Eicosanoids最新文献

The involvement of arachidonic acid and eicosanoids in glucose absorption and metabolism was investigated in isolated mouse jejunum. Characteristics of glucose absorption and its metabolic fate are reported. Reduction in the dietary precursor of arachidonic acid, linoleic acid, and inhibition of phospholipid hydrolysis with mepacrine reduced glucose absorption with no effect on metabolism, although mepacrine increased the proportion of luminal to serosal lactate release. Bradykinin and n-FMLP enhanced metabolism by 2.1- and 2.4-fold, respectively, both reducing the percentage of metabolised glucose converted to lactate, while neither influenced absorption. Both indomethacin and NDGA decreased absorption and enhanced metabolism. The percentage of metabolised glucose converted to lactate decreased and the ratio of luminal to serosal lactate release was unchanged. In the absence of inhibitors, PGE2 (5 microM) decreased absorption by 28%, metabolism by 24% and total lactate production by 32% and LTB4 (20 nM) increased only absorption by 32%. PGE2 release into the perfusates was predominantly serosal (1-10 nM) and was inhibited by indomethacin. PGE2 could not reverse the indomethacin-induced decrease in absorption, but reversed the enhancement of metabolism by 89% and total lactate production by 60%. In conclusion, while the specificity of the drug-related absorptive effects remain unclear, alterations in the utilisation of the absorbed glucose via drug-induced changes in arachidonic acid synthesis and metabolism are apparent. Furthermore, exogenous PGE2 may protect against the effects of indomethacin and itself reduces active glucose absorption, the metabolism of the absorbed glucose and the amount of lactate formed.

To examine the role of prostanoid release during vascular contraction and endothelium-dependent relaxation, isolated rat thoracic aortic rings were contracted with norepinephrine (NE) or the thromboxane analog U46,619 and then exposed to acetylcholine (ACh). Pretreatment of aortic rings with the cyclooxygenase inhibitor indomethacin decreased (P < 0.05) NE and U46,619-induced contraction. Subsequent ACh-mediated relaxation was also reduced (P < 0.05) in the indomethacin-treated rings. These observations suggest that cyclooxygenase products participate in the rat aortic contractile response to agonists and the relaxation response to ACh. Since prostacyclin has been claimed to contract rat aortic rings, other sets of aortic rings were precontracted to different preloads with NE and then exposed to varying concentrations to prostacyclin (0.02 to 4000 ng/ml). Prostacyclin in modest amounts uniformly decreased aortic ring tension, while greater (> or = 2000 ng/ml) concentrations resulted in a modest contractile response. Prostacyclin per se had minimal contractile effect on quiescent rat aortic rings, but only at unphysiological concentrations. These observations indicate that the primary effect of prostacyclin on rat aortic rings is vasorelaxation, but very high, unphysiological concentrations may result in contraction.

Gas chromatographic-(tandem) mass spectrometric (GC-MS(-MS)) methods for the analysis of cysteinyl leukotrienes (LTs) and leukotriene B4 (LTB4) in biological fluids were developed. The enzymatic synthesis of the stable-isotope labelled analogues [1,1-18O2] LTE4 and [14,15,17,17,18,18-2H6] LTB4 in high isotopic purity is described. Utilizing [1,1-18O2] LTE4 as an internal standard and GC-MS-MS enhanced cysteinyl LTs synthesis was found in patients with multiple trauma and psoriasis compared to healthy volunteers, respectively. The metabolism of LTB4 by human monocytes was investigated and two novel LTB4 metabolites were structurally identified by GC-MS as 10,11-dihydro-LTB4 and 10,11-dihydro-12-oxo-LTB4.

