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 been demonstrated in relation to labor and delivery in several species using 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 critical intrauterine tissues in the pregnant sheep in relation to the myometrial electromyographic activity patterns that accompany labor.

METHODS

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' gestation. Tissues were also obtained from ewes in labor following the infusion of cortisol to the fetus beginning at 127 days' gestation.

RESULTS

In both the myometrium and endometrium, oxytocin receptor mRNA was significantly increased in both spontaneous term labor and cortisol-induced labor as compared with appropriate gestational age-matched controls. In contrast, oxytocin receptor message was unchanged at the time of labor in the mesometrium and cervix in all groups studied.

CONCLUSIONS

In the pregnant sheep, myometrial and endometrial oxytocin receptor mRNA increase significantly in both spontaneous and cortisol-induced labor as compared with appropriate controls. In contrast, there was no increase in oxytocin receptor mRNA in either the cervix or the mesometrium.