The Expression And Significance Of P2X₂in The Colon Of Rat Model With Slow Transit Constipation

Background: Constipation is a complex symptoms caused by the pathologicalprocesse of many diseases. Currently, clinical constipation usually divided into threecategories:â‘ slow transit constipation（STC）;â‘¡outlet obstructio constipation;â‘¢m ixed constipation. STC is known as an intractable constipation withgastrointestinal tract transmission dysfunction, and it is characterized by slow colonictransit. With the accelerated pace of modern life, improved living standards andchanged diet composition, the incidence of STC has increased year by year. It hasbecome a common disease which affects the life quality of modern people. Althoughit is very early to commence the study of STC, the etiology and pathogenesis ofgastrointestinal motility damage in STC patients has not been entirely clear so farbecause its incidence is affected by many factors and the etiology is complex.Recently, studies have shown that enteric nervous system, intestines neurotransmitters, gastrointestinal hormone, Cajal cell play a role in the pathogenesis ofSTC. In addition, some scholars have found that constipation has the phenomenon offamily aggregation, therefore they considered genetic factors have an impact on theetiology of STC.P2X receptors are ATP-gated cation channels with important roles in diversepathophysiological processes. It is widely distributed in various tissues, includingneurons, glial cells, immune cells, heart, blood vessels, respiratorysystem, gastrointestinal tract and urogenital system. It has been shown that P2X₂receptors expressed in detrusor tissue, which play an important role inregulation of detrusor contraction and relaxation. In addition, the expression ofP2X₂in the rat ICC （interstitial cells of Cajal, ICC） cells suggested thatP2X₂-mediated purinergic signaling have an impact on the function of ICC cells. Studies of P2X₂in the gastrointestinal tract have shown that it is expressed inintestinal epithelial cells and myenteric ganglia of enteric nervous system. P2X₂receptors contribute to fast excitatory postsynaptic potentials （fEPSPs）, and regulatesmooth muscle contraction and relaxation function. Thus, it has a close relationshipbetween P2X₂receptors and the function of the intestinal smooth muscle andneurotransmitter release, but the role of P2X₂receptor in the development of STC hasnot been reported.Objective: To establish a model of slow transit constipation by gavage with rhubarb,study the expression of P2X₂receptor in the colon of normal rats and rats with slowtransit constipation, and investigate the relationship between P2X₂receptor and slowtransit constipation.Methods:1.Establish slow transit cinstipation model in rats by gavaging with rhubarb.Then the rats were randomly divided into two groups, control group（n=15） and testgroup（n=15）. Control group given common soft diet and the others gavaged withrhubarb. Initial dose100mg/（kgï¹'d）, after a day on the basis of eve until double, andcaused diarrhoea appear half, keeping the dose to80%of dilute disappeard, and thenbased on this double dosing, finally dosage for3200mg/（kgï¹'d）, such methods wereraised45d. Fecal character were recorded daily and transit function of intestinalmovement was measured by activated charcoal suspension pushing test in order tocompare with test groups and control groups.2.After establishing the rat model, ratswere killed dislocation. The intestinal canal about5cm away from the anus was taken,prepared for paraffin specimens and freeze-stored fresh organization respectively, andthe expression of P2X₂receptor in the colon of normal rats and rats with slow wastested by RT-PCR, immunohistochemical and Western blot.Results:1.Fecal character in test group was more dry and hard （Bristol classes:1-2grade） than in control group （Bristol classes:4-5grade）. Intestinal transit rate in testgroup was39.903.01ï¼…, and control group was52.811.27ï¼…, the test group waslower than the control group （P<0．05）. The rat model complies with STC clinical andpathologic physiological characteristic.2．RT-PCR results showed that the expressionof P2X₂in the colon of test group is less than the expression of P2X₂in the colon of control group. Immunohistochemical results showed that P2X₂expressed in plexusand submucosal plexus of test group and control group. And Western blot alsoconfirmed that the expression of P2X₂in the colon of test group was less than in thecolon of control group.Conclusions:1.There are dry and hard fecal character and decrease of intestinaltransit rate in rat of rhubarb induced colon slow-transit motility. Basically, this ratmodel conform to clinic character of slow transit constipation.2. The expression ofP2X₂receptor was decreased in the colon of rat constipation model suggested thatP2X₂receptor maybe one of the etiological factors cause colon slow-transit motility.There is correlation between P2X₂and the slow transit constipation.