Cell homogenates were obtained from chick osteoblast-like cells and epiphyseal growth plates. The lipid fraction was extracted with ethyl acetate and separated by RP-phase HPLC. Reverse-phase HPLC analysis of this fraction showed a major peak displayed a conjugated tetraene structure and this endogenous synthetic compound could be partially blocked by heat treatment at 100 degrees C for 5 min. After methylation, this peak was further purified by SP-HPLC and a major peak was identified by an U.V. absorption at lambda max of 271 nm and shoulders at 261 and 281 nm. The compound was hypothetically proposed by gas chromatography and mass spectrometry (GC/MS) as the cyclohexadiene derivative of 5S,12S-dihydroxy-6,8,10,14-(E,Z,E,Z)-eicosatetraenoic acid (5S,12S-diHETE) with a ring closure at C6 and C11. These results demonstrated that the 5S,12S-diHETE is an endogenous eicosanoid in both intramembranous and endochondral skeletal tissues.

Prostaglandin A2 (PGA2) is known to be actively incorporated into mammalian cells and thereby evokes its biological effects. To explore the transport mechanism of PGA2 and the possible role of cellular glutathione (GSH) in the transport process, we prepared GSH-enriched and -depleted L-1210 cells and then incubated with [3H] PGA2. In GSH-depleted cells, the total amount of PGA2 incorporated was reduced to about 50% of that in the control and GSH-enriched cells, accompanied by marked reduction of the PG in the cytosol but not in the nuclei. The kinetics of uptake revealed that the apparent Vmax was reduced by GSH depletion. Subsequent study of L-1210 cells under culture conditions provided similar results; GSH-depletion caused suppression of PG uptake and a reduction in the amount of PGA2 in cytosol, while its nuclear accumulation was little influenced. Comparison of the effect of PGA2 on the growth of control and GSH-depleted cells showed that the PG suppressed cell proliferation to the same extent. Our results suggest that, though uptake of PGA2 may be significantly influenced, its accumulation, and hence the manifestation of its biological effects are not influenced by GSH status.

Intracolonic administration of trinitrobenzene sulfonic acid in ethanol results in the development of colitis in the rat. Previous studies have demonstrated that the severity of this colitis can be markedly reduced by repeated treatment with inhibitors of leukotriene synthesis, although such treatment does not appear to affect the initial migration of granulocytes into the colon. The present study evaluated the contribution of leukotrienes and interleukin-1 to the recruitment of granulocytes into the colon during the first 12 h after induction of colitis. Rats were treated with a leukotriene synthesis inhibitor (PF-5901), a leukotriene B4 receptor antagonist (SC-41930), an IL-1 receptor antagonist or a corticosteroid (prednisolone) prior to induction of colitis. Granulocyte infiltration was assessed by measurement of colonic myeloperoxidase activity and severity of colonic damage was blindly scored. Despite significant inhibition of leukotriene synthesis, PF-5901 did not affect colonic myeloperoxidase activity or the severity of colonic injury at any time point. Similarly, SC-41930 was without significant effect. However, both the interleukin-1 receptor antagonist and prednisolone significantly reduced colonic myeloperoxidase activity (by approximately 50%) and severity of colonic damage at 6 h after induction of colitis, without significantly affecting colonic leukotriene synthesis. These beneficial effects were no longer apparent at 12 h after induction of colitis. This study demonstrates that the infiltration of granulocytes into the colon during the acute phase of colitis in the rat occurs independent of leukotriene synthesis and appears to be at least in part attributable to interleukin-1.

