[Effect of vasoactive intestinal peptide on defecation and VIP-cAMP-PKA-AQP3 signaling pathway 
in rats with constipation].

To observe the effect of vasoactive intestinal peptide (VIP) on the metabolism of intestinal fluid and cyclic AMP protein kinase A signaling pathway (cAMP-PKA) and water channel protein 3 (AQP3) in rats with constipation, and to explore the mechanism of VIP in the treatment of constipation. Methods: A total of 45 healthy adult rats were randomly divided into a control group, a model group, a model +VIP group. After 4 weeks of VIP treatment, the first black stool time were examined with the ink gastric method; the water content in feces was calculated; the morphological changes in colonic tissues were observed by HE staining. The expression of VIP and AQP3 protein levels in colon tissues were detected by Western blot; and the cAMP, PKA, AQP3 mRNA expression levels were detected by quantitative real time polymerase chain reaction (qPCR). Results: Compared with the control group, the first black stool time was prolonged, the water content of fecal decreased significantly (both P<0.01); part of the colon mucosa epithelial cells were destructed; the goblet cell volume decreased and quantity was reduced; the contents of AQP3 and VIP in colon tissues were significantly decreased, and the cAMP, PKA and AQP3 mRNA levels were decreased in the model group (all P<0.05). Compared with the model group, the first black stool time in the model +VIP group was shortened, the fecal water content increased significantly (both P<0.05); the mucosal epithelium integrity improved, the number of goblet cells increased; the content of AQP3 and VIP in colon tissues was increased, and the cAMP, PKA, and AQP3 mRNA levels were elevated (all P<0.05). Conclusion: Intravenous injection of VIP can regulate intestinal fluid metabolism and improve the symptoms of constipation in rats, which might be related to the regulation of VIP-cAMP-PKA-AQP3 signaling pathway.目的：观察血管活性肠肽(vasoactive intestinal peptide，VIP)对便秘大鼠肠道水液代谢、环磷酸腺苷-蛋白激酶A信号通路(cyclic AMP protein kinase A signaling pathway，cAMP-PKA)和水通道蛋白3(water channel protein 3，AQP3)的影响，探讨VIP治疗便秘的作用及机制。方法：45只健康成年Sprague-Dawley大鼠随机分为空白对照组、模型组、模型+ VIP组。给药4周后，墨汁灌胃法检测大鼠首粒黑便排出时间；根据大鼠粪便干湿重计算粪便含水率；HE染色观察各组大鼠结肠组织形态学变化；Western 印迹检测各组大鼠结肠组织中 VIP和AQP3蛋白表达水平；定量即时聚合酶链锁反应(quantitative real time polymerase chain reaction，qPCR)检测各组大鼠结肠组织中cAMP，PKA和AQP3 mRNA的表达水平。结果：与空白对照组比较，模型组大鼠首粒黑便出现时间延长，粪便含水率明显减少(均P<0.01)；结肠黏膜上皮部分破坏，杯状细胞体积减小，数量明显减少；结肠组织中VIP和AQP3蛋白含量明显减少，AQP3，cAMP和PKA mRNA相对表达水平均有所降低(均P<0.05)。与模型组比较，模型+VIP组大鼠首粒黑便出现时间缩短，粪便含水率明显增加(均P<0.05)；结肠黏膜上皮完整性明显改善，杯状细胞体积增大，数量增多；结肠组织中VIP和 AQP3蛋白含量增多，CAMP，PKA和AQP3 mRNA相对表达水平升高(均P<0.05)。结论：VIP静脉注射能够调节肠道水液代谢，改善大鼠便秘症状，其机制可能与调节VIP-cAMP-PKA-AQP3信号通路有关。.