Subcellular distribution of steroids in the rat adrenal cortex after incubation in vitro

Abstract

Following incubation of rat adrenal tissue in vitro, the distribution of steroids between tissue and incubation medium, and in the subcellular compartments of the tissue, were studied using glc methods. Five steroids, known to be secreted by the gland in vivo, were sought, viz: corticosterone, deoxycorticosterone, 18-hydroxydeoxycorticosterone, 18-hydroxycorticosterone and aldosterone. In contrast to previous studies on cholesterol, pregnenolone and progesterone, but in agreement with studies on corticosterone, it was found that the major intracellular location of these steroids was in the cytosol, and only minor amounts were found in the organelles. Concentrations, especially of the 18-oxygenated steroids in the cytosol were high, however, and suggested retention against the concentration gradient across the cell membrane. Dexamethasone pretreatment or sodium depletion prior to incubation and comparison with controls suggested that the cytosol content of steroids, particularly of 18-hydroxydeoxy-corticosterone and corticosterone, could vary independently. In particular, the fraction of 18-hydroxy-deoxycorticosterone retained in the glomerulosa cytosol was increased by dexamethasone pretreatment while corticosterone was decreased. The effect was less marked in inner zones. Sodium depletion had no effect on this parameter in either tissue. The results suggest mechanisms, possibly involving steroid-protein interaction, responsible for maintenance of “stores” of steroids within the gland, and their distribution to sites of enzyme activity.