Glucocorticoids do not share with progesterone the potent inhibitory action on prostaglandin synthesis in human proliferative phase endometrium

Delay of preterm birth in sheep by THG113.31, a prostaglandin F2alpha receptor antagonist

OBJECTIVE

A novel prostaglandin F2alpha receptor antagonist, THG113.31, was tested for the suppression of uterine contractility and delay of preterm labor in sheep.

STUDY DESIGN

We determined the tocolytic effectiveness of THG113.31 on contractions that were stimulated in vitro by prostaglandin F2alpha and E2 in longitudinal and circular myometrial strips. We also tested the ability of THG113.31 in vivo to lower uterine electromyographic activity that was induced by the progesterone receptor blocker, RU486, and to delay preterm birth.

RESULTS

THG113.31 suppressed the amplitude of prostaglandin F2alpha, but not prostaglandin E2-induced contractions of both circular and longitudinal myometrium (P<.01). The times to delivery after RU486 were 34.8+/-1.1 hours (saline solution) and 41.9+/-0.5 hours (THG113.31; P<.001) or an average delay of 7.1 hours. There were no changes in fetal blood gases (PaO2 , PaCO2 , pH, or SaO2) because of THG113.31. Fetal cortisol levels rose in each group, and fetal and maternal prostaglandin E2 and F2alpha metabolite concentrations rose similarly in both groups.

CONCLUSION

THG113.31 specifically suppresses prostaglandin F2alpha-induced myometrial contractility and delays delivery.

Chemokines and human reproduction

OBJECTIVE

To review the available information regarding chemotactic cytokines and their possible implications in human reproduction.

DESIGN

A thorough literature and MEDLINE search was conducted to identify studies relating to the role of chemokines in ovulation, menstruation, implantation, cervical ripening and preterm labor, and endometriosis.

RESULT(S)

Chemokines mediate leukocyte traffic through their specific receptors in various tissues. Although four families have been described to date, two remain the major subfamilies: alpha-chemokines (with interleukin-8 as representative for this group), and beta-chemokines (with monocyte chemotactic protein-1 as representative). Interleukin-8, monocyte chemotactic protein-1, and growth-regulated oncogene-alpha are involved in follicular development and atresia, ovulation, steroidogenesis, and corpus luteum function. Interleukin-8 showed cycle-dependent expression in human endometrium, and at the same time, stimulated endometrial stromal cell growth, acting as an autocrine growth factor. Interleukin-8 has been identified in human amnion, chorion, decidua, and villous placenta, and its level increases during labor. Levels of interleukin-8 correlate with the release of collagenases, a crucial step that regulates the process of cervical extracellular matrix remodeling. The levels of monocyte chemotactic protein-1; regulated on activation, normal T-expressed and secreted (RANTES); interleukin-8; and growth-regulated oncogene-alpha are elevated in the peritoneal fluid of women with endometriosis, and they correlate with the stage of the disease.

CONCLUSION(S)

Chemokines play a relevant role in many physiologic and pathologic situations, such as ovulation, menstruation, implantation, cervical ripening and preterm labor, and endometriosis. Their regulation soon may provide new therapeutic strategies.

Potential implications of chemokines in reproductive function: an attractive idea

Chemokines are a new family of cytokines specialised in attracting leukocytes, acting in physiological conditions and in pathological processes. A wide variety of cell types in response to exogenous irritants or endogenous mediators of the inflammatory reaction produce them. Pivotal parts of reproductive function are based on inflammatory like processes wherein different leukocytes subsets are recruited and activated to produce paracrine autocrine effects in which cytokines and growth factors are implicated. Since chemokines control leukocyte trafficking and belong to the cytokine superfamily, in this review we analyze the implications of these molecules and related cells in ovulation, embryonic implantation, menstruation, parturition and their role in pathological process such as preterm delivery, endometriosis, ovarian hyperstimulation syndrome and HIV infection.

The control of prostaglandin production by the endometrium in relation to luteolysis and menstruation

Oestradiol acting on a progesterone-primed uterus stimulates prostaglandin (PG) F2 alpha synthesis by the endometrium. In some species (notably the sheep, cow and goat) oxytocin released from the ovary also forms part of the physiological stimulus for increased endometrial PGF2 alpha production. The corpus luteum contains high concentrations (> 1 microgram/g tissue) of this peptide in these species. The intracellular mechanisms by which these three hormones control endometrial PGF2 alpha synthesis and release are far from clear. Oxytocin stimulates the synthesis of inositol phosphates and diacylglycerol in the endometrium of some species, but whether this pathway is involved in endometrial PGF2 alpha synthesis is still open to question. There is evidence that increased endometrial PGF2 alpha synthesis is dependent upon increased endometrial protein synthesis but, apart from the recorded effects of steroid hormones on the concentrations of phospholipase A2, prostaglandin H synthase and oxytocin receptors, it is not known what other endometrial proteins are involved. Some disorders of menstruation are associated with abnormal PG production by the endometrium, but the reasons for this abnormality are not clear. During early pregnancy an increase in PGF2 alpha synthesis by the endometrium is prevented, except in the pig where the PGF2 alpha produced is directed from the venous drainage to the uterine lumen. In those species in which endometrial PGF2 alpha synthesis is dependent upon oxytocin secreted by the ovary, the conceptus secretes an interferon-tau (previously named trophoblast protein-1) which prevents oestradiol and oxytocin acting on a progesterone-primed uterus from stimulating endometrial PGF2 alpha synthesis. The identities of the factors produced by the conceptus which prevent endometrial PGF2 alpha synthesis during early pregnancy in other species are not known, although it is clear that they are not interferons.

