Hypocortisolemic clamp unmasks jointly feedforward- and feedback-dependent control of overnight ACTH secretion

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Abstract
Background: ACTH secretion is under hypothalamic stimulatory (feedforward) and adrenal inhibitory (feedback) control.Hypothesis: Assessment of overnight ACTH secretion during a hypocortisolemic clamp will permit the estimation of changing feedforward and feedback.Subjects: Seven healthy men.Interventions: An oral dose of placebo (PLAC), metyrapone (METY, 3 g), or ketoconazole (KTCZ, 1.2 g) was given at midnight (MN) to block glucocorticoid synthesis. Plasma ACTH was sampled every 10 min (MN to 0800 h).Analysis: Variable-waveform deconvolution analysis of ACTH secretion and approximate entropy (ApEn) analysis of pattern regularity.Results: Compared with PLAC, administration of METY and KTCZ reduced morning cortisol concentrations by ≥77 and 54% respectively (PPP=0.020). ACTH secretory-burst shape and half-life were stable. ApEn of ACTH release declined overnight (P=0.021) and with the drug (P=0.001), denoting enhanced feedforward coordination.Conclusion: The combined data predict overnight amplification and coordination of hypothalamic feedforward drive onto ACTH release. Therefore, disruption of either mechanism might contribute to clinical pathophysiology, such as late-day elevations of cortisol output in fasting, alcoholism, depression, or aging.

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