Circadian rhythms of plasma corticosterone at different times after induction of diabetes. Responses to corticoadrenal stimulation in light and dark phases

Abstract

In this study we have tried to determine the effects of streptozotocin-induced (50 mg/kg) diabetes (15 and 30 day duration) on circadian rhythms of plasma corticosterone concentrations and on the responsiveness of the adrenal glands to exogenously administered ACTH at the time of maximum and minimum levels of plasma corticosterone. Rats were kept under controlled lighting 12h light/12h dark (12L/12D) and fed ad libitum. The corticosteroid circadian pattern in control (C) rats is characterized as one in which peak corticosterone concentrations occur at the beginning of the dark phase (activity period), with a decrease over the remainder of the 24h period. Circadian rhythmicity of plasma corticosterone concentration was absent in the diabetic rats 15 days after induction (D15 rats), with higher mean levels than the C. However, in the diabetic rats 30 days after induction (D30 rats) there is a recovery of this rhythm with similar acrophase and amplitude to the C rats. One hour after stimulation by ACTH (5 IU/kg) at the time of maximum and minimum levels of plasma corticosterone, the C rats showed similar plasma corticosterone levels. In the D15 rats, levels of corticosterone in the light phase one hour after ACTH administration were higher than in the dark phase; being lower than C in this phase. The loss of capacity to respond during the dark phase may be due to adrenal blunting in this phase with high levels of plasma corticosterone. In D30 rats, there is a more noticeable loss of capacity for adrenal response in the light than in the dark phase, with values lower than C and D15 rats in both phases. These findings suggest that the duration of diabetes has a significant role in both plasma corticosterone rhythms and adrenal sensitivity to ACTH administration.