The uptake of immune complexes by macrophages (MP) may be important in disease states in which circulating immune complexes are increased. We undertook the present study to determine the effects of prostaglandin E2 (PGE2) and adenosine 3',5'-cyclic monophosphate (cAMP) on the uptake of immunoglobulin G complexes (IgG complexes) by MP. The uptake of 125I-IgG-gold particles (IgG-gold) was measured in the established MP cell line J774.16 following pretreatment with PGE2, the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX), PGE2 plus IBMX, the cyclooxygenase inhibitor indomethacin (IM), and dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP). Preincubation with PGE2 at concentrations from (10(-12)) to (10(-5) M) revealed significantly diminished uptake of IgG-gold at (10(-6)) and (10(-5) M) (in counts per min per well, PGE2 [10(-6) M], 5,401 +/- 140; control, 17,150 +/- 493, p less than 0.001); (PGE2 [10(-5) M], 3,835 +/- 172; control, 17,150 +/- 493, p less than 0.001). IBMX (10(-3) M) alone did not significantly alter IgG-gold uptake (IBMX, 14,450 +/- 1938; control, 14,840 +/- 995, p less than 1.0). PGE2 (10(-6) M) plus IBMX (10(-3) M) significantly suppressed IgG-gold uptake (in counts per min per well, PGE2 plus IBMX, 3,659 +/- 129; control 18,296 +/- 486, p less than 0.001). PGE2 (10(-6) M) alone also suppressed IgG-gold uptake versus control (PGE2, 4,578 +/- 105; control, 18,296 +/- 486, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

In this study, the effect of bacterial endotoxin (lipopolysaccharide; LPS) and of LPS priming on the in vitro release of PGE2 from human placental explants was investigated. Both LPS and the calcium ionophore A23187 significantly stimulated PGE2 release (P less than 0.05). Simultaneous exposure of placental explants to both LPS and A23187 revealed no additive or synergistic stimulation of PGE2 release. LPS priming of placental tissue significantly increased A23187-stimulated PGE2 release when compared to non-LPS-primed tissues. The addition of exogenous arachidonic acid (the substrate for PGE2 synthesis) also significantly (P less than 0.05) stimulated PGE2 release. There was, however, no significant further stimulation of PGE2 release following LPS priming in arachidonic acid treated explants. These data suggest that LPS not only increases basal PGE2 release in human placentae, but also potentiates agonist-stimulated PGE2 release, possibly by increasing tissue capacity for endogenous arachidonic acid liberation.

The influence of HDL, isolated from normolipidemic human blood and blood of normo- and hyperlipidemic rabbits, on in vitro 6-keto-PGF1 alpha synthesis by rabbit aorta and on TXB2 synthesis by platelets of clotting human and rabbit blood was tested. The HDL fraction from normolipidemic subjects, when incubated with blood from normolipidemic humans or rabbits, inhibited TXB2 formation. The same fraction stimulated the formation of 6-keto-PGF1 alpha after incubation with rabbit aorta taken from normolipidemic animals. HDL taken from hyperlipidemic rabbits inhibited 6-keto-PGF1 alpha formation in rabbits and had no influence on TXB2 formation. These results support the hypothesis that not only is the absolute amount of HDL important for its influence on prostanoid formation, but also the origin and the composition of the HDL fraction.

In the present studies, ex vivo-, in vitro-, and in vivo-effects of three structurally different angiotensin I-converting enzyme (ACE) inhibitors on the kallikrein-kinin and eicosanoid systems are described. In the ex vivo- and in vitro-experiments using isolated rat aorta, vascular prostacyclin (PGI2) production is dose-dependently stimulated by the ACE inhibitors captopril, lisinopril, and ramipril. Furthermore, the ACE inhibitor-induced augmentation of vascular PGI2 synthesis observed in vitro was completely inhibited by the competitive bradykinin antagonist D-Arg[Hyp3,Thi5,8,D-Phe7]bradykinin suggesting that ACE inhibitors stimulate PGI2 generation by an enhancement of kinin activity. In the in vivo studies in healthy volunteers, we used platelet cyclic adenosine-5'-monophosphate (cAMP) and cyclic guanosine-5'-monophosphate (cGMP) as indirect parameters of the activity of prostacyclin and the endothelium-derived relaxing factor, respectively. Since platelet cAMP and cGMP were unaffected by an acute dose of 10 mg of lisinopril, our data do not support the concept that the interference of ACE inhibitors with the kallikrein-kinin-prostaglandin system observed ex vivo and in vitro participates in the haemodynamic effects of these agents in humans in vivo.