Objective:To investigate the effect of changes in 5-HT2B receptor on the pathogenetic mechanism of irritable bowel syndrome (IBS) subgroups in rat models. Methods:Forty-five SD rats were divided into the D-IBS group,C-IBS group and control group. The D-IBS model was established in rats by intracolonic instillation of acetic acid and by restraint stress. The C-IBS model was established in rats by gastric instillation of 0-4℃ cool water daily for 14 days. The control group was also made. Weight and water content of the feces expelled by the rats were calculated. Abdominal contractions induced by distension of a colonically inserted balloon (0-60 mmHg) were recorded in rats by implanting electrodes in the abdominal external oblique muscle. Histological analysis of colonic tissue was performed. The distributions of 5-HT2B receptor in colon tissues of the D-IBS,C-IBS and control groups were detected by immunohistochemistry. The expressions of 5-HT2B receptor protein and mRNA in colon tissues in the D-IBS,C-IBS and control group were detected by Western blot and reverse transcription PCR,respectively. Results:The wet weight and water content of the feces expelled by the rats in the C-IBS were significantly lower than those in the control group(P < 0.05),while those of the D-IBS group were higher than the control group (P < 0.05). The amplitude of the abdominal muscle contraction was higher in the D-IBS group and C-IBS group compared with the control group when the balloon was distended at the pressure of 40 and 60 mmHg. The amplitude of the contraction in the D-IBS group was higher than the C-IBS group(P < 0.01). Histological analysis of the colon showed no colonic inflammation in any group. These aspects suggested that IBS subgroups were successfully made. Immunohistochemistry demonstrated that the 5-HT2B receptor was mainly localized in the myenteric nerve plexus,longitudinal muscle and colon mucosa. Western blot and reverse transcription PCR analyses showed that the expressions of 5-HT2B receptor protein and mRNA in the D-IBS group were higher than those in the control group (P < 0.05);however,the levels of 5-HT2B receptor protein and mRNA in the C-IBS group were lower than those in the control group (P < 0.05). Conclusion:The results indicate that 5-HT2B receptor plays a role in the pathogenetic mechanism of the IBS subgroup.