Corticosteroid-Binding Globulin in the Rat: Isolation and Studies of Its Influence on Cortisol Action in Vivo1

Corticosteroid—binding globulin (CBG) was isolated from pooled rat plasma by affinity chromatography. The purified protein migrated as a single band on polyacrylamide gel electrophoresis. Scatchard analysis revealed an equilibrium constant for cortisol of 3.1 X 106 L/M at 37 C and 1.1 binding sites/mole of protein. The induction of hepatic tyrosine aminotransferase activity and the fall in lymphocyte concentration in peripheral blood was measured after the intravenous injection of unbound cortisol or cortisol bound to CBG. The studies reported demonstrate that the presence of CBG affected neither the time course nor the amplitude of the response of these two cortisol—responsive variables. (Endocrinology91: 626, 1972)