Effects of gestational age on prostaglandin EP receptor expression and functional involvement during in vitro contraction of the guinea pig uterus

Prostaglandin E(2) (PGE(2)) exerts diverse biological effects through four G-protein-coupled cell surface receptor subtypes, EP1-4. This study's objective was to characterize EP1-4 receptor mRNA expression within pregnant guinea pig myometrium during early implantation stage (gestation day [GD] 6) and late stage gestation (GD 50) and evaluate in vitro contractile activity of receptor subtype selective agonists. Using RT-PCR, qualitative gene expression patterns of EP2, EP3, and EP4 mRNA were detected in the myometrium and remained unchanged between the gestational ages. EP1 mRNA remained undetected in pregnant tissue. In vitro contractile activity was evaluated in GD 6 and GD 50 myometrium using vehicle and EP agonists PGE(2), 17-phenyl trinor PGE(2), sulprostone, misoprostol, and CP-533,536. All spasmogens in pregnant myometrium were EP1/EP3 selective agonists, though likely acting via EP3 receptors in this test model. CP-533,536--a highly selective EP2 receptor agonist--and the vehicle failed to induce myometrial contraction at both gestational ages.     

ChTX induces oscillatory contraction in guinea pig trachea: role of cyclooxygenase-2 and PGE2

We examined the possible role of cyclooxygenase (COX) in charybdotoxin (ChTX)-induced oscillatory contraction in guinea pig trachea. Involvement of prostaglandin E(2) (PGE(2)) in ChTX-induced oscillatory contraction was also investigated. ChTX (100 nM) induced oscillatory contraction in guinea pig trachea. The mean oscillatory frequency induced by ChTX was 10.7 +/- 0.8 counts/h. Maximum and minimum tensions within ChTX-induced oscillatory contractions were 68.4 +/- 1.8 and 14.3 +/- 1.7% compared with K(+) (72.7 mM) contractions. ChTX-induced oscillatory contraction was completely inhibited by indomethacin, a nonselective COX inhibitor. Valeryl salicylate, a selective COX-1 inhibitor, did not significantly inhibit this contraction, whereas N-(2-cyclohexyloxy-4-nitro-phenyl)-methanesulfonamide, a selective COX-2 inhibitor, abolished this contraction. Exogenously applied arachidonic acid enhanced ChTX-induced oscillatory contraction. SC-51322, a selective PGE receptor subtype EP(1) antagonist, significantly inhibited ChTX-induced oscillatory contraction. Exogenously applied PGE(2) induced only a slight phasic contraction in guinea pig trachea, but PGE(2) induced strong oscillatory contraction after pretreatment with indomethacin and ChTX. Moreover, ChTX time-dependently stimulated PGE(2) generation. These results suggest that ChTX specifically activates COX-2 and stimulates PGE(2) production and that ChTX-induced oscillatory contraction in guinea pig trachea is mediated by activation of EP(1) receptor.     

Prostaglandin E(2)-induced interleukin-6 release by a human airway epithelial cell line

Human airway epithelial cell release of interleukin (IL)-6 in response to lipid mediators was studied in an airway cell line (BEAS-2B). Prostaglandin (PG) E(2) (10(-7) M) treatment caused an increase in IL-6 release at 2, 4, 8, and 24 h. IL-6 release into the culture medium at 24 h was 3,396 +/- 306 vs. 1,051 +/- 154 pg/ml (PGE(2)-treated cells vs. control cells). PGE(2) (10(-7) to 10(-10) M) induced a dose-related increase in IL-6 release at 24 h. PGF(2 alpha) (10(-6) M) treatment caused a similar effect to that of PGE(2) (10(-7) M). PGE(2) analogs with relative selectivity for PGE(2) receptor subtypes were studied. Sulprostone, a selective agonist for the EP-3 receptor subtype had no effect on IL-6 release. 11-Deoxy-16,16-dimethyl-PGE(2), an EP-2/4 agonist, and 17-phenyl trinor PGE(2), an agonist selective for the EP-1 > EP-3 receptor subtype (10(-6) to 10(-8) M), caused dose-dependent increases in IL-6 release. 8-Bromo-cAMP treatment resulted in dose-related increases in IL-6 release. RT-PCR of BEAS-2B cell mRNA demonstrated mRNA for EP-1, EP-2, and EP-4 receptors. After PGE(2) treatment, increases in IL-6 mRNA were noted at 4 and 18 h. Therefore, PGE(2) increases airway epithelial cell IL-6 production and release.     

