Female serotonin transporter-knockout rat: A potential model of irritable bowel syndrome.

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disease. Although visceral hypersensitivity (VH) and disturbed gastrointestinal motility are typical pathophysiological features of IBS, the pathological mechanisms underlying this disease remain unclear. Serotonin system abnormalities are considered to play an important role in the pathomechanisms of IBS. Here, we hypothesize that similar alterations, including VH and colonic motility, induced by serotonin transporter (SERT) knockout result from altered serotonin signaling. We sought to determine the molecular mechanism underlying VH and colonic dysmotility induced by SERT knockout. We found that female SERT (slc6a4)-knockout (KO; ie, slc6a4-/- ) rats exhibited lower pain pressure thresholds (PPTs) than wild-type (WT; ie, slc6a4+/+ ) rats in response to colorectal distension (CRD). Significantly increased fecal pellet output and reduced concentration of serum tryptophan were observed in the female SERT KO rats. The concentrations of 5-hydroxytryptamine (5-HT) in platelet-rich plasma (PRP) and serum in SERT KO rats were lower than those in WT rats, but the numbers of enterochromaffin cells (ECs) and the concentrations of 5-HT in colon of SERT KO rats were higher than those of WT rats. Finally, increased expression levels of 5-HT1B receptors, 5-HT2C receptors, 5-HT3A receptors, 5-HT3B receptors, 5-HT6 receptors, 5-HT7 receptors, and glycosylated dopamine transporters (DATs) were found in the female SERT KO rats. We concluded that alterations in the serotonin system induced by the knockout of slc6a4 might result in VH and accelerated gastrointestinal motility in female SERT KO rats, which can be used as an animal model of IBS.

[Tongxie Yaofang inhibits the contraction of colonic smooth muscle isolated from rats through a mechanism related to calcium mobilization].

OBJECTIVE: To study the relationship between the inhibitory effects of Tongxie Yaofang, a compound traditional Chinese herbal medicine, on the contraction of the colonic smooth muscle isolated from rats and calcium mobilization. METHODS: By measuring the tension of the isolated colonic smooth muscle strips, the inhibitory effects of Tongxie Yaofang on the contraction induced by acetylcholine (ACh), KCl and exhausting Ca(2+) of internal calcium store were assessed respectively. RESULTS: Tongxie Yaofang could concentration-dependently inhibit the contraction of isolated rat colonic smooth muscle strips induced by KCl and exhausting the Ca(2+) of internal calcium store. Tongxie Yaofang could also inhibit the tension of the second contractile phase induced by ACh (P<0.01, vs control), but had no influence on the first contractile phase. CONCLUSION: Tongxie Yaofang can inhibit the contraction of isolated rat colonic smooth muscle strips mainly by preventing the influx of extracellular Ca(2+), which may be associated with blocking voltage-dependent channel, store-operated channel and receptor-operated channel, but not by preventing the release of internal Ca(2+) from calcium store.