Prostaglandin E2 production by uterine stromal cell line UIII: regulation by estradiol and evidence of an ethanol action

Hydrolysis of nuclear phospholipids in relation with proliferative state in uterine stromal cells

The current study examined the metabolism of phospholipid (PL) in the whole cell homogenate and in the nuclear fraction in proliferative and non-proliferative uterine stromal cells (U(III) cells). Growth arrested cells were obtained either from contact-inhibited confluent cells or from proliferative cells treated with aristolochic acid (AR) for 2 days. Fatty acid composition and fatty acid amount of both total and nuclear PL were not significantly different between proliferative, confluent and AR-treated cells. In contrast, marked differences were observed in the incorporation of [(3)H]AA, with greater incorporation in proliferative cells than in confluent or AR-treated cells, particularly in nuclear PL. Considering endogenous level of arachidonic acid (AA) in total and nuclear PL, we found that AA turnover in nuclear PL was especially high compared to that in total PL and that this difference was accentuated in proliferative cells compared to non-proliferative cells. Interestingly, [(3)H]AA incorporation and AA turnover in proliferative, confluent and AR-treated cells vary accordingly to the expression, activity and/or content of pancreatic phospholipase A(2) (PLA(2)-I) in the nuclear compartment of these cells that we reported in previous studies. The changes in metabolism of nuclear PL during cell proliferation are consistent with an enhanced PL hydrolysis that could involve PLA(2)-I.

Evidence that ibuprofen antagonizes selective actions of estrogen and tamoxifen on rat bone

Studies were performed to determine if the nonsteroidal anti-inflammatory drug ibuprofen alters bone and mineral metabolism in female rats. In experiment 1, four groups of growing rats underwent either sham operation or ovariectomy (OVX). One week later, controlled-release pellets with ibuprofen or placebo were implanted subcutaneously at the back of the neck. Following 3 weeks of treatment, rats were sacrificed and blood and bone samples were removed for serum assays and histomorphometric analysis. Body growth rate and the static cortical bone measurements made at the tibial diaphysis did not change in response to OVX. OVX, however, did increase radial bone growth, lowered serum 17beta-estradiol, reduced uterine weight, and decreased the cancellous bone area of the tibial metaphysis in the rats. Ibuprofen did not alter serum 17beta-estradiol or uterine weight but reduced radial bone growth as well as cancellous bone area of the tibial metaphysis in both sham-operated and OVX animals. In experiments 2 and 3, we tested the influence of ibuprofen on the effects of the tissue-selective estrogen agonist tamoxifen and of exogenous 17beta-estradiol in the OVX rat. Ibuprofen completely blocked the effects of tamoxifen and partially blocked the effects of 17beta-estradiol to prevent cancellous osteopenia. In contrast, ibuprofen did not influence the effects of tamoxifen and 17beta-estradiol to reduce radial bone growth. Besides the skeletal effects, ibuprofen suppressed estrogen-induced uterine growth. Our data suggest that ibuprofen blocks selective estrogen receptor-mediated activities in the rat.

Nuclear location of PLA2-I in proliferative cells

We have previously demonstrated that pancreatic PLA2 (PLA2-I) stimulates the proliferation of UIII cells, a stromal cell line derived from normal rat uterus. In order to gain further insight into the mechanism of action of PLA2-I, we have investigated the intracellular processing of PLA2-I. Either highly proliferative or growth arrested UIII cells were analyzed. Growth arrested cells were obtained from a contact inhibited monolayer or from aristolochic acid-treated cultures. Using cellular fractionation, western blotting, immunocytochemistry and confocal microscopy, we demonstrate that endogenous PLA2-I was mainly located in the nucleus in highly proliferative cells whereas its location was cytoplasmic in non proliferative cells. When non confluent UIII cells were incubated with nanomolar amounts of exogenous PLA2-I, the enzyme was internalized and, in the majority of cells, appeared within the nucleus. Both internalization and nuclear location of exogenous PLA2-I were suppressed by the addition of aristolochic acid to the culture medium. Binding experiments performed on purified nuclear preparations showed the presence of specific cooperative binding sites for PLA2-I. Collectively our data suggest that the proliferative effect exerted by pancreatic PLA2 in UIII cells is mediated by a direct interaction of the enzyme at the nuclear level. Putative mechanisms and targets are discussed.

Arachidonic acid up-regulates and prostaglandin E2 down-regulates the expression of pancreatic-type phospholipase A2 and prostaglandin-endoperoxide synthase 2 in uterine stromal cells

It is well known that arachidonic acid, as a substrate of prostaglandin G/H synthase (PGHS), is converted into prostaglandins of the two-series. In this work, we attempted to determine whether arachidonic acid and prostaglandin E2 might regulate the expression of PGHS and the pancreatic-type phospholipase A2 (PLA2I), which may be involved in the liberation of arachidonic acid from membrane phospholipids. For this purpose, we used the uterine stromal cell line UIII, which produces prostaglandin E2 and expresses both the constitutive and inducible PGHS enzymes (PGHS1 and PGHS2) and PLA2 I. The results show that PGHS1, which is expressed at a high level in UIII cells, was not modified by arachidonic acid. The expression of PGHS2 and PLA2 I was up-regulated by increasing arachidonate concentrations (1-10 microM). The maximal response was obtained at 24 h, reaching a 2.3-fold and 2.6-fold increase for PGHS2 and PLA2 I expression, respectively, compared to the control level. To discriminate between the effect of arachidonic acid and that of prostaglandins, which are highly increased in the presence of exogenous arachidonic acid, we treated the cells with two inhibitors of PGHS activity, aspirin and meclofenamic acid. Both inhibitors failed to suppress the arachidonate-induced increase of PLA2 I and PGHS2 expression and even enhanced it either in the presence or absence of arachidonic acid. In contrast, the addition of prostaglandin E2 to the culture medium decreased the expression of both enzymes in a dose-dependent manner, the maximal response being reached at 1 microM. We conclude that arachidonic acid up-regulates the expression of PLA2 I and PGHS2 in the uterine stromal cells, independently of prostanoids, and that prostaglandin E2 is capable of down-regulating enzyme expression.