Progesterone Receptor Expression Declines in the Guinea Pig Uterus during Functional Progesterone Withdrawal and in Response to Prostaglandins

Progesterone withdrawal is essential for parturition, but the mechanism of this pivotal hormonal change is unclear in women and other mammals that give birth without a pre-labor drop in maternal progesterone levels. One possibility suggested by uterine tissue analyses and cell culture models is that progesterone receptor levels change at term decreasing the progesterone responsiveness of the myometrium, which causes progesterone withdrawal at the functional level and results in estrogen dominance enhancing uterine contractility. In this investigation we have explored whether receptor mediated functional progesterone withdrawal occurs during late pregnancy and labor in vivo. We have also determined whether prostaglandins that induce labor cause functional progesterone withdrawal by altering myometrial progesterone receptor expression. Pregnant guinea pigs were used, since this animal loses progesterone responsiveness at term and gives birth in the presence of high maternal progesterone level similarly to primates. We found that progesterone receptor mRNA and protein A and B expression decreased in the guinea pig uterus during the last third of gestation and in labor. Prostaglandin administration reduced while prostaglandin synthesis inhibitor treatment increased progesterone receptor A protein abundance. Estrogen receptor-1 protein levels remained unchanged during late gestation, in labor and after prostaglandin or prostaglandin synthesis inhibitor administration. Steroid receptor levels were higher in the non-pregnant than in the pregnant uterine horns. We conclude that the decreasing expression of both progesterone receptors A and B is a physiological mechanism of functional progesterone withdrawal in the guinea pig during late pregnancy and in labor. Further, prostaglandins administered exogenously or produced endogenously stimulate labor in part by suppressing uterine progesterone receptor A expression, which may cause functional progesterone withdrawal, promote estrogen dominance and foster myometrial contractions.     

Biological activity and anti-prostaglandin effects of prostaglandin analogue, ent-11-epi-15-epi PGE2 methyl ester

The biological activity and anti-prostaglandin property of the prostaglandin analogue, ent-11-epi-15-epi PGE2 methyl ester, were studied on isolated guinea pig ileum. Ent-11-epi-15-epi PGE2 methyl ester contracted guinea pig ileum and produced a concentration-response curve parallel to that of PGE2. However, the former exhibited a lower maximal effect than PGE2. At concentrations greater than 10(-6)M, ent-11-epi-15-epi PGE2 methyl ester selectively antagonized contractile actions of PGE2 and PGE2 alpha without affecting contractions induced by acetylcholine. These observations suggest that the PG analogue acted like a competitive antagonist to PGE2 and PGF2 alpha on guinea pig ileum in vitro.     

