Circadian rhythm of intestinal disaccharidases of rats fed with adiurnal periodicity.

The circadian rhythm of the activities of maltase and sucrase of the small intestine were examined in rats kept under conditions of continuous lighting with various fixed feeding periodicities for 20 days. When rats were fed once every 24 h, the enzymes showed circadian rhythmic changes with high activities around the feeding time, and the enzyme rhythm persisted even during subsequent starvation. Similar rhythmic changes in the enzyme activities were found in rats fed once every 48 h. When rats were fed once every 32 h, the enzymes showed rhythmic changes with a period of 32 h, but the activities were lowest during the feeding time. The enzyme rhythm with a period of 32 h was replaced by a 24-h circadian rhythm as soon as the rats were starved. It was concluded that the circadian rhythmic changes in disaccharidase activities are controlled by an endogenous mechanism, and that some circadian time-keeping system participates in this mechanism.