Release Of PGF2 Alpha Research Articles

Activation of phospholipase A2 and phospholipase C by endothelin-1 in human endometrium.

Human endometrium contains specific binding sites for iodinated endothelin (ET)-1, ET-2 and ET-3, and ET-1 stimulates prostaglandin (PG) F2 alpha synthesis from explants of proliferative endometrium in short-term culture. This study has investigated the cellular responses of normal proliferative endometrium to ET-1. Radioimmunoassay was used to measure PG release and Dowex anion-exchange column chromatography was utilized to assess the accumulation of inositol phosphates. Endothelin-1 induced a significant increase in PGF2 alpha release (basal median: 1465 pg/mg per 60 min (range: 541-3935 pg/mg per 60 min); ET-1-stimulated: 1813 pg/mg per 60 min (1021-5714 pg/mg per 60 min); P < 0.04 using Wilcoxon signed rank test). The effect of ET-1 was attenuated in the presence of the phospholipase A2 inhibitor quinacrine. Endothelin-1 induced a rapid, transient and concentration-dependent hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2), measured by the accumulation of tritiated inositol phosphates. Following a 1-min stimulation with ET-1 (100 nmol/l), [3H]inositol mono-, bis- and trisphosphate fractions increased from median values of 490.0 d.p.m./mg dry wt (range: 348.0-807.0 d.p.m./mg dry wt), 120.0 d.p.m./mg dry wt (93.6-144.1 d.p.m./mg dry wt) and 67.0 d.p.m./mg dry wt (54.2-85.0 d.p.m./mg dry wt) to 939.0 d.p.m./mg dry wt (635.9-1596.0 d.p.m./mg dry wt; P < 0.03), 145.0 d.p.m./mg dry wt (127.0-293.9 d.p.m./mg dry wt; P < 0.05) and 146.0 d.p.m./mg dry wt (77.5-187.0 d.p.m./mg dry wt; P < 0.03) respectively. These results suggest that ET-1 activates the phospholipase A2 and PtdIns(4,5)P2-specific phospholipase C in human proliferative endometrium, resulting in the generation of PGF2 alpha and second messengers respectively which are pivotal to endometrial function.

IN VITRO DISPLACEMENT OF VASOACTIVE MEDIATORS FROM PLASMA PROTEINS: A POSSIBLE MECHANISM FOR PSEUDO-ALLERGIC REACTIONS TO NEUROMUSCULAR BLOCKING DRUGS

We have studied the release of prostaglandin F2 alpha (PGF2 alpha) and histamine from serum proteins by neuromuscular blocking drugs using equilibrium dialysis, with tracer quantities of radio-labelled mediators as probes. Small concentrations (0.05-0.25 mmol litre-1) of competitive neuromuscular blocking drugs displaced 16-67% of bound histamine. Greater concentrations of suxamethonium (2 mmol litre-1) were required for histamine displacement (19%). There was a significant release of PGF2 alpha by atracurium 1 mmol litre-1 and pancuronium 0.69 mmol litre-1. These findings suggest an alternative mechanism of histamine release by neuromuscular blocking drugs which may be relevant to adverse reactions during use.

Exposure of human amnion to amniotic fluid obtained before labor causes a decrease in chorion/decidual prostaglandin release.

Prostaglandin (PG) production by fetal membranes has been implicated in the initiation of human parturition, but its regulation is not well understood. We used an in vitro system to study paracrine control of term, fetal membrane PG production. Using a modified Ussing chamber, full thickness fetal membranes with attached decidua were sealed into a chamber so that each hemichamber was a compartment for either the fetal (amnion) or maternal (chorion/decidua) side. Released PGs from maternal and fetal sides were then measured after exposure of the amnion to either buffer or amniotic fluid. We found that basal release of PGs from both the fetal and maternal sides was 2- to 3-fold higher in membranes obtained after labor compared to those obtained before labor. When amnion obtained after labor was exposed to amniotic fluid, we found a 3- to 5-fold increase in the net release of PGE2 from the amnion; however, the maternal side showed an unexpected relative decrease in PGE2 and PGF2 alpha release. This was a paracrine effect, since direct exposure of chorion/decidua to amniotic fluid caused increased release of the PG precursor, arachidonic acid. Direct transfer of radiolabeled PG from fetal to maternal side was minimal.

