Changes in prostacyclin synthase in pregnant sheep myometrium, endometrium, and placenta at spontaneous term labor and regulation by estradiol and progesterone

OBJECTIVE: Our purpose was to investigate, first, whether there were change s in the abundance of prostacyclin synthase protein in intrauterine tissues of pregnant ewes in association with spontaneous term labor. Second, we ex amined the effect of either estradiol or progesterone, or both, on regulati on of prostacyclin synthase protein abundance in uterine tissues using an o variectomized nonpregnant sheep model. STUDY DESIGN: The abundance of prostacyclin synthase protein was quantified by Western Mot analysis in the myometrium, endometrium, and placenta of pr egnant ewes in spontaneous term labor (n = 6) and term control ewes not in labor (n = 6). The changes of prostacyclin synthase in the myometrium and e ndometrium of 20 ovariectomized nonpregnant sheep (n = 5 for each group) we re evaluated after treatment with estradiol, progesterone, or both. RESULTS: Prostacyclin synthase protein was present in pregnant and nonpregn ant sheep myometrium, endometrium, and placenta at a molecular weight of ab out 55 kd. At spontaneous term labor the level of prostacyclin synthase dec reased in endometrium (P < .05), increased in myometrium (P < .05), and rem ained unchanged in placenta. Estradiol and progesterone had no effect on pr ostacyclin synthase protein abundance in nonpregnant ovine endometrium and myometrium. CONCLUSIONS: The decrease in prostacyclin synthase in pregnant sheep endome trium during labor may indicate paracrine interactions between the endometr ium, the myometrium, fetal membranes, or a combination of these. The signif icant increase of prostacyclin synthase in pregnant sheep myometrium at spo ntaneous term labor may contribute to the increased uterine sensitivity to oxytocin or stimulate vasodilatation during labor to increase myometrial bl ood flow. Neither estradiol nor progesterone at the dosages studied changed prostacyclin synthase expression in the nonpregnant myometrium and endomet rium. The molecular mechanism or mechanisms that differentially regulate pr ostacyclin synthase expression in pregnant uterine tissues merit further st udy.