ISSN:0009-7330    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

This study was undertaken to investigate the enzymatic regulation of the biosynthesis of vasoconstrictor prostanoids by resting and interleukin (IL)-1 beta-stimulated human umbilical vein endothelial cells (HUVECs). Biosynthesis of eicosanoids in response to IL-1 beta, exogenous labeled arachidonic acid (AA), or histamine, as well as their spontaneous release, was evaluated by means of HPLC and RIA. HUVECs exposed to IL-1 beta produced prostaglandin (PG) I2for no longer than 30 seconds after the substrate was added irrespective of the cyclooxygenase (COX) activity, whereas the time course of PGE2and PGD2formation was parallel to the COX activity. The ratio of PGE2to PGD2produced by HUVECs was similar to that obtained by purified COX-1 and COX-2. Production of PGF2alpha from exogenous AA was limited and similar in both resting and IL-1 beta-treated cells. PGF2alpha was the main prostanoid released into the medium during exposure to IL-1 beta, whereas when HUVECs treated with IL-1 beta were stimulated with histamine or exogenous AA, PGE2was released in a higher quantity than PGF2alpha. PGF2alpha released into the medium during treatment with IL-1 beta and the biosynthesis of PGE2and PGD2in response to exogenous AA or histamine increased with COX-2 expression, whereas this did not occur in the case of PGI2. We observed that PGI synthase (PGIS) mRNA levels were not modified by the exposure to IL-1 beta, but the enzyme was partially inactivated. When SnCl2was added to the incubation medium, the transformation of exogenous AA-derived PGH2into PGE2and PGD2was totally diverted toward PGF2alpha. Overall, these results support the conclusions that PGE2and PGD2(and also probably PGF (2) alpha) were nonenzymatically derived from PGH2in HUVECs. The concept that a high ratio of PGH2was released by the IL-1 beta-treated HUVECs and isomerized outside the cell into PGE2and PGD2was supported by the biosynthesis of thromboxane B2by COX-inactivated platelets, indicating the uptake by platelets of HUVEC-derived PGH2. The IL-1 beta-induced increase in the release of PGH (2) by HUVECs was suppressed by the COX-2-selective inhibitor SC-58125 and correlated with both COX-2 expression and PGIS inactivation. An approach to the mechanism of inactivation of PGIS by the exposure to IL-1 beta was performed by using labeled endoperoxides as substrate. The involvement of HO[center dot] in the PGIS inactivation was supported by the fact that deferoxamine, pyrrolidinedithiocarbamate, DMSO, mannitol, and captopril antagonized the effect of IL-1 beta on PGIS to different degrees. The NO synthase inhibitor NG-monomethyl-L-argininealso antagonized the PGIS inhibitory effect of IL-1 beta, indicating that NO[center dot] was also involved. NO[center dot] reacts with O2-[center dot] to form peroxynitrite, which has been reported to inactivate PGIS. Homolytic fission of the O-O bond of peroxynitrite yields NO2[center dot] and HO[center dot]. The fact that 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO), which reacts with NO[center dot] to form NO2[center dot], dramatically potentiated the IL-1 beta effect suggests that NO2[center dot] could be a species implicated in the inactivation of PGIS. Cooperation of HO[center dot] was supported by the fact that DMSO partially antagonized the effect of carboxy-PTIO. Although our results on the exact mechanism of the inactivation of PGIS caused by IL-1 beta were not conclusive, they strongly suggest that both NO[center dot] and HO[center dot] were involved. (Circ Res. 1998;83:353-365.)

ISSN:0009-7330    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

probucol. Antioxidant treatment reduced aortic cholesterol concentrations 21% to 56%, 29% to 86%, and 19% to 75% for the aortic arch, descending thoracic aorta, and abdominal aorta, respectively (P<0.025 to P<0.0003 by ANOVA), with slightly greatly reductions for areas of atherosclerotic lesions. Some treatments reduced plasma cholesterol concentrations, but none altered the distribution of cholesterol among lipoproteins. Corrected for differences in plasma cholesterol concentrations, aortic cholesterol concentrations were reduced up to 72% (P<0.02) by the antioxidant treatments, with equal reductions by vitamin E+selenium and by probucol. Aortic alpha-tocopherol standardized by aortic cholesterol as a measure of aortic lipids was lower in the abdominal aorta than in the aortic arch of rabbits not given alpha-tocopherol and increased relatively more in the abdominal aorta than in the aortic arch with alpha-tocopherol supplementation. The results of this study suggest that vitamin E+selenium inhibited atherosclerosis as effectively as an equally hypocholesterolemic dose of probucol by a mechanism(s) that is in part independent of effects on plasma and lipoprotein cholesterol concentrations. The tendency for greater efficacy of antioxidant treatments in the abdominal aorta than aortic arch may relate to the lower concentrations of alpha-tocopherol in the abdominal aorta of unsupplemented rabbits. (Circ Res. 1998;83:366-377.)