Decrease in human plasma gravidin levels after medical abortion

The aim of this study was to determine if loss of pregnancy is associated with a decrease in plasma levels of gravidin, a phospholipase inhibitor thought to maintain pregnancy. Blood was taken from 28 women in the first trimester of pregnancy who had requested an abortion. The progesterone receptor antagonist, RU-486 was given on Day 0 for termination of pregnancy. Plasma gravidin levels were measured on day 0 and on day 2 just before the patients were given misoprostol, a prostaglandin E1 analogue (600 micrograms). In a small group of patients, plasma measurements were continued up to 42 days. By day 2, plasma gravidin levels had fallen significantly (100% to 94%, p = 0.010 in a paired t-test). Following treatment with prostaglandins and pregnancy loss, plasma gravidin levels continued to fall until day 14 when the non pregnant level was reached at 80% of the pregnant level. We conclude that a decrease in plasma gravidin levels is associated with loss of pregnancy. This may occur because progesterone action is blocked.

Myometrial connexin 43 trafficking and gap junction assembly at term and in preterm labor

Modulation of connexin 43 (cx43) in the myometrium of timed pregnant rats was studied using enzyme-linked immunosorbent assay (ELISA), immunocytochemical localization, and immunoblot. These techniques utilized site-specific antibodies directed against a portion of the carboxyl tail of cx43. We found that cx43 is synthesized several days prior to labor but accumulates within the cytoplasm until parturition, when it is rapidly transported to the plasma membrane and assembled into gap junction plaques at the cell surface. These cx43-positive gap junctions begin to disappear from the plasma membrane within hours of delivery of the last pup and are completely absent within 24 hr following delivery. These structures are apparently internalized and degraded within the cytoplasm. ELISA documents a reduction of total cellular cx43 to baseline levels within 5 days following parturition. While the timing of synthesis, cytoplasmic storage, concentration in apparent Golgi vesicles, and transport to and assembly in the plasma membrane are accelerated in three models of preterm labor, the sequence of these events and the correlation of parturition with the formation of gap junctions are identical to those documented in normal labor. These results support the hypothesis that effective labor requires the synthesis and assembly of cx43 into functional gap junctions at the myometrial cell surface.

Prostaglandin E and E2 alpha secretion by glandular and stromal cells of the pig endometrium in vitro: effects of estradiol-17 beta, progesterone, and day of pregnancy

Prostaglandins (PGs) are believed to play important roles in the establishment of pregnancy. Glandular and stromal cells were isolated from pig endometrium on days 11 through 19 of pregnancy and cultured in the presence of estradiol-17 beta (E2) and progesterone (P4) to determine the effect of day of pregnancy and steroids on the secretion of PGE and PGF2 alpha. Estradiol at concentrations between .01 and 1 microM did not affect PGE and PGF2 alpha secretion into the medium by glandular and stromal cells. Progesterone (.1 microM) suppressed (P less than .001) PGE and PGF2 alpha production from both cell types. Glandular cells secreted more (P less than .01) PGF2 alpha than PGE, whereas stromal cells collected on days 11, 12, 13, and 19 secreted more (P less than .05) PGE than PGF2 alpha. Stromal cells isolated from tissues collected on day 13 of pregnancy produced PGs with higher (P less than .01) PGE:PGF2 alpha ratio than those from tissues harvested on other days of pregnancy. Glandular cells isolated from tissues collected on days 13 and 19 and stromal cells isolated from tissue collected on day 13 of pregnancy secreted more (P less than .05) PGE and PGF2 alpha than cells isolated on other days of pregnancy. We conclude that: 1) P4 has a suppressing effect on PG secretion; 2) endometrial glandular and stromal cells each produce a unique profile of PGs; and 3) endometrial cells harvested on different days of pregnancy secrete different amounts of PGE and PGF2 alpha.

Effects of mifepristone in vivo on decidual prostaglandin synthesis and metabolism

Mifepristone is an effective abortifacient in combination with an exogenous prostaglandin but its mechanism of action is unknown. Mifepristone stimulates prostaglandin production from decidua in tissue culture. To determine whether this effect also operates in vivo, we treated women with mifepristone 24, 36 and 48 hours prior to surgical termination. Decidua was removed at operation and the ability of the tissue to generate prostaglandin in culture subsequently assessed. Pretreatment with mifepristone 36 hours prior to termination of pregnancy resulted in an increased production of PGF2 alpha in tissue culture (p less than 0.01). A significant decrease in PGFM production was seen 24 hours after pretreatment with mifepristone in vivo (p less than 0.01). These results suggest that the increased uterine activity observed after administration of mifepristone may be due to stimulation of endogenous prostaglandin production and inhibition of prostaglandin metabolism.

