To further investigate the role of intestinal apo A-IV in the management of daily food intake, we examined the diurnal patterns in apo A-IV gene and protein expression in freely feeding (FF) and food restricted (FR, food provided 4 h daily for 4 weeks) rats, which were sacrificed at 3-h intervals throughout the 24-h diurnal cycle. In FF rats, the intestinal apo A-IV mRNA and protein levels showed a circadian rhythm concomitant with the feeding pettern. The daily pattern of fluctuation of apo A-IV, however, was altered in FR rats, which had a marked increase in intestinal apo A-IV levels during the 4 h feeding period of light phase. In both FF and FR rats, increased plasma corticosterone (CORT) levels temporally coincided with the increasing phase of intestinal apo A-IV mRNA and protein expression. Depletion of CORT by adrenalectomy abolished the diurnal rhythm by decreasing the apo A-IV expression during the dark period, but did not change the feeding rhythm. Exposure of adrenalectomized rats to consistent CORT level (50 mg continuous release CORT pellet) resulted in fixed apo A-IV levels throughout the day. These results indicate that intestinal apo A-IV exhibits a diurnal rhythm, which can be regulated by endogenous CORT independently of the light/dark cue. The fact that intestinal apo A-IV levels were consistent with the food intake during the normal diurnal cycle as well as during the cycle of 4 h feeding each day suggests that intestinal apo A-IV is involved in the regulation of daily food intake.