Purification of prostaglandin E2-9-oxoreductase from human decidua vera

Opposite effects of methanandamide on lipopolysaccharide-induced prostaglandin E2 and F2α synthesis in uterine explants from pregnant mice

Prostaglandins (PG) are effective abortifacients and are important mediators of lipopolisaccharide (LPS)-induced embryonic resorption (ER). Besides, anandamide (AEA) has been described as one of the major endocannabinoids present in the uterus suggesting that it might play a role in reproduction. It has been reported that high levels of AEA are associated with pregnancy failure and that LPS increases AEA production. Also, it has been observed that AEA modulates PG production in different tissues. In this sense, we studied whether LPS-induced PG production is modulated by AEA and we also assessed the effect of this endocannabinoid on PG metabolism in an in vitro model. Uterine explants from BALB/c implantation sites were cultured in the presence of LPS plus cannabinoid receptor (CB) specific antagonists and PG production was assessed. Then, we studied the effect of exogenous AEA on different steps of PG metabolic pathway. We showed that AEA is involved in LPS-induced PG biosynthesis. Also, we observed that AEA exerts opposite effects on PGE(2) and PGF(2α) biosynthesis, by inhibiting PGE(2) production and increasing PGF(2α) levels. We suggest that AEA could be involved in the mechanisms implicated in LPS-induced ER. A better understanding of how AEA could be affecting ER could help developing specific interventions to prevent this pathology.

Estradiol-17beta, prostaglandin E2 (PGE2), and the PGE2 receptor are involved in PGE2 positive feedback loop in the porcine endometrium

Before implantation, the porcine endometrium and trophoblast synthesize elevated amounts of luteoprotective prostaglandin estradiol-17beta (E(2)) (PGE(2)). We hypothesized that embryo signal, E(2), and PGE(2) modulate expression of key enzymes in PG synthesis: PG-endoperoxide synthase-2 (PTGS2), microsomal PGE synthase (mPGES-1), PGF synthase (PGFS), and PG 9-ketoreductase (CBR1) as well as PGE(2) receptor (PTGER2 and -4) expression and signaling within the endometrium. We determined the site of action of PGE(2) in endometrium during the estrous cycle and pregnancy. Endometrial tissue explants obtained from gilts (n = 6) on d 11-12 of the estrous cycle were treated with vehicle (control), PGE(2) (100 nM), E(2) (1-100 nm), or phorbol 12-myristate 13-acetate (100 nm, positive control). E(2) increased PGE(2) secretion through elevating expression of mPGES-1 mRNA and PTGS2 and mPGES-1 protein in endometrial explants. By contrast, E(2) decreased PGFS and CBR1 protein expression. E(2) also stimulated PTGER2 but not PTGER4 protein content. PGE(2) enhanced mPGES-1 and PTGER2 mRNA as well as PTGS2, mPGES-1, and PTGER2 protein expression. PGE(2) had no effect on PGFS, CBR1, and PTGER4 expression and PGF(2alpha) release. Treatment of endometrial tissue with PGE(2) increased cAMP production. Cotreatment with PTGER2 antagonist (AH6809) but not PTGER4 antagonist (GW 627368X) inhibited significantly PGE(2)-mediated cAMP production. PTGER2 protein was localized in luminal and glandular epithelium and blood vessels of endometrium and was significantly up-regulated on d 11-12 of pregnancy. Our results suggest that E(2) prevents luteolysis through enzymatic modification of PG synthesis and that E(2), PGE(2), and endometrial PTGER2 are involved in a PGE(2) positive feedback loop in porcine endometrium.

