ROLES OF GLUCOCORTICOID IN CIRCADIAN CHANGES IN THE PLASMA INSULIN RESPONSE TO FOOD INTAKE IN RATS

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Circadian variations in the plasma insulin response to food intake, and effects of adrenalectomy and treatment with corticosterone were examined in rats which had been fed during a restricted time of day (2000-2400) for 2 weeks. When rats were refed at 2000 after starvation, the plasma insulin level increased to a much higher level than when they were refed at 0800. In adrenalectomized rats, the plasma insulin response to refeeding was much attenuated at 2000 and its clock-time difference was abolished. When corticosterone was administered to adrenalectomized rats immediately before refeeding, the clock-time difference in the postprandial insulin response was restored, with a greater response at 2000. From these results, together with the previous finding that the plasma corticosterone level was higher at the scheduled feeding time (2000), it was concluded that the circadian difference in the postprandial insulin response was attributable to the circadian adrenocortical rhythm.