Corticosterone rhythmicity in the rat: interactive effects of dietary restriction and schedule of feeding.

Effects of changes in diet composition and schedule of restricted feeding on the circadian rhythm of plasma corticosterone in the adult rat were examined. Three restricted feeding schedules were used: diet presented 3 hours after lights-on, 1 hour before lights-off or continuously by automated feeder. Animals were paired to controls (consuming 24% protein diet and libitum) and provided 80% of control food intake/g body weight/day. A fourth experimental group was offered 2.4% protein diet ad libitum. Plasma corticoids were measured every 4 hours from 0800 to 0400 hours. Corticoid levels 20 min after food presentation were also determined. Both control and protein-restricted animals displayed a typical circadian rhythm, with corticoids lowest at 0800 hours and a peak at 2000 hours. Animals fed at 0900 hours exhibited a 12-hour shift in peak corticoids, while the circadian rhythm was totally abolished in animals fed by automated feeder. Offering the restricted ration at 1700 hours, however, resulted in a diurnal rhythm similar to that of controls. While pre and post-feeding corticoids were similar in control and protein-restricted animals, a post-feeding suppression was found in all three food-restricted groups. Clearly, the relationship between feeding schedule and diurnal rhythm must not be ignored in nutritional paradigms.