Interaction between oxytocin and prostaglandin F2 alpha during luteal regression and early pregnancy in sheep.

The pulsatile release of oxytocin from the corpus luteum in the sheep is responsible for the pulsatile release of prostaglandin F2 alpha (PGF2 alpha) from the uterus at luteolysis. It has been proposed that PGF2 alpha also reinforces this process by stimulating the release of oxytocin from the corpus luteum. It is, however, unlikely that PGF2 alpha is the major stimulus for oxytocin release at this time. Although the stimulus for the pulsatile release of oxytocin from the corpus luteum appears to reach the ovary from the peripheral circulation, the nature of the stimulus is unknown. Pulses of oxytocin originating from the corpus luteum have also been observed during early pregnancy, but the release of PGF2 alpha, in response to this signal, is abrogated in some way by ovine trophoblast protein-1 (oTP-1). This protein has been shown to inhibit endometrial prostaglandin production and to decrease the amount of PGF2 alpha released in response to oxytocin. Reduction of uterine oxytocin receptor concentrations by conceptus secretory proteins or by interferons related to oTP-1 remains equivocal. Inhibition of uterine oxytocin receptors is, however, probably the major mechanism that prevents luteal regression during early pregnancy. In cyclic sheep the specific inhibition of uterine oxytocin receptors by 1-deamino-2-D-Try (oET)-4-Thr-8-Orn-oxytocin (CAP), a synthetic oxytocin receptor antagonist, inhibits luteal regression and suppresses pulsatile, but not basal, secretion of uterine PGF2 alpha. Thus, the effects of CAP directly parallel the endocrinological changes that occur in early pregnancy in the sheep.

Interleukin-1 beta and interleukin-6 specifically increase the release of prostaglandin E2 from rat hypothalamic explants in vitro.

It has previously been shown that the cytokines interleukin-1 beta and interleukin-6 (IL-1 beta and IL-6) stimulate directly the release of corticotrophin-releasing-hormone-41 from the rat hypothalamus in vitro, while IL-1 beta can also stimulate the release of somatostatin. These effects can be antagonized by drugs which block prostaglandin (PG) synthesis. PGs are also involved in the control of hypothalamic neuropeptides by other neurotransmitters. In the present study, we have characterized the production of PGs from the rat hypothalamus in vitro, and investigated the effects of IL-1 beta and IL-6, as well as the neurotransmitters norepinephrine, acetylcholine and 5-hydroxytryptamine, on the acute release of PGs, using a well-validated acute hypothalamic incubation system. The rate of release of PGs [PGE2, PGF2 alpha, 6-keto-PGF1 alpha (6KPGF1 alpha) and thromboxane B2 (TXB2) in the medium was found to stabilize after 60 min of preincubation and thereafter remain constant, with TXB2 being the predominant species. Twenty-minute incubation in the presence of human recombinant IL-1 beta or IL-6, in the dose range 1-100 U/ml, had no effect on the release of PGF2 alpha, 6KPGF1 alpha or TXB2; however, the release of PGE2 was significantly increased by both IL-1 beta and IL-6. The effect of IL-1 beta was antagonized by both indomethacin and dexamethasone. None of the other neurotransmitters tested had any effect on the release of any of the PGs.(ABSTRACT TRUNCATED AT 250 WORDS)

Endocrine events associated with endometrial function and conceptus development in cattle.

