Diurnal change in digestion and absorption of sucrose in vivo in rats.

To clarify the physiological significance of circadian rhythmic changes in the activity of intestinal sucrase, the activity of digestion and absorption of sucrose in vivo were assessed during the daytime and the nighttime in rats fed ad libitum. When the jejunum was perfused at night with a solution containing sucrose in situ, the disappearance rate of sucrose from the lumen was higher than when perfused during the daytime, in parallel with the day/night difference in sucrase activity. The early response of plasma glucose to oral sucrose load in unanesthetized free-moving rats was also greater during the nighttime than the daytime. It was concluded that the digestion and absorption rate of sucrose shows circadian fluctuations under normal physiological conditions.