ISSN:0009-7330    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Unstable human atherosclerotic plaques are characterized by a thin fibrous cap that contains few smooth muscle cells (SMCs) and numerous foam cells of macrophagic origin. Apoptosis of SMCs in the fibrous cap could destabilize the plaque and promote plaque rupture. In an experimental approach, we have studied apoptotic cell death and related proteins in atherosclerotic plaques of cholesterol-fed rabbits and examined the effects of cholesterol withdrawal. The induced atherosclerotic plaques at the thoracic aorta were composed of both fibromuscular tissue and foam cells. The presence of SMCs overlying macrophage accumulation was reminiscent of the structure of human atherosclerotic plaques. The plaques showed signs of cell replication and apoptotic cell death (1.8 +/- 0.5% terminal deoxynucleotidyl transferase end-labeling [TUNEL]-positive nuclei). Cell replication was confined mostly to the macrophages, whereas 34% of the TUNEL-labeled cells were SMCs. Both the macrophages and SMCs in the plaques expressed BAX, a proapoptotic protein of the BCL-2 family. After 6 months of cholesterol withdrawal, the thickness of the plaques in all localizations of the aorta was unchanged, but apoptosis was nearly absent (<0.1% of nuclei). Moreover, macrophages disappeared from the plaques, whereas the SMCs that remained present lost their lipid accumulation and strongly reduced their BAX expression. These changes were associated with a reduction of cell replication and increased deposition of fibrillar collagen fibers in the plaques, which pointed to plaque stabilization. In conclusion, the cell composition but not the thickness of atherosclerotic plaques was profoundly altered after a 6-month cholesterol withdrawal period. These changes were associated with a strong reduction of cell replication and apoptotic cell death. Moreover, the expression of the proapoptotic factor, BAX, was reduced in the remaining cells, which were mainly SMCs. These findings could help to explain the benefit of lipid-lowering therapy on plaque stabilization. (Circ Res. 1998;83:378-387.)

ISSN:0009-7330    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

There is evidence that estrogen can upregulate nitric oxide (NO) synthase expression. There is also evidence that NO increases the activity of prostaglandin H synthase (PGHS). Our initial hypothesis was that removal of ovarian steroids would decrease endothelium/NO-dependent relaxation responses but that estrogen replacement would increase NO and PGHS activity, leading to increased vasodilation. Resistance-sized (<250 [micro sign]m) mesenteric arteries from ovariectomized Sprague-Dawley rats without and with 17 beta-estradiol replacement (0.15 or 0.5 mg/pellet, 60-day release) for 4 weeks were studied in a myograph system. The vasodilator response to methacholine, an endothelium-dependent muscarinic agonist, was reduced in the arteries of the ovariectomized rats compared with estradiol-replaced rats. In the presence of PGHS inhibitors (meclofenamate, valeryl salicylate, and NS-398) or a thromboxane A2(TxA2)/prostaglandin H2(PGH2) receptor blocker (SQ-29548), there was no longer a significant difference among the groups. Contrary to our initial hypothesis, inhibition of the PGHS pathway significantly enhanced the relaxation response in the arteries from the ovariectomized rats, which was similar to the response in the arteries from estradiol-replaced rats, indicating that a PGHS-dependent vasoconstrictor had modified the response to methacholine. Confirming these data, in response to exogenous arachidonic acid, arteries from ovariectomized rats exhibited constriction, whereas the arteries from the estradiol-replaced rats exhibited vasodilation. In the ovariectomized rats, pretreatment with inhibitors of the PGHS pathway reversed the vasoconstriction to a vasodilation. In addition, the vasoconstrictor response to the thromboxane mimetic U-46619 as well as PGH2was enhanced in endothelium-denuded arteries from the ovariectomized rats compared with the estradiol-replaced rats. These data demonstrate that removal of ovarian steroids increased endothelium-mediated PGHS-dependent vasoconstriction that was associated with augmented sensitivity of the TxA2/PGH2receptor. Chronic estrogen replacement in the ovariectomized rat suppressed this PGHS-dependent vasoconstrictor response. (Circ Res. 1998;83:388-395.)

