Effects of Steroid Hormones on the Level of Corticotropin Messenger RNA Activity in Cultured Mouse‐Pituitary‐Tumor Cells

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Abstract
Studies have been made with the mouse pituitary tumor cell line AtT-20 in culture to determine whether or not the suppression of pituitary corticotropin messenger RNA activity observed upon the administration of glucocorticoids to adrenalectomized rats is due to a direct action of these steroid hormones on the pituitary. The levels of corticotropin messenger RNA activity in AtT-20 cells treated with various steroid hormones were measured with the use of the cell-free protein-synthesizing system derived from wheat germ. The addition of dexamethasone to culture medium reduced the level of corticotropin messenger RNA activity to 30–40% of that in untreated cells. Corticosterone and cortisol exhibited a suppressive effect to a lesser extent. In contrast, nonglucocorticoids such as testosterone and 17β-estradiol were essentially ineffective. These results indicate that at least part of the glucocorticoid action is exerted directly on the pituitary to suppress corticotropin messenger RNA activity.