Eicosanoids and preterm labour

Products of arachidonic acid metabolism (eicosanoids, e.g. some prostaglandins and leukotrienes) have important roles in the maintenance of pregnancy, and certain diseases of pregnancy such as pregnancy-induced hypertension and the machanism(s) of parturition both at term and before term. The volume of literature describing these last relationships dictates that the present review has to be focused rather than global in nature. Only studies of preterm labour in women and the use of human tissues will be discussed in detail despite the limitations in experimental designs that are imposed on such studies. Emphasis will be placed on studies of cyclo-oxygenase and to a lesser extant lipoxygenase pathways of arachidonic acid metabolism mentioning only briefly the pathways for catabolism of these eicosanoids. It should be noted also that eicosanoids from the epoxygenase pathways and those not derived from arachidonic acid will not be discussed here. The review of literature will not be comprehensive but rather selective in order to focus on specific issues of importance or controversy. In developing concepts of regulation I have emphasized studies with amnion since this tissue has received most attention experimentally. The significance of the eicosanoids in the mechanisms of labour at term and before will be described primarily in a section in which I have attempted to deleneate those regulatory mechanisms that are considered most significant in, or specific to, pregnancy and parturition. Studies of labour at term will be freely interspersed with studies specific to preterm labour since the latter are limited, and we need a ‘strandard’ for comparison; moreover, results from one series of studies helps the development of concepts for the other. Finally, the reader is directed to several excellent reviews that concentrate on areas not emphasized in this review.1–7

Nitric oxide (NO) inhibits prostaglandin E2 9-ketoreductase (9-KPR) activity in human fetal membranes

Nitric oxide (NO) synthesized by fetal membranes may act either directly inhibiting myometrium contractility or indirectly interacting with tocolytic agents as prostaglandins (PGs). Here we examined if NO could modulate prostaglandin E(2) 9-ketoreductase (9-KPR) activity in human fetal membranes (HFM). 9-KPR is the enzyme that converts PGE(2) into PGF(2alpha), the main PGs known to induce uterine contractility at term. Chorioamnion explants obtained from elective caesareans were incubated with aminoguanidine (AG), an iNOS inhibitor, or NOC-18, a NO donor. NOC-18 (2mM) increased PGE(2) production and diminished PGF(2alpha) synthesis in HFM. AG presented the opposite effect. When we evaluated the activity of 9-KPR by the conversion of [(3)H]-PGE(2) into [(3)H]-PGF(2alpha) and 13,14-dihidro-15-keto prostaglandin F(2alpha) (the PGF(2alpha) metabolite), we found that NOC-18 inhibited 9-KPR activity. Interestingly, AG did not elicit any effect on 9-KPR but l-NAME, a non-selective NOS inhibitor, significantly increased its activity. Our data suggests that exogenous NO inhibits 9-KPR activity in HFM, thus modulating the synthesis of important labor mediators as PGF(2alpha).

Effect of LH on prostaglandin F2α and prostaglandin E2 secretion by cultured porcine endometrial cells

LH appears to be a potent stimulator of the release of endometrial prostaglandins (PGs) in the pig. The aim of the present studies was to examine the effect of LH on PGF2αand PGE2secretion by cultured porcine endometrial cells on days 10–12 and 14–16 of the oestrous cycle and to compare its action with oxytocin. A time-dependent effect of LH (10 ng/ml) on PGF2αrelease from luminal epithelial and stromal cells on days 10–12 was observed (experiment 1). The highest increase in PGF2αsecretion in response to LH was detected in stromal cells after 6 h of incubation (P< 0.001). Epithelial cells responded to LH after a longer exposure time (P< 0.01). A concentration-dependent effect of LH (0.1–100 ng/ml) on PGF2αrelease from stromal cells was examined after 6 h and from epithelial cells after 12 h (experiment 2). Effective concentrations of LH were 10 and 100 ng/ml. LH (10 ng/ml) and oxytocin (100 nmol/l) affected PGF2αand PGE2secretion from endometrial cells on days 10–12 and 14–16 of the oestrous cycle (experiment 3). LH stimulated PGF2αsecretion from both cell types and its action was more potent on days 10–12. LH induced PGE2release, especially in epithelial cells on days 14–16. A stimulatory effect of oxytocin on PGF2αwas confirmed in stromal cells, but this hormone was also shown to enhance PGE2output. These results indicated that LH, like oxytocin, a very effective stimulator of PGF2αrelease, could play an important role in the induction of luteolysis.