Studies on the mechanism of action of antifertile PG in animal models

Antifertile effects of PGF2 alpha, PGE2, PGE1, sulprostone and other PGs were evaluated in different pregnancy models in rats, guinea pigs and rhesus monkeys and the underlying mechanisms of action were investigated. Quantitative and qualitative species differences and pregnancy stage dependency were recorded. Basic regulatory differences of the pregnant uterus seem to exist in these species. In early pregnant rats, abortifacient effects were based on luteolytic effects, independent of the PG used. The myometrium was found to be refractory to the injected PG as long as serum progesterone levels were kept high. By contrast, in guinea pigs after the luteoplacental shift of progesterone secretion (tested after day 40 p.c.) and in rhesus monkeys even before this shift (tested day 20 p.c.) abortifacient effects were found to be exerted by direct stimulation of the myometrium. Uterine stimulation was possible in the presence of any level of serum progesterone. The induction of uterine PG synthesis was probably of importance supporting the expulsion. The role of obvious tissue damage within the conceptus remained uncertain. In contrast to rats there seems to be a pre-existing PG-sensitivity of the pregnant myometrium in guinea pigs and primates. In guinea pigs sensitivity slightly increased for E- but not for F-type PG toward term. Oxytocin sensitivity was found to increase by a factor of more than 100 between days 23-63 of pregnancy. Time dependent changes in uterine receptivity to PG and oxytocin may be considered as a regulatory principle which might permit parturition to occur in the presence of progesterone as an evolutionary adaptation to a placental progesterone secretion which cannot be abolished. It was concluded that in the presence of already established gradual uterine responsiveness to PG (and Oxytocin) during gestation efficient blocking mechanisms for uterine PG-formation must exist in order to explain uterine quiescence. Almost complete resistance of pregnancy to oestrogen which exists in humans, monkeys and guinea pigs was considered as to be pharmacological evidence of such a mechanism. The principles of endocrine control of the myometrium and its pharmacology seem similar in guinea pig and primate pregnancy. The guinea pig might therefore provide a relevant model to study potential drug effects on the regulatory balance of the pregnant uterus and also to achieve a better understanding of human uterine physiology.     

Regional expression of prostaglandin E2 and F2alpha receptors in human myometrium, amnion, and choriodecidua with advancing gestation and labor

The change from uterine quiescence to enhanced contractile activity may be due to the differential expression of prostaglandin receptors within the myometrium and fetal membranes, in a temporal and topographically distinct manner. To address this question, we determined the localization and expression of the PGE2 receptor subtypes (PTGER1-4) and the PGF2alpha receptor (PTGFR) in paired upper and lower segment myometrium, amnion, and choriodecidual samples throughout human pregnancy, with and without labor. All receptor subtypes were found throughout the muscle layers in both the upper and lower uterine segments, colocalizing with alpha smooth muscle actin. A change in intracellular localization was observed at term labor, where PTGER1 and PTGER4 were predominately associated with the nucleus. Minimal changes in the expression of the PGE2 and PGF2alpha receptor subtypes were observed with gestational age, labor, or between the upper and lower myometrial segments. Receptor expression in maternal and fetal tissues differed between the receptor subtypes; PTGER1 and PTGER4 were predominately expressed in the fetal membranes, PTGER2 was greatest in the myometrium, whereas PTGER3 and PTGFR were similarly expressed in the myometrium and fetal membranes. Myometrial activation through the prostaglandin receptors is perhaps more subtle and may be mediated by a balance between one or several of the prostaglandin receptor subtypes together with other known contraction associated proteins. Lack of coordination in receptor expression between the myometrium and fetal membranes may indicate different regulatory mechanisms between these tissues, or it may suggest a function for these receptors in the amnion and choriodecidua that is independent of that seen in the myometrium.     

Prostaglandin E receptor subtypes involved in stimulation of gastroduodenal bicarbonate secretion in rats and mice.

We investigated prostaglandin E (EP) receptor subtypes responsible for the HCO3- stimulatory action of prostaglandin E2 (PGE2) in the gastroduodental mucosa, by examining the effects of various prostanoids with subtype specific EP receptor agonists in rats and those of PGE2 in knockout mice lacking EP1 or EP3 receptors. In rats, gastric HCO3- secretion was stimulated by i.v. administration of PGE2, 17-phenyl PGE2 the selective EP1 agonist as well as sulprostone the EP1 and EP3 agonist, but was not affected by other EP agonists such as butaprost the selective EP2 agonist, ONO-NT-012 the selective EP3 agonist or 11-deoxy PGE1 the EP3 and EP4 agonist. In contrast, the HCO3- secretion in rat duodenums was stimulated by PGE2, sulprostone, ONO-NT-012 as well as 11-deoxy PGE1 but not affected by either 17-phenyl PGE2 or butaprost. The HCO stimulatory effect of sulprostone in the stomach was significantly inhibited by ONO-AE-829, the selective EP1 antagonist. On the other hand, PGE2 applied topically to the mucosa for 10 min caused a dose-dependent increase of HCO3- secretion in both the stomach and duodenum of wild-type mice. The HCO3- stimulatory action of PGE2 in the stomach was also observed dose-dependently in knockout mice lacking EP3-receptors but was absent in EP1-receptor knockout mice, while the stimulatory effect in the duodenum was observed in EP1-receptor knockout mice, similar to wild-type animals, but not in knockout mice lacking EP3-receptors. These results indicate that PGE2 stimulates HCO3- secretion via different EP receptor subtypes in the stomach and duodenum; the former is mediated by EP1-receptors, while the latter mediated by EP3-receptors.     

