Hypothalamic-Pituitary-Adrenal Axis Recovery Following the 1-mg Overnight Dexamethasone Suppression Test in Healthy Volunteers

Background: The recovery of hypothalamic-pituitary-adrenal (HPA) axis suppression following pharmacological doses of various steroids has been studied previously. However, no study has been conducted using the more commonly used 1-mg dexamethasone in the overnight dexamethasone suppression test (ODST). Hence, we aimed at evaluating HPA axis recovery after the 1-mg ODST. Objectives: This study aimed at investigating the pattern and time of recovery of the HPA axis following the 1-mg ODST in healthy subjects. Methods: Ten healthy volunteers aged 18 - 40 years, BMI 30 kg/m^2, with neither exposure to steroids nor interfering drugs were included. The 1-mg ODST was performed, and the adrenocorticotropic hormone (ACTH) and cortisol samples were withdrawn at regular intervals. The serum cortisol of 1.8 µg/dL was considered as HPA axis suppression, whereas the cortisol value equal to or more than baseline was deemed as recovery. Results: Cortisol and ACTH levels were suppressed in all subjects 9 hours following the 1-mg ODST. Although ACTH showed an early increase after 8 hours, the upsurge was noticed following 24 hours (mean ± SD, 34.42 ± 18 pg/mL). Later, cortisol accompanied ACTH, and both reached their baseline after 72 hours (mean ± SD, ACTH, 37.48 ± 12.44 pg/mL; cortisol, 8.45 ± 3.32 μg/dL). A small dip in ACTH and cortisol (mean ACTH, 23.84 pg/mL; mean cortisol, 2.3 μg/dL) was observed after 24 - 36 hours indicating the return of the diurnal rhythm before complete recovery. Conclusions: The complete recovery of the HPA axis occurs only 72 hours following the 1-mg ODST. ACTH begins to recover as early as 8 hours after the maximal suppression and diurnal rhythm of ACTH and cortisol resume 24 to 36 hours later.