Effects of inhibition of prostaglandin synthesis on uterine oxytocin receptor concentration and myometrial gap junction density in parturient rats

The development of oxytocin (OT) sensitivity in the parturient uterus is associated with increases in myometrial OT receptor concentration, gap junction formation, and prostaglandin (PG) production. To investigate whether PGs mediate these responses, we measured OT responsiveness, OT receptor concentrations, and gap junction formations in uteri of Day 19, 20, 21, 22, 23 pregnant and Day 2 postpartum rats. Inhibition of endogenous PG synthesis was produced by infusion of naproxen sodium delivered by an implanted osmotic pump. Naproxen treatment, but not placebo treatment, markedly attenuated in vitro uterine PGE2, PGF2 alpha, and PGI2 releases, suppressed OT responsiveness, and prolonged gestation. The increase of OT receptor concentration that normally occurred on Day 23 term pregnancy was delayed to Day 24. Co-administration of PGF2 alpha reversed the suppressive effects of naproxen. Naproxen treatment did not significantly affect gap junction formations on Day 23 but appeared to delay both the onset and disappearance of gap junction formations. PGF2 alpha co-administration with naproxen also had no apparent effect on gap junction development. The inhibition of OT receptor formation but not gap junction formation on Day 23 in the presence of naproxen indicates that these two events are controlled independently. Furthermore, the failure of naproxen-treated rats to deliver at term suggests that gap junction formation in the absence of an increase in OT receptors is insufficient to initiate labor. It appears that increases in both OT receptor concentrations and gap junction densities may be required for labor.     

Uterine and placental prostaglandins and their modulation of oxytocin sensitivity and contractility in the parturient uterus

The parturient uterus develops a markedly enhanced sensitivity to the uterotonic action of oxytocin (OT). The mechanism leading to this enhanced OT sensitivity is not known. Our previous work suggested that prostaglandins (PGs) may be involved. To define the relationship between OT sensitivity and uterine PG production, we measured uterine sensitivity to OT by a quantitative dose-response procedure in rats on Days 19, 20, 21 and 22 of pregnancy and monitored uterine and placental tissue concentrations of PGF2 alpha and PGE2. In addition, we determined the effects of inhibition of endogenous PG synthesis on OT sensitivity and uterine contractility. We found that both OT sensitivity and spontaneous contractility are positively related to uterine PGF2 alpha production. An abrupt increase in OT sensitivity was observed on Days 21 and 22 of pregnancy. The increase in OT sensitivity was coincidental with the marked increase in PGF2 alpha production in the uterus on Days 21 and 22 of pregnancy. Suppression of in vivo PG synthesis caused a reduction in both spontaneous uterine contractility and OT-induced contractions. Uterine PGE2 concentrations and release were 3-5 times lower than PGF2 alpha. There were no significant fluctuations of uterine PGE2 concentration measured on these last 4 days of gestation. Placental PG levels were also found not to be related to uterine contractility. Placental PGE2 levels were higher than PGF2 alpha and may play a regulatory role in placental perfusion. However, placental PGs did not vary with gestational age.     

The biosynthesis of the 3-series prostaglandins in rat uterus after alpha-linolenic acid feeding: Mass spectroscopy of prostaglandins E and F produced by rat uteri in tissue culture