Regulation and timing of luteolysis during the bovine oestrous cycle is controlled by the initiation and length of progesterone stimulation. Results have demonstrated that early administration of progesterone shortens the interoestrous interval in the ewe and cow, and removal of progesterone stimulation through a progesterone receptor antagonist delays luteolysis in sheep. Current data suggest that down-regulation of progesterone receptors in the uterine epithelium may initiate events involved in the synthesis and release of prostaglandin F2 alpha (PGF2 alpha) for luteolysis. Progesterone is also involved in the stimulation of the uterine secretions that regulate conceptus growth and the release of the bovine trophoblast protein-1 (bTP-1) necessary for inhibiting endometrial PGF2 alpha release. Conceptus secretion of bTP-1, a Type I trophoblast interferon, increases the concentration of the cellular enzyme 2',5'-oligoadenylate synthetase within the endometrium. The biological role of 2',5'-oligoadenylate synthetase in the establishment of pregnancy is discussed.

Concentration-dependent effects of protein kinase C-activating and -nonactivating phorbol esters on myocardial contractility, coronary resistance, energy metabolism, prostacyclin synthesis, and ultrastructure in isolated rat hearts. Effects of amiloride.

An extensive investigation of the cardiac actions of phorbol esters and the potential role of the Na(+)-H+ exchanger in those actions was carried out using isolated rat hearts. Sixty minutes of perfusion with 10(-9) M phorbol 12-myristate 13-acetate (PMA) or 10(-8) M phorbol 12,13-dibutyrate (PDBu) produced marked cardiac dysfunction associated with depressed contractility, coronary constriction, and elevated resting tension, the latter being particularly evident with PMA. These effects were also associated with disturbances in tissue levels of energy metabolites manifested primarily by a reduction in ATP and an elevation in lactate. Furthermore, both phorbols produced a sustained stimulation of the release of 6-ketoprostaglandin F1 alpha (6-keto PGF1 alpha), the hydrolysis product of prostacyclin (prostaglandin I2). Amiloride, an inhibitor of the Na(+)-H+ exchanger, significantly attenuated the loss in contractility and elevation in coronary pressure as well as the stimulated release of 6-keto PGF1 alpha but was without effect on elevations in resting tension or on changes in energy metabolites. Increasing concentrations of PMA or PDBu 10-fold resulted in a much more rapid and severe (greater than 80% loss in contractile function after 30 minutes) effect that was nonetheless qualitatively identical to that seen with the lower concentrations of phorbol. However, the effects were not prevented by amiloride. Surprisingly, 4 alpha-phorbol 12,13-didecanoate (alpha-PDD, 10(-6) M), which does not activate protein kinase C, was found to be a potent inhibitor of cardiac function (greater than 80% loss in contractility and 50% increase in resting tension) after 30 minutes of perfusion, although these effects were not associated with changes in levels of energy metabolites or with elevations in coronary pressure. Similarly, none of the actions of this compound were attenuated by amiloride. In contrast to the sustained effects of other phorbols on 6-keto PGF1 alpha release, the effect of alpha-PDD was transient (less than 10 minutes). In all hearts studied, the marked depression in contractile function caused by all phorbol esters occurred in the absence of any ultrastructural changes. 4 alpha-Phorbol (10(-6) M), which does not activate protein kinase C, was without effect on any parameter studied. Our results demonstrate very complex effects of phorbol esters on numerous parameters of cardiac function, including an amiloride-sensitive component that occurs at low concentrations. The latter observation suggests the involvement of Na(+)-H+ exchange activation, possibly occurring as a consequence of protein kinase C stimulation, in mediation of the effects of phorbol esters at low concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of a Prostaglandin F2α Analogue Prostinfenem (15-Methyl-PGF2α), to Induce Luteolysis and Oestrus in Heifers

Different doses of 15-methyl-PGF2 alpha (0.125-10 mg) were used to induce luteolysis and oestrus in 7 heifers with 28 treatments on day 8-12 of the oestrous cycle. Twenty-three out of 28 treatments gave the desired response and the animals showed signs of oestrus within 5 days post-injection. The doses of 0.25-10 mg can be used to induce luteolysis and oestrus. The dose of 0.125 mg was not effective to induce luteolysis and only 1 out of 4 treatments responded. When higher doses were given (1-10 mg), progesterone levels decreased more rapidly and reached 1 nmol/l 16.2 h earlier than in animals which responded to doses less than 1 mg. The minimum effective dose was considered to be 0.25 mg. Clinical signs of oestrus, regression of corpus luteum and variation in the interval to oestrus were similar as for PGF2 alpha or its other analogues. By measurement of the main circulating prostaglandin F2 alpha metabolite, it was found that an endogenous PGF2 alpha release occurred 1-3 days post-injection of 15-methyl-PGF2 alpha. Furthermore in cases of post-oestrous bleedings an endogenous PGF2 alpha release was also seen concomitantly with the bleeding. This prostaglandin analogue seems to be useful for farm management and can be an alternative to other PGF2 alpha analogues.

