Attenuation of LPS-induced neutrophil thromboxane b2 release and chemiluminescence.

Polymorphonuclear leukocytes (PMN) may play a key role in acute lung injury and ARDS. The mechanisms of PMN-mediated lung injury include the release of inflammatory mediators, such as oxygen free radicals which cause direct tissue injury, and arachidonic acid metabolites which cause pulmonary vasoconstriction and increased vascular permeability. The goals of this in vitro study were 1) to assess the effects of PMN-activating agents (lipopolysaccharide, LPS; phorbol myristate acetate, PMA; tumor necrosis factor, TNF) on PMN thromboxane B2 (TXB2) release and oxygen free radical production and 2) to determine the effects of agents purported to suppress PMN activity (pentoxifylline, PTX; adenosine; dibutyryl cyclic AMP, DBcAMP; and terbutaline, TBN) on activator-induced PMN TXB2 release and oxygen free radical production. PMN TXB2 release was determined by radioimmunoassay and oxygen free radical production was monitored by chemiluminescence. Our results show that 1) LPS and PMA significantly increase PMN TXB2 release, whereas tumor necrosis factor (TNF) has no effect; 2) LPS and PMA significantly increase PMN chemiluminescence; 3) DBcAMP and TBN significantly reduce LPS-induced PMN TXB2 release whereas PTX and adenosine do not; 4) TBN significantly reduces PMA-induced PMN TXB2 release whereas other agents do not; 5) All agents (PTX, adenosine, DBcAMP, and TBN) significantly reduce LPS-induced PMN chemiluminescence but none attenuate PMA-induced PMN chemiluminescence. We conclude that: LPS and PMA activate PMN manifested by TXB2 release and chemiluminescence. Additionally, all the PMN suppressing agents do attenuate some PMN functions. Of interest, PTX, adenosine, DBcAMP, and TBN have different effects depending upon functional assay and activating agent. It will be important to investigate the mechanisms by which PMN suppressing agents alter signal transduction resulting in differential effects on PMN function.     

Effect of single oral administrations of non steroidal antiinflammatory drugs to healthy volunteers on arachidonic acid metabolism in peripheral polymorphonuclear and mononuclear leukocytes

The effects of a single oral administration of acetylsalicylic acid (500 mg), indomethacin (50 mg) and piroxicam (40 mg) to healthy volunteers on functional and biochemical parameters of platelets, polymorphonuclear (PMN) and mononuclear (MNL) leukocytes were evaluated. Blood was collected before and two hours after the drug intake and blood cells separated according to conventional techniques. The considered drugs almost completely suppressed the aggregation of platelets, whereas they did not affect either PMN and MNL aggregation. Superoxide anion generation by leukocytes was (PMN), or no effect (MNL) was observed after piroxicam and indomethacin respectively. The formation of arachidonate metabolites via the 5-lipoxygenase pathway by PMN and MNL challenged with 10 microM A23187 was unchanged following aspirin and indomethacin. In this respect a selective increase of 5-HETE and LTC4 synthesis by MNL only was detected after piroxicam administration. The three drugs similarly reduced TXB2 synthesis by platelets and PMN (-80% for aspirin and indomethacin, and -40% for piroxicam). As far as MNL is concerned, aspirin inhibited this metabolite by 80%, while indomethacin reduced it by 40% only. In contrast piroxicam increased TXB2 synthesis by stimulated MNL. It can be concluded that the considered antiinflammatory drugs 1) differently affect the cyclooxygenase enzyme in platelets and leukocytes; 2) at variance with the situation in platelets, the inhibition of thromboxane formation by leukocytes is not related to modifications of cellular function; 3) the formation of arachidonate metabolites via the 5-lipoxygenase pathway is affected by piroxicam only.     

