We employ rapid-
ACTH stimulation test under
dexamethasone (DEX) suppression to assess the adrenal function in daily clinic. However, we have little knowledge about the excretion of urinary free
cortisol (FF) and
cortisone (FE) in pooled urine in this setting. The purpose was to examine the changes of FF and FE as well as FF/FE ratio in pooled urine after rapid-
ACTH stimulation test under DEX suppression using stable
isotope dilution-gas chromatography/mass spectrometry (
SID-GC/MS). Pooled urine samples were collected from 8 patients (age 33-71 years) who were suspected to have primary aldsteronism. They all were finally diagnosed as having normal
glucocorticoid secretion. We performed rapid-
ACTH stimulation test with DEX suppression for consecutive 4 days as follows. (1) 24 hour urine samples were serially collected from 2300 h on day 1 for 72 hours (Basal, DEX1mg, and DEX8mg-
ACTH). (2) 1 and 8 mg DEX was given at 2300 h on day 2 and 3, respectively. (3) 250 µg of
ACTH was given at 0900 h on day 4. Urine free
steroids were delivered with bismethylenedioxy-
heptafluorobutyric anhydride and analyzed by
SID-GC/MS (µg/day). From DEX1mg to DXE8mg-ACTH, (1) FF and FE were significantly increased (3.9±1.3 to 21.3±14.6 and 12.4±4.8 to 26.1±11.0 µg/day, respectively), but (2) FF/FE ratio significantly increased (0.32±0.05 to 0.77±0.23). These data suggested that newly synthesized
cortisol by
ACTH stimulation was not efficiently metabolized to
cortisone.