| Objective: To explore the expression of AQP4 in ascending and decending colon mucosa of diarrhea rats, and to study the relationship between AQP4 expression and colonic water metabolic, this will help us to well understand the diseases that have relation with AQP4.Method: Adult forty male Sprague Dawley Rat (180–200g) were utilized and divided into five groups randomly, 3h, 9h, 15h after diarrhoea groups and blank and 0.9%Nacl intragastric administration control group ,eight rats in each group. Diarrhoea model were established by intragastric administration of 20%mannitol with 10g/kg, while the contro1 group were by 0.9%Nacl instead, blank group give no intervention. We used diarrhea index number to test our diarrhea model success or not. The success rats were deeply anesthetized with 3.6% chloral hydrate (8ml/kg) administered intraperitoneally (i.p), and tissue specimens were taken from the proximal ascending colon and the distal descending colon, two tissues in each position. Hemi-quantitative RT-PCR and Immunohistochemistry were used to detect the colonic mRNA and protein expression of AQP4 in this study.Results: 1. All experiment group rats were diarrhoead after 2 hours of intragastric administration of 20%mannitol , while both control group were not after 24 hours of intragastric administration of 0.9%Nacl . We found that the diarrhea index number of diarrhea groups were different from that of control group(P﹤0.01), in diarrhea guoups also different(P﹤0.05),9h group was significantly high, and diarrhea was most serious.2. AQP4 was expressed in ascending and decending colon of both normal and diarrhoea rats(3,9 and 15hours groups),and its expression was higher in ascending colon (AQP4 mRNA expression of ascending colon: 1.633±0.105,1.621±0.117,1.121±0.019,0.455±0.017,1.284±0.046; AQP4 protein expression of ascending colon: 14.4±1.7,14.2±1.9,9.3±1.0,3.8±0.6,10.2±1.0)than that of decending (AQP4 mRNA expression of decending colon: 1.264±0.066,1.259±0.161,0.975±0.028,0.319±0.012,1.023±0.011 AQP4 protein expression of decending colon: 9.3±0.8,9.2±0.1,7.8±0.9,2.3±0.4,8.5±1.3)(P﹤0.01).3. AQP4mRNA and protein expression were lower in diarrhea groups than that of control both in ascending and decending colon(P﹤0.05), in 9 hour group was most obvious,while there were no difference between control groups(P﹤0.01).4. AQP4 expression level was changed along with diarrhea degree, this indicate that AQP4, which is expressed in absorptive cells of colonic, have an important role for colonic water reabsorption, its expression down-regulated will result in water absorption reduce ,then diarrhea happened. Conclusions: 1. Mannitol can be used to establish Diarrhoea model, and intragastric adminis- tration only once will not result in diarrhea. 2. AQP4 were expressed both in ascending and decending colon ,and its expression were higher in ascending colon than that of decending, this show that ascending colon has great water absorption ability than that of decending colon.3. In diarrhoea rats, AQP4mRNA and protein expression were lower both in ascend- ing and decending colon, as a result, absorption of water is reduced, which causes loose stool and diarrhoea, this indicate that AQP4 play an important role in colonic water reabsorption.
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