Discovery of CP-533536: An EP2 receptor selective prostaglandin E2 (PGE2) agonist that induces local bone formation

Sulfonamides, exemplified by 3a, were identified as highly selective EP₂ agonists. Lead optimization led to the identification of CP-533536, 7f, a potent and selective EP₂ agonist. CP-533536 demonstrated the ability to heal fractures when administered locally as a single dose in rat models of fracture healing.     

Prostaglandin E2 inhibits eosinophil trafficking through E-prostanoid 2 receptors

The accumulation of eosinophils in lung tissue is a hallmark of asthma, and it is believed that eosinophils play a crucial pathogenic role in allergic inflammation. Prostaglandin (PG) E(2) exerts anti-inflammatory and bronchoprotective mechanisms in asthma, but the underlying mechanisms have remained unclear. In this study we show that PGE(2) potently inhibits the chemotaxis of purified human eosinophils toward eotaxin, PGD(2), and C5a. Activated monocytes similarly attenuated eosinophil migration, and this was reversed after pretreatment of the monocytes with a cyclooxygenase inhibitor. The selective E-prostanoid (EP) 2 receptor agonist butaprost mimicked the inhibitory effect of PGE(2) on eosinophil migration, whereas an EP2 antagonist completely prevented this effect. Butaprost, and also PGE(2), inhibited the C5a-induced degranulation of eosinophils. Moreover, selective kinase inhibitors revealed that the inhibitory effect of PGE(2) on eosinophil migration depended upon activation of PI3K and protein kinase C, but not cAMP. In animal models, the EP2 agonist butaprost inhibited the rapid mobilization of eosinophils from bone marrow of the in situ perfused guinea pig hind limb and prevented the allergen-induced bronchial accumulation of eosinophils in OVA-sensitized mice. Immunostaining showed that human eosinophils express EP2 receptors and that EP2 receptor expression in the murine lungs is prominent in airway epithelium and, after allergen challenge, in peribronchial infiltrating leukocytes. In summary, these data show that EP2 receptor agonists potently inhibit eosinophil trafficking and activation and might hence be a useful therapeutic option in eosinophilic diseases.     

Retrograde and local destination transfer of uterine prostaglandin E2 in early pregnant sow and its physiological consequences

The local destination transfer of prostaglandin E2 (PGE2) from the uterine lymph to arterial blood supplying the ovary and its retrograde transfer to arterial blood supplying the uterine horn and the effect of additional delivery of PGE2 into the ovary on the secretion of steroid hormones was studied in early pregnant gilts. The injection of PGE2 under the perimetrium caused an increase (P<0.001) in PGE2 concentration in both uterine venous effluent and ovarian and uterine arterial blood. The infusion of PGE2 into the ovarian artery increased the concentration of progesterone in ovarian venous blood on day 13 of pregnancy during (P<0.05) and after (P<0.001) infusion, and on day 14 of pregnancy after infusion (P<0.01). In conclusion, local destination transfer of PGE2 from uterine lymph and venous blood to the ovary may affect luteal function, and retrograde transfer of PGE2 to the arterial blood supplying the uterus may contribute to the prevention of regressive changes of the endometrium in early pregnant gilts.     

