No abstract

Birth in many animal species and in humans is associated with activation of hypothalamic-pituitary-adrenal function in the fetus and the increased influence of glucocorticoids on trophoblast cells of the placenta and fetal membranes. We suggest that in ovine pregnancy glucocorticoids directly increase fetal placental prostaglandin production, and indirectly increase prostaglandin production by maternal uterine tissues through the stimulation of placental estradiol synthesis. The events of ovine parturition are compared with those of human parturition. In the latter, we suggest similar direct effects of glucocorticoids on prostaglandin synthesis and metabolism in fetal membranes and similar indirect effects mediated by glucocorticoid-stimulated increases in intrauterine corticotropin-releasing hormone expression.

Increased uterine contractility at term and preterm results from activation and then stimulation of the myometrium. Activation can be provoked by mechanical stretch of the uterus and by an endocrine pathway resulting from increased activity of the fetal hypothalamic-pituitary-adrenal (HPA) axis. In fetal sheep, increased cortisol output during pregnancy regulates prostaglandin H synthase type 2 (PGHS2) expression in the placenta in an estrogen-independent manner, resulting in increased levels of PGE2 in the fetal circulation. Later increases in maternal uterine expresssion of PGHS2 require elevations of estrogen and lead to increased concentrations of PGF2alpha in the maternal circulation. Thus, regulation of PGHS2 at term is differentially controlled in fetal (trophoblast) and maternal (uterine epithelium) tissue. This difference may reflect expression of the glucocorticoid receptor (GR), but not estrogen receptor (ER), in placental trophoblast cells. In women, cortisol also contributes to increased PG production in fetal tissues through upregulation of PGHS2 (amnion and chorion) and downregulation of 15-OH PG dehydrogenase (chorion trophoblasts). The effect of cortisol on chorion expression of PGDH reverses a tonic stimulatory effect of progesterone, potentially through a paracrine or autocrine action. We have interpreted this interaction as a reflection of "progesterone withdrawal" in the primate, in relation to birth. Other agents, such as proinflammatory cytokines, similarly upregulate PGHS2 and decrease expression of PGDH, indicating the presence of several mechanisms by which labor at term or preterm may be initiated. These different mechanisms need to be considered in the development of strategies for the detection and management of the patient in preterm labor.

NAD+-dependent 15-hydroxyprostaglandin dehydrogenase (PGDH) is the key catabolic enzyme controlling levels of biologically active PGs. PGDH is localized to syncytiotrophoblast in placenta, and to trophoblast cells in chorion. To examine the regulation of PGDH by steroids and to determine any changes with labor, we obtained placenta and chorion from term elective cesarean section or spontaneous delivery and isolated trophoblast cells using a Percoll density gradient. Cells were treated with varying concentrations of cortisol, progesterone, the synthetic progestins R5020, and medroxyprogesterone acetate with or without RU486 or the specific progesterone receptor antagonist, onapristone, and the 3beta-hydroxysteroid dehydrogenase inhibitor, trilostane. The activity of PGDH was assessed by measurement of 13,14-dihydro-15-keto-PGF2alpha. PGDH messenger ribonucleic acid was quantified by in situ hybridization and computerized image analysis. The basal output of 13,14-dihydro-15-keto-PGF2alpha was lower in placenta or chorion collected at spontaneous labor than in that obtained at elective cesarean section. Cortisol had a significant dose-dependent inhibitory effect on PGDH activity in both placental and chorion trophoblast cells and significantly decreased levels of PGDH messenger ribonucleic acid. Responses were similar between tissues from laboring and nonlaboring women. PGDH activity was increased by R5020 and medroxyprogesterone acetate and was inhibited by RU486, onapristone, and trilostane. We conclude that cortisol inhibits PGDH activity and expression and that progestagens increase PGDH activity in human chorion and placenta.

Although significant advances to patient care have been made in various branches of obstetrics and gynaecology, the incidence of preterm birth has not changed in the past 40 years. Indeed there are signs that factors such as low socioeconomic status of some inner city populations, the tendency for women to choose to start a family at an older age and the impact of fertility treatments are leading to an increase in the incidence of preterm delivery. Improved neonatal care over this period has significantly reduced the mortality rate due to prematurity, although it remains the primary cause of neonatal death. The morbidity rate in preterm infants, however, has not substantially changed due largely to the resuscitation of neonates at or close to the limits of gestational age viability. This has inevitably had a tremendous economic impact upon health care systems and upon society in general. Neonatal care in the USA alone cost over $5 billion annually in the 1980s – the vast majority of which was due to prematurity. When one adds the costs of chronic care for some of these infants with major motor and/or mental handicaps as well as the loss of potential earnings, prematurity ranks as one of the most costly of medical complications.