The abnormal uterine activity associated with dietary n-3 fatty acids may result from competitive inhibition of PG2 production. Uterine synthesis of 2- and 3-series prostaglandins F(PGF) and E(PGE) was studied using mass spectrophotometry in rats fed diets containing predominantly n-3 fatty acid, n-6 fatty acid, or control pelleted diet. Mass spectra of PGF (Me, TMS and Me, TBDMS derivatives) synthesised by uteri of n-3 fed rats were characterised by 8 ions containing the n-3 double bond, and m.i.d. of the 651/653 ions of PGF-Me, TBDMS indicated PGF3 alpha synthesis (44 +/- 8% and 13 +/- 2% of PGF release by uteri incubated + or -5 micrograms/ul calcium ionophore A23187 respectively). In uteri from the control diet group incubated with ionophore, PGF3 alpha ions were detected and PGF 3 alpha represented 9.5 +/- 1.0% of PGF alpha release. Similarly, analysis of PGE from uteri of n-3 fed rats indicated that PGE3 (16 +/- 6% of PGE) was released in the presence of ionophore A23187. Synthesis of 3-series PG by rat uteri was detected after only 3 weeks of n-3 diet. The capacity to synthesise 3-series PG increased at intracellular calcium concentrations which mimicked cell calcium during decidual autolysis at parturition. These experiments suggest that uterine synthesis of 3-series PG is regulated by the specifity of enzymes incorporating fatty acids, rather than by the cyclooxygenase enzyme.     

The effect of the antioxidant, butylated hydroxy anisole, on peroxide-induced and spontaneous activity of the uterus from the pregnant rat

Chorioamnionitis is associated with preterm labor. Leukocytes infiltrate infected tissue and secrete hydrogen peroxide (H2O2) and other reactive oxygen products as part of their bactericidal activity. We have therefore investigated the effect of H2O2 on activity of in vitro uteri from pregnant rats. Uteri from 18-day pregnant rats exposed to H2O2 showed a dose-dependent increase in both contractile activity and production of prostaglandins (PG) E2 and F2 alpha compared to untreated controls. The antioxidant butylated hydroxy anisole (BHA) inhibited the H2O2-induced uterine activity. Furthermore, BHA inhibited contractions and PG production from spontaneously contracting uteri from 21-day pregnant rats. H2O2 increased chemiluminescence of uterine tissue, an index of oxygen or lipid radical formation, whereas BHA inhibited this effect. The BHA inhibition of uterine activity was reversed by addition of PGE2 to the incubation chamber. These data support the hypothesis that reactive oxygen can regulate PG production by the uterus and suggests a role for reactive oxygen in infection-induced labor and perhaps normal term labor as well.     

Effect of oestradiol 17 beta on prostaglandin biosynthesis by the uterus of ovariectomized rat and guinea pig

In vitro prostaglandin biosynthesis by uteri of ovariectomized rats and guinea pigs treated or untreated with oestradiol 17 beta, administered subcutaneously, was measured by R.I.A. of PGF2 alpha and PGE2. Incubations with [1-14C] arachidonic acid were also performed and labelled metabolites were analyzed by TLC. The main metabolite in rats was 6 keto PGF1 alpha and in decreasing order of magnitude, PGF2 alpha and PGE2. In guinea pig PGF2 alpha was the main product. Ovariectomy in rats completely changed the pattern of synthetized prostanoids : PGI2 production was doubled when compared to cycling rats and PGE2 increased 10 fold. PGF2 alpha values were similar to the mean value measured during the cycle. OE2 treatment almost completely inhibited PGI2 synthesis and reduced PGE2 by half. Total PG synthesis in OE2 treated animals was decreased by 5 fold when compared to spayed rats. Endogenous PGF2 alpha synthesis was slightly stimulated. In the guinea pig OE2 treatment of ovariectomized animals increased the total synthesis from 50 per cent. PGF2 alpha was always the main metabolite. In conclusion OE2 regulation of uterine PG synthesis is depending on the animal species and cannot be explained by a unique effect on the cyclooxygenase, but rather by an interplay on the various enzymes of the arachidonic acid cascade.     