Activity of Phospholipase C and Release of Prostaglandin F2α by Endometrial Tissue from Ovariectomized Ewes Receiving Progesterone and Estradiol1

Progesterone and estradiol interact to regulate secretion of prostaglandin (PG) F2 alpha from the ovine endometrium in response to oxytocin. Two experiments were conducted to determine if these effects were due to changes in activity of phospholipase C or in the second messenger responsive pathways that regulate production of PGF2 alpha. In both experiments, ovariectomized ewes were assigned to one of four treatment groups (control, estradiol, progesterone, progesterone and estradiol). Steroids were administered, in vivo, to mimic the changes that occur during the estrous cycle. On Day 16 of steroid treatment, endometrial tissue was collected and incubated, in vitro, to measure activity of phospholipase C and release of PGF2 alpha. Treatment with progesterone, in vivo, enhanced basal and oxytocin-induced activity of phospholipase C and release of PGF2 alpha, in vitro. Estradiol suppressed oxytocin-induced activity of phospholipase C, both in the presence and absence of progesterone. In contrast to its effects on phospholipase C, estradiol inhibited basal and oxytocin-induced release of PGF2 alpha when administered alone, but not when administered with progesterone. Steroids had similar effects on the release of PGF2 alpha induced by phorbol 12-myristate 13-acetate and A23187. It was concluded that progesterone and estradiol regulate endometrial release of PGF2 alpha by affecting both the activity of phospholipase C and its associated second messenger responsive pathways that may regulate production of PGF2 alpha.

Effect of (2-benzoylethyl)trimethylammonium and vesamicol on acetylcholine and prostaglandin release from human placental explants

Human placental explants were incubated in the presence of physostigmine (3.08 microM), and release of acetylcholine (ACh) and prostaglandin (PG) were measured in the fourth hour by bioassay and radioimmunoassay, respectively. The choline acetyltransferase inhibitor (2-benzoylethyl)trimethylammonium (100 microM, n = 6) significantly reduced ACh release by 36 +/- 6%, PGE2 release by 23 +/- 8% and PGF2 alpha release by 29 +/- 10%. The inhibitor of vesicular acetylcholine storage, vesamicol (100 microM, n = 7), significantly reduced ACh release by 22 +/- 4%, PGE2 release by 46 +/- 13% and PGF2 alpha release by 32 +/- 9%. In the absence of physostigmine, ACh release was reduced by 89 +/- 2%, whereas PG release did not change compared with that in the presence of physostigmine. The presence of atropine (14.4 microM) did not affect PG release. These results suggest that if there is a relationship between human placental production of ACh and PGs, it does not appear to depend on muscarinic receptor activation or the activity of placental cholinesterase.

Release of prostaglandins from bone and muscle after femoral osteotomy in rats

In rats after nonstabilized femoral osteotomies, the changes in the release of prostaglandins (PGs) during bone healing (from bone and surrounding muscle tissue) were determined for PGE2, PGF2 alpha, 6-keto-PGF1 alpha, and thromboxane B2. A unilateral osteotomy, with contralateral soft-tissue dissection, was performed. After 4 or 10 days, the rats were killed and soft tissue and femoral bone were incubated, and the release of PGs was measured with specific radioimmunoassays. The release of PGs from rat femurs without previous surgery and from the sham-operated on side did not differ after 180 minutes' incubation. The release of PGE2, 6-keto-PGF1 alpha, and thromboxane-B2 from the osteotomy site was increased for bone on Day 4 and for muscle on Day 10 when compared with the controls. The release of PGF2 alpha from bone and muscle was about the same on both days, but increased as compared with the controls on Day 10 for bone. On Day 10, the other PGs for muscle and bone tissue were decreased as compared with Day 4. The most pronounced release of PGs occurred during the early healing phase after osteotomy; as early as 10 days after surgery, most of the PGs were not increased when compared with the sham-operated on side.

