In Vivo Evidence for Stimulation of Placental, Myometrial, and Endometrial Prostaglandin G/H Synthase 2 by Fetal Cortisol Replacement after Fetal Adrenalectomy

Abstract

Fetal glucocorticoid-induced premature labor in sheep is an established model of premature labor. However, the pathways by which fetal cortisol triggers subsequent maternal endocrine changes, including enhanced PG synthesis, leading to labor are unclear. The current study was undertaken to determine whether cortisol administration to adrenalectomized fetuses to clamp fetal cortisol at levels present early in the late gestation rise, which are inadequate to produce labor, can stimulate placental, myometrial, and endometrial prostaglandin G/H synthase 2 mRNA and protein expression. At 109--13 d gestation, fetal sheep adrenals were removed (n = 8), or sham surgery was performed (n = 4). From d 6 postadrenalectomy, maternal and fetal plasma cortisol were determined daily by RIA. From d 7 postadrenalectomy, cortisol (4 micro/min) was continuously infused iv to four adrenalectomized fetuses. Endometrium, myometrium, and placentome were collected from all three groups of ewes (n = 4 for each group), and total RNA and proteins were extracted from each intrauterine tissue and analyzed by Northern and Western for prostaglandin G/H synthase 2 mRNA and protein. P45017 alpha hydroxylase mRNA was analyzed in the placentome by Northern blot. Data were analyzed by ANOVA. Plasma cortisol levels remained low in sham-operated and adrenalectomized fetus, whereas during cortisol infusion to adrenalectomized and cortisol-treated fetuses, plasma cortisol increased to the late gestation level. After adrenalectomy, prostaglandin G/H synthase 2 did not change in any tissue studied. Fetal plasma cortisol replacement to late gestation levels increased prostaglandin G/H synthase 2 to levels similar to term levels in all three tissues. PGHS1 mRNA and protein did not change in any group studied. There was a minimal increase in P45017 alpha hydroxylase mRNA in the placentome in the adrenalectomized and cortisol-treated group. Cortisol- induced labor further increased P45017 alpha hydroxylase mRNA in the placentome compared with that in adrenalectomized and cortisol-treated animals. These data provide evidence for in vivo cortisol up-regulation of prostaglandin G/H synthase 2, but not PGHS1, in late gestation in the ovine placentome, myometrium, and endometrium. As stimulation of the estrogen biosynthetic pathway was minimal in the adrenalectomized and cortisol-treated group, these data provide support for the concept that cortisol has a direct effect on prostaglandin G/H synthase 2 expression in addition to its classical indirect pathway on prostaglandin G/H synthase 2 as a result of estrogen synthesis.

Prostaglandin Mediates Premature Delivery in Pregnant Sheep Induced by Estradiol at 121 Days of Gestational Age

“…In the present study, failure of fetal cortisol to rise in the estradiol-treated groups, compared with controls, indicates that the increased PG production by maternal intrauterine tissues is regulated by an estrogen-dependent pathway (4,5). However, other factors, such as oxytocin, recruited by estradiol may play a role in mediating estradiol's effect on induction of PG synthesis.…”

“…Although our data support a role for estradiol in the regulation of PG synthesis by intrauterine, nontrophoblast tissues, we cannot exclude the regulatory function of estradiol on trophoblast tissues because administered estradiol was increased only in the maternal plasma. However, in light of the observation that fetal placental PGHS2 increases in late gestation (7), well before the rise in maternal plasma estradiol at the end of gestation, we and others have proposed that in late gestation fetal adrenal cortisol induces fetal placental PGHS2 expression and PG production (4,5). Indeed, we recently reported that fetal cortisol at concentrations seen in late gestation, independent of any other steroids of fetal origin, are able to stimulate fetal placental PGHS2 expression (5).…”

“…However, in light of the observation that fetal placental PGHS2 increases in late gestation (7), well before the rise in maternal plasma estradiol at the end of gestation, we and others have proposed that in late gestation fetal adrenal cortisol induces fetal placental PGHS2 expression and PG production (4,5). Indeed, we recently reported that fetal cortisol at concentrations seen in late gestation, independent of any other steroids of fetal origin, are able to stimulate fetal placental PGHS2 expression (5). Therefore, it is likely that the increase in placentome PGHS2 in late gestation is under the control of late gestation rise of fetal cortisol, whereas estradiol may control PGHS2 expression in maternal intrauterine tissues associated with the onset of labor in pregnant sheep.…”

“…Polyadenylated RNA was extracted from myometrium and endometrium by oligo dT cellulose affinity chromatography using a commercial kit (Invitrogen, San Diego, CA). Samples of total RNA (30 g) or polyadenylated RNA (2 g) were separated by electrophoresis on a 1.4% (wt/vol) agarose-0.66 m formaldehyde gel and transferred onto a nylon membrane (NEN Life Science Products, Boston, MA) and then subjected to Northern blot analysis for PGHS2 and P450 c17 ␣ hydroxylase mRNAs as described previously (5,7). ␤-Actin or 18S were used to control RNA loading.…”

“…These enzymatic steps constitute the estrogen-dependent pathway of PG synthesis. However, recent studies have led several investigators including us to propose a supportive role for an additional pathway, the stimulation of intrauterine PG production by cortisol (4,5). The involvement of this pathway is suggested by the following observations: 1) the timing of rise in fetal plasma PGE2 and endometrial and placental PG H synthase (PGHS) 2, both of which occur with a time course that precedes the rise in maternal plasma estradiol (4,6,7); and 2) the expression of P450 c17 ␣ hydroxylase, the rate-limiting enzyme of estradiol synthesis from C21 precursors in the ovine placenta, does not increase until after the onset of the early stages of labor, well after the increase in placental PGHS2 expression (8).…”