Hormonal control of implantation in guinea pigs

In the guinea pig, for which implantation is supposedly progesterone-dependent, actual hormonal requirements were assessed by measuring the levels of circulating estradiol and progesterone and correlating them with their content in the ovaries and uterus, and uterine concentrations of their receptors prior to, during, and immediately after implantation. Ovarian and uterine content and plasma levels of estradiol and progesterone, as well as uterine cytosolic receptors of these two hormones, were high at proestrus. Up to day 3 of pregnancy, estradiol remained high in peripheral plasma, ovarian and uterine tissues, but reached low levels at the time of implantation. The levels of progesterone showed a gradual increase in plasma and ovaries till the time of implantation, with the embryonic site of the uterus accumulating more of progesterone compared to estradiol. As pregnancy progressed, a gradual translocation of cytosolic to nuclear receptors occurred, both with estradiol and progesterone receptors. Comparing the receptor values for estradiol at each uterine site showed no significant alterations between embryonic and interembryonic cytosolic receptors. While significantly high levels of nuclear estradiol receptor were found at the inter-embryonic site on day 9 of pregnancy, the cytosolic and nuclear progesterone receptor concentrations were greater at the embryonic site on the same day. These findings demonstrated that the uterus is adequately exposed to estradiol and progesterone prior to ovulation and again in early pregnancy (day 1-3), thus facilitating implantation in the guinea pig (on days 7-8).     

Changes in phospholipase A2 in myometrium of the guinea pig uterus during pregnancy.

Phospholipase A2 activity has been measured in membrane and cytosolic fractions from non-pregnant and pregnant guinea pig myometrium has been studied. Enzyme activity was measured with 1-stearoyl-2- [3H]arachidonoyl-phosphatidylcholine exhibiting Michaelis-Menton kinetics with Km of 83.8 +/- 21.6 and 53.2 +/- 14.1 for membrane and cytosolic enzymes respectively. Fractionation of the myometrium from non-pregnant guinea pigs suggested that 35% of the activity was membrane associated compared with 20% (P < 0.01) in tissue from pregnant animals. In the presence of 1 mM calcium total activity rose from 3.03 +/- 0.41 to 1737 +/- 368 nmol/h per uterus between non-pregnant and late pregnancy. Calcium activated the membrane enzyme, but the effect was greater late in pregnancy with almost a 6-fold increase in activity at 1 mM calcium compared with a doubling in membrane from non-pregnant guinea pigs. The K0.5 for calcium activation was about 150 microM. Immunoblotting with anti-human-110 KDa phospholipase A2 showed in guinea pig uterus a 34 KDa form of the enzyme that, consistent with changes in activity, showed a fifteen-fold increase in quantity between non-pregnant and late pregnancy. The data are consistent with dramatic increases in the capacity for arachidonic acid release and prostaglandin production in the guinea pig myometrium late in pregnancy.     

Prostaglandin E2 synthesis elicited by adrenergic stimuli in guinea pig trachea is mediated primarily via activation of beta 2 adrenergic receptors.

