these samples was counted and the degranulation rate of MCs calculated.Results The total number of MCs and the number of degranulated MCs were significantly more in the EB extravasation points(correspon-ding to BL 20/BL 21 area) of AGMI group than those in the control spots of AGMI group and than those in the normal control group(P<0.05

P<0.001).The degranulation rate of MCs was significantly higher in the EB extravasation points of AGMI group than those in the control spots of AGMI group and in the normal control group(P<0.01).In comparison with normal control group

the SP expression level was increased consideraly in the control spots of AGMI group and AGMI group(P<0.01).Conclusion After AGMI

the numbers of MCs and the degranulated MCs

and the SP expression level in BL 20/BL 21 area were increased signi-ficantly

suggesting an involvement of MCs and SP in the process of AGMI-induced activation of acupoints.