IMMUNOREACTIVE PARATHYROID HORMONE-RELATED PROTEIN - ITS ASSOCIATION WITH PRETERM LABOR

Objective: Parathyroid hormone-related protein (PTHrP) is a 141 amino acid protein which contains a 1-36 N-terminal domain resembling parath yroid hormone which has smooth muscle relaxant activity and a mid (67- 86) domain which reportedly alters placental calcium transport. Using specific antibodies to these regions of PTHrP, the objective of this s tudy was to determine changes in the levels and localization of the pe ptides in placenta and membranes that might be indicative of their bio logical activity and role during term and preterm labor. Study design: Placenta and fetal membranes were collected from patients with preter m delivery (PTL) (n = 16), term cesarean section in the absence of lab or (n = 10) and term vaginal delivery (n = 5). Immunohistochemistry, w as performed with specific antisera visualized by the avidin-biotin pe roxidase method and the staining intensity; was quantified with an ima ge analysis system MCID. Results: Immunoreactive (ir)-PTHrP(1-34) and ir-PTHrP(67-86) were localized to the amnionic epithelium chorionic tr ophoblasts, decidual cells and placental syncytiotrophoblast. Intense immunostaining was observed for ir-PTHrP(67-86) but not for ir-PTHrP(1 -34) in the endothelial lining of the villous capillaries. Ir-PTHrP(1- 34) staining was lower in placenta and fetal membranes of PTL patients compared with term cesarean section in the absence of labor (P < 0.05 Mann-Whitney test). In contrast, there was no difference in ir-PTHrP [67-86] staining intensity between delivery categories. Conclusion: Th ese results showing differential localization of PTHrP(1-34) and PTHrP (67-86) suggest cell specific processing of PTHrP precursor in the hum an placenta. Moreover, the changes in ir-PTHrP(1-34) but not ir-PTHrP( 67-86) with labor are indicative of a particular role for this peptide in the delivery process.