Prostaglandin (PG) E2 synthesis elicited by adrenergic agonists in the guinea pig trachea has been shown to be mediated via activation of beta-adrenergic receptors. The purpose of this study was to examine arachidonic acid (AA) metabolism and to characterize the subtype of beta receptor involved in PG synthesis. [14C]AA was incubated with guinea pig tracheal rings, and the radiolabelled products were extracted from the medium. Thin layer chromatographic analysis and radioimmunoassay of the extract showed that [14C]AA was incorporated into guinea pig tracheal rings and metabolized mainly into radiolabeled and immunoreactive PGE2 (iPGE2) and smaller amounts into PGF2 alpha. Trace amounts of PGD2, TxB2 and 6-keto-PGF1 alpha but not LTB4 or LTC4 were detected by enzyme immunoassay. Incubation of guinea pig tracheal rings for 10 min with isoproterenol or salbutamol resulted in a significant increase in PGE2 synthesis (optimum concentration 0.1 microM for both compounds). In contrast, dobutamine, BRL 37344, BRL 28410, norepinephrine, phenylephrine, and xylazine (up to 1 microM) did not significantly increase PGE2 production. Isoproterenol-induced iPGE2 production was inhibited by the selective beta 2 receptor antagonist butoxamine (0.1-1.0 microM) and somewhat reduced by the beta 1 receptor antagonist practolol (1 microM). The increase in PGE2 synthesis was diminished with increasing concentrations of isoproterenol (0.5-5.0 microM) or salbutamol (0.5-1.0 microM); but it was reversed by pretreatment of tracheal rings with the protein synthesis inhibitors cycloheximide (0.9 microM) and actinomycin D (2 microM) but not by phenylisopropyl adenosine (0.1-1.0 microM), an inhibitor of adenylyl cyclase. These data suggest that isoproterenol-induced iPGE2 synthesis is primarily via activation of a beta 2 adrenergic receptor. Failure to enhance iPGE2 synthesis by a high concentration of isoproterenol is likely to be due to an induction of new inhibitory protein synthesis.     

Effect of polyphloretin phosphate on the response of non-gravid rat uterus to folkloric and standard oxytocics in vitro

Polyphloretin phosphate (PPP) has been reported by previous workers to be a specific antagonist of prostaglandin (PGE(1), PGE(2) & PGF(2 alpha))-induced contractions of isolated jird colon, gerbil colon, guinea pig ileum, and rabbit jejunum. In the present study, we examined the effect of PPP on uterotonic activities of crude papaya latex (a folkloric oxytocic), PGF(2 alpha), oxytocin, acetylcholine, and 5-hydroxytryptamine (standard oxytocics) on non-gravid, oestrogen-primed (50 microg/kg) rats in vitro. The effect of PPP on the oxytocics was evaluated qualitatively by incubating the tissues in PPP (25 - 400 microg/ml) for 20 min prior to the addition of a constant concentration of each oxytocic. PPP concentration dependently inhibited the contractile response of the uterine muscles to all the oxytocics. The inhibition was reversible after washing out the drugs. Results of the present study suggest that PPP is a non-specific and reversible antagonist of the response of non-gravid rat uterine smooth muscle to oxytocics in vitro. The specificity of PPP as a prostaglandin antagonist could therefore be species/tissue dependent.     

Adenosine (A2) antagonist inhibits induction of long-term potentiation of evoked synaptic potentials but not of the population spike in hippocampal CA1 neurons.

The effects of adenosine A2 receptor antagonist (CP-66713) on long-term potentiation were studied using guinea pig hippocampal slices in a perfusion system. Tetanic stimulation of Schaffer collateral input which was applied during perfusion of CP-66713 (10 microM), did not induce long-term potentiation but rather long-term depression of evoked synaptic potentials (field EPSP), but induced long-term potentiation of the population spike in CA1 neurons. Thus, adenosine derivatives which accumulate in the synaptic cleft during the tetanic stimulation may be involved in induction of the long-term potentiation via A2 receptors at the synapse. The clear discrimination between long-term depression of the field EPSP and long-term potentiation of the population spike suggests EPSP-spike potentiation at the postsynaptic sites.     

Interleukin-1beta induces interleukin-6 production through the production of prostaglandin E(2) in human osteoblasts, MG-63 cells.

This study was conducted to investigate the mechanism of interleukin-1beta (IL-1beta)-induced IL-6 production in human osteoblasts (MG-63 cells). Stimulation with IL-1beta resulted in the production of IL-6 and prostaglandin E(2) (PGE(2)). IL-6 production gradually increased and peaked 96 h after stimulation. IL-6 mRNA was detected between 4 and 72 h after IL-1beta stimulation. The patterns of PGE(2) production and the expression of cyclooxygenase-2 (COX-2) mRNA were biphasic after stimulation. Actinomycin D, cycloheximide, indomethacin, and NS-398 (COX-2 inhibitor) suppressed the production of IL-6 and PGE(2). Anti-PGE(2) antibody markedly reduced the production of IL-6. In addition, stimulation with 17-phenyl-PGE(2), a PGE receptor-1 (EP-1 receptor) agonist, led to the expression of IL-6 mRNA after pretreatment with IL-1beta. These findings indicate that IL-1beta-induced IL-6 production in MG-63 cells involves the following sequence of steps: IL-1beta-induced COX-2 activation, PGE(2) production, and EP-1 receptor signaling prior to IL-6 production.     

