Circadian rhythms of intestinal sucrase and glucose transport: cued by time of feeding.

In the rat, under constant illumination, the activities of the digestive enzyme sucrase and the absorptive transport system for glucose follow circadian rhythms on ad lib. and controlled feeding regimens. In response to controlled feeding, (1400-1800 h or 0200-0600 h, EST), both rhythms shift with time and the general level of activities are enhanced. Sucrase activity peaks before feeding and transport activity peaks during feeding. Feeding is a synchronizer for these digestive-absorptive functions, and the maximum activity of a function may occur prior to as well as subsequent to the daily onset of the synchronizer. The rhythms of these functions results from previous days' feeding patterns.