Cyclooxygenase and lipoxygenase metabolite synthesis by polymorphonuclear neutrophils: in vitro effect of dipyrone

Functional activity of polymorphonuclear neutrophils (PMN) is associated with the metabolism of Arachidonic Acid (AA) released from membrane phospholipids. In this study the in vitro effect of dipyrone, a non steroidal anti-inflammatory drug, on the production of AA metabolites through cyclooxygenase (CO) and lipoxygenase (LO) pathways by stimulated PMN has been investigated. PMN isolated by counterflow centrifuge elutriator were greater than 98% pure and viable. Metabolite production was evaluated by RIA of Thromboxane A2 (TxA2), Prostaglandin E2 (PGE2), Leukotriene B2 (LTB4) and Leukotriene C4 (LTC4) after PMN stimulation with calcium ionophore A 23187 (20 microM). The levels of beta-thromboglobulin (RIA) lower than 5 ng/ml allowed us to rule out activation of residual contaminant platelets. In these experimental conditions, in the absence of dipyrone the products (ng/10(6) cells) of AA metabolism were LTB4 (3.51 +/- 0.22), LTC4 (0.81 +/- 0.08), TxB2 (0.144 +/- 0.025) and PGE2 (0.150 +/- 0.017). Incubation with dipyrone induced changes of PGE2 and TXB2 production in a dose dependent fashion (r = 0.83 and r = 0.87, p less than 0.001), obtaining already at the lowest drug concentration (5 micrograms/ml) a significant inhibition (33 and 40% for TxB2 and PGE2 p less than 0.005). No significant changes of LTB4 and LTC4 production have been observed. The results of this study indicate that dipyrone relevantly affects CO metabolite synthesis by stimulated PMN at concentrations comparable to those reached in therapeutic use. The inhibition of PGE2 synthesis which is present in inflamed tissues and actively participates in inflammatory reactions, could contribute to the therapeutic anti-inflammatory action of dipyrone.     

Evaluation of inhibitors of eicosanoid synthesis in leukocytes: possible pitfall of using the calcium ionophore A23187 to stimulate 5' lipoxygenase

The effect on arachidonate metabolism of two compounds (BW755C and benoxaprofen) which have been reported to inhibit 5' lipoxygenase in leukocytes has been evaluated in human polymorphonuclear leukocytes (PMN) stimulated with the calcium ionophore A23187 and serum-treated zymosan (STZ). The syntheses of leukotriene B4 (LTB4) and thromboxane B2 (TXB2) from endogenous substrate were determined by specific radioimmunoassays as indicators of 5' lipoxygenase and cyclo-oxygenase activity in the PMN respectively. Benoxaprofen inhibited the synthesis of leukotriene B4 by human PMN stimulated with the calcium ionophore A23187, but it was approximately 5 times less potent than BW755C. However, benoxaprofen (IC50 1.6 X 10(-4)M) was approximately 100 times less potent than BW755C (IC50 1.7 X 10(-6)M) at inhibiting leukotriene B4 synthesis induced by serum-treated zymosan. Both drugs inhibited thromboxane synthesis by leukocytes stimulated with A23187 or serum-treated zymosan at similar concentrations (approximately 5 X 10(-6)M). The data obtained using STZ as stimulus are consistent with previous in vivo studies and indicate that benoxaprofen is a relatively selective inhibitor of cyclo-oxygenase. However, this selectivity was far less apparent when A23187 was used as a stimulus to release the eicosanoids which suggests that this inhibition could be via an indirect mechanism and therefore A23187 should be used with caution as a stimulus of 5' lipoxygenase for evaluating inhibitors of eicosanoid synthesis.     

Human polymorphonuclear leukocyte-mediated cytotoxicity against varicella-zoster virus-infected fibroblasts

Polymorphonuclear leukocytes (PMN) were studied for their ability to mediate cytotoxicity against varicella-zoster virus (VZV)-infected and uninfected human fibroblasts in 51Cr release assays. PMN were capable of mediating antibody-dependent cellular cytotoxicity (ADCC) against VZV-infected targets. Maximal ADCC was obtained with effector-to-target ratios of 100:1 and 18 h of incubation. Percent 51Cr release for 26 normal adults was 14.1 +/- 0.6 (mean +/- standard error) in the presence of pooled human seropositive sera (final dilution, 1:100) and 0.5 +/- 0.6 in the presence of pooled human seronegative sera. Addition of phorbol myristate acetate (PMA) enhanced PMN-mediated cytotoxicity against VZV-infected and uninfected targets. PMA-stimulated cytotoxicity was optimal with PMA concentrations of 200 ng/ml and effector-to-target ratios of 10:1, and antibody was not required; killing was detected as early as 3 h after incubation and was maximal after 18 h. Highly purified PMN were capable of mediating both ADCC and PMA-stimulated lysis. Catalase completely inhibited PMA-stimulated PMN cytotoxicity, but had no effect on PMN-mediated ADCC. PMN from patients with chronic granulomatous disease were capable of mediating ADCC, but not PMA-stimulated killing, against VZV-infected targets. Thus, PMN could kill VZV-infected targets by two different mechanisms: ADCC, which required antibody but not hydrogen peroxide (H2O2), and PMA-stimulated cytotoxicity, which required H2O2 but not antibody.     