The effect of progesterone on oxytocin-stimulated intracellular mobilization of Ca2+ and prostaglandin E2 and F2alpha secretion from porcine myometrial cells

Our past studies have shown that porcine myometrium produce prostaglandins (PG) during luteolysis and early pregnancy and that oxytocin (OT) and its receptor (OTr) support myometrial secretion of prostaglandins E2 and F2alpha (PGE2 and PGF2alpha) during luteolysis. This study investigates the role of intracellular Ca2+ [Ca2+]i as a mediator of OT effects on PG secretion from isolated myometrial cells in the presence or absence of progesterone (P4). Basal [Ca2+]i was similar in myometrial cells from cyclic and pregnant pigs (days 14-16). OT (10(-7)M) increased [Ca2+]i in myometrial cells of cyclic and pregnant pigs, although this effect was delayed in myometrium from pregnant females. After pre-incubation of the myocytes with P4 (10(-5)M) the influence of OT on [Ca2+]i)was delayed during luteolysis and inhibited during pregnancy. Myometrial cells in culture produce more PGE2 than PGF2alpha regardless of reproductive state of the female. OT (10(-7)M) increased PGE2 secretion after 6 and 12 h incubation for the tissue harvested during luteolysis and after 12 h incubation when myometrium from gravid females was used. In the presence of P4 (10(-5)M), the stimulatory effect of OT on PG secretion was diminished. In conclusion: (1) porcine myometrial cells in culture secrete PG preferentially during early pregnancy and produce more PGE2 than PGF2alpha, (2) OT controls myometrial PGF2alpha secretion during luteolysis, (3) release of [Ca2+]i is associated with the influence of OT on PG secretion, and (4) the effects of OT on PG secretion and Ca2+ accumulation are delayed by P4 during luteolysis and completely inhibited by P4 during pregnancy.     

Developmental changes in synthesis of and responsiveness to prostaglandins I2 and E2 in hypoxic lamb lungs

Previous studies have shown that the attenuated hypoxic pulmonary vasoconstriction (HPV) of young newborn lamb lungs was enhanced by cyclooxygenase inhibition. We sought to determine whether this reflected greater synthesis of and (or) responsiveness to dilator prostaglandins (PG). Protocol 1 measured responses to graded hypoxia and perfusate concentrations of 6-keto-PGF1alpha (the stable metabolite of PGI2) and PGE2 in isolated lungs from 1-day- and 1-month-old lambs. Protocol 2 compared dose responses and segmental vascular resistances during infusion of PGI2 and PGE2 in hypoxic, cyclooxygenase-inhibited, lungs from 1- to 2-day-old and 1- to 3-month-old lambs. Lungs of 1-day-old lambs with attenuated responses to 4% O2 had significantly higher perfusate concentrations of 6-keto-PGF1alpha and PGE2, but responses to both PGE2 and the more potent vasodilator, PGI2 did not differ with age. These data support the hypothesis that attenuated HPV in young newborn lamb lungs is due to increased synthesis of dilator PG, particularly PGI2.     

Probable influence of ova and embryo prostaglandins in the differential ovum transport in pregnant and cycling rats.

In this study we explored the possible underlying mechanism(s) of the differential transport of unfertilized and fertilized ova in cycling and pregnant rats. The number of ova recovered from rat oviducts and uterus was not significantly different in estrus, metestrus and diestrus but dropped sharply at proestrus. When estrus rats were injected with indomethacin (10(-6)), a well known inhibitor of cyclooxygenase, delivered into both ovarian bursae, and sacrificed next day at metestrus, the number of ova in the oviduct was significantly smaller (p less than 0.025) than in controls at metestrus. On the other hand, when diestrus rats were injected with PGE1 (10(-6)) delivered into both ovarian bursae, and sacrificed next day at proestrus, no ova were found in the oviducts, and only a few of them were in the uterus. When fertilized ova were recovered from oviducts and uteri at day 4 of pregnancy (corresponding to proestrus of cycling rats) an average of 4 embryos were still found in the oviducts, proving a differential ovum transport between cycling and pregnant rats. In order to establish if there exists any ova or embryo releasing factor responsible for this difference, the prostaglandins released to the incubation medium by ovum or 3-day embryo were measured. Unfertilized ova produced significantly more PGE1 (p less than 0.05) than PGE2 or PGF2 alpha. The same pattern of PG production was observed with incubated embryos, but in this case the amount of PGE1 released was significantly higher (p less than 0.01) that the PGE1 released by unfertilized ova.(ABSTRACT TRUNCATED AT 250 WORDS)     

