The Nature of the Circadian Periodicity and Suppressibility of Immunoreactive ACTH Levels in Addison's Disease

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Abstract
A circadian periodicity of plasma immunoreactive ACTH levels (half-hourly sampling) in the presence of virtually constant plasma cortisol levels, was evident in a patient with Addison's disease who had been withdrawn from corticosteroid maintenance medication 16 hours prior to the start of study. The actual levels of ACTH were greatly elevated compared to those seen in normal subjects for corresponding times of day. This would indicate the lack of involvement of feedback mechanisms in the genesis of ACTH periodicity, and that in the absence of such feedback this periodicity oscillates about a higher ACTH level than in the normal subject. The elevated plasma ACTH levels in 2 Addisonian patients were rapidly suppressible with hydrocortisone or dexamethasone administration, but not to the levels reported in normal subjects. Estimates of apparent ACTH halflife ranged from 15 to 30 min in these patients.

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