The human placenta was found to contain a cytosol receptor for glucocorticoids. The concentration of this receptor in term placenta was 27-fold higher than that found in cytosol from first trimester placenta. The levels of cytosol glucocorticoid receptor in three trophoblastic cell lines (JAr, BeWo, and JEG) were also determined and all were found to be low. The ability of prednisolone, a potent glucocorticoid, to stimulate heat-stable alkaline phosphatase activity found in these cells was tested. Although control experiments demonstrated that the conditions were adequate to stimulate HeLa cell alkaline phosphatase, none of the trophoblastic lines responded to prednisolone administration. This result may be explained by the observation that the JAr cells lacked any detectable glucocorticoid receptor and the receptor levels in cytosol prepared from JEG and BeWo cells were 12% and 2%, respectively, of those measured in HeLa cytosol. Our studies also suggest that the increase in serum levels of heat-stable alkaline phosphatase observed during pregnancy may reflect increasing placental sensitivity to glucocorticoids as a result of increased receptor levels.
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