An analysis of the levels of plasma ACTH in 20 normal subjects

The levels of plasma ACTH were determined by radioimmumoassay in 20 normal subjects （10 males and 10 females）, It was found that the levels of the plasma ACTH at 8 a. m.,4 p.m.,O a. m. and 8 a. m. the next morning ranged 10.5～82, 7.6～76, 0~39.7 and 12～89 pg/ml, respectively. In 95% of these subjects, the levels of ACTH showed apparent circadian periodicity. Forty five minutes after injection of 0.12 U/kgw of regular insulin, the levels of ACTH increased to 185-680 pg/ml in 19 normal subjects. The suppressive effect of 0.75mg dexamethasone administrated at midnight on the plasma ACTH was quite definite. In 85% of subjects, the suppression rates of the hormone were more than 50%. The authors consider that the levels of plasma ACTH determined by radioimmunoassay and their circadian periodicity were useful for the diagnosis of Cushing’s disease and for the evaluation of axis function of the hypothelamus-pituitary-adrenal cortex. The clinical applications of insulin stimulation and dexamethasone suppression tests were discussed in some detail.