Background We analysed and compared the aquaporin 8(AQP8)expression in ascending and descending colonmucosa between patients with diarrhoea-predominant irritable bowel syndrome(D-IBS)and healthy volunteers,in orderto study the relationship between the clinical feature of IBS,the expression of AQP8 and the pathological mechanism ofD- IBS.Methods Specimens were taken from the proximal ascending colon or distal descending colon of D-IBS patients(n=26)and healthy volunteers(n=30),and AQP8 mRNA expression of each specimen was determined by fluorescentquantitative reverse transcription polymerase chain reaction(FQ-RT-PCR).In patients with D-IBS,the relationship wasanalysed between AQP8 expression in both ascending and descending colons and clinical features including gender,age of onset,duration of illness,frequency of defecation,and stool characteristics.Results Although AQP8 was present in the epithelium of the ascending and descending colons in healthy persons andD-IBS patients,the AQP8 level of the D-IBS patients was significantly lower than that of the healthy persons(P<0.01 inthe ascending colon,P<0.05 in the descending colon).AQP8 expression was not correlated with the age of patients withD-IBS(P>0.05 both in the ascending and descending colons)or the age at the onset(P>0.05 both in the ascending anddescending colons),but closely with the duration of illness(P<0.05 in the ascending colon,P<0.01 in the descendingcolon),frequency of defecation(P<0.01 in the ascending colon,P<0.05 in the descending colon)and stool characteristics(P<0.01 in the ascending colon,P>0.05 in the descending colon).Conclusions The decreased AQP8 expression in D-IBS patients indicates that dysfunction of colonic absorption maycause reduced water absorption,loose stool and diarrhoea.The expression of AQP8 may be related to D-IBS.Chin Med J 2007;120(4):313-316 Background We have analyzed and compared the aquaporin 8 (AQP8) expression in ascending and descending colon mucosa between patients with diarrhea-predominant irritable bowel syndrome (D-IBS) and healthy volunteers, in orderto study the relationship between the clinical feature of IBS, the expression of AQP8 and the pathological mechanism of D-IBS. Methods Specimens were taken from the proximal ascending colon or distal descending colon of D-IBS patients (n = 26) and healthy volunteers (n = 30), and AQP8 mRNA expression each by fluorescent quantitative reverse transcription polymerase chain reaction (FQ-RT-PCR). In patients with D-IBS, the relationship was wasted between AQP8 expression in both ascending and descending colons and clinical features including gender, age of onset, duration of illness, frequency of defecation, and stool characteristics. Results Although AQP8 was present in the epithelium of the ascending and descending colons in healthy persons and D-IBS patients, the AQP8 l Evel of the D-IBS patients was significantly lower than that of the healthy persons (P <0.01 inthe ascending colon, P <0.05 in the descending colon) .AQP8 expression was not correlated with the age of patients with D-IBS (P> 0.05 both in the ascending and descending colons) or the age at the onset (P> 0.05 both in the ascending and descending colons), but closely with the duration of illness (P <0.05 in the ascending colon, P <0.01 in the descendingcolon) frequency of defecation (P <0.01 in the ascending colon, P <0.05 in the descending colon) and stool characteristics (P <0.01 in the ascending colon, P> 0.05 in the descending colon) .Conclusions The decreased AQP8 expression in D-IBS patients indicates that dysfunction of colonic absorption may reduce the water absorption, loose stool and diarrhea. The expression of AQP8 may be related to D-IBS. Chin Med J 2007; 120 (4): 313-316