[Binding of cortisol, fluocortolone and difluocortolone to human plasma proteins (author's transl)]

The binding properties of [3H]cortisol, [3H]fluocortolone and [3H]difluocortolone by human plasma, human albumin, human- beta- and gamma-globulins have been studied by equilibrium dialysis. Cortisol, in physiological concentrations (0,4 micromol/l), is 98% bound in human plasma at 25 degrees C, fluocortolone 96% and diflucortolone 85%. Uncer physiological conditions cortisol is mainly bound to the corticosteroid binding globulin (transcortin). 2/3 of fluocortolone is bound to transcortin and 1/3 to albumin and globulins, whereas difluocortolone is mainly bound to albumin and to globulins but not to transcortin. The binding affinities of beta- and gamma-globulins are -ery low for the corticoids investigated, but they are higher for fluocortolone and difluocortolone than for cortisol.