Platelet aggregation and thromboxane release induced by arachidonic acid, collagen, ADP and platelet-activating factor following low dose acetylsalicylic acid in man

The present study was undertaken in order to characterize the dose-dependent nature of acetylsalicylic acid (ASA) on platelet aggregation and plasma thromboxane B2 (TXB2) release in healthy volunteers. Volunteers received either 25, 50, 100 or 500 mg daily for five consecutive days. At the end of the five day period, all dosages of ASA were capable of completely suppressing TXB2 production and arachidonic acid-induced platelet aggregation. At that time, the second phase of ADP-induced aggregation was also blocked. However, while the inhibition following 500 mg ASA was complete after 24 hours, total inhibition with 100, 50 and 25 mg was attained only after two, three and four days, respectively, indicating the cumulative effect of ASA on platelets. Aggregation induced by collagen was also inhibited dose-dependently- yet slower and at no time complete. ASA had no inhibitory effect on aggregation by platelet-activating factor (PAF). It is concluded that a daily dose of 50 mg ASA would suffice in blocking platelet TXA2 production and aggregation induced by most physiological agents.     

IL-8 production by human polymorphonuclear leukocytes. The chemoattractant formyl-methionyl-leucyl-phenylalanine induces the gene expression and release of IL-8 through a pertussis toxin-sensitive pathway.

IL-8 is a novel chemotactic cytokine, produced by a variety of blood and tissue cells, that has marked activating effects on polymorphonuclear leukocytes (PMN). We report that IL-8 is produced and released by human PMN after stimulation with the chemotactic agonist FMLP. Release of IL-8 in response to FMLP was transient and not influenced by PMN adherence or by the absence of serum in the medium. Maximum yields were usually obtained with 10 nM FMLP within 2 h of stimulation (0.5-3.5 ng/ml/7 x 10(6) cells, range of 17 different donors). IL-8 release was dependent on FMLP-induced de novo protein synthesis because it was inhibited by cycloheximide, was paralleled by enhanced expression of IL-8 mRNA and was potentiated from two- to sixfold after preincubation of PMN with cytochalasin B. The FMLP effect was direct and not dependent on LPS or on contaminating monocytes, which showed only low responsiveness to FMLP. Pretreatment of PMN with pertussis toxin prevented FMLP-dependent IL-8 production, the effect being evident both at the level of mRNA expression and protein secretion. In addition, two other chemoattractans, platelet-activating factor and C5a, were found capable to induce release of IL-8 by PMN. The results of this study suggest that chemotactically stimulated PMN may be able to amplify the recruitment process of PMN to the inflammatory site by releasing IL-8. As a long-lived cytokine, IL-8 could markedly prolong the attractant effect.     

Changes in urinary thromboxane level in man during cardiopulmonary bypass: effect of thromboxane on renal tubules

ONO-3708, a thromboxane A2 (TXA2) antagonist, was administered at a dose of 2 micrograms/kg/min by a double blind method as compared with inactive placebo during cardiopulmonary bypass (CPB) procedure to study the changes of thromboxane B2 (TXB2) levels in plasma and urine and N-acetyl-glucosaminidase (NAG) level in urine. TXB2 levels in plasma and urine increased significantly (P less than 0.01) during CPB in the patients given ONO-3708 (ONO-3708 group) and in those given placebo (placebo group). The plasma TXB2 level as expected from the urinary TXB2 level was higher than the measured plasma TXB2 level showing increases in TXB2 originating from the kidney. The urinary NAG level, increased significantly (P less than 0.01) during CPB the NAG level in ONO-3708 group was significantly low as compared to placebo group. The levels of TXB2 in plasma and urine in ONO-3708 group were not different from those of the patients receiving placebo, indicating that ONO-3708 does not have any effect on TXA2 production. We concluded that the elevation of urinary TXB2 level might be due to increased TXA2 production in the kidney under hypoxic condition induced by hypotension and lowered perfusion during CPB. Furthermore, the increased production of TXA2 appears to suppress the functions of the renal proximal tubules.     

