Acute and chronic stress differently affect visceral sensitivity to rectal distension in female rats

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Abstract
Stressful life events are frequently associated with outward signs of irritable bowel syndrome (IBS). Increasing evidence suggests that acute and chronic stress stimuli implicate different physiological mechanisms and neuroendocrine responses. Therefore, we investigated the influence of acute and chronic stress on visceral nociception in female rats and the involvement of colonic mast cells in this effect. The effect of acute and chronic partial restraint stress (PRS) on visceral sensitivity to rectal distension (RD) was assessed by abdominal muscle electromyography. Colonic mast cell activation was determined by measuring histamine release after in vitro stimulation with substance P (SP) in colonic samples from rats experiencing RD vs. controls. Acute PRS significantly enhanced abdominal response to RD compared with sham PRS for all volumes of distension. In contrast, chronic PRS induced a hyperalgesic response for the highest volumes of distension (0.8 and 1.2 mL), but did not affect the number of abdominal contractions for the lowest volume (0.4 mL) compared with controls. Both acute and chronic PRS increased in vitro SP‐induced histamine release without affecting mast cell numbers. RD induced similar in vitro histamine release from colonic samples from both acute and chronic PRS rats; this release, however, was significantly higher than that measured in sham‐PRS rats. Acute and chronic PRS differently influence visceral sensitivity in response to RD in female rats. This difference, however, cannot be attributed to a different effect of either stress paradigm on mast cell histamine release.