Increase in vasoactive prostaglandin E production after perfusion in human placental cotyledons

Studies from our laboratory indicate that prostaglandins may be mediators of at least some of the teratogenic actions of ethanol in both mouse and human tissue model systems. The present studies were designed to evaluate the relationship between ethanol and prostaglandin E (PGE) production in isolated human placental cotyledons. Placentas were obtained immediately after cesarean section delivery. A fetal artery supplying a single cotyledon was identified and cannulated, and the isolated cotyledon was placed in a perfusion chamber where maternal circulation was established and dual circulation continued throughout the perfusion procedure. Antipyrine clearance, oxygen consumption, and placental production of human chorionic gonadotropin were measured to verify tissue viability. PGE levels of the perfusate were measured by radioimmunoassay. Study 1 evaluates the effect of perfusion with 25 and 100 mM ethanol on placental PGE production. It was found that PGE production increased after perfusion with 25 mM ethanol, but not during the perfusion period per se. The paradigm for study 2 was identical to that of study 1, with the addition of a buffer washout period after 100-mM ethanol perfusion. Again, results indicate that perfusate PGE levels were increased in the buffer washout periods after the 25-mM and the 100-mM ethanol perfusions. The effect was not concentration dependent. An increase in circulating PGE associated with ethanol administration may be teratogenic actions and represent a potential mechanism underlying at least some aspects of fetal alcohol syndrome.

Prolactin up-regulates prostaglandin E2 production through increased expression of pancreatic-type phospholipase A2 (type I) and prostaglandin G/H synthase 2 in uterine cells

Uterine stromal cells produce and release PGE2, both processes being regulated by hormonal factors. In this study, we examined the effect of PRL on the PGE2 production and release measured by radioimmunoassay. For this purpose, we used a rat uterine stromal cell line, UIII cells, which produce PGE2 and contain PRL receptors. The expression of sPLA2I and PGHS (PGHS1 and PGHS2), enzymes required for PGE2 production, was also estimated by immunocytochemistry and 'Western blotting' in response to PRL. PRL (10 to 60 ng/ml) significantly increased the PGE2 release (up to 6-fold) and production, in a dose-dependent manner. Results show that PGHS1 and PGHS2 are both expressed constitutively in the uterine UIII cells, although PGHS2 is expressed at a low level. PRL did not increase PGHS1 expression, but stimulated the expression of sPLA2I and PGHS2 by 3.5- and 2.5-fold, respectively. These data show for the first time a regulation of sPLA2I and PGHS2 expression by PRL and may indicate that, in uterine cells, PRL enhances the PGE2 release and production by increasing the expression of both sPLA2I and PGHS2.

The level of pancreatic PLA2 receptor is closely associated with the proliferative state of rat uterine stromal cells

Rat uterine stromal cells (U(III)) express pancreatic type PLA2 (PLA2-I) receptor and internalize the enzyme bound to receptors. Here, we investigate the proliferating effect and alterations in binding of PLA2-I. There is a dramatic decline in PLA2-I binding in U(III) cells as they progress from a non-confluent proliferating state (40,000 sites/cell) to a confluent state (1300 sites/cell). Intracellular concentration of PLA2-I changed with the alteration in binding, suggesting that regulation in the PLA2 binding capacity may have important implications in growth control mechanisms.

Effects of prostaglandin F2 alpha (PGF2 alpha) on secretion of estradiol-17 beta and cortisol in 90 to 100 day hysterectomized, intact and ovariectomized pregnant ewes

Vehicle or 8 or 16 mg PGF2 alpha/58 kg/body weight (BW) was given intramuscularly to intact, hysterectomized and ovariectomized 90 to 100 day pregnant ewes in three separate experiments. Hysterectomy alone decreased (P < or = 0.05) estradiol-17 beta in jugular venous blood by 80 percent within 16 hours and profiles of estradiol-17 beta did not differ (P > or = 0.05) among vehicle or 8 or 16 mg PGF2 alpha/58 kg/BW-treated ewes. Profiles of estradiol-17 beta differed (P < or = 0.05) in intact pregnant ewes treated with 8 or 16 mg PGF2 alpha/58 kg/BW when compared to controls and in ovariectomized (P < or = 0.10) 90 to 100 day pregnant ewes treated with 16 mg PGF2/58 kg/BW. Estradiol-17 beta decreased (P < or = 0.05) over time in vehicle and 8 mg PGF2 alpha/58 kg/BW-treated intact and in vehicle-treated ovariectomized 90 to 100 day pregnant ewes. Cortisol decreased (P < or = 0.05) over time in hysterectomized, intact, and ovariectomized 90 to 100 days pregnant ewes, but did not differ (P < or = 0.05) among vehicle or 8 or 16 mg PGF2 alpha/58 kg/BW-treated ewes. It is suggested that estradiol-17 beta has a role in regulating ovine placental steroidogenesis.