Antithrombotic effect of onion in streptozotocin-induced diabetic rat

In the present study, we investigated whether onion has antithrombotic effect in streptozotocin (STZ)-induced diabetic rats. In diabetic rats, serum thromboxane B(2) (TXB(2)) level was elevated compared to that in normal, and this elevation in diabetes was significantly inhibited by treatment with onion (0.5 g/ml/kg/day, i.p.) for 4 weeks. In normal rats, the serum TXB(2) level remained unaltered after the treatment with onion. To investigate in vitro effect of onion, we examined its effect on TXB(2) formation, platelet aggregation and arachidonic acid (AA)-release in platelets from diabetic and normal rats. Onion showed a significant inhibitory effect on collagen- or AA-induced TXB(2) formation with greater potency in diabetic platelets than in normal. Similarly, more potent inhibitory effects of onion in diabetes were observed in collagen- or AA-induced platelet aggregation and collagen-induced AA release response. In conclusion, these results suggest that onion can produce more beneficial antithrombotic effect in diabetes.     

Differential response to dexamethasone on the TXB2 release in guinea-pig alveolar macrophages induced by zymosan and cytokines

Glucocorticosteroids reduce the production of inflammatory mediators but this effect may depend on the stimulus. We have compared the time course of the effect of dexamethasone on the thromboxane B2 (TXB2) release induced by cytokine stimulation and zymosan in guinea-pig alveolar macrophages. Interleukin-1beta (IL-1beta), tumour necrosis factor-alpha (TNF-alpha) and opsonized zymosan (OZ), all stimulate TXB2 release. High concentrations of dexamethasone (1-10 microM) inhibit the TXB2 production induced by both cytokines and OZ, but the time course of this response is different. Four hours of incubation with dexamethasone reduce the basal TXB2 release and that induced by IL-1beta and TNF-alpha, but do not modify the TXB2 release induced by OZ. However, this stimulus was reduced after 24 h incubation. Our results suggest that the antiinflammatory activity of glucocorticosteroids shows some dependence on stimulus and, therefore, may have more than one mechanism involved.     

Ethanol increases PGE and thromboxane production in mouse pregnant uterine tissue

The teratogenic effect of ethanol in the C57BL/6J mouse can be attenuated by pretreatment with aspirin (ASA). One prominent effect of ASA is to inhibit prostaglandin (PGE) and thromboxane (TXB2) production. We examined the effect of in vivo ethanol exposure on PGE and TXB2 production in a uterine-embryo tissue sample of C57BL/6J mice either before or after in vivo ASA pretreatment on day 10 of gestation. Ethanol increased both PGE and TXB2 production by approximately 20%. ASA caused a marked reduction of PGE and TXB2 in both control and ethanol groups by approximately 80-90%. The mouse strain, gestation time, and study parameters used in this study were the same as in the previously reported ASA attenuation of the teratogenic effect of ethanol. Therefore, the present data add additional support to the hypothesis that prostaglandin and/or thromboxane production may be involved in at least some aspects of fetal alcohol syndrome.     

Stimulation of prostaglandin E2 and thromboxane B2 production by human monocytes in response to interleukin-2

Interleukin 2 (IL-2) is a potent lymphokine involved in the regulation of immune responses and is classically regarded as a stimulus for the activation and growth of T-cells. Recent reports have demonstrated the IL-2 dependent activation of human peripheral blood lymphocytes into lymphokine activated killer cells capable of lysing tumor cells both in vitro and in vivo. In this study we report data which clearly show IL-2 may also act to down-regulate the immune response by inducing the synthesis of arachidonic acid metabolites with known immunosuppressive actions. Stimulation of peripheral human blood monocytes with IL-2 caused an increased production of prostaglandin E2 (PGE2) and thromboxane (TXB2) in a dose-dependent manner. Kinetic analysis showed no increase above controls after 6 hours and maximal levels by 10 hours; elevated levels were maintained after 45 hours of incubation. After 20 hours of stimulation with 2000 U/ml IL-2, the level of PGE2 and TXB2 were greater than three-fold above controls, 0.7 and 19 ng/10(6) cells, respectively. The stimulation was relatively specific in that neither prostacyclin nor leukotrienes were produced in response to IL-2. These data demonstrate that IL-2 acts on human monocytes to induce the secretion of PGE2 and TXB2.     

