Influence of Change in Feeding Regime and Food Deprivation on Circadian Rhythm of Adrenal Cortical Activity in Rats

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Abstract
The effects of food deprivation on circadian periodicity of plasma corticosterone levels were studied in adult male rats kept under regular light-dark alternation (light: 7 AM - 7 PM). Blood samples were obtained by tail vein sampling method. Plasma levels of corticosterone determined by this method were comparable to those obtained by decapitation both in the morning and evening. Twenty-four hour patterns of plasma corticosterone levels determined at 4 hour intervals using these two different methods were also essentially similar, indicating that the tail vein sampling method is reliable and useful for the study on adrenocortical rhythm. A restriction of feeding time between 10 AM and 6 PM for 2 weeks resulted in a phase shift of the circadian rhythm of plasma corticosterone levels. A peak appeared at 8 AM and the value was significantly higher than that at 6 PM. These findings confirmed the facts reported by Johnson and Levine, and Krieger. Overt circadian periodicity of plasma corticosterone levels persisted in rats fasted for three days. However, after the 5th day of food deprivation, the circadian rhythm was abolished and a flat 24 hour pattern of higher levels was observed. These results indicated that the feeding pattern plays an important role in establishing of circadian rhythm of adrenocortical activity.

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