Interperson Variability but Intraperson Stability of Baseline Plasma Cortisol Concentrations, and Its Relation to Feedback Sensitivity of the Hypothalamo-Pituitary-Adrenal Axis to a Low Dose of Dexamethasone in Elderly Individuals

In the present study, we investigated whether the negative feedback action of glucocorticoids (GCs) on the hypothalamo-pituitaryadrenal (HPA) axis changes with age.We performed a 1-mg dexamethasone (DEX) suppression test in 216 healthy elderly individuals.To investigate individual variability of feedback sensitivity in more detail, 2.5 yr later a 0.25-mg DEX suppression test was carried out in 164 of the same individuals.We investigated whether there was an effect of age or gender on both basal and post-DEX cortisol levels, as well as on the concentration of DEX.Furthermore, we examined whether the reactions to the two doses of DEX differed, and whether indications for an intraperson stability of baseline cortisol levels could be found.Neither the pre-nor the post-1-mg DEX plasma cortisol concentrations showed a correlation with age, and there were no differences between men and women.The same was true for the pre-and post-0.25-mgDEX cortisol concentrations.In reaction to 1 mg DEX, over 90% of the subjects investigated showed a cortisol suppression to levels below 50 nmol/L.After the administration of 0.25 mg DEX,