Chronic restraint stress has no more stimulatory effects on colonic motility in rats

Previous studies have shown that acute stress stimulates colonic motor function via a central corticotropin releasing factor (CRF) in rodents. However, little is known whether colonic motility is altered following chronic stress. We studied the changes of colonic motor function in response to chronic stress or daily administration of CRF in rats. Rats were subjected to restraint stress for 90 min for 5 consecutive days (chronic stress). Another group of rats received intracisternal (IC)-injection of CRF (1 microg) for 5 consecutive days. At the 1st day of restraint stress, calculated motility index was significantly increased by over 200% of basal in the proximal and distal colon. Similar results were obtained in response to the 2nd and 3rd day of restraint stress. In contrast, at the 5th day, restraint stress caused no more significant increase of colonic motility. Similarly, accelerated colonic transit induced by acute stress was no more observed following chronic stress. Increased, colonic motility and accelerated colonic transit induced by CRF were not attenuated at the 5th day. It is suggested that adaptation mechanism is developed following chronic stress. The decrease in colonic motor function in chronic stress is not due to reduced sensitivity to central CRF.