Prostaglandin E(2) 9-keto reductase activity in bovine retained and not retained placenta

Prostaglandin E(2) 9-keto reductase (9-KPR) activity shifts reversibly PGE(2) into PGF(2 alpha) and may be responsible for the control of prostaglandins (PGs) levels in, among others, placental tissues. The retention of fetal membranes in cows is the postpartum disorder where the disturbances in PGs metabolism have been reported. It has been argued whether these disturbances are due to alterations in 9-KPR activity. In this study, the activity of the enzyme was determined in maternal and fetal bovine placental tissues which were divided into 6 groups as follows: (A) caesarian section before term without retained fetal membranes (n=10), (B) caesarian section before term with retained fetal membranes (n=10), (C) caesarian section at term without retained fetal membranes (n=12), (D) caesarian section at term with retained fetal membranes (n=12), (E) spontaneous delivery at term without retained fetal membranes (n=12), (F) spontaneous delivery at term with retained fetal membranes (n=12). The enzyme activity was measured spectrophotometrically and expressed in nanokatals (nkat) per protein content. The activity increased towards parturition and was significantly higher in maternal than in fetal part of placenta in all groups examined. The significantly higher values in retained than in not retained placental tissues were observed in the samples examined. The present results indicate that the disturbances in 9-KPR activity in bovine retained placenta exist but their reasons still require further experiments.

Transfer and metabolism of prostaglandin E(2)in the dual perfused human placenta

Prostaglandins (PGs) are potent paracrine hormones that are important for the control of several functions in the uterus and fetus during pregnancy and parturition. PGs are rapidly metabolized to inactive metabolites by prostaglandin dehydrogenase (PGDH). However, the regulation of transfer and metabolism of PGs across the placenta is not well understood. This study used an in vitro dual perfused human placental cotyledon preparation to examine the production of the potent vasoactive and myometrial stimulants PGE(2)and PGF(2alpha), transfer of PGs from the maternal to the fetal circulation and the metabolism of PGs by PGDH. Secretion of PGE(2)was greater into the fetal compared to the maternal circulation. PGE(2)output was higher than PGF(2alpha)and concentrations of PGE(2)and PGF(2alpha)metabolites (PGEM and PGFM) were greater in both fetal and maternal outputs when compared to the primary prostaglandins. Infusion of PGE(2)into the maternal circulation did not result in increased PGE(2)efflux but PGEM was output was increased, demonstrating a rapid and efficient metabolism by the placenta. There was no significant transfer of PGE(2)across to the fetal circulation, although there was some transfer but in the form of inactivated PGEM. There was no significant interconversion of PGE(2)to PGF(2alpha)by the 9-keto-reductase pathway. Expression of PGDH as detected by immunoblot was high in placenta. This PGDH was localized throughout the syncytiotrophoblast at the fetal-maternal interface and also in extravillous trophoblast cells. The presence of PGDH at this site acts to stabilize output of primary PG from the placenta and also as a barrier preventing transfer to the fetal circulation, resulting in the separation of PG homeostasis in the fetus and mother.

The enzymes responsible for the metabolism of prostaglandins in bovine placenta

The following review presents some data on the enzymes of synthesis and catabolism of prostaglandins in bovine placenta. The available literature confirms the anabolic and catabolic ability of bovine placenta to metabolise prostaglandins, but there is little direct information about the pathways involved. The aim of the review is to describe what is known about the physico-chemical properties and activity of enzymes involved in prostaglandin metabolism in bovine placenta.

Pulsatile output of prostaglandin F(2alpha) does not increase around the time of luteolysis in the pregnant goat

Prostaglandin (PG) F(2alpha) secreted from the uterus is the luteolysin of the estrous cycle and is also believed to be responsible for luteolysis in the pregnant doe at term. We have reported that basal progesterone concentrations decrease before basal PGF(2alpha) concentrations increase, which is inconsistent with this view. In this study we investigated whether luteolysis is associated with increased frequency or amplitude of pulsatile PGF(2alpha) secretion in does over the last 2 wk of gestation. Progesterone concentrations decreased approximately 1 wk before parturition. There was no accompanying increase in PGF(2alpha) concentrations or pulse frequency, and those pulses that were observed were of lesser amplitude and duration than those that have been associated with luteolysis in cycling ewes. A small increase in PGF(2alpha) pulse frequency was identified during the 3 days before parturition, but this was not associated with any change in progesterone concentrations. The biological significance of these small changes in PGF(2alpha) pulse frequency is obscure, although the high concentration of this eicosanoid at labor may have been related to the final, precipitous decline in plasma progesterone concentrations. These findings do not support the notion that PGF(2alpha) is the principal luteolysin in the pregnant doe at term.

