AIM:To examine the effects of ovarian hormone on theexpression of 5-hydroxytryptamine 3 receptors (5-HT_3R)in rat colon of restraint stress-induced bowel dysfunction.METHODS:Twenty-four female Sprague-Dawley rats wererandomly divided into three groups of 8 each:sham operation,ovariectomy (OVX) and ovariectomy with estrogen (E_2) andprogesterone (P) replacement therapy (OVX+E_2+P).The ratswere subjected to 1-h restraint stress 4 wk after operation.The changes of defecation were monitored by collectionof fecal pellets.The gonadal steroids were measured induplicate by radioimmunoassay (RIA).The expression of5-HT_3R mRNA in the colon was studied by RT-PCR.RESULTS:Compared with sham group and OVX+E_2+Pgroup,OVX group showed increase in fecal pellets anddecrease in the time of vitreous pellets excretion (P<0.01).Serum levels of E_2 and P were suppressed in OVX group andrestored following treatment with ovarian steroids (P<0.01),and the levels of 5-HT_3R mRNA in the colon of ovariectomizedrats were significantly increased,the expression of 5-H_3RmRNA was significantly decreased in hormone replacementtherapy group (P<0.01).CONCLUSION:Ovarian hormone plays a role in the regulationof 5-HT_3R expressions in restraint stress-induced boweldysfunction of rats.The interactions between ovarian steroidsand gastrointestinal tract may have major pathophysiologicalimplications in 5-HT-related disorders,such as irritablebowel syndrome (IBS). AIM: To examine the effects of ovarian hormone on the expression of 5-hydroxytryptamine 3 receptors (5-HT_3R) in rat colon of restraint stress-induced bowel dysfunction. METHODS: Twenty-four female Sprague-Dawley rats were randomly divided into three groups of 8 each: sham operation, ovariectomy (OVX) and ovariectomy with estrogen (E_2) and progesterone (P) replacement therapy (OVX + E_2 + P). The ratswere subjected to 1-h restraint stress 4 wk after operation. The changes of defecation Monitored by collection of fecal pellets.The gonadal steroids were measured induplicate by radioimmunoassay (RIA). The expression of 5-HT_3R mRNA in the colon was studied by RT-PCR. RESULTS: Compared with sham group and OVX + E_2 + Pgroup, OVX group showed increase Serum levels of E_2 and P were suppressed in OVX group andrestored following treatment with ovarian steroids (P <0.01), and the levels of 5-HT_3R mRNA in the colon of ovariectomizedrat s were significantly increased, the expression of 5-H_3R mRNA was significantly decreased in hormone replacement therapy group (P <0.01). CONCLUSION: Ovarian hormone plays a role in the regulation of 5-HT_3R expressions in restraint stress-induced boweldysfunction of rats. The interactions between ovarian steroids and gastrointestinal tract may have major pathophysiological implications in 5-HT-related disorders, such as irritable bowel syndrome (IBS).