Comparison of antiprogestin stimulation of uterine prostaglandin synthesis in vitro

Progesterone has an inhibitory effect on prostaglandin synthesis in urine tissue and this effect is reversible with progesterone receptor antagonists. Although antiprogesterone steroids such as RU486 (Mifepristone) are effective at inducing abortion in women they have an improved efficacy when used with exogenous synthetic prostaglandin. In the guinea-pig such antagonists sensitize the uterus but do not result in increased myometrial activity and therefore may not induce endogenous PG synthesis. In this study the effects of antiprogestins on a preparation of rat uterus perifused with progesterone were studied. ZK98 734 caused a rapid and sustained increase in 6-oxoPGF synthesis which rose within the first 90 minutes. This rapid response suggested that some mechanism other than the induction of fresh protein synthesis was involved. A similar increase was not seen with pregnant guinea-pig myometrium/decidua perifused in a similar manner, suggesting that some other mechanism was responsible for the relatively low PG production in pregnancy. However increases in 6-oxoPGF in response to antiprogestins were recorded when pregnant guinea-pig decidua/myometrium was incubated for 4 hours. In these experiments 1 microM ZK98 734 and 1 microM ZK98 299 (Onapristone) gave a 2.7 fold increase in PG production whereas RU486 gave a 1.6 fold increase. Both 1 microM ZK98 734 and 1 microM ZK98 299 also gave a significant increase in PGE production but no increase in PGF was observed. These findings suggest that some antiprogestins might have a better effect on the stimulation of endogenous PG synthesis or on the rate of catabolism of prostanoids.

Is the inhibitory effect of progesterone on endometrial prostaglandin F2 alpha production due to an inhibition of protein synthesis?

Progesterone and a high concentration of oestradiol (i) reduced the outputs of prostaglandin (PG) F2 alpha and, to a lesser extent, PGE2 from Day-7 and Day-15 guinea-pig endometrium in culture, but had little or no effect on the output of 6-keto-PGF1 alpha, (ii) prevented the increase in PGH synthase concentrations which normally occur in Day-7 and Day-15 guinea-pig endometrium during culture, and (iii) reduced the synthesis of secreted proteins by Day-15 guinea-pig endometrium in culture. These findings suggest that the inhibitory effect of progesterone and of high concentrations of oestradiol on endometrium PGF2 alpha synthesis is due to an inhibition of the syntheses of proteins involved in PGF2 alpha production.

The effect of cortisol on the synthesis of prostaglandins (PGF2 alpha, PGE2) by human endometrial fibroblasts in vitro with and without addition of estradiol-17 beta or progesterone

Cortisol is known as a potent inhibitor of phospholipase A2 activity in several tissues. In fibroblast monolayer cell cultures from proliferative human endometrium cortisol alone does not affect the basal PGF2 alpha or PGE2 synthesis. After stimulation of PGF2 alpha production by 10(-7) mol/l estradiol-17 beta increasing concentrations of cortisol up to 10(-5) mol/l dosedependently reduce the PGF2 alpha production. Also the progesterone (10(-4) mol/l) stimulated increase of PGF2 alpha and PGE2 synthesis is inhibited by cortisol (10(-7) mol/l).

The release of PGF2 alpha and PGE2 from separated cells of human endometrium and decidua

The capacity of separated glandular and stromal cells from endometrium and first trimester decidua to release prostaglandins (PGs) was studied over 48 hours in culture. Glandular preparations released more PGs than stromal preparations in all tissues. Stromal release of PGs did not alter throughout the cycle or in early pregnancy but the capacity of glandular preparations to release PGs varied considerably. Proliferative glands released most PGF2 alpha and PGE2 followed by secretory glands and decidua. Histamine (10(-5)) stimulated PG release from endometrial and decidual glands but the response of proliferative glands was greatest. Actinomycin D stimulated release of PGF2 alpha and PGE2 from glandular cells of secretory endometrium and decidua. These results suggest that in vitro release of PGs is suppressed after ovulation and is in part due to inhibition of PG release by a protein or proteins synthesized in the glandular fraction of secretory endometrium or decidua.

The effect of estradiol-17 beta and actinomycin D on the release of PGF and PGE from separated cells of human endometrium

Estradiol-17 beta selectively stimulated the release of PGF from separated glandular but not stromal cells of human secretory endometrium (p less than 0.025) but had no effect on PGF release from either type of cells obtained from proliferative endometrium. PGE release was not affected by estradiol-17 beta. Actinomycin D did not antagonise the effect of estradiol-17 beta on PGF release from secretory, glandular cells. Basal release of PGF from these cells was stimulated by actinomycin D alone (100 ng/ml) (p less than 0.025) and PGE release stimulated in the presence of estradiol-17 beta. Actinomycin D had no effect on PGF or PGE release from proliferative endometrium. These findings suggest that estradiol-17 beta stimulates PGF release by a mechanism that does not affect PGE release and which is not dependent on the synthesis of new protein. The basal release of PGF and PGE by glandular cells of secretory endometrium in vitro is regulated by protein/proteins which reduce PG release.