CHANGES IN OXYTOCIN RECEPTOR MESSENGER-RNA IN THE ENDOMETRIUM, MYOMETRIUM, MESOMETRIUM, AND CERVIX OF SHEEP IN LATE-GESTATION AND DURING SPONTANEOUS AND CORTISOL-INDUCED LABOR

OBJECTIVE: Changes in oxytocin binding in intrauterine tissues have be en demonstrated in relation to labor and delivery in several species u sing ligand-binding techniques. Little information is available in any species on changes in mRNA for the oxytocin receptor in intrauterine tissues in relation to the changes in myometrial activity at term. The objective of this study was to quantify oxytocin receptor mRNA in cri tical intrauterine tissues in the pregnant sheep in relation to the my ometrial electromyographic activity patterns that accompany labor. MET HODS: Uterine tissues were removed under halothane general anesthesia from control ewes not in labor at two stages of gestation, 131 and 140 -145 days, and from ewes in spontaneous term labor at 140-145 days' ge station. Tissues were also obtained from ewes in labor following the i nfusion of cortisol to the fetus beginning at 127 days' gestation. RES ULTS: In both the myometrium and endometrium, oxytocin receptor mRNA w as significantly increased in both spontaneous term labor and cortisol -induced labor as compared with appropriate gestational age-matched co ntrols. fn contrast, oxytocin receptor message was unchanged at the ti me of labor in the mesometrium and cervix in all groups studied. CONCL USIONS: In the pregnant sheep, myometrial and endometrial oxytocin rec eptor mRNA in ct eases significantly in both spontaneous and cortisol- induced labor as compared with appropriate controls. In contrast, ther e tr,as no increase in oxytocin receptor mRNA in either the cervix or the mesometrium.