Daily cortisol patterns and adrenal responses to ACTH remain normal in dexamethasone-treated capuchin monkeys

Dexamethasone treatment reduced cortisol levels to 1/10 of control values while preserving a circadian rhythm.

• Capuchin monkeys displayed a clear rhythm of adrenocorticotropic hormone (ACTH) and plasma cortisol levels.
• The adrenal cortex may have intrinsic oscillatory properties that contribute to the circadian rhythm of cortisol secretion.
• Cortisol levels remained rhythmic even when ACTH was suppressed by dexamethasone.
• The response of cortisol to exogenous ACTH was dependent on the time of day, peaking at 0800 h.

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