Objective: To determine quantitative changes of parathyroid hormone-related protein (PTHrP) mRNA in sheep myometrium and endometrium during late gestation and labor.
Methods: Tissues were obtained from 22 pregnant ewes under halothane anesthesia: early controls at 131 days' gestational age (dGA) not in labor (ECNL; n = 6); during cortisol-induced premature labor (CPL at 131 dGA; n = 6); in term spontaneous labor (STL at 140-145 dGA; n = 5); or term control animals not in labor (TCNL at 140-145 dGA; n = 5). Total RNA was extracted and subjected to Northern blot analysis. Blots were probed with a human PTHrP cDNA probe, stripped, and rehybridized with an 18s rRNA nucleotide probe to normalize PTHrP mRNA levels.
Results: Endometrial PTHrP mRNA:18s was unaffected by gestational age or labor in tissues from the four groups. In contrast, myometrial PTHrP mRNA:18s ratio was decreased when TCNL and STL were compared with both ECNL and CPL groups (P < .05).
Conclusions: Significant changes occur at the end of gestation in pregnant ovine myometrium PTHrP mRNA but not in the endometrium. In myometrium PTHrP mRNA levels were down-regulated at term regardless of whether labor was present. It seems that PTHrP mRNA levels in myometrium are related to gestational age rather than to labor per se in sheep. We hypothesize that PTHrP may play a role in maintaining uterine quescence until term, at which time levels fall allowing myometrial contractile activity to increase unopposed by PTHrP.
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