Reduced binding of progesterone receptor to its nuclear response element after human labor onset

OBJECTIVE: There is indirect evidence of decreased progesterone-activated transcription after human labor onset. Binding of the progesterone receptor to its response element is a prerequisite of progesterone-activated transcription. We established an assay to investigate whether there is reduced binding of progesterone receptor to its nuclear response element after, compared with before, labor onset. STUDY DESIGN: The binding of progesterone receptor from the decidua to its nuclear response element was measured in gel shift assays. Tissues from 52 patients who were term, preterm, in labor, and not in labor were compared. RESULTS: A 9-fold decrease in progesterone receptor binding to its response element was observed in tissues obtained after, compared with before, the onset of labor (P = .0008). In both preterm and term not-in-labor tissues, binding was higher than for in-labor tissues (P = .0172 for preterm; P = .0147 for term, Mann-Whitney U test). CONCLUSION: These findings provide a mechanism for the effective withdrawal of progesterone in human parturition.