The placenta, prostaglandins and parturition: a review

It is proposed that in sheep, during the last third of gestation, a progressive increase in the production of prostaglandin E2 (PGE2) by the fetal trophoblast activates the fetal hypothalamic-pituitary-adrenal axis leading to an increase in fetal cortisol concentrations. High cortisol levels increase placental 17 alpha-hydroxylase activity causing a decrease in maternal progesterone concentrations and an increase in oestrogen concentrations. The increase in the E/P ratio results in an increase in PGF2 alpha release from the maternal placenta, increased uterine activity and parturition. The increased production of PGE2 by the placenta has been linked to the rapid increase in the growth of the fetus from day 110 of gestation onwards. It is speculated that the growth pattern of the fetus represents a genetically programmed 'clock' which acts by stimulating placental PGE2 production leading to maturation of key organ systems in the fetus and finally parturition.

Aspirin-Sensitive Asthma: Significance of the Cyclooxygenase-Inhibiting and Protein-Binding Properties of Analgesic Drugs

The in vitro release of endogenous and exogenous PgF2 alpha from plasma and serum proteins by aspirin and other analgesic drugs has been studied by RIA and equilibrium-dialysis techniques, respectively. Before aspirin addition, the mean plasma level of PgF2 alpha measured by RIA was significantly lower in aspirin-sensitive asthma (ASA) patients (11.3 +/- 6.5 pg/ml; n = 8) than in aspirin-tolerant asthma (ATA) patients (25.0 +/- 11.4 pg/ml; n = 21). After aspirin addition (50 micrograms/ml) the mean PgF2 alpha level detected in plasma by RIA was higher in ASA patients (97.6 +/- 5.5 pg/ml) than in ATA patients (66.9 +/- 4.5). The binding of [3H]PgF2 alpha to serum protein was significantly inhibited by NSAIDs but not by paracetamol (0.2-1.0 mM). These results implicate PgF2 alpha and the protein-binding property of analgesic drugs in the pathogenesis of aspirin-sensitive asthma.

Platelet-activating factor stimulates eicosanoid production in cultured feline tracheal explants.

Eicosanoids have been shown to be major mediators of airway inflammation. Platelet-activating factor (PAF), a potent bronchoconstrictor and stimulator of respiratory mucous secretion, may mediate some of its effects via eicosanoid production. To explore eicosanoid generation by cultured feline tracheal explants, eicosanoids were measured following PAF stimulation. After labeling the explants with [3H]arachidonic acid, supernatant from control and PAF treated explants was fractionated by reverse phase high-performance liquid chromatography (HPLC). The resulting elution pattern suggested the release of arachidonic acid (AA), 15-hydroxyeicosatetraenoic acid (HETE), leukotriene (LT)B4, C4, prostaglandin (PG) D2/E2/F2 alpha, and 6-keto-PGF1 alpha. Radioimmunoassay (RIA) following HPLC resolution confirmed that PAF induced a significantly increased release of peptido-leukotrienes, PGD2, PGE2, PGF2 alpha, LTB4, and 5-HETE, as well as thromboxane (TX) B2. The most remarkable increase was LTC4/D4/E4 (15 x control) and PGD2 (4 x control). The PAF antagonist Ro 19-3704 had an inhibitory effect on the PAF-stimulated release of peptido-leukotrienes. We conclude that PAF stimulates the production of a variety of lipoxygenase and cyclooxygenase pathway metabolites in feline airways.

