Objective: To test the expression of AQP8 in ascending and descending colon mucosa of diarrhea-irritable bowel syndrome (D-IBS) patients and to study the relationship between IBS and AQP8 as well as the pathological mechanism for D-IBS.
Methods: The proximal ascending colon and the distal descending colon of 26 D-IBS sufferers were resected. Total RNA was purified from each sample of mucosa and AQP8 mRNA expression was analyzed with fluorescent quantitative RT-PCR. Analysis was conducted with regard to five aspects of the sufferers, i.e. their sex, age at first incidence, duration of illness, frequency of defecation and characteristics of stool. Correlation analysis of the level of AQP8 mRNA expression in the ascending colon and descending colon was made, and relationship between the expression of AQP8 and the incidence and clinical features of D-IBS explored.
Results: AQP8 expression was present in specimens of the ascending colon and descending colon of both healthy persons and D-IBS sufferers. Sufferers of D-IBS showed a remarkably lower level of AQP8 expression than the normal controls (Mean 3.1 x 10(4) copies/microg RNA and 2.8 x 10(4) copies/microg RNA vs 8.2 x 10(4) copies/microg RNA and 3.8 x 10(4) copies/microg RNA). The level of AQP8 expression was not correlated with the age of the sufferers or age at first incidence, but was closely correlated with the duration of illness, frequency of defecation and characteristics of stool. The longer the illness lasted, the higher the frequency of defecation and the larger the amount of water was found in stool, the lower the level of AQP8 mRNA expression in colonic mucosa.
Conclusions: The decrease in AQP8 expression in sufferers of D-IBS indicates that colonic absorption function is disordered. As a result, absorption of water is reduced, thus loose stool and diarrhoea occur. There may be some correlation between the variation in AQP8 and the incidence of D-IBS.