Prostaglandin E2 9-keto reductase from bovine term placenta

The aim of the following study was to determine the activity and physico-chemical properties of prostaglandin E2 9-keto reductase from bovine placenta. Placental tissues obtained immediately after parturition were subjected to purification procedure consisting of homogenization, affinity chromatography, gel filtration and allowed to electrophoresis. The activity of enzyme was measured spectrophotometrically. The purification procedures receive 135-fold purified enzyme preparate of the molecular weight of 45 kDa with the following kinetic values: Michaelis constant for PGE2, 117 microM and max velocity 183 pmol/min. The activity of enzyme was also detected with 20 alpha-hydroxypregn-4en-3-one and with 9,10-phenanthrenquinone (Michaelis constant 22 microM and 6 microM, respectively). The determination of physico-chemical properties of prostaglandin E2 9-keto reductase, performed for the first time in bovine placenta, should aid the understanding of the metabolism of prostaglandins and their biological importance in physiological and pathological conditions in cattle.

Activation of protein kinase C stimulates collagenase production by cultured cells of the cervix of the pregnant guinea pig

OBJECTIVE

Dilatation of the uterine cervix at parturition is achieved by an estrogen-induced, collagenase-mediated degradation of type I collagen in the cervix. The objective was to test the hypothesis that collagenase production in the cervix of pregnant guinea pig in culture is mediated by activation of protein kinase C.

STUDY DESIGN

The effects of 17 beta-estradiol, prostaglandin F2 alpha, or activation of protein kinase C by phorbol-12-myristate-13-acetate, 1-stearoyl-2-arachidonyl-sn-glycerol and phospholipase C on collagenase production was studied with primary monolayer cultures of cervical cells from Hartley guinea pigs at 50 days' gestation. Results are analyzed for statistical significance with analysis of variance.

RESULTS

Collagenase production is increased twofold to threefold by 17 beta-estradiol, prostaglandin F2 alpha, or activation of protein kinase C. The observed stimulation of collagenase production by 17 beta-estradiol and prostaglandin F2 alpha was blocked by the protein kinase C inhibitor 1-(5-isoquinoline sulfonyl) 2-methylpiperazine dihydrochloride.

CONCLUSION

Collagenase production in cultured cervical cells of pregnant guinea pig is stimulated by activation of protein kinase C.

Purification and properties of prostaglandin 9-ketoreductase from pig and human kidney. Identity with human carbonyl reductase

Prostaglandin 9-ketoreductase (PG-9-KR) was purified from pig kidney to homogeneity, as judged by SDS/PAGE using an improved procedure. The enzyme is pro-S stereoselective with regard to hydrogen transfer from NADPH with prostaglandin E2 as substrate and reduces its 9-keto group with approximately 90% stereoselectivity to form prostaglandin F2 alpha. Approximately 8% of the prostaglandin F formed has the beta-configuration. In addition to catalyzing the interconversion of prostaglandin E2 to F2 alpha, PG-9-KR also oxidizes prostaglandin E2, F2 alpha and D2 to their corresponding, biologically inactive, 15-keto metabolites. Incubation of PG-9-KR with prostaglandin F2 alpha and NAD+ leads to the preferential formation of 15-keto prostaglandin F2 alpha rather than prostaglandin E2. This suggests that the prostaglandin E2/prostaglandin F2 alpha ratio is not determined by the NADP+/NADPH redox couple. The enzyme also reduces various other carbonyl compounds (e.g. 9,10-phenanthrenequinone) with high efficiency. The catalytic properties measured for PG-9-KR suggest that its in vivo function is unlikely to be to catalyze formation of prostaglandin F2 alpha. The monomeric enzyme has a molecular mass of 32 kDa and exists as four isoforms, as judged by isoelectric focusing. PG-9-KR contains 1.9 mol Zn2+/mol enzyme and no other cofactors. Human kidney PG-9-KR was also purified to homogeneity. The human enzyme has a molecular mass of 34 kDa and also exists as four isoforms. Polyclonal antibodies raised against pig kidney PG-9-KR cross-react with human kidney PG-9-KR and also with human brain carbonyl reductase, as demonstrated by Western blot analysis. Sequence data of tryptic peptides from pig kidney PG-9-KR show greater than 90% identity with human placenta carbonyl reductase. From comparison of several properties (catalytical, structural and immunological properties), it is concluded that PG-9-KR and carbonyl reductase are identical enzymes.