Acrolein stimulates eicosanoid release from bovine airway epithelial cells

Injury to the airway mucosa after exposure to environmental irritants is associated with pulmonary inflammation and bronchial hyperresponsiveness. To better understand the relationships between mediator release and airway epithelial cell injury during irritant exposures, we studied the effects of acrolein, a low-molecular-weight aldehyde found in cigarette smoke, on arachidonic acid metabolism in cultured bovine tracheal epithelial cells. Confluent airway epithelial cell monolayers, prelabeled with [3H]arachidonic acid, released significant levels of 3H activity when exposed (20 min) to 100 microM acrolein. [3H]arachidonic acid products were resolved using reverse-phase high-performance liquid chromatography. Under control conditions the released 3H activity coeluted predominantly with the cyclooxygenase product, prostaglandin (PG) E2. After exposure to acrolein, significant "peaks" in 3H activity coeluted with the lipoxygenase products 12-hydroxyeicosatetraenoic acid (HETE) and 15-HETE, as well as with PGE2, PGF2 alpha, and 6-keto-PGF1 alpha. Dose-response relationships for acrolein-induced release of immunoreactive PGF2 alpha and PGE2 from unlabeled epithelial monolayers demonstrated 30 microM acrolein as the threshold dose, with 100 microM acrolein inducing nearly a fivefold increase in both PGF2 alpha and PGE2. Cellular viability after exposure to 100 microM acrolein, determined by released lactate dehydrogenase activity, was not affected until exposure periods were greater than or equal to 2 h. These results implicate the airway epithelial cell as a possible source of eicosanoids after exposure to acrolein.

Regulation of Prostaglandin Biosynthesis with Flunixin Meglumine in the Bovine Species

Flunixin meglumine (FM) was injected in 2 oophorectomized cows to follow changes in basal levels of the main circulating prostaglandin (PG)F2 alpha metabolite, 15-ketodihydro-PGF2 alpha. A rapid decrease in the levels was seen after FM and the effect was lasting for about 6 h. Thus, to obtain a full effect of the drug on prostaglandin synthesis it is recommended that FM should be injected 4 times daily. This concept was further studied in 3 cycling heifers which obtained FM 4 times daily from day 15 of the estrous cycle for 7 days (totally 28 injections). During the period of drug administration, prostaglandin metabolite levels were decreased and the expected pulsatile release seen during luteolysis was delayed. The pulsatile release started about one day after cessation of treatment and then luteolysis occurred. Progesterone levels were normal during the FM treatment and dropped concomitantly with the pulsatile release of PGF2 alpha. The levels of progesterone decreased to low levels before the heifers showed signs of estrus and ovulated. The administration of FM causes a situation resembling that seen during early pregnancy and FM can be a useful tool in understanding the mechanism behind maternal recognition of pregnancy.

The effect of inhibitors of prostaglandin formation on contraction of the rat, rabbit and human vas deferens

1. The rat vas deferens releases both PGE2 and PGF2 alpha under basal conditions in vitro but the human vas deferens synthesizes prostaglandins only when arachidonic acid is supplied exogenously. 2. The release of PGE2 and PGF2 alpha is augmented by alpha-adrenoceptor activation or by BaCl2, both of which cause contraction. 3. Release of PGE2 and PGF2 alpha is substantially inhibited by indomethacin 10 micrograms ml-1 which does not affect contraction. 4. Contraction is strongly inhibited by higher concentrations of indomethacin (50-80 micrograms ml-1). 5. It is concluded that the release of PGE2 and PGF2 alpha from the rat and human vas deferens is not correlated with contraction.

In vitro synthesis of prostaglandin E and F2 alpha by pig endometrium in the presence of estradiol, catechol estrogen and ascorbic acid.

