Prostaglandins最新文献

The human placenta at term produces large quantities of corticotropin releasing hormone (CRH) and prostanoids. These hormones play an important role in the maintenance of pregnancy, and the initiation and progress of labor; yet little is known of factors affecting their regulation and the interrelationship of CRH and prostanoid production. In these studies we have investigated the effect of dexamethasone on the production of CRH and prostanoids from fresh human term placental tissues.

The basal release of prostaglandin E₂ (PGE₂), prostaglandin F_2α (PGF_2α), thromboxane B₂ (TxB₂) and 6-keto-prostaglandin F_1α (6-keto-PGF_1α) from human term placental explants increased from the fifth hour in culture, while the release of 13,14-dihydro-15-keto-PGE_2α (PGFM) was not significantly changed during this period. The addition of dexamethasone (10⁻⁸ M) to the perifusing medium resulted in a rapid and dramatic inhibition of PGE₂, PGF_2α, PGFM, TxB₂ and 6-keto-PGF_1α release. On the other hand, CRH release was not significantly changed throughout the seven hours of incubation with dexamethasone.

These data demonstrate that glucocorticoids at physiologic concentrations can inhibit human term placental prostanoid production, and thus glucocorticoid production may play an important role in the physiological regulation of placental prostanoid production in the human placenta. However, dexamethasone did not alter CRH release, demonstrating that the inhibition of placental prostanoids by dexamethasone is not a CRH mediated event.

Prostaglandin production in amnion and decidua is considered important for human parturition. We investigated in pregnant guinea pigs, a species similar to women in regard to the endocrinology of pregnancy, whether the production rates of PGE₂ and PGF_2α in various intrauterine tissues are compatible with a role in parturition. Net production rates were measured at 45, 55 and 65 days of gestation and during labor in amnion, chorion, myo-endometrium, the outer layer of the myometrium, the site of placental implantation, and placenta. Net production rates in amnion increased between 45 days and labor (30-fold for PGE₂ and 8-fold for PGF_2α, P < 0.0001). During labor, the production rates in amnion of PGE₂ (P = 0.006) and PGF_2α (P = 0.019) were higher than at 45, 55, and 65 days of gestation. In myo-endometrium, the production rates of PGF_2α were higher at 65 days of gestation than at 55 days and during labor (P = 0.046). Addition of arachidonic acid (10⁻⁵ M) increased production of PGE₂ and/or PGF_2α in all tissues (P < 0.05) except placenta. In amnion, the response to arachidonic acid increased with advancing gestation. This suggests that 1) PGE₂ and PGF_2α produced by amnion have a potential role in the initiation and maintenance of labor, 2) PGF_2α produced by myo-endometrium has a potential role in the initiation of labor, 3) cyclooxygenase(s) are not rate-limiting except in placenta, and 4) the expression of cycloxygenase in amnion increases with advancing gestation.

We explored the action of β-endorphin (βE) and naltrexone (Na1) on the number of oocytes and on prostaglandins (PGE and PGF_2α) production by the ovaries from PMSG/hCG-primed immature and cycling rats. Superovulated rats were injected with β-endorphin (0.5 μg) intraperitoneally 4 hours after hCG. The number of ova ovulated was inhibited and this effect was blocked with naltrexone injected into the ovarian bursa (0.1 μg) 30 minutes before β-endorphin. Furthermore, β-endorphin (10⁻⁸ M) decreased prostaglandins production by ovaries isolated 4 hours after hCG. Intraperitoneal injection of β-endorphin (0.5 μg) at 17:00 hr on proestrus decreased (−23%) the number of ova within oviducts on the day after (estrus). Naltrexone injected intraperitoneally (5 μg) at 16:30 hr on proestrus increased the number of ova (+23%). On the other hand, β-endorphin increased the number of oocytes obtained by puncture of antral follicles (+37%) and naltrexone decreased the number of oocytes (−33%). Prostaglandins content in the ovary of adult rats at 23:00 hr, approximately 4 hr before the onset of ovulation, was diminished when the rats received β-endorphin at proestrus. Moreover, when the rats were injected with naltrexone, ovarian production of prostaglandins was increased. Our results further support the hypothesis that β-endorphin affects ovulation at the level of the ovary in the rat and that endogenous opioids may be modulating this physiological process.

Mounting epidemiological and experimental evidence implicates nonsteroidal antiinflammatory drugs as anti-tumorigenic agents. Our previous work showed that nonsteroidal antiinflammatory drug treatment of src-transformed chicken embryo fibroblasts caused apoptosis -- a mechanism by which these drugs might exert their anti-tumorigenic effect. The present studies employ a sensitive technique for detecting single- and double-stranded DNA cleavage (the comet assay) to quantitate apoptosis. By this method pp60^v-src, which antagonizes apoptosis in many cell systems, was found to induce apoptosis in 11–23% of serum-starved fibroblasts. However, treatment with diclofenac following pp60^v-src activation produced a much stronger response beginning within 6 hours of treatment that resulted in 100% lethality. During cell death, cyclooxygenase-2 but not cyclooxygenase-1 mRNA was found to be uniformly increased by all apoptotic drugs tested.

