Attenuated blood corticosterone rhythm in rats with jejunal resection.

Circadian rhythmic changes in blood corticosterone concentration were studied in rats after resection of the jejunum or the ileum. The rats with ileal resection showed a normal corticosterone rhythm, with a peak at the beginning of the dark period when they were fed ad libitum, and the phase of the rhythm shifted when the feeding time was restricted to a specific time of day during the light period. The rats with jejunal resection also showed a similar corticosterone rhythm, but its amplitude was lower compared to that of the rats with ileal resection. There were no differences in body weight and the circadian rhythm of blood urea concentration between two groups of rats. We conclude that the jejunum is an important site where the sense of food is received as an entraining signal for the corticosterone rhythm.