Effects of saturated fatty acids on prostaglandin E 9-keto-reductase

We examined the effects of three saturated fatty acids (myristic acid 14:0, palmitic acid 16:0, and stearic acid 18:0) on prostaglandin E 9-ketoreductase (PGE-9-KR, EC 1.1.1.189), which catalyzes the conversion of prostaglandin E2 (PGE2) into prostaglandin F2 alpha (PGF2 alpha). Palmitic acid inhibited PGE-9-KR activity dose-dependently, whereas the other two fatty acids had no effect. In spite of the structural similarity of these fatty acids, our findings suggest that, of the three, only palmitic acid has an inhibitory effect on PGE-9-KR.

Prostaglandin E2 metabolism in the human fetal membranes

Prostaglandins play a pivotal role in the initiation and maintenance of labor, but the sources that contribute to the production of primary prostaglandins (prostaglandin E2 and prostaglandin F2 alpha) remain controversial. In decidua, prostaglandin F2 alpha may be formed de novo or from prostaglandin E2 through 9-ketoreductase activity, although it has been suggested that metabolism to 13,14-dihydro-15-ketoprostaglandin E2 through 15-hydroxyprostaglandin dehydrogenase is dominant. To examine this possibility, and to determine changes with labor, we examined interconversions of prostaglandin E2 to prostaglandin F2 alpha, 13,14-dihydro-15-ketoprostaglandin E2 and 13,14-dihydro-15-ketoprostaglandin F2 alpha by dispersed cells of decidua, chorion, and amnion obtained from patients at term elective cesarean section or after spontaneous labor. Incubations were performed with increasing concentrations (1 to 100 ng/ml) of prostaglandin E2 for 2 and 4 hours, and products were measured by radioimmunoassay. The 13,14-dihydro-15-ketoprostaglandin E2 was measured as 11-deoxy-13,14-dihydro-15-keto-11 beta, 16 psi-cycloprostaglandin E2. Basal output of prostaglandin E2 increased between cesarean section and spontaneous labor from 190.6 +/- 109 pg/10(5) cells (+/- SE) to 605.2 +/- 346.8 in amnion, nondetectable to 24.5 +/- 11.2 in chorion, and 18 +/- 16 to 69 +/- 25.8 in decidua. For both cesarean section and spontaneous labor patients there was very little conversion of prostaglandin E2 by the amnion, substantial conversion to 13,14-dihydro-15-ketoprostaglandin E2 by the chorion, and some conversion to 13,14-dihydro-15-ketoprostaglandin E2 by the decidua. Percentage conversions did not change with labor. Prostaglandin F2 alpha was formed by all tissues but only in trace amounts. All tissues from one cesarean section patient showed substantial conversion of prostaglandin E2 to prostaglandin F2 alpha, but very little 13,14-dihydro-15-ketoprostaglandin E2 or 13,14-dihydro-15-ketoprostaglandin F2 alpha formation, indicating either a decrease or deficiency in the 15-hydroxyprostaglandin dehydrogenase activity. We conclude that conversion of exogenous prostaglandin E2 to prostaglandin F2 alpha can occur in intrauterine tissues, but this does not normally contribute significantly to the prostaglandin F2 alpha output by the human decidua and fetal membranes.