Physiological involvement of placental endothelin-1 and prostaglandin F2alpha in uteroplacental circulatory disturbance in pregnant rats exposed to heat stress

Several studies suggest that heat stress affects placental functions including uteroplacental circulation, subsequently leading to pregnancy failure and birth weight reduction. To clarify the involvement of endothelin and placental prostaglandin (PG) systems in the uteroplacental circulation during heat stress, we examined the effects of i.v. administration of the endothelin receptor antagonist bosentan and the cyclooxygenase inhibitor indomethacin on uteroplacental blood flow and on placental PGE2 and PGF2alpha levels and their 13,14-dyhydro-15-keto-metabolites (PGEM and PGFM, respectively) in heat-exposed or non-heat-exposed pregnant rats. The administration of bosentan or indomethacin did not change uteroplacental blood flow in non-heat-exposed pregnant rats. In contrast, heat reduced uteroplacental blood flow in pregnant rats, but the reduction was reversed by the administration of bosentan or indomethacin before heat exposure. Heat did not change placental PGE2 or PGEM levels, but in pregnant rats it increased placental PGF2alpha and PGFM levels, which were reversed by bosentan or indomethacin. Our results suggest that the activation of placental endothelin receptor and PGF2alpha systems are involved in the uteroplacental circulatory disturbances produced by heat. PGF2alpha systems activated by heat may be involved in the vasoconstricting effects of endothelin-A and -B receptors during heat exposure.     

A novel enhancing effect of platelet activating factor (PAF) on glucose oxidation in uteri from pregnant rats. Participation of prostaglandins and leukotrienes

The effects of platelet activating factor (PAF) on glucose oxidation in uterine strips isolated from rats in the 4 th and 5 th day of pregnancy, were explored. PAF, at a concentration of 10(-10) and 10(-8) M, augmented significantly the generation of 14CO2 from labelled glucose in uteri from pregnant rats in the 4 th day of pregnancy. When the tissue was obtained from 5 days pregnant rats, the addition of PAF at 10(-8) increased significantly more than PAF at 10(-10) M the metabolism of glucose. On the other hand, PAF at 10(-8) M failed to alter the uterine basal production of 14CO2 from labelled glucose in animals at estrus. BN52021, a specific PAF antagonist employed at 10(-5) M, blocked completely the action of PAF in the pregnant rat uterus. PGE1, PGE2 and PGF2 alpha enhanced significantly the formation of 14CO2 from labelled glucose in uteri from 5 days pregnant rats. Indomethacin, a well known inhibitor of prostaglandin synthesis, did not alter the basal glucose metabolism in uteri from 5 days pregnant rats, but antagonized completely the stimulating action of PAF on 14CO2 production from labelled glucose an effect that was partially reverted by the addition of PGE1, PGE2 or PGF2 alpha (10(-7) M). Furthermore, nordihydroguaiaretic acid (NDHGA), a specific inhibitor of 5-lipoxygenase at 10(-5) M, as well as FPL-55712, an antagonist of leukotrienes (LTs), at the same concentration, blocked the action of PAF on the metabolism of glucose. The action of NDHGA was partially counteracted by the addition of LTC4 at 10(-7) M.(ABSTRACT TRUNCATED AT 250 WORDS)     

Histamine alters prostaglandin output from diestrous rat uteri. Involvement of H2-receptors and 9-keto-reductase

