Miniature gel filtration: a simple and inexpensive method for the measurement of protein- and non-protein-bound cortisol: application to guinea pig plasma

Abstract

1. 1. A method is described for the accurate and rapid measurement of protein- and non-protein-bound cortisol by miniature gel filtration in small volumes of plasma, e.g. of rodents. 2. 2. Binding of cortisol by guinea pig plasma proteins is strongly reduced at elevated temperature (4°C: 102 ± 12ng/ml; 40°C: 5 ± 2 ng/ml). 3. 3. Incubation of guinea pig plasma with 1–5000 ng cortisol resulted in a dose-dependent increase in cortisol bound to proteins (specific binding by corticosteroid binding globulin: 230 ± 12 ng/ml). 4. 4. Administration of 20 IU (1–24)ACTH induced a significant increase of total protein-bound and non-protein-bound cortisol. 5. 5. Values reported in this study agree well with those of previous investigations, in which bound and non-bound glucocorticosteroids were separated by gel filtration on large Sephadex® columns.