Inhibition of prostaglandin synthesis up-regulates cyclooxygenase-2 induced by lipopolysaccharide and peroxisomal proliferators.
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Primary cultures of fetal hepatocytes expressed cyclooxygenase-2 (COX-2) upon stimulation with bacterial lipopolysaccharide (LPS) or peroxisomal proliferators. This enzyme was active and a good correlation between the mRNA levels, the amount of protein, and the synthesis of prostaglandin E2 was observed. However, when cells were incubated in the presence of indomethacin or the COX-2-specific inhibitor NS398, the amount of COX-2 protein increased 5-fold after activation with LPS and 2-fold after treatment with clofibrate. This up-regulation of COX-2 was not observed at the mRNA level. The mechanism of protein accumulation might involve either a direct stabilization of the enzyme by the inhibitors or the absence of prostaglandins involved in the regulation of its turnover. Among the prostaglandins assayed, only 15-deoxy-Prostaglandin J2 exerted a statistically significant decrease in the COX-2 levels in cells stimulated with LPS or LPS plus NS398. The accumulation of COX-2 in the presence of inhibitors was also observed in peritoneal macrophages treated under identical conditions. These results indicate that COX-2 protein accumulates after enzyme inhibition, and because removal of the inhibitors restored the enzyme activity, suppression of treatment with reversible COX-2 inhibitors may cause a transient overproduction of prostaglandins. (+info)
The cyclo-oxygenase-dependent regulation of rabbit vein contraction: evidence for a prostaglandin E2-mediated relaxation.
(2/327)
1. Arachidonic acid (0.01-1 microM) induced relaxation of precontracted rings of rabbit saphenous vein, which was counteracted by contraction at concentrations higher than 1 microM. Concentrations higher than 1 microM were required to induce dose-dependent contraction of vena cava and thoracic aorta from the same animals. 2. Pretreatment with a TP receptor antagonist (GR32191B or SQ29548, 3 microM) potentiated the relaxant effect in the saphenous vein, revealed a vasorelaxant component in the vena cava response and did not affect the response of the aorta. 3. Removal of the endothelium from the venous rings, caused a 10 fold rightward shift in the concentration-relaxation curves to arachidonic acid. Whether or not the endothelium was present, the arachidonic acid-induced relaxations were prevented by indomethacin (10 microM) pretreatment. 4. In the saphenous vein, PGE2 was respectively a 50 and 100 fold more potent relaxant prostaglandin than PGI2 and PGD2. Pretreatment with the EP4 receptor antagonist, AH23848B, shifted the concentration-relaxation curves of this tissue to arachidonic acid in a dose-dependent manner. 5. In the presence of 1 microM arachidonic acid, venous rings produced 8-10 fold more PGE2 than did aorta whereas 6keto-PGF1alpha and TXB2 productions remained comparable. 6. Intact rings of saphenous vein relaxed in response to A23187. Pretreatment with L-NAME (100 microM) or indomethacin (10 microM) reduced this response by 50% whereas concomitant pretreatment totally suppressed it. After endothelium removal, the remaining relaxing response to A23187 was prevented by indomethacin but not affected by L-NAME. 7. We conclude that stimulation of the cyclo-oxygenase pathway by arachidonic acid induced endothelium-dependent, PGE2/EP4 mediated relaxation of the rabbit saphenous vein. This process might participate in the A23187-induced relaxation of the saphenous vein and account for a relaxing component in the response of the vena cava to arachidonic acid. It was not observed in thoracic aorta because of the lack of a vasodilatory receptor and/or the poorer ability of this tissue than veins to produce PGE2. (+info)
The role of prostaglandins in chemically induced inflammation.
(3/327)
Dye leakage in rats, produced by intracutaneous injections of irritants into the abdominal skin, was quantitated using the Evans blue technique of Harada et al. (1971). In control rats and in rats pretreated with indomethacin (an inhibitor of prostaglandin synthesis) concentration-response lines were obtained for 5-hydroxytryptamine, histamine, bradykinin and prostaglandin E1, bradykinin in the presence of prostaglandin E1 (10-6 M), adenosine-5'-triphosphate, compound 48/80, capsaicin and silver nitrate. In rats pretreated with indomethacin the dye leakage responses to histamine, prostaglandin E1, adenosine-5'-triphosphate and silver nitrate were significantly reduced, but no significant changes were observed in the responses to the other irritants. It is suggested that part of the action of histamine, adenosine-5'-triphosphate and prostagland in E1 is produced indirectly by releaseor stimulation of the synthesis of prostaglandins or their precursors. These results might have important implications in the understanding of the inflammatory response. (+info)
Inhibition of prostaglandin and nitric oxide synthesis prevents cortisol-induced renal vasodilatation in sheep.
