CIRCADIAN RHYTHMICITY IN SEROTONIN-INDUCED ACUTE GASTRIC-MUCOSAL INJURY IN RATS

Time-dependent patterns in the susceptibility of the rat gastric mucos a to ulcerogenic stimuli involving stress or chemical injury have been described. The purpose of this study was to evaluate whether serotoni n (5-MT)-induced gastric mucosal injury is produced in a circadian fas hion in the rat model. In fasted Wistar rats (adapted for 3 weeks to a standard 12-h light-dark cycle), 5-HT administered subcutaneously (20 mg/kg, 4h before autopsy) produced gastric mucosal injury. The stomac hs were removed and the ulcers were scored for intensity, using a scal e of 0-4. In studies performed at 4-h intervals, beginning 1h after li ghts-on, most of the mucosal injury occurred at 2000h, i.e. early in t he dark phase. Likewise, serum corticosterone levels were also found t o be high at the same time period. The time of 2000h is approximately determined to be the beginning of the rats' active period. These resul ts suggest that the extent of acute 5-HT-induced gastric mucosal injur y varies with the time of day and that elevations in corticosterone co ncentrations might be responsible for the 5-HT-induced gastric mucosal injury.