Parathyroid hormone-related protein (PTHrP) was detected at 32.8 ± 3.9 pmol l−1 in uterine luminal fluid from immature rats treated with oestradiol. As mRNA encoding PTHrP has previously been localized to implantation sites in pregnant rats, the role of luminal PTHrP during pregnancy was explored. Infusion of a parathyroid hormone (PTH)/PTHrP receptor antagonist, [Asn10,Leu11]PTHrP(7–34) amide, into the uterine lumen during pregnancy in rats resulted in excessive decidualization. This effect was also observed after intrauterine infusion of a monoclonal antibody raised against PTHrP. The effect of infusion of PTH/PTHrP receptor antagonist was dependent upon successful implantation, was dose-dependent and confined to the treated horn. A decrease in the number of apoptotic decidual cells in antagonist-infused uterine horns compared with vehicle or non-infused horns was detected immunohistochemically at day 13 of pregnancy, and this decrease is likely to contribute to the 'over-decidualization' observed. In pseudopregnant rats, infusion of PTH/PTHrP receptor antagonist into the uterine lumen resulted in an increase in uterine wet weight of the infused horn compared with the non-infused horn, indicating a direct effect on deciduoma formation. Thus, activation of the PTH/PTHrP receptor by locally produced PTHrP appears to be crucial for normal decidualization during pregnancy in rats.
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