Dexamethasone suppressibility of plasma dehydroepiandrosterone (3beta-hydroxy-5-androsten-17-one) in normal men

9 AM and overnight dexamethasone suppression tests were performed in normal adult subjects and plasma dehydroepiandrosterone (DHA) levels were radioimmunoassayed. The results were as follows: 1) In the 9 AM test, plasma DHA was suppressed to the lowest level at the time between 4 hours and 6 hours after dexamethasone; 2) 2 mg (overnight test) or 3 mg (9AM test) of dexamethasone induced the maximum DHA suppression; 3) after dexamethasone administration in both the tests, plasma DHA was not suppressed below 30% of the basal level, nor below 2 ng/ml; and 4) there was no significant difference in dexamethasone suppressibility of plasma DHA between 9 AM test and overnight test.