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J Clin Endocrinol Metab. 2007 May;92(5):1927-33. Epub 2007 Mar 6.

Nuclear progesterone receptors in the human pregnancy myometrium: evidence that parturition involves functional progesterone withdrawal mediated by increased expression of progesterone receptor-A.

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  • 1Department of Reproductive Biology, Case Western Reserve University, 11100 Euclid Avenue, Cleveland, OH 44106-5034, USA.

Abstract

CONTEXT:

We examined whether human parturition involves functional progesterone withdrawal mediated by changes in myometrial expression of progesterone receptors (PRs)-A and -B.

OBJECTIVE:

Our objectives were to: 1) measure PR-A and PR-B protein levels in human pregnancy myometrium and determine whether the PR-A to PR-B ratio changes with advancing gestation and labor onset; and 2) determine how changes in the PR-A to PR-B ratio affect myometrial cell progesterone responsiveness.

DESIGN:

PR protein levels and cellular localization were measured by Western blotting and immunohistochemistry, respectively, in lower uterine segment uterine wall tissue from preterm (<37 wk; not laboring; n = 5) and term (37-40 wk; not in labor: n = 6; in labor: n = 5) cesarean delivery. The capacity for PR-A and PR-B, alone and in combination, to mediate genomic progesterone responsiveness measured by the activity of a progesterone-responsive reporter plasmid was examined by artificially modulating their levels in the PHM1-31 myometrial cell line.

RESULTS:

PR-A and PR-B immunostaining was detected only in the nucleus of myometrial cells. The PR-A to PR-B protein ratio was 0.49 +/- 0.082 (mean +/- sem) in preterm tissue; increased to 1.03 +/- 0.071 (P < 0.001) in nonlaboring term tissue; and increased further to 2.65 +/- 0.344 (P < 0.001) in laboring term tissue. Only PR-B mediated progesterone-induced transcriptional activity. PR-A had no effect alone but markedly decreased PR-B-mediated progesterone responsiveness.

CONCLUSIONS:

Functional progesterone withdrawal in human parturition may be mediated by an increase in the myometrial PR-A to PR-B ratio due to increased PR-A expression.

[PubMed - indexed for MEDLINE]
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