Objective To explore the mechanism of vitamin D in the genesis of irritable bowel syndrome (IBS).Methods A total of 50 newborn Sprague Dawley (SD) rats were divided into three model groups and two control groups (saline control group and normal control group).The model was induced by dilute acetic acid enema.After rats were weaned,the rats of three IBS model groups were fed with normal diet,vitamin D deficient diet and vitamin D sufficient diet,respectively.The visceral sensitivity of the rats was assessed by the colorectal distention experiment.The intestinal tissues of rats was taken for histological score,and the intestinal mast cell (MC) was also counted.The mRNA level of vitamin D receptor (VDR) in colon tissues of rats was determined by real-time reverse transcription-polymerase chain reaction (RT-PCR).T test or rank sum test was performed for statistical analysis.Results When the water volume of balloon was 0.5 mL and 1.0 mL,the abdominal withdrawal reflex (AWR) scores of male rats of the vitamin D deficient model group were 2.67±0.33 and 3.60±0.28,which were higher than those of normal vitamin D model group (1.93±0.15 and 3.20±0.18),and the differences were statistically significant (t=4.491 and 2.683,both P＜0.05).When the water volume of balloon was 1.0 mL and 1.5 mL,the AWR scores of female rats of the vitamin D sufficient model group were 3.00 (3.00,3.00) and 3.33 (3.33,3.67),which were lower than those of normal vitamin D model group (3.67,3.33 to 4.00;and 4.00,4.00 to 4.00),and the differences were statistically significant (Z=-2.362 and-2.390,both P＜0.05).There was no statistically significant difference in histological scores of intestinal mucosal tissues of ileum distal segment and sigmoid between the model groups with different vitamin D concentration and saline control group as well as normal control group (all P＞0.05).The number of MC in the mucosal tissue of the sigmoid colon of female rats in IBS model group was 41.00± 19.80,which was higher than that in normal control group (12.40 ± 5.35),and the difference was statistically significant (t=3.118,P=0.030).The number of MC in the mucosal tissue of ileum of the female rats in vitamin D deficiency model group was 16.00 ± 3.71,which was higher than that in normal vitamin D model group (7.30± 2.66),and the difference was statistically significant (t =4.263,P =0.003).The VDR mRNA level in the colon tissues of male model rats of normal vitamin D model group was 1.48±0.33,which was higher than that of saline control group and normal control group (0.97± 0.21 and 1.00±0.21;t=2.590 and 2.482,both P＜0.05).The VDR mRNA levels in colon tissues of female rats of vitamin D deficient model group was 1.90 ± 0.66,which was higher than that of normal control group (1.00 ± 0.14),and the difference was statistically significant (t =2.649,P =0.038).Conclusions Vitamin D may affect visceral hypersensitivity in IBS,and MC may involve in vitamin D induced visceral hypersensitivity.