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 2300h on day 1 for 72 hours (Basal, DEX1mg, and DEX8mg-ACTH). (2) 1 and 8 mg DEX was given at 2300h on day 2 and 3, respectively. (3) 250μg of ACTH was given at 0900h 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.
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