Gel filtration on Sephadex columns has been used to study the influence of steroids in vitro on the cortisol-binding capacity of human plasma transcortin (De Moor, Heirwegh, Heremans & Declerck-Raskin, 1962; De Moor, Deckx & Steeno, 1963). Testosterone and progesterone, added in the same amounts as cortisol, displaced 25 and 23% respectively of bound cortisol.
In view of their similar structure, various anabolic steroids as well as progestagens were tested in the same manner. Plasma with a low concentration of corticosteroids taken at 12 p.m. from a normal sleeping individual, was overloaded either with cortisol or with cortisol and an equal amount of the steroid to be tested. The loading dose was always 500 ng./ml. After 15 min. of incubation at room temperature, the plasma samples were submitted to gel filtration (also at room temperature) and the protein-bound corticosteroid was determined fluorimetrically. The results are expressed as percentual decrease of