To establish a relatively stable internal haemorrhoid model in rats. A total of 48 SPF SD rats were selected and randomly divided into a blank group of 16 and a model group of 32. The model was created by croton oil-mixed liquid stimulation combined with standing and swimming experiments, and the modelling times were 1 week and 2 weeks, respectively. By observing the symptoms and signs of rats, pathological morphology and immunohistochemical staining of anorectal tissue, anorectal laser speckle blood-flow imaging and defecation contrast, etc., the effect of different modelling times was evaluated. The stability of the model was evaluated after feeding for 2 weeks. Both model-formation times caused rats to produce local symptoms of tissue bulging in the haemorrhoid area. Microscopy showed that the rectal submucosal interstitial blood vessels were dilated, and inflammatory cell infiltration and other manifestations were observed. Laser speckle blood-flow imaging revealed increased anorectal blood perfusion and capillary dilatation, and defecography showed a longitudinal and continuous rectal mucosa. After 2 weeks of normal feeding, lifting of the haemorrhoidal tissue was still present. The effect of modelling for 1 week was most in line with the clinical manifestations of internal haemorrhoids. The 1-week modelling scheme in this study can effectively establish a rat internal haemorrhoid model that closely approximates clinical internal haemorrhoid symptoms and pathological manifestations. The operation is simple, the success rate is high, and the model has certain stability. This model can be used as an important basis for studying various treatment methods for internal haemorrhoids.
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