The effects of exogenous histamine (H) on prostaglandin (PG) generation and release in uteri isolated from diestrous rats and the influences of H2-receptors blockers (cimetidine and metiamide) on the output of uterine PGs, were explored. Moreover, the action of H on the uterine 9-keto-reductase, was also studied. Histamine (10(-4) M) failed to alter the basal output of PGE1 but reduced significantly the generation and release of PGE2 and augmented the output of PGF2 alpha. On the other hand, cimetidine (10(-5) M) enhanced the basal release of PGE2 but had no action on the outputs of PGs E1 or F2 alpha. The enhancing effect of H on the production and release of PGF2 alpha was abolished in the presence of cimetidine. Also, the antagonist reversed the influence of H on the output of PGE2. Metiamide, another H2-receptor antagonist, did not alter the basal control generation and release of uterine PGs, but antagonized the augmenting influence of H on PGF2 alpha uterine output, as much as cimetidine did, and prevented the depressive action of H on the release of PGE2 from uteri. Histamine (10(-4) M) significantly stimulated uterine formation of cyclic-adenosine monophosphate, an action which was antagonized by the presence of cimetidine (10(-5) M), a blocker of H2 receptors. Also, histamine (10(-5) M) and dibutyrylcyclic-adenosine monophosphate (DB-cAMP) at 10(-3) M, enhanced significantly the formation 3H-PGF2 alpha from 3H-PGE2. Results presented herein demonstrate that H is able to diminish the generation of PGE2 in uteri from rats at diestrus augmenting the synthesis of PGF2 alpha, apparently via the activation of H2-receptors, enhancing adenylate-cyclase. These effects appear to increase uterine 9-keto-reductase activity which transforms PGE2 into PGF2 alpha. Relationships between the foregoing results and those evoked by estradiol, are also discussed.     

Expression of enzymes of cyclooxygenase pathway and secretion of prostaglandin E2 and F2alpha by porcine myometrium during luteolysis and early pregnancy

Past studies of uterine prostaglandin (PGs) and pig reproduction have focused on endometrial rather than myometrial PGs. This study documents the synthesis and secretion of myometrial prostaglandins (PGs) in pigs and the involvement of oxytocin (OT) in these processes. Cyclooxygenase-2 (COX-2) expression was similar in myometrial explants from cyclic and pregnant pigs (days 14-16) and OT (10(-7) M) in vitro significantly increased COX-2 protein regardless of reproductive state. Basal expression of prostaglandin E2 synthase (PGES) was higher during pregnancy than during luteolysis. Conversely, prostaglandin F synthase (PGFS) was highest during luteolysis and lower in myometrium from gravid animals. OT had no influence on the expression of PGES and PGFS. In another tissue culture experiment, myometrial slices produced more PGE2 than PGF2alpha regardless of reproductive state of the female. OT stimulated PGE2 production in myometrium harvested during luteolysis and increased PGF2alpha production in all tissues examined. Progesterone (P4; 10(-5) M) blocked stimulatory effect of OT on myometrial PG release. Myometrial OTr mRNA was higher (P=0.03) during luteolysis than during pregnancy. In conclusion: (1) oxytocin increases myometrial COX-2 expression, but does not influence the expression of terminal enzymes of PGs synthesis (PGES and PGFS); (2) porcine myometrium preferentially produces PGs during early pregnancy and secretes more PGE2 than PGF2alpha; (3) myometrial OT and OTr support secretion of PGs from myometrium during luteolysis.     

Effects of prostaglandins and of leukotriene C4 on the metabolism of labelled glucose in uteri isolated from ovariectomized-diabetic rats. Influences of 17-beta-estradiol and of insulin.