Examination of the expression of apoptosis-associated genes showed that c-rel and p53 (found in normal or v-src-transformed chicken embryo fibroblasts at moderate levels), and bcl-2 (present at an extremely low level) were largely unchanged by treatment with eight different nonsteroidal antiinflammatory drugs. However, over-expression of human bcl-2 inhibited diclofenac-mediated apoptosis by 90%, demonstrating directly that bcl-2 expression can regulate nonsteroidal antiinflammatory drug induction of cell death.

The proto-oncogene c-myc is known to cause apoptosis in chicken embryo fibroblasts when artificially overexpressed in cells deprived of trophic factors. We found that nonsteroidal antiinflammatory drug treatment following pp60^v-src activation persistently induced myc protein and mRNA by more than 20-fold above that evoked by pp60^v-src activation alone. Moreover, transfection of antisense c-myc oligonucleotides reduced drug-induced myc expression by 80% and caused a concomitant 50% reduction in cell death. These findings suggest that nonsteroidal antiinflammatory drug-induced apoptosis proceeds through a src/myc dependent pathway which is negatively regulated by bcl-2.

The mechanism for the production of increased gastric secretion following massive intestinal resection is not clearly defined. The loss of an intestinal inhibitor has been most frequently suggested to explain this hypersecretion. The role of endogenous prostaglandins which can inhibit gastric secretion is not established. The present study was undertaken to determine the effect of 50% proximal small bowel resection on Prostaglandin E₂ (PGE₂) levels in rat gastric mucosa. This study was performed in 30 rats divided into three groups. The first group of rats served as unoperated controls, the second group was sham operated and the third group underwent 50% resection of proximal small intestine. The PGE₂ levels in rat gastric mucosa was decreased significantly (p < 0.001) in the resection group (422.85 ± 7.66 pg/gm) as compared with the sham group (478.77 ± 7.25 pg/gm) and the control group (493.38 ± 4.61 pg/gm). Total gastric acidity was increased significantly (p llt 0.001) in the resection group (63.05 ± 2.64 mEq/L) as compared with the sham group (15.21 ± 0.99 mEq/L) and the control group (17.19 ± 0.80 mEq/L). The PGE₂ levels and total gastric acidity were not significantly changed in either the control or sham operation groups (p > 0.05). The results suggest that endogenous prostaglandin synthesis has a regulatory role in gastric hyperacidity after 50% proximal small bowel resection in rats.

The present study was undertaken to evaluate the effects of the glucocorticoid hormones betamethasone and hydrocortisone, and of progesterone on the relative production of prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) by explants of human fetal membranes at term gestation in the absence of labor.

Tissues (n = 7) were incubated either in the presence or in the absence of the above mentioned hormones. PGE2 and LTB4 were measured in culture medium by radioimmunoassays.

Glucocorticoids and progesterone did not affect PGE2 output by tissues; however, they greatly stimulated LTB4 production. Moreover, both betamethasone and hydrocortisone significantly increased the ratio of LTB4 to PGE2 formation by tissues.

These results suggest that glucocorticoid hormones and progesterone might influence arachidonic acid metabolism in human fetal membranes by stimulating the production of lipoxygenase rather than cyclooxygenase substances before the onset of labor.

Thromboxane A₂ (T×A₂) augments hypothalamus-pituitary-adrenal axis activity in both fetal and adult animals. We have proposed that T×A₂ acts as a neuromodulator within the brain to stimulate the release of corticotropin releasing hormone (CRH) or arginine vasopressin (AVP) into the hypophyseal-portal blood[1]. We performed the present experiments to identify immunoreactive thromboxane synthase (T×S) within fetal brain regions and to quantify developmental changes in the T×S immunoreactivity measurable within those regions. We found that immunoreactive T×S was present in fetal hypothalamus, pituitary, brainstem, and lung. In fetal hypothalamus, we found immunoreactive T×S in three identifiable molecular weights, approximately 65, 42, and 35 kD. In fetal pituitary and lung, we found the 65 and 35 kD forms, and in the brainstem we found only the 35 kD form. In fetal pituitary, there was a clear ontogenetic change in T×S immunoreactivity. The 42 kD T×S immunoreactivity was not present in the youngest fetal sheep studied (86–90 days' gestation), but was expressed in the other age groups (125–128, 135–139, 141-term, and postnatal ages). The other molecular weight forms appeared to increase in the older fetuses, but the changes were not significant. In the hypothalamus, all three forms of T×S were measurable at all ages, and there was no signficant change in relative abundance. We conclude that immunoreactive T×S is present in the fetal brain throughout the last half of fetal gestation, but that the significance of multiple molecular weight forms is not clear.