Regulation of TXB(2) and PGE(2) production by TGF-beta(1) in in vitro silica dust-exposed rat alveolar macrophage

We investigated the effect of transforming factor factor-beta(1) (TGF-beta(1)) on thromboxane B(2) (TXB(2)) and prostaglandin E(2) (PGE(2)) production in in vitro silica dust-exposed rat alveolar macrophages (AM). In the presence of 5 mug of anti-TGF-beta(1) antibodies, TXB(2) production decreased, but PGE(2) production increased. Addition of 2 ng of TGF-beta(1) to the culture medium potentiated TXB(2) production, but PGE(2) production apparently did not change. At 50 ng of TGF-beta(1), TXB(2) production decreased, and PGE(2) production varied. Our data suggest that in rat AM: (1) both endogenous and exogenous TGF-beta(1) regulate TXB(2) production; and (2) in the absence of endogenous TGF-beta(1) the liberation of PGE(2) increases; however, exogenous TGF-beta(1) does not have a regulatory effect on PGE(2).     

Modulation of platelet aggregation by areca nut and betel leaf ingredients: roles of reactive oxygen species and cyclooxygenase

There are 2 to 6 billion betel quid (BQ) chewers in the world. Areca nut (AN), a BQ component, modulates arachidonic acid (AA) metabolism, which is crucial for platelet function. AN extract (1 and 2 mg/ml) stimulated rabbit platelet aggregation, with induction of thromboxane B2 (TXB2) production. Contrastingly, Piper betle leaf (PBL) extract inhibited AA-, collagen-, and U46619-induced platelet aggregation, and TXB2 and prostaglandin-D2 (PGD2) production. PBL extract also inhibited platelet TXB2 and PGD2 production triggered by thrombin, platelet activating factor (PAF), and adenosine diphosphate (ADP), whereas little effect on platelet aggregation was noted. Moreover, PBL is a scavenger of O2(*-) and *OH, and inhibits xanthine oxidase activity and the (*)OH-induced PUC18 DNA breaks. Deferoxamine, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) and neomycin prevented AN-induced platelet aggregation and TXB2 production. Indomethacin, genistein, and PBL extract inhibited only TXB2 production, but not platelet aggregation. Catalase, superoxide dismutase, and dimethylthiourea (DMT) showed little effect on AN-induced platelet aggregation, whereas catalase and DMT inhibited the AN-induced TXB2 production. These results suggest that AN-induced platelet aggregation is associated with iron-mediated reactive oxygen species production, calcium mobilization, phospholipase C activation, and TXB2 production. PBL inhibited platelet aggregation via both its antioxidative effects and effects on TXB2 and PGD2 production. Effects of AN and PBL on platelet aggregation and AA metabolism is crucial for platelet activation in the oral mucosa and cardiovascular system in BQ chewers.     

Thromboxane-B(2) levels in serum of rabbits receiving a single intravenous dose of aqueous extract of garlic and onion

We have shown previously that fresh garlic extract is effective in reducing thromboxane formation by platelets both in vivo and in vitro animal models of thrombosis. In the present study, the effect of different concentrations of a single dose of aqueous extracts of garlic and onion were evaluated on serum thromboxane-B(2)synthesis in rabbits. Different concentrations of garlic and onion were administered as single doses in the ear vein of rabbits. Rabbits were bled before and at different intervals after the infusion of garlic or onion extracts. Venous blood was collected and allowed to clot at 37 degrees C for 1 h. Thromboxane-B(2)level was measured in the serum by radioimmunoassay. It was observed that garlic inhibits the thrombin-induced platelet synthesis of TXB(2)in a dose-and time-dependent manner. Maximum inhibition of TXB(2)occurred between 0.5 h and 6 h at 25 and 100 mg kg(-1)garlic. At 24 h post-garlic infusion TXB(2)inhibition was reduced to 15% of the control and TXB(2)levels were comparable to that of the control values at 72 h pots-garlic infusion. Infusion of 100 mg kg(-1)onion extract did not elicit any inhibitory effect on TXB(2)synthesis in the serum of rabbit during the treatment period. The rapid recovery of platelet cyclooxygenase activity after infusion of a single dose of garlic suggests that garlic should be taken more frequently in order to achieve beneficial effects in the prevention of thrombosis.     

