Role of nocturnal feeding in the development of the diurnal rhythm of jejunal sucrase activity.

A diurnal rhythm of jejunal sucrase activity has been shown previously to make its developmental appearance in the rat at the time of weaning (Day 22). In this study we found that the rhythm was not present on Day 23 if the onset of feeding was not coordinated with the onset of darkness. Conversely, the sucrase rhythm appeared precociously (Day 19) in pups weaned onto chow on a schedule in which the onset of feeding is coordinated with the onset of the dark period. It is concluded that the normal developmental appearance of the sucrase rhythm is due, at least in part, to the fact that ad libitum feeding becomes nocturnal around Day 22.