Diminished adrenal sensitivity and ACTH efficacy in obese premenopausal women.

BACKGROUND: The ACTH-cortisol axis in women is activated and associated with decreased ACTH potency, estimated by relating ACTH and cortisol pulse masses. Recently, a new accurate method for constructing the endogenous dose-response relationship was introduced, which is based on the relation between ACTH concentrations and associated cortisol secretion rates within cortisol bursts. HYPOTHESIS: The endogenous dose-response relation between ACTH and cortisol in obesity is changed, leading to diminished responsiveness.
SUBJECTS: Twenty-five obese premenopausal women and 16 normal weight premenopausal women were studied by 10-min blood sampling for 24 h. OUTCOMES: ACTH and cortisol secretion rates, analytical dose-response estimates of endogenous ACTH efficacy (maximal cortisol secretion), dynamic ACTH potency, and adrenal sensitivity (slope term) from 24-h ACTH-cortisol profiles were quantified.
RESULTS: The initial potency (negative logarithm) was -7.83 ± 0.75 (mean ± s.e.m.) in obese women and -10.14 ± 1.08 in lean women (P=0.10), and the corresponding values for the recovery phase were -26.62 ± 2.21 and -36.67 ± 1.66 (P=0.004). The sensitivity (curve slope) amounted to 0.468 ± 0.05 in obese women and 0.784 ± 0.09 in normal weight women (P=0.004). The efficacy (maximal value) was 17.6 ± 4.9 nmol/l per min in obese women and 26.3 ± 3.8 nmol/l per min in normal weight women (P=0.009). Basal secretion rate, inflection point, and EC(50) values were not different. Bromocriptine or acipimox did not change the dose-response curve.
CONCLUSION: The ACTH-cortisol relation in obesity in women is characterized by decreased sensitivity and efficacy, thus explaining non-elevated serum cortisol concentrations despite increased plasma ACTH levels.