Prostaglandin E2 binding site distribution and subtype classification in the rabbit iris-ciliary body.

The distribution and characteristics of specific binding sites for tritium labeled prostaglandin E2 (3H-PGE2) were examined in membrane preparations from rabbit iris-sphincter, iris and ciliary body. The majority of 3H-PGE2 specific binding sites were found in the ciliary body (46%) followed by the iris (37%) and the iris-sphincter muscle (5%). Scatchard analysis of saturable 3H-PGE2 binding sites in the ciliary body indicated a single binding site with a Kd of 2.81 nM and Bmax value of 84 fmoles bound/mg protein. Competition by agonists selective for the EP1, EP2 and EP3 receptor subtypes of the EP (PGE2) prostanoid receptor indicated that the majority of rabbit ciliary body 3H-PGE2 binding sites are of the EP2 subtype. Incomplete displacement of labeled 3H-PGE2 from its binding sites by the EP2 selective agonist 11-deoxy PGE1 suggests the presence of additional EP or non-EP binding sites. There was essentially no binding to EP1 receptor sites as defined by the displacement of 3H-PGE2 by 17-phenyl-trinor PGE2. A weak displacement of 3H-PGE2 by the EP3/EP1 specific agonist, sulprostone, may account for the presence of a small number of EP3 specific binding sites in this tissue. The predominant distribution of PGE2 binding sites in the ciliary body and their identification as EP2 selective, supports recent functional studies where topical application of prostanoids with EP2 but not EP1 or EP3 agonist activity resulted in breakdown of the blood-aqueous barrier.     

The effects on stretching and prostaglandin F2alpha on the contractile and bioelectric activity of the uterus in rat.

The effects of stretching and of prostaglandin F2alpha on spontaneous and induced with local deformation contractile activity of rat uterus were studied. It was found that stretching the uterus up to the length of the decontracted organ in vivo increased the contractile and bioelectric activity. The rise in spontaneous uterine activity was a factor reducing induction of additional contractions. The fall in the level of endogenous prostaglandins in the uterus following administration of indomethacin inhibited the spontaneous contractile activity but was without effect on the contractions induced by local deformation of the myometrium. Prostaglandin F2alpha added to the bath in a concentration of 0.001 ng/ml exerted an inhibitory action on the different tested parameters of the contractile activity. After high doses stimulation of the uterine activity was observed.     

Involvement of lipoxygenase products in myometrial contractions

Studies with an in situ preparation of guinea pig uterus suggest the possible involvement of the lipoxygenase pathway of arachidonic acid (AA) metabolism in myometrial contractions. Female guinea pigs were sensitized to ovalbumin (OA) on day one of their estrous cycle. On day 14, these pigs were anesthetized and the uterus was cannulated for measuring contractions. OA challenge, with histamine antagonism (methapyrilene) resulted in uterine contractions which significantly raised myometrial tonus, presumably due to AA metabolites. Pretreatment with high doses of indomethacin resulted in only 60% inhibition of the OA induced contraction, suggesting the remaining contraction was due to something other than cyclooxygenase products. In the presence of indomethacin and methapyrilene, the addition of AA to increase available substrate caused increased myometrial tone following antigen challenge. This increase in uterine tone was inhibited in a dose dependent fashion by FPL-55712 demonstrating that leukotrienes can contract the uterus and that antigen challenge may provide a means for studying leukotriene involvement in uterine pathophysiology.