These experiments were undertaken to determine the potential for estradiol-17 beta (E2), 2-hydroxyestradiol-17 beta (2-OH-E2) and 4-hydroxyestradiol-17 beta (4-OH-E2) to regulate prostaglandin (PG) E and F2 alpha synthesis by pig endometrium. Endometrium was collected from pigs on d 10 of pregnancy and incubated (15 to 20 mg/well) for three 2-h periods in 2 ml of medium in 24-well culture plates. At the end of each period, the medium was removed and frozen. Later media were thawed and assayed for PGE and PGF2 alpha. During Periods 2 and 3, the medium contained 0, 25, 50, 100 or 150 microM 2-OH-E2 (Exp. 1); 0, 25 or 50 microM 4-OH-E2 (Exp. 2); or 0, 25 or 50 microM E2 (Exp. 3). Each experiment was a factorial with 2-OH-E2, 4-OH-E2 or E2 as one main effect and 0 or 1 mM ascorbate as a second main effect. Ascorbate decreased (P less than .01) PGE and PGF2 alpha release in all experiments. Two-hydroxyestradiol-17 beta decreased (P less than .01) PGE and PGF2 alpha release into the medium during Periods 2 and 3 in a dose-dependent manner (Exp. 1). In Exp. 2, 4-OH-E2 decreased (P less than .07) endometrial release of PGE and PGF2 alpha in Periods 2 and 3 and increased (P less than .01) the PGE:PGF2 alpha in Period 3. In Exp. 3, E2 decreased release of PGE during Period 3 and PGF2 alpha release during Period 2. The PGE:PGF2 alpha was not altered by E2.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical localization of prostaglandin synthase in the ovine uterus during the oestrous cycle and in early pregnancy

Prostaglandin (PG) synthase has been localized by immunocytochemistry within the ovine uterus throughout the oestrous cycle and in early pregnancy. On Day 4 of the cycle, PG synthase was located primarily in the stromal cells in caruncular and intercaruncular tissue with little staining in the epithelium. On Days 14 through to 16, the most intense staining was in the luminal epithelial cells (caruncular and intercaruncular) and in epithelial cells of glands close to the uterine lumen. PG synthase was also located in the intercaruncular stromal cells, particularly close to the myometrium. Staining for the enzyme on Day 10 was intermediate between that of Day 4 and Day 14. On Day 15 of pregnancy, the pattern of staining was identical to that on Day 15 of the cycle, with no detectable difference in intensity. When endometrial cells (cycle, Day 14) were cultured with and without ovine trophoblast protein-1 (3 ng mL-1) in vitro, release of PGE and PGF2 alpha was attenuated (54% and 47% of control respectively) but no differences were observed in the intensity of staining for PG synthase in the cells. These results demonstrate marked cyclical changes in the endometrial cell types producing PGs, suggesting differential regulation of PG synthase. In addition, it appears that conceptus-induced changes in PGF2 alpha release do not occur via changes in the concentration or cellular localization of PG synthase, but rather that the activity of the enzyme is modified.

Embryo-derived platelet activating factor: interactions with the arachidonic acid cascade and the establishment and maintenance of pregnancy

Two classes of potent lipid mediators are produced by the mouse and human pre-embryo: platelet activating factor (PAF) and prostaglandins (PGs). This paper reviews the evidence for their production by the pre-embryo and for their role in embryo development and the successful establishment of pregnancy. The biosynthesis of PAF and arachidonic acid may be linked, the synthesis of PAF resulting in the generation of arachidonic acid with its subsequent conversion to prostaglandins. Pharmacological inhibitor studies show that a major site of action of PAF is the embryo itself, acting as an embryonic autocrine growth factor, whereas PGs appear to act primarily on maternal tissues although they do modulate some aspects of early embryo metabolism. It is the maternal tissues that are the primary source of PG production in early pregnancy. Maternal PGs have a variety of functions including involvement in the proinflammatory response of early pregnancy and the control of corpus luteum function. In the ewe, pregnancy is associated with an attenuation of oxytocin-induced production of the luteolysin, prostaglandin F2 alpha (PGF2 alpha). PAF can mimic the effect of pregnancy, preventing the release of PGF2 alpha in response to exogenous oxytocin and, when administered into the uterine lumen, extending the life span of the corpus luteum. Thus, embryo-derived PAF appears to have an essential role in the establishment of pregnancy by acting as an autocrine growth factor for the embryo and by exerting a variety of effects on maternal physiology, including modulating maternal prostaglandin secretion and action.