PARATHYROID HORMONE-RELATED PROTEIN MESSENGER-RNA IN SHEEP ENDOMETRIUM AND MYOMETRIUM DURING LATE-GESTATION AND LABOR

OBJECTIVE: To determine quantitative changes of parathyroid hormone-re lated protein (PTHrP) mRNA in sheep myometrium and endometrium during late gestation and labor. METHODS: Tissues were obtained from 22 pregn ant ewes under halothane anesthesia: early controls at 131 days' gesta tional age (dGA) not in labor (ECNL; n = 6); during cortisol-induced p remature 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 Norther n blot analysis. Blots were probed with a human PTHrP cDNA probe, stri pped, 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 contra st, myometrial PTHrP mRNA:18s ratio was decreased when TCNL and STL we re compared with both ECNL and CPL groups (P < .05). CONCLUSIONS: Sign ificant changes occur at the end of gestation in pregnant ovine myomet rium PTHrP mRNA but not in the endometrium. In myometrium PTHrP mRNA l evels were down-regulated at term regardless of whether labor was pres ent. It seems that PTHrP mRNA levels in myometrium are related to gest ational age rather than to labor per se in sheep. We hypothesize that PTHrP may play a role in maintaining uterine quiescence until term, at which time levels fall allowing myometrial contractile activity to in crease unopposed by PTHrP. Copyright (C) 1998 by the Society for Gynec ologic Investigation.