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Glucocorticoids increase renal blood flow (RBF) and glomerular filtration rate in many species, but the mechanisms involved are unclear. We investigated whether cortisol-induced renal vasodilatation in conscious sheep depends on interactions with prostaglandins or angiotensin II. Intravenous infusion of cortisol (5 mg/h) for 5 h increased renal conductance (RC) by 1.06 +/- 0.24 ml. min-1. mmHg-1 more than vehicle. During intrarenal infusion of indomethacin (0.25 mg. kg-1. h-1), the cortisol-induced increase in RC (0.28 +/- 0.21 ml. min-1. mmHg-1) was significantly reduced. The cortisol-induced rise in RBF (103 +/- 17 ml/min) was not significantly reduced by indomethacin treatment (76 +/- 9 ml/min). Combined intrarenal infusion of indomethacin (0.25 mg. kg-1. h-1) with Nomega-nitro-L-arginine (2.0 mg. kg-1. h-1), a nitric oxide synthase inhibitor, abolished the cortisol-induced increases in both RC and RBF. Inhibition of angiotensin II synthesis with intravenous captopril (40 mg/h) blocked the renal vasoconstrictor action of angiotensin I but did not inhibit the cortisol-induced increases in RBF and RC. This study provides evidence that nitric oxide and prostaglandins play a role in cortisol-induced renal vasodilatation but indicates that this response is independent of an interaction with angiotensin. (+info)
Osmotic regulation of airway reactivity by epithelium.
(5/327)
Inhalation of nonisotonic solutions can elicit pulmonary obstruction in asthmatic airways. We evaluated the hypothesis that the respiratory epithelium is involved in responses of the airways to nonisotonic solutions using the guinea pig isolated, perfused trachea preparation to restrict applied agents to the mucosal (intraluminal) or serosal (extraluminal) surface of the airway. In methacholine-contracted tracheae, intraluminally applied NaCl or KCl equipotently caused relaxation that was unaffected by the cyclo-oxygenase inhibitor, indomethacin, but was attenuated by removal of the epithelium and Na+ and Cl- channel blockers. Na+-K+-2Cl- cotransporter and nitric oxide synthase blockers caused a slight inhibition of relaxation, whereas Na+,K+-pump inhibition produced a small potentiation. Intraluminal hyperosmolar KCl and NaCl inhibited contractions in response to intra- or extraluminally applied methacholine, as well as neurogenic cholinergic contractions elicited with electric field stimulation (+/- indomethacin). Extraluminally applied NaCl and KCl elicited epithelium-dependent relaxation (which for KCl was followed by contraction). In contrast to the effects of hyperosmolarity, intraluminal hypo-osmolarity caused papaverine-inhibitable contractions (+/- epithelium). These findings suggest that the epithelium is an osmotic sensor which, through the release of epithelium-derived relaxing factor, can regulate airway diameter by modulating smooth muscle responsiveness and excitatory neurotransmission. (+info)
Prostaglandin endoperoxide-dependent vasospasm in bovine coronary arteries after nitration of prostacyclin synthase.
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In the present study we used a bioassay to study the effects of peroxynitrite (ONOO-) on angiotensin II (A-II)-triggered tension in isolated bovine coronary arteries in order to show the consequences of the previously reported PGI2-synthase inhibition by ONOO- in this model. The following results were obtained: 1. 1 micromol L(-1) ONOO- impaired A-II-induced vasorelaxation and caused a second long lasting constriction phase. Indomethacin (10(-5)M) prevented both effects. U51605, a dual blocker of PGI2-synthase and thromboxane (TX)A2-synthase mimicked the effects of ONOO-. 2. The selective TXA2/prostaglandin endoperoxide (PGH2) receptor antagonist SQ29548 antagonized the second vasoconstriction phase after ONOO- -treatment. Since a generation of TXA2 and 8-iso-prostaglandin F2alpha could be excluded a direct action of unmetabolized PGH2 on the TXA2/PGH2 receptor was postulated. 3. ONOO- dose-dependently inhibited the conversion of 14C-PGH2 into 6-keto-PGF1alpha in isolated bovine coronary arteries with an IC50-value of 100 nM. 4. Immunoprecipitation of 3-nitrotyrosine-containing proteins with a monoclonal antibody revealed PGI2-synthase as the only nitrated protein in bovine coronary arteries treated with 1 micromol 1(-1) ONOO-. 5. Using immunohistochemistry a co-localization of PGI2-synthase and nitrotyrosine-containing proteins was clearly visible in both endothelial and vascular smooth muscle cells. We concluded that ONOO- not only eliminated the vasodilatory, growth-inhibiting, antithrombotic and antiadhesive effects of PGI2 but also allowed and promoted an action of the potent vasoconstrictor, prothrombotic agent, growth promoter, and leukocyte adherer, PGH2. (+info)
SC-19220, a prostaglandin E2 antagonist, inhibits osteoclast formation by 1,25-dihydroxyvitamin D3 in cell cultures.
