Circadian variation of susceptibility to gastric mucosal injury by acidified aspirin or absolute ethanol in the rat.

Circadian rhythms of physiologic processes allow coordination of interdependent functions and separation of incompatible functions. Several gastrointestinal processes, which potentially alter the balance between gastric mucosal protection and injury, show regular fluctuations. We investigated the possibility that susceptibility to gastric mucosal injury by acidified aspirin and absolute ethanol may vary with phases of the light/dark cycle in the rat. We found that acidified aspirin caused significantly more gastric mucosal lesions when administered early in the light phase compared with administration early in the dark phase. The differences in susceptibility were not altered by pretreatment conditions such as immobilization or length of the fasting period. Absolute ethanol also caused significantly greater gastric mucosal injury when administered in the light than in the dark phase, but this difference was only evident in rats immobilized during the pretreatment fasting period. In contrast to the acidified aspirin group, rats unrestrained during pretreatment fasting did not have light/dark differences in susceptibility to ethanol injury. We concluded that rats show circadian variation in susceptibility to gastric mucosal injury by acidified aspirin.