Shugan Decoction Improves Colonic Dysmotility Of SERT Knockout Rats By Acting On M₃ Receptor

Objective:To investigate the abnormal intestinal motility in the serotonin transporter knockout（SERT KO）rat and find out whether it can be used as an animal model of irritable bowel syndrome（IBS）with intestinal dysmotility.On the base of this research,to investigate the effect of shugan decoction（SGD）on the regulation of intestinal motility abnormalities in SERT KO rats and some of its mechanisms.Methods:1.Preparation and grouping of experimental animalsPrepare six wild type（WT）female SD rats and twelve SERT KO female SD rats which were SPF level,each weighing 200±20g.All animals were kept in the experimental animal center of Shanghai university of Chinese medicine.Animals were divided into groups according to the random number table,as follows:WT group,SERT KO group,and SGD intervention（KO+SGD）group.2.Defecation countingThe number of defecation particles of each rat in the three groups was observed for consecutive 10 days at a fixed time every day.Rats in the KO+SGD group were administrated with SGD for consecutive 7 days.Since the 4th day,rats in the WT and SERT KO groups were given the same dose of normal saline.3.Measurement of small intestinal propulsion functionThe small intestine propulsive function of rats in the three groups was observed by the charcoal meal experiments.4.Testing of the contractile activities of isolated intestinal longitudinal smooth muscle stripsThe spontaneous contractions of longitudinal smooth muscle strips isolated from small intestines and colons and their responses to ACh and KCl were observed.5.Detecting of muscarinic receptor expression in colonWestern blot was used to detect the expression of muscarinic receptor protein in colon tissues of rats.Results:1.Compared with WT rats,the defecation amount of SERT KO rats was significantly increased,while the small intestinal propulsion function was not significantly changed.2.Compared with WT rats,SERT KO rats showed no significant changes in the amplitude,frequency and tension of spontaneous contraction of ileal smooth muscle,but the amplitude of spontaneous contraction of colonic smooth muscle significantly enhanced.No significant changes in the amplitude,frequency and tension of ileal smooth muscle contraction induced by ACh and KCl were observed.The amplitude,frequency and tension of colonic contraction induced by KCl did not change significantly,but the tension of colonic contraction induced by ACh significantly increased.3.The expression of M₃R in the colon of SERT KO rats significantly increased compared with that of WT rats.4.SGD can reduce the defecation of SERT KO rats,but has no obvious effect on the propulsion function of the small intestine.5.SGD can reduce the amplitude of colonic spontaneous contraction and the frequency and tension of colonic contraction induced by ACh in SERT KO rats.6.SGD can down-regulate the expression of M₃R in the colon of SERT KO rats.Conclusions:1.SERT KO rats showed abnormal colonic motility and increased defecation.It can be used as an animal model to study colonic dysmotility of IBS.2.Down-regulating the expression of M₃R in the colon maybe the mechanisms of SGD to improve colonic dysmotility and reduce defecation in SERT KO rats.