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Context: Hypothalamic-pituitary-adrenal (HPA) axis dysregulation may underlie disorders including obesity, depression, cognitive decline and the metabolic syndrome. Conventional tests of HPA axis negative feedback rely on glucocorticoid receptor (GR) agonists such as dexamethasone, but do not test feedback by endogenous cortisol, potentially mediated by both GR and mineralocorticoid receptors (MR).

Objective: To use a combination of GR (RU38486, mifepristone) and MR (spironolactone) antagonists to explore the poorly understood activation of the HPA axis that occurs in obesity.

Design: Double blind, placebo-controlled randomized cross-over study.

Setting: Clinical research facility.

Participants: 15 lean (BMI 22.0+/-1.6 kg/m(2)) and 16 overweight/obese (BMI 30.1+/-3.5 kg/m(2)) men.

Intervention: Subjects attended on four occasions for blood and saliva sampling every 30 minutes between 1800h and 2200h. At 1100h and 1600h before visits subjects took either 200mg spironolactone, 400mg RU38486, 200mg spironolactone + 400mg RU38486, or placebo orally.

Main outcome measures: serum cortisol levels following drug or placebo.

Results: Cortisol levels did not differ between lean and obese following placebo. Spironolactone and RU38486 alone had modest effects, increasing cortisol by <50% in both groups. However, combined spironolactone plus RU38486 elevated cortisol concentrations substantially, moreso in lean than obese men (2.9(0.3) vs 2.2(0.3) fold elevation, p=0.002).

Conclusions: Combined receptor antagonist stimulation of the HPA axis reveals redundancy of MR and GR in negative feedback in humans. Obese men have impaired responses to combined receptor antagonist stimulation, suggesting impaired negative feedback by endogenous cortisol. Such an approach may be useful to dissect abnormal HPA axis control in neuropsychiatric and other disorders.