Plasma cortisol response to synacthen (beta-1-24 Ciba) at different times of the day in patients with rheumatic diseases.

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Abstract
The response of the adrenal cortex to stimulation with the short-acting synthetic tetra-icosapeptide Synacthen ([beta]1-24 Ciba) was measured in the morning, afternoon, and evening in 18 subjects with rheumatic disorders. The mean plasma cortisol levels after Synacthen stimulation were the same at each time of day. In view of the physiological diurnal variation of basal (unstimulated) plasma cortisol, it follows that the increment in plasma cortisol after Synacthen stimulation shows a diurnal variation, a larger rise being observed in the afternoon and evening than in the morning These results suggest that, because of the diurnal rhythm of the basal cortisol level and the incremental response to Synacthen, both these criteria of adrenal function are unsuitable when outpatients are tested at different times of the day. The lovel of plasma cortisol attained 30 min. after Synacthen administration would seem to be an acceptable criterion of the normal response, as this parameter remains constant throughout the day.