The influences of exogenous PGE1, PGE2, PGF2 alpha, LTC4 and insulin (INS) on glucose oxidation in uterine strips isolated from ovariectomized-diabetic (OVD) and ovariectomized-estrogenized-diabetic (OVED) rats, were studied. The spayed animals were made diabetic by a single injection of streptozotocin (65 mg.kg-1 body weight). The effects of prostaglandins were studied in the presence of indomethacin (INDO) in the incubation medium and the effects of LTC4 in the presence of INDO and nordihydroguaretic acid (NDGA). These procedures were followed in order to avoid the possible influences of endogenous derivatives of arachidonic acid formed by the activity of cyclooxygenase and of lipoxygenases. INDO and NDGA did not modify significantly the formation of 14CO2 from U-14C-glucose in uteri from OVD and from OVED rats. INS (0.5 U.ml-1) augmented significantly labelled glucose metabolism, both in OVD as well as in OVED rats. On the other hand, added PGE1, PGE2, PGF2 alpha or LTC4 failed to alter glucose metabolism in uteri from OVD rats. Only PGE1 was able to increase significantly (p less than 0.05) 14CO2 production from labelled glucose in uterine strips from OVED rats. In OVD rats the stimulatory action of INS on uterine glucose metabolism was significantly enhanced by exogenous PGE1, but not modified by PGE2, by PGF2 alpha or by LTC4. PGE1, PGE2 and LTC4 sensitized uterine strips obtained from OVED rats to the effects of INS. The possible importance of PGE1 in improving uterine glucose metabolism in diabetic animals is discussed.     

Stimulation of prostaglandin synthesis in rabbit gastric antral mucosal slices by desferrioxamine in vitro.

Desferrioxamine is an iron-chelating agent used in the treatment of iron overload. It is a powerful inhibitor of iron-dependent radical reactions. The effect of desferrioxamine of prostaglandin (PG) synthesis and metabolism in rabbit gastric antral mucosal slices has been examined. Desferrioxamine significantly enhanced the production of PGE2 and PGF2 alpha. The formation of 13,14-dihydro-15-keto PGE2 and 13,14-dihydro-15-keto PGF2 alpha was also increased slightly by desferrioxamine. The addition of Fe3+ or Al3+ blocked the stimulatory action of desferrioxamine on PGE2 and PGF2 alpha production. Desferrioxamine appears to be stimulating the activity of PG cyclooxygenase through the removal of endogenous antral mucosal iron. These results suggest that desferrioxamine has the potential to increase the PG levels in gastric mucosa by primarily stimulating PG biosynthesis. The possibility that desferrioxamine may be of therapeutic value in the treatment of ischemic injury in the stomach is discussed.     

The effect of supplementation with n-6 polyunsaturated fatty acids on 1-, 2- and 3-series prostaglandin F production by ovine uterine epithelial cells

Linoleic acid (LA, 18:2n-6) has variously been found to increase or inhibit synthesis of 2-series prostaglandins (PGs), derived from arachidonic acid (AA, 20:4n-6). gamma-linolenic acid (GLA, 18:3n-6) containing oils are promoted to women for a variety of reproductive problems. Little is known concerning their actual effects on reproduction. We investigated the effects of LA, GLA and AA supplementation (25-100 microM) on basal and oxytocin (OT) stimulated production of 1-, 2- and-3 series PGs by uterine epithelial cells isolated from non-pregnant ewes, used as a model system to study endometrial PG production. PGF isomers were measured using radioimmunoassays following separation by high performance chromatography (HPLC). OT challenge increased the proportion of PGF2alpha in relation to PGF1alpha and PGF3alpha in control medium. LA supplementation decreased all PGF isomer production and reduced responsiveness to OT. GLA increased both absolute and proportional PGF1alpha production and slightly enhanced PGF2alpha generation. AA increased PGF2alpha generation and raised its isometric proportion. Both GLA and AA increased overall PGF output significantly but prevented the cells from responding to OT. These results suggest that consumption of LA and GLA are likely to differentially alter both uterine PG metabolism and responsiveness to OT. This may have implications for the control of a variety of reproductive processes.     