Prostaglandin-E2 9-ketoreductase from swine kidney. Production of antisera and application to development of a radioimmunoassay

Prostaglandin-E2 9-ketoreductase (PGE2-9-KR, EC 1.1.1.189), the enzyme which catalyzes the reaction from prostaglandin E2 (PGE2) to prostaglandin F2 alpha (PGF2 alpha), was purified 580-fold from swine kidney. The molecular mass of the enzyme determined by SDS-gel electrophoresis was 33 kDa. Antiserum against the purified enzyme was raised in three rabbits. The antiserum was able to precipitate PGE2-9-KR from swine kidney and to crossreact with pGE2-9-KR from several reproductive organ tissues, such as rabbit ovary, rabbit corpus luteum, rabbit endometrium and human decidua vera. When swine kidney PGE2-9-KR was labelled with 125I and incubated with affinity-purified antiserum in the presence of increasing amounts of unlabelled enzyme, competitive binding of the unlabelled enzyme to the antibody was observed. A radioimmunoassay for the quantitation of the enzyme was developed. The standard curve was linear from 5 to 500 ng enzyme. The intra- and interassay coefficients of variation were 6.4 and 13.2%, respectively. The assay may be useful for the quantitation of PGE2-9-KR in several tissues under various physiological conditions.

Inactivation of prostaglandins in human decidua vera (parietalis) tissue: substrate specificity of prostaglandin dehydrogenase

Prostaglandin dehydrogenase catalyzes the initial reaction in the inactivation of prostaglandin E2 and F2 alpha. To address the potential importance of this enzyme in regulating the tissue levels of active prostaglandins, we evaluated the kinetic properties of prostaglandin dehydrogenase in uterine decidua vera tissue of women. Specifically, we characterized the enzyme activity under optimal in vitro conditions in cytosolic fractions of uterine decidua vera tissue obtained at term and compared the substrate and cosubstrate specificities of prostaglandin dehydrogenase in cytosolic fractions of decidual tissues. The incubation conditions were optimized with either prostaglandin E2 or F2 alpha and nicotinamide-adenine dinucleotide or nicotinamide-adenine dinucleotide phosphate as substrates to ensure linearity of product formation with time of incubation and protein concentration. The apparent Michaelis-Menten constant of nicotinamide-adenine dinucleotide-dependent prostaglandin dehydrogenase for prostaglandin E2 was 5.5 mumol/L. The apparent Michaelis-Menten constant of nicotinamide-adenine dinucleotide phosphate-dependent prostaglandin dehydrogenase for prostaglandin F2 alpha was 15 mumol/L. Prostaglandin E2 serves as a better substrate for prostaglandin dehydrogenase than does prostaglandin F2 alpha, irrespective of the cosubstrate. In cytosolic fractions of decidual tissues, the specific activity (apparent Vmax) of nicotinamide-adenine dinucleotide-dependent prostaglandin dehydrogenase was greater than that of nicotinamide-adenine dinucleotide phosphate-dependent prostaglandin dehydrogenase. In addition, we found that in decidual tissue obtained before or after the onset of labor, the specific activity of prostaglandin dehydrogenase varied widely. In tissues obtained after delivery by cesarean section, no significant differences were apparent in the specific activity of the enzyme before (9.3 to 125.8 nmol/min/mg protein) and after (27.8 to 103.4 nmol/min/mg protein) the onset of labor. In cytosolic fractions of decidual tissue obtained after vaginal delivery, the specific activity of nicotinamide-adenine dinucleotide-dependent prostaglandin dehydrogenase ranged from undetectable levels to 38.4 nmol/min/mg protein. We speculate that nicotinamide-adenine dinucleotide-dependent prostaglandin dehydrogenase in decidua serves to regulate the levels of bioactive prostaglandins in decidua vera tissue and the amounts of prostaglandins (and metabolites) produced in decidua or fetal membranes that reach myometrium and fetal membranes and enter maternal blood and amniotic fluid.