To identify the arrhythmogenic and the antiarrhythmic eicosanoids, cultured, spontaneously beating, neonatal rat cardiac myocytes were used to examine the effects of various eicosanoids added to the medium superfusing the cells at different concentrations on the contraction of the myocytes. Superfusion of the myocytes with the prostaglandins (PGD₂, PGE₂, PGF_2α) or the thromboxane (TXA₂)-mimetic, U 46619, induced reversible tacharrhythmias characterized by an increased beating rate, chaotic activity and contractures. These effects are concentration-dependent. PGF_2α and U 46619 were much more potent than PGD₂ or PGE₂ in the production of tachyarrhythmias. Prostacyclin (PGI₂) induced a marked reduction in the contraction rate of the cells with a slight increase in the amplitude of the contractions and showed a protective effect against the arrhythmias induced by PGF_2α and TXA₂ (U 46619). PGE₁ exerted a dose-dependent dual effect on the contraction of the myocytes. At low concentrations (<2 μM), PGE₁ reduced the contraction rate of the cells with an increase in the amplitude of the contractions and effectively terminated the tachyarrhythmias induced by arrhythmogenic agents, such as isoproterenol, ouabain and U 46619. At higher concentrations (>5 μM), PGE₁ caused cell contractures and chaotic activity. In contrast, the lipoxygenase products [leukotriene (LT) B₄, LTC₄, LTD₄

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The eicosanoids derived from eicosapentaenoic acid (EPA), including both the cyclooxygenase products (PGD₃, PGE₃, PGF_3α, TXB₃) showed lesser effects on the contraction of the myocytes. The lipoxygenase products (LTB₅, LTC₅, LTD₅ & LTE₅), as with the AA metabolites showed little effect on the contraction of cardiac myocytes. The arrhythmias induced by the arrhythmogenic prostaglandins and thromboxane A₂ could be suppressed by the nonmetabolizable AA analog eicosatetraynoic acid (ETYA) or free AA and EPA, indicating a distinction in the effect on cardiac arrhythmia between the precursor fatty acids (AA & EPA) themselves and their metabolites. In conclusion, the major arrhythmogenic eicosanoids are the cycloxygenase products of AA, whereas those products of EPA are much less or not effective; PGE₁, PGI₂, ETYA and EPA have antiarrhythmic effects.

One of the most abundant F₂ isoprostanes formed under pathological conditions is 8-epi-prostaglandin F_2α (8-epi-PGF_2α), a potent vasoconstrictor. The purpose of this study was to determine the signal transduction events initiated by 8-epi-PGF_2α-induced vasoconstriction. Isolated arterial rings from male Sprague-Dawley rats were suspended in tissue baths containing Krebs-Henseleit salt solution, stretched to optimal resting tension and stimulated. 8-epi-PGF_2α induced concentration-dependent contractions in pulmonary arteries (EC₅₀: 7.7 ± 2.1 μM; n = 3) and aortas (EC₅₀: 0.9 ± 0.1μM; n = 4) which were blocked by the TXA₂ receptor antagonists SQ29548, L657925 and L657926. The contractile response to 8-epi-PGF_2α was significantly (★p < 0.05; n = 4) diminished by: 1) indomethacin and ibuprofen; 2) Ca⁺⁺ free media; 3) verapamil, a voltage gated Ca⁺⁺ channel blocker; 4) flunarizine, a T-type Ca⁺⁺ channel blocker; and 5) calphostin C, a protein kinase C inhibitor. These data suggest that the contractile response to 8-epi-PGF_2α is: 1) mediated via activation of TXA₂ receptors; 2) partially dependent on the synthesis and release of other cyclooxygenase derived products; 3) dependent on an influx of extracellular Ca⁺⁺ possibly via Ca⁺⁺ channels; and 4) may be PKC dependent.

Prostaglandin (PG) E₂ binds to four PGE receptor subtypes, EP1, EP2, EP3 and EP4, and induces a variety of functions through the interaction of carboxylic acid of PGE₂ and Arg residue in the seventh transmembrane domain of the receptor. To assess the role of the interaction of the carboxylic acid group of agonists and the Arg residue, which can form both ionic bonding and hydrogen bonding as a hydrogen donor, we examined the agonist activities of three types of agonist, PGE₂ with a negatively charged carboxylic acid, PHE₂ methylester, which is a hydrogen acceptor, and 1-OH PGE₂, which can accept as well as donate hydrogen but prefers to donate hydrogen rather than accept it, for four PGE receptor subtypes. Although PGE₂ methylester had slightly lower agonist activities than PGE₂ for EP1 and EP4 receptors, PGE₂ and its methylester showed the same agonist activities for EP2 and EP3 receptors, indicating that PGE₂ methylester is a potent agonist for all of the four subtypes. In contrast, 1-OH PGE₂ was a very weak agonist for all receptors. These findings demonstrate that the hydrogen bonding interaction of agonists and the Arg residue is generally sufficient for the functional activation of all of the PGE receptor subtypes.