Effect of oxytocin receptor blockade on rat myometrial responsiveness to prostaglandin f(2)(alpha)

In the present study we have shown that the genetic expression of prostaglandin (PG)F(2alpha) receptor (R) and cyclooxygenase (COX)-2 increases in laboring rat myometrium. This finding was associated with a relatively weak contractile in vitro response (E:(max)) of isolated uterine strips when challenged with PGF(2alpha). Five days postpartum PGF(2alpha)-R mRNA values exceeded those during labor while COX-2 mRNA was reduced to preparturient values. Maximal contractility of isolated strips stimulated with PGF(2alpha) at this time was enhanced and E:C(50) decreased. Oxytocin treatment of estrogen-primed nonpregnant rats down-regulated uterine contractile responsiveness to PGF(2alpha), leaving mRNA values for this receptor unchanged, whereas oxytocin receptor blockade with atosiban (an oxytocin receptor antagonist) left E:(max) unaltered. In contrast, atosiban treatment of pregnant rats resulted in a 2.5-fold increase in E:(max) and a considerably reduced EC(50) during labor when compared to untreated delivering rats. The increased contractile ability was associated with a threefold increase in PGF(2alpha)-R mRNA production, indicating that the regulation by atosiban of the PGF(2alpha)-induced response is exerted at the genetic level. Based on the present data we suggest that 1) PGF(2alpha)-R stimulation may not primarily exert a contracting role in the normally delivering myometrium, and 2) the presence of the PGF(2alpha)-R system in rat myometrium may explain the apparent functional redundancy of the oxytocinergic system during the process of birth in animals lacking oxytocin or where the oxytocin receptor is blocked. In this context PGF(2alpha) receptor stimulation may, in the absence of oxytocin receptor stimulation, exert the contractile forces needed for proper propulsion of the fetus.     

Prostaglandin E production by uteri of ovariectomized pregnant rats receiving antiprogesterone steroid or in which progesterone has been withdrawn.

Antiprogesterone steroid, ZK98299 (Schering, Germany) or RU38486 (Roussel Uclaf, France), has been administered to ovariectomized early pregnant rats receiving continuous steroid replacement. At 24 h later, uterine explants of rats treated with ZK98299 produced significantly greater amounts of prostaglandin E (PGE) than did controls or animals treated with RU38486. The PGE/PGF2 alpha production ratio for uteri of rats treated with ZK98299 or RU38486 was markedly lowered compared to controls, and a significant decrease occurred in the PGE/6-keto PGF1 alpha production ratio for rats treated with RU38486. For ovariectomized early pregnant rats in which progesterone has been withdrawn, a significant reduction in uterine PGE production occurred when compared to control animals. There was also a marked decrease in PGE/PGF2 alpha production ratio, and the PGE/6-keto PGF1 alpha production ratio tended to be lowered relative to controls. The stimulated production (as by ZK98299) or unchanged production of PGE (as by RU38486) indicates a selective action on uterine PGE synthesis among the antiprogesterone steroids, and these findings cannot be explained simply in terms of a blockage of progesterone receptors.     

Down-regulation of oxytocin-induced cyclooxygenase-2 and prostaglandin F synthase expression by interferon-tau in bovine endometrial cells

Oxytocin (OT) is responsible for the episodic release of luteolytic prostaglandin (PG) F2alpha from the uterus in ruminants. The attenuation of OT-stimulated uterine PGF2alpha secretion by interferon-tau (IFN-tau) is essential for prevention of luteolysis during pregnancy in cows. To better understand the mechanisms involved, the effect of recombinant bovine IFN-tau (rbIFN-tau) on OT-induced PG production and cyclooxygenase-2 (COX-2) and PGF synthase (PGFS) expression in cultured endometrial epithelial cells was investigated. Cells were obtained from cows at Days 1-3 of the estrous cycle and cultured to confluence in RPMI medium supplemented with 5% steroid-free fetal calf serum. The cells were then incubated in the presence or absence of either 100 ng/ml OT or OT+100 ng/ml rbIFN-tau for 3, 6, 12, and 24 h. OT significantly increased PGF2alpha and PGE2 secretion at all time points (p < 0.01), while rbIFN-tau inhibited the OT-induced PG production and reduced OT receptor binding in a time-dependent manner. OT increased the steady-state level of COX-2 mRNA, measured by Northern blot, which was maximal at 3 h (9-fold increase) and then decreased with time (p < 0.01). OT also caused an increase in COX-2 protein, which peaked at 12 h (11-fold increase), as measured by Western blot. Addition of rbIFN-tau suppressed the induction of COX-2 mRNA (89%, p < 0.01) and COX-2 protein (50%, p < 0.01) by OT. OT also increased PGFS mRNA, and this stimulation was attenuated by rbIFN-tau (p < 0.01). To ensure that the decrease in COX-2 was not solely due to down-regulation of the OT receptor, cells were stimulated with a phorbol ester (phorbol 12-myristate 13-acetate; PMA) in the presence and absence of rbIFN-tau. The results showed that rbIFN-tau also decreased PMA-stimulated PG production and COX-2 protein. It can be concluded that rbIFN-tau inhibition of OT-stimulated PG production is due to down-regulation of OT receptor, COX-2, and PGFS.     

