<i>In Vitro</i>Physiological Activity of Protein-Bound and Unbound Cortisol

Abstract

Cortisol will inhibit the oxidation of glucose to CO2 by mouse ear strips. This in vitro system was used to study the action of cortisol in the presence of albumin or transcortin. The proportion of bound and unbound cortisol was determined in the albumin and transcortin solutions. The in vitro activity of cortisol in protein solution was not found to be related to its total concentration or to its concentration in protein- bound form, but correlated well with the non-protein-bound concentration of the steroid. Estradiol could not be shown to have any effect on glucose oxidation in vitro. Two weeks of low dosage estrogen therapy stimulated glucose oxidation in the isolated mouse ear, whereas high dosage estrogen therapy had an opposite effect. It is concluded that in this tissue the unbound cortisol level determines the extent of cortisol action on cellular function. Estrogen, when administered in a certain dose range, may result in a net antagonism of some cortisol effects at the tissue level. (Endocrinology78:1159,1966)