In summary, these studies have suggested that prostaglandin dehydrogenase may have a central role to play in the mechanisms which determine biologically active prostaglandin concentrations within human fetal membranes and placenta at the time of labor, at term or preterm. Moreover, our studies indicate that the regulation of PGDH may by multifactorial (figure 3). In certain regions of the membranes, we suggest that PGDH expression may be influenced by levels of anti-inflammatory and pro-inflammatory cytokines. In other regions of the membranes, we suggest that PGDH may be regulated at a transcriptional level by competing activities of progesterone and cortisol. The action of progesterone could be effected through systemically-derived steroid, or by locally synthesized steroid, acting in a paracrine and/or autocrine fashion. The effects of cortisol in placenta must be due to glucocorticoid derived from the maternal or fetal compartment, since the placenta lacks the hydroxylases required for endogenous cortisol production. However, metabolism of cortisol by 11 beta-HSD-2 reduces the potency of this glucocorticoid in placental tissue. In chorion however, cortisol may be formed locally, from cortisone, in addition to its being derived from the maternal circulation and/or from the amniotic fluid. Our current studies do not allow us to delineate whether the effects of progesterone and cortisol on PGDH are exerted through the glucocorticoid receptor (GR) or progesterone receptor (PR) or both. It is possible that through pregnancy, PGDH activity is maintained by progesterone acting either through low levels of PR in membranes, or, more likely, acting through GR. At term, elevated levels of cortisol compete with and displace progesterone from GR, resulting in inhibition of PGDH transcription and activity. In this way, local withdrawal of progesterone action would be effected within human intrauterine tissues, without requiring changes in systemic, circulating progesterone concentrations. Since glucocorticoids appear also to increase expression of prostaglandin synthesizing enzymes within the amnion and chorion, directly by upregulating PGHS-2, or indirectly through the intermediary action of a paracrine effector such as CRH, their role in coordinating processes of parturition remains central. Further understanding of the regulation of PGDH may be of therapeutic importance. For example, it is possible that PGDH activity in lower segment chorion may be reduced in those patients with premature cervical softening, or may be particularly high in those patients with an unfavorable cervix, presenting with a low Bishop score and poor progression at the time of labor. If the enzyme in this region crucially determines the passage and availability of biologically active prostaglandins from amnion and chorion to underlying cervix, then pharmacologic manipulation of PGDH activity may effectively regulate PG transfer in these clinical conditions. Glucocorticoids appear to have a central role in promoting production of agents that are u...

Prostaglandin dehydrogenase (PGDH) metabolizes prostaglandins (PGs) to render them inactive. We reported previously that cortisol (F) decreases and progesterone (P(4)) maintains PGDH activity/expression in human chorion and placenta. Furthermore, we have shown that F and P(4) compete for regulation of PGDH. We hypothesized that P(4) maintains PGDH activity through interaction with the glucocorticoid receptor (GR) and that elevations in F compete with P(4) at the GR, resulting in a decrease in PGDH at term. By immunohistochemistry and Western blotting analysis, we localized immunoreactive GR and progesterone receptor (PR) to chorion and placental trophoblast cells. We treated chorion and placental trophoblast cells in culture with F, dexamethasone (DEX), beta-methasone, P(4), trilostane (a 3 beta-hydroxysteroid dehydrogenase inhibitor), medroxyprogesterone acetate (MPA), and/or 21-hydroxy-6,19-oxidopregn-4-ene-3,20-dione (21OH-6OP; a GR antagonist). By RIA and Northern blotting analysis, all glucocorticoids (GCs) decreased PGDH activity/expression. Coincubation with 21OH-6OP reversed GC inhibition of PGDH; MPA, but not P(4), treatment stimulated PGDH activity. Trilostane inhibited PGDH activity, and coincubation with P(4) or MPA reversed trilostane inhibition of PGDH. Treatment with trilostane, P(4), 21OH-6OP, or MPA plus 21OH-6OP reversed P(4) and MPA up-regulation of PGDH activity. Our findings suggest that F inhibition and P(4) stimulation of PGDH may be mediated by PR, but also via the GR, in chorion and placenta.

NAD+-dependent 15-hydroxy-PG dehydrogenase (PGDH) is the major enzyme involved in the initial inactivation of PGs, and its activity is reduced by glucocorticoids, cortisol (F), and dexamethasone (DEX). In turn, glucocorticoid regulation of PGDH activity in placenta and chorion could be regulated indirectly by 11beta-hydroxysteroid dehydrogenase (11beta-HSD) activity. In the placenta, 11beta-HSD2 is the dominant isoform, acting as a dehydrogenase [F to cortisone (E)]; and in chorion, 11beta-HSD1 predominates as a reductase (E to F). The present study was designed to determine whether glucocorticoid regulation of PGDH activity in placenta and chorion could be regulated indirectly by 11beta-HSD activity. We obtained Percoll-purified human placental and chorion trophoblast cells from uncomplicated term pregnancies, cultured them for 72 h, then treated the cells with cortisol (100 nmol/L), cortisone (1 micromol/L), or DEX (100 nmol/L), in the presence or absence of carbenoxolone (CBX, 800 nmol/L), an 11beta-HSD inhibitor, for 24 h. Activity of PGDH was assessed by incubation (4 h) with PGF2alpha (282 nmol/L) and measurement of conversion to 13,14-dihydro-15-keto PGF2alpha. CBX alone had no effect on PGDH activity in either placenta or chorion trophoblast cells. In chorion, E significantly inhibited PGDH activity, and this effect was reversed by addition of CBX. F and DEX significantly inhibited PGDH, and this effect was unaltered by coadministration of CBX. In contrast, in placenta, there was no effect of E, or of E with CBX, on PGDH activity. However, F and DEX inhibited PGDH, and the effect of F (but not DEX) was greater in the presence of CBX. In conclusion, we suggest that effects of E and F on PGDH are modified by the tissue-specific expression of 11beta-HSD isoforms.