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1,25 Dihydroxy vitamin D3 (1,25(OH)2D3), prostaglandin (PG) E2 and parathyroid hormone (PTH) induce osteoclast formation in cell cultures. Previously, we have shown that SC-19220, an antagonist of the EP1 subtype of PGE receptors, inhibited tartrate-resistant acid phosphatase (TRAP)-positive cell formation by PGE2 and PTH in adherent cell cultures taken from neonatal rats. Since 1,25(OH)2D3 has been shown to induce osteoclast formation through PGE2 synthesis, in this study we have examined the effect of SC-19220 on osteoclast formation induced by 1,25(OH)2D3 in cell cultures by measuring bone resorption as well as TRAP-positive cell formation. SC-19220 inhibited osteoclast formation by 1,25(OH)2D3 as well as by PGE2 in cell cultures. The addition of SC-19220 to the later half but not to the earlier half of the culture inhibited 1,25(OH)2D3-induced formation. In the culture in which hydroxyurea was added in the later half period, SC-19220 inhibited osteoclast formation by 1, 25(OH)2D3. Under these conditions, 17-phenyl PGE1, an EP1 agonist, induced osteoclast formation. Thus, SC-19220 inhibits certain reactions in the later processes of osteoclast formation induced by 1,25(OH)2D3. In addition, SC-19220 also inhibited osteoclast formation induced by interleukin (IL)-11 and IL-6 as well as by PTH. It is suggested that the SC-19220 inhibiting reactions are shared by all the inducers including 1,25(OH)2D3 and are essential for osteoclast formation. (+info)
Sensitivity of bovine corpora lutea to prostaglandin F2alpha is dependent on progesterone, oxytocin, and prostaglandins.
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Prostaglandin (PG) F2alpha that is released from the uterus is essential for spontaneous luteolysis in cattle. Although PGF2alpha and its analogues are extensively used to synchronize the estrous cycle by inducing luteolysis, corpora lutea (CL) at the early stage of the estrous cycle are resistant to the luteolytic effect of PGF2alpha. We examined the sensitivity of bovine CL to PGF2alpha treatment in vitro and determined whether the changes in the response of CL to PGF2alpha are dependent on progesterone (P4), oxytocin (OT), and PGs produced locally. Bovine luteal cells from early (Days 4-5 of the estrous cycle) and mid-cycle CL (Days 8-12 of the estrous cycle) were preexposed for 12 h to a P4 antagonist (onapristone: OP; 10(-4) M), an OT antagonist (atosiban: AT; 10(-6) M), or indomethacin (INDO; 10(-4) M) before stimulation with PGF2alpha. Although OP reduced P4 secretion (p < 0.001) only in early CL, it reduced OT secretion in the cells of both phases examined (p < 0.001). OP also reduced PGF2alpha and PGE2 secretion (p < 0.01) from early CL. However, it stimulated PGF2alpha secretion in mid-cycle luteal cells (p < 0.001). AT reduced P4 secretion in early and mid-cycle CL (p < 0.05). Moreover, PGF2alpha secretion was inhibited (p < 0.05) by AT in early CL. The OT secretion and the intracellular level of free Ca2+ ([Ca2+]i) were measured as indicators of CL sensitivity to PGF2alpha. PGF2alpha had no influence on OT secretion, although [Ca2+]i increased (p < 0.05) in the early CL. However, the effect of PGF2alpha was augmented (p < 0.01) in cells after pretreatment with OP, AT, and INDO in comparison with the controls. In mid-cycle luteal cells, PGF2alpha induced 2-fold increases in OT secretion and [Ca2+]i. However, in contrast to results in early CL, these increases were magnified only by preexposure of the cells to AT (p < 0.05). These results indicate that luteal P4, OT, and PGs are components of an autocrine/paracrine positive feedback cascade in bovine early to mid-cycle CL and may be responsible for the resistance of the early bovine CL to the exogenous PGF2alpha action. (+info)