Abstract: Objective To observe the expressions of calcitonin gene-related peptide (CGRP) and cholinesterase (AchE) in colon and rectum of the rat model of functional defecation induced by low fiber diet combined with local methylene blue anal injection, and explore the possible mechanism of the occurrence of functional defecation disorder. Methods SD rats were randomly divided into blank control group, low-fiber diet group, lidocaine group and model group. The blank control group was fed with ordinary feed, and the other groups were fed with low-fiber feed. The lidocaine group and model group were given 2 mL of 2% lidocaine and 0.1% methylene blue injection once around the perianal and perirectal space respectively on the 63rd day of rearing. Fecal characteristics, fecal quality and defecation function of rats were observed. ELISA was used to detect AchE content in colon and rectum of rats. Real-time PCR (qPCR) was used to detect the expressions of CGRP mRNA and protein in rat colon and rectum respectively. Immunohistochemistry and Western blot assay were used to evaluate CGRP protein expression. Results After perianal injection, compared with the blank control group, the stools were dry and hard, and dark brown in the low-fiber diet group and lidocaine group, and the quality of the stool was decreased in the model group. The simulated balloon discharge was longer in the model group than that of the other groups, and the resting pressure in colon and rectum was lower than that of the other groups. The AchE contents in the colon and rectum were lower in model group than those of the blank control group and low-fiber diet group (P＜0.05). The expression of CGRP mRNA in the rectum was increased than that of the blank control group, but there was no significant difference between the blank control group, low-fiber diet group and lidocaine group. The expression of CGRP mRNA in rectum was higher than that of the other groups. The expression of CGRP protein detected by immunohistochemistry was higher in model group than that of the other groups (P＜0.05), while the expression of CGRP protein detected by Western blot assay was not statistically significant between four groups. Conclusion The abnormal expressions of CGRP and AchE in rat colon and rectum may be related to the neural mechanism of functional defecation disorder.

Key words: calcitonin gene-related peptide, acetylcholinesterase, colon, rectum, functional defecation disorder