Intranuclear Binding of Hydrocortisone In Liver and Thymus Tissues 1

Abstract

Summary

Intranuclear uptake and binding of hydrocortisone was determined in several tissues of the rat. The first experiment was a time-uptake study designed to determine the relative distribution of ³H-hydrocortisone between the cytosol and nuclear fractions of liver and hypothalamus tissue. Maximum uptake was observed in each tissue as early as 1 min after the addition of the isotope. This was followed by a rapid migration of the radioactivity into the nucleus. Maximum nuclear uptake had occurred by 20 min. The increased nuclear uptake was accompanied by a decreased cytoplasmic radioactivity.

The second experiment was designed to determine if pretreatment of rats. with hydrocortisone increased specific nuclear binding in the cerebral cortex, heart, liver, and thymus. These tissues were selected because the liver and thymus are known to respond greatly to glucocorticoids, whereas, the cerebral cortex and heart have now shown such a response. It was observed that pretreatment with hydrocortisone increased nuclear binding in the liver and thymus, but hydrocortisone treatment had no effect on the cortex or the heart.

The inability of nonglucocorticoids to drive receptors into the nucleus was apparent since pretreatment with either aldosterone or testosterone did not increase the number of specific nuclear binding sites in either the liver or the thymus.

The nuclear receptors in the liver and thymus were shown to be specific for hydrocortisone by the ability of non-radioactive hydrocortisone to compete for the receptor sites, whereas, aldosterone or testosterone offered no competition.