Mammary epithelial cells isolated from midpregnant mice and cultured on collagen gels contain soluble glucocorticoidreceptors. The kinetics of binding of dexamethasonereveal a saturable binding site [dissociation constant (Kd), -1nm], and the binding site obeys a steroid specificity characteristicof a glucocorticoid receptor. As with the receptor isolatedfrom intact glands, the receptor from the cultured cells alsorequires the addition of dithiothreitol for maximal binding ofdexamethasone. The receptors are maintained at in vivo levels(-1.3 pmol/mg DNA) for at least a period of 10 days in culture.However, the presence of both cortisol and PRL is required forthe maintenance of the receptors, and the effect of both thesehormones is dose dependent. (Endocrinology116: 2656-2662,1985)

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