Selective inhibition by antiflamrnin-2 of thromboxane B(2) release from isolated and perfused guinea-pig lung

Antiflammin-2 (AF2) is a nonapeptide corresponding to the amino acid residues 246-254 of lipocortin-1 showing anti-inflammatory activity both in vitro and in vivo. The effect of AF2 on the thromboxane B(2) (TXB(2)) and histamine release from isolated and perfused guinea-pig lungs has been studied. AF-2 (10-100 nM) inhibited leukotriene C(4)- (LTC(4)) (3 ng) and antigen-induced (ovalbumin, 1 mg) TXB(2) release in normal and sensitized lungs, respectively. In contrast AF-2 (100 nM) did not modify TXB(2) release induced by histamine (5 mug) or bradykinin (5 mug) in normal lungs. Antigen-induced histamine release was not affected by 100 nM AF-2 infusion. When tested in chopped lung fragments AF-2 (0.1-25 muM) did not modify the release of histamine and TXB(2) induced by antigen (ovalbumin, 10 mug ml(-1)) or calcium ionophore A 23187 (1 muM). Our results show that the inhibitory effect of AF-2 on TXB(2) release is selective and depends on the stimulus applied. In this respect AF-2 mimics, at least in part, the actions of both glucocorticoids and lipocortin-1.     

Stimulation of eicosapentaenoic acid metabolism in washed human platelets by 12-hydroperoxyeicosatetraenoic acid

Washed human platelets were not able to convert eicosapentaenoic acid (EPA) to thromboxane B3 (TXB3) and 12-hydroxyeicosapentaenoic acid (AA) to washed human platelets induced conversion of EPA to TXB3 and 12-HEPE. Esculetin, a specific inhibitor of 12-lipoxygenase, prevented the effect of AA, but cyclooxygenase inhibitor did not. The conversion of AA to TXB2 was not affected by the same dose of esculetin. These data suggest that products of AA formed by 12-lipoxygenase in human platelets have stimulatory effects on EPA metabolism. When AA was preincubated with washed human platelets, its effect on EPA conversion was reduced, suggesting that a labile product of AA formed by 12-lipoxygenase is involved in the facilitation of EPA metabolism. Addition of 12-hydroperoxyeicosatetraenoic acid directly to washed human platelets caused dose-dependent synthesis of TXB3 and 12-HEPE, while addition of 12-hydroxyeicosatetraenoic acid had no effect. Thus, 12-hydroperoxyeicosatetraenoic acid formed from AA promotes the metabolism of EPA in washed human platelets.     

Thromboxane B2, 6-keto-prostaglandin F1 alpha, and prostaglandin F2 alpha production by contracting pregnant rate uteri in vitro

While prostaglandin production by uterine tissue has been shown to be involved in the contractile mechanism of this tissue, less attention has focused upon the involvement of other prostanoids. We have simultaneously measured in vitro isometric contractility of pregnant rat uteri with the release of prostaglandin F2 alpha (PGF), 6-keto-prostaglandin F1 alpha (6-k-PGF1 alpha) and thromboxane B2 (TXB2) into the bathing medium under various conditions. Frequency of uterine contractions and integrated contractile force (ICF) increased from 15 days of gestation and peaked at the time of parturition. Activity was generally greatest during the first 15 min of incubation except during parturition and on Day 1 postpartum when the uterine segment remained active for 1 h experimental period. Indomethacin (INDO) significantly reduced contractile activity regardless of gestational stage. PGF, TXB2, and 6-k-PGF1 alpha increased with gestational age, peaking at the time of parturition. Production was greatest during the first 15 min of incubation and INDO inhibited production of each prostanoid regardless of gestational stage. Imidazole (100 micrograms/ml) inhibited TXB2 production without affecting PGF or 6-k-PGF1 alpha levels. Frequency of contraction and ICF were not affected by imidazole treatment despite TXB2 reduction. These data demonstrate that the in vitro uterus from pregnant rats is capable of producing prostanoids other than prostaglandins and their production generally parallels uterine contractile activity. Thus, the possibility that these prostanoids are involved in physiologic changes during parturition warrants further investigation.