Activity-stress ulcers in rats: the role of preentrainment to meal time.

Rats housed in activity wheels (A-W) or hanging cages (H-C) received food restriction to 4 h/day for 15 days. Food was given at fixed times to entrain the feeding entrainable oscillator or at irregular times to prevent entrainment. One half of the rats received food in the light phase, the other half in the dark phase of the light-dark cycle. Food was then reduced to 6 g/day for 4 days for A-W rats or 7 days for H-C rats. Stomachs were removed 24 h after the last meal and the ulcerated area was quantified. Twenty one of 32 A-W rats and 19 of 32 H-C rats had ulcers in the glandular stomach. Ulcers were significantly larger in A-W rats (p < 0.01). Activity levels (in A-W rats), % body weight loss and terminal body weight (in both groups) were significantly correlated with the area of ulcers. There was no significant time of day effect on the ulcer severity. However, an unexpected finding was that for A-W rats, those fed at fixed times had larger ulcers than those fed at irregular times (p < 0.01) while H-C rats showed an expected trend in the opposite direction. One possible explanation for this result is that for A-W rats, the reduced food supply at an expected time of day generated a greater stress response than in rats whose feeding time was unpredictable.