Some physiological factors affecting the binding of cortisol by human plasma proteins.

Steady-state gel filtration has been used to study the binding of cortisol to human plasma proteins in vitro. Raising the temperature from 37 degrees C to 41 degrees C results in the mean proportion of free (non-protein-bound) cortisol rising approximately from 7% to 11%. Addition of cortisol to plasma identical to 275 nmol/l) also increased the proportion of free cortisol by approximately 50%. Cortisone is less strongly bound to plasma proteins than cortisol. The mean values (+/- S.D.) for five samples were free cortisol 8.4 +/- 1.1% and free cortisone 26.0 +/- 3.8%.