Myometrial oxytocin receptors and prostaglandin in the parturition process in the rat.

Parturition in rats is associated with an abrupt and marked increase in myometrial oxytocin (OT) receptor concentrations. In this study, we investigated the role of myometrial OT receptors in the initiation and the process of parturition. We produced chronic OT receptor blockade during the last 3 days of gestation by administration of a specific OT antagonist at 100 micrograms/day and 300 micrograms/day. We also suppressed OT receptor formation by inhibiting prostaglandin synthesis with naproxen sodium at 2 mg/day and 5 mg/day. We found that chronic blockade of OT receptors inhibited the uterotonic response to OT in Day 22 and Day 23 pregnant rats in a dose-dependent manner. OT antagonist treatment did not prolong the gestation period. However, the duration of parturition, fetal mortality, and the mortality incidence were increased in rats treated with the high dose of the OT antagonist compared to controls. Naproxen sodium at both dosage levels prolonged gestation by 24 h or longer, doubled the duration of parturition, and markedly increased fetal mortality and mortality incidence. Combined OT antagonist and naproxen treatment produced adverse outcomes similar to that produced by naproxen treatment alone. Myometrial OT receptor concentrations were markedly increased in all rats immediately postpartum, ranging from 210 to 425 fmol/mg protein compared to the 50 to 100 fmol/mg found in Day 21 and Day 22 pregnant rats. Correlation analyses between OT receptor concentrations and various parameters associated with gestation and parturition showed that there was a correlation between low OT receptor concentrations and long gestation period, prolonged parturition, and high fetal mortality rate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution of cyclooxygenase products with cyclooxygenase inhibition in isolated dog lung

Arachidonic acid metabolism can lead to synthesis of cyclooxygenase products in the lung as indicated by measurement of such products in the perfusate of isolated lungs perfused with a salt solution. However, a reduction in levels of cyclooxygenase products in the perfusate may not accurately reflect the inhibition of levels of such products as measured in lung parenchyma. We infused sodium arachidonate into the pulmonary circulation of isolated dog lungs perfused with a salt solution and measured parenchymal, as well as perfusate, levels of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), prostaglandin F2 alpha (PGF2 alpha), prostaglandin E2 (PGE2), and thromboxane B2 (TxB2). These studies were repeated with indomethacin (a cyclooxygenase enzyme inhibitor) in the perfusate. We found that indomethacin leads to a marked reduction in perfusate levels of PGF2 alpha, PGE2, 6-keto-PGF1 alpha, and TxB2, as well as a marked reduction in parenchymal levels of 6-keto-PGF1 alpha and TxB2 when parenchymal levels of PGF2 alpha and PGE2 are not reduced. We conclude that, with some cyclooxygenase products, a reduction in levels of these products in the perfusate of isolated lungs may not indicate inhibition of levels of these products in the lung parenchyma and that a reduction in one parenchymal product may not predict the reduction of other parenchymal products. It can be speculated that some of the physiological actions of indomethacin in isolated lungs may result from incomplete or selective inhibition of synthesis of pulmonary cyclooxygenase products.