Prostaglandin E2 9-ketoreductase activity in human decidua vera tissue

Amnion is believed to be a tissue of central importance in the biochemical processes of parturition. In this tissue, prostaglandin E2 is the near exclusive prostaglandin produced. And although the production of prostaglandin E2 is increased during labor in women, the levels of the major metabolite of prostaglandin E2 in maternal plasma are not elevated; rather, the levels of 13,14-dihydro-15-ketoprostaglandin F2 alpha, the major circulating metabolite of prostaglandin F2 alpha, are increased strikingly. Because of this apparent paradox, we considered the possibility that prostaglandin E2, originating in amnion, chorion laeve, or decidua vera, is converted to prostaglandin F2 alpha in decidua vera by the action of prostaglandin E2-9-ketoreductase. We found that prostaglandin E2 9-ketoreductase, the enzyme that catalyzes the conversion of prostaglandin E2 to F2 alpha, is present in cytosolic fractions prepared from homogenates of uterine decidua vera tissue. The specific activity of 9-ketoreductase in cytosolic fractions of decidua of six women varied from 3.2 to 155 pmol X min-1 X mg-1 protein. We also evaluated the conversion of exogenous prostaglandin E2 to F2 alpha in intact human endometrial stromal cells in monolayer culture. We found that prostaglandin E2, added to the culture medium, was converted to prostaglandin F2 alpha by endometrial stromal cells that were maintained in the presence of inhibitors of prostaglandin synthase. The extent of conversion of exogenous prostaglandin E2 to F2 alpha, however, was low relative to the specific activity of prostaglandin E2 9-ketoreductase found in decidual cytosol. These findings are consistent with the possibility that prostaglandin E2 formed in decidua vera tissue may be converted in that tissue to prostaglandin F2 alpha by 9-ketoreductase; on the other hand, prostaglandin E2 formed in contiguous tissues probably is not converted significantly to prostaglandin F2 alpha by decidual 9-ketoreductase.

Prostaglandin-E2 9-ketoreductase from human uterine decidua vera

Prostaglandin-E2 9-ketoreductase, the enzyme which catalyzes the reaction from prostaglandin E2 (PGE2) to prostaglandin F2 alpha (PGF2 alpha), has been purified 232-fold from human uterine decidua vera. The molecular mass of the enzyme, as estimated by fast protein liquid chromatography, was 29 kDa. Sodium dodecyl sulfate disc gel electrophoresis of the denatured enzyme revealed a molecular mass of 31 kDa. These data suggest that the enzyme consists of a single polypeptide chain. The rate equation of the enzyme reaction for two substrates was used for the determination of five kinetic constants. The equilibrium constant with respect to PGE2 was 83 microM, the Michaelis constant, Km, for PGE2 was 93 microM. For NADPH, the equilibrium constant was 1.0 microM and Km was 1.6 microM. The maximal velocity for the forward reaction was V1 = 217 pmol/min. The inhibition constants for the analgesic agents indomethacin and fentiazac were Ki = 850 microM and Ki = 450 microM and for the steroid progesterone Ki = 1.5 mM, respectively. Prostaglandin-E2 9-ketoreductase might be responsible for the control of the PGE2/PGF2 alpha ratio in human decidua vera. The enzyme, therefore, might be an important factor in the cascade of events leading to uterine contractions and parturition.

Prostaglandin synthesis from endogenous and exogenous arachidonic acid in the rat uterus. Effect of estradiol and progesterone

Regulation of uterine prostaglandin (PG) synthesis by steroid sex hormones was studied in female rats. Animals were ovariectomized (OVX) and received silastic implants of estradiol (E2) or progesterone (Pg); the implants were maintained for 7 days. The animals were sacrificed and their uteri homogenized at 4 degrees C. Basal levels of PGs and PGs synthesized during 20 min incubations at 37 degrees C, either without exogenous arachidonic acid (AA), or in the presence of 2.10(-5)M added AA were measured by RIA. Comparison between the various treatments shows that the regulation of uterine PG synthesis in the rat is a multistep process and depends on the type of PG. PGI2 (6 keto PGF1 alpha) is synthesised in very large amounts but is not very significantly influenced by hormonal treatment. PGF2 alpha and PGE2 are synthesized in much smaller quantities but are very dependent on hormonal treatment. E2 stimulates PGF2 alpha and inhibits PGE2, shifting the ratio from 0.5 in untreated OVX rats to 3.3 in OVX E2-treated rats. TXA2 (TXB2) is stimulated by E2. Pg significantly stimulates endogenous PGF2 alpha levels but does not change the profile of PGs synthesized from the endogenous substrate. It inhibits PGE2 synthesis from exogenously added AA. These results show that E2 favors PGF2 alpha synthesis at the expense of PGE2 and that the synthesis of PGI2, which is the main AA metabolite in the rat uterus is not hormone dependent, (at least not under the conditions of our experiments).