ISSN:0009-7330    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Heme oxygenase (HO)-1 generates CO, a gas with vasodilatory properties, during heme metabolism. HO-1 is expressed highly in vascular tissue after endotoxin stimulation, and generation of CO through the HO-1 pathway contributes to the hemodynamic compromise of endotoxic shock. Shock related to endotoxemia is an immune-mediated process that involves the generation of proinflammatory cytokines such as interleukin (IL)-1 beta. Because transforming growth factor (TGF)-beta 1 is a modulator of immune-mediated inflammatory responses and it blocks the hypotension of endotoxic shock, we determined whether TGF-beta 1 could be used to reduce expression of HO-1 in vascular tissue and smooth muscle cells. In a rat model of endotoxic shock, lipopolysaccharide-induced HO-1 mRNA and protein expression was reduced by TGF-beta 1 in highly vascularized tissue, such as heart and lung, by Northern and Western analysis. Furthermore, TGF-beta 1 downregulated HO-1 mRNA after its induction by IL-1 beta in vascular smooth muscle cells in culture. TGF-beta 1 also decreased HO-1 but not HO-2 protein expression in these cells. TGF-beta 1 decreased HO enzyme activity induced in IL-1 beta-treated vascular smooth muscle cells to a level not different from that in vehicle-treated cells. These studies suggest that this downregulation of HO-1 mRNA and protein expression and decrease in IL-1 beta-induced HO enzyme activity may contribute to the beneficial effect of TGF-beta 1 on endotoxic shock. (Circ Res. 1998;83:396-403.)

ISSN:0009-7330    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Oxidized LDLs (Ox-LDLs) inhibit endothelium-dependent dilation of isolated conduit arteries in a manner comparable to the impairment demonstrated in atherosclerotic vessels. However, it is not known whether the microvessels, which do not develop atherosclerotic lesions, are susceptible to Ox-LDL. Since endothelial release of NO plays an important role in vasodilation and since its dysfunction associated with atherosclerosis has been shown to extend into the coronary microcirculation, we hypothesized that Ox-LDLs impair endothelium-dependent vasodilation of coronary arterioles by reducing the synthesis and/or release of NO. To test this hypothesis, porcine subepicardial vessels (50 to 100 [micro sign]m) were isolated, cannulated, and pressurized to 60 cm H2O without flow for in vitro study. Isolated vessels developed basal tone and dilated in a dose-dependent manner to the endothelium-dependent vasodilators serotonin, ATP, and ionomycin. These vasodilatory responses were inhibited by the NO synthase inhibitor NG-monomethyl-L-arginineand were subsequently reversed by extraluminal administration of the NO precursor L-arginine (3 mmol/L), suggesting the involvement of NO in these vasomotor responses. Intraluminal incubation of the vessels with native LDL (N-LDL) or Ox-LDL (1 mg protein/mL) significantly attenuated dilations to serotonin, ATP, and ionomycin. Ox-LDL produced more severe inhibition than did N-LDL, and the inhibitory effect was comparable to that of N (G-monomethyl-L-arginine). The inhibitory effects of N-LDL and Ox-LDL were reversed by exogenous L-arginine (3 mmol/L) and were prevented by sodium dihydroxybenzene disulfonate (Tiron), a cell-permeable superoxide scavenger. In contrast, administration of the cell-impermeable superoxide scavenger superoxide dismutase prevented the inhibitory effect of N-LDL but not of Ox-LDL. In addition, the inhibitory effects of LDL were not restored by D-arginine or by removal of intraluminal LDL. Neither N-LDL nor Ox-LDL altered endothelium-independent vasodilation to sodium nitroprusside. These results indicate that coronary arterioles are susceptible to LDLs that specifically impair endothelium-dependent vasodilation by reducing NO synthesis. It is suggested that the initiation of superoxide anion production and the subsequent L-arginine deficiency may be responsible for the detrimental effect of LDL. (Circ Res. 1998;83:404-414.)

ISSN:0009-7330    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

T474I/WT. In addition to decreases in slope conductance for all 3 mutants, the voltage dependence of steady-state inactivation was shifted to negative potentials for V630L/WT and A614V/WT. Consequently, channel availability at positive potentials was diminished, and inward rectification was enhanced for these 2 mutants. Thus, missense mutations of HERG caused dominant-negative suppression through multiple mechanisms. The shift in voltage dependence of HERG inactivation and the resulting enhanced inward rectification in A614V/WT and V630L/WT provide a novel mechanism for suppression of the HERG current carrying outward current during the repolarization phase of the action potential. (Circ Res. 1998;83:415-422.)

ISSN:0009-7330    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Antioxidants are known to mitigate the cardiac contractile dysfunction that follows brief periods of ischemia ("myocardial stunning"). Stunning decreases contractility at the level of the contractile proteins; therefore, we asked whether antioxidant treatment preserves myofilament Ca2+responsiveness after global ischemia and reflow. Right ventricular trabeculae were dissected from rat hearts subjected either to 20 minutes ischemia and reperfusion in the absence of drugs (stunned group) or to the same protocol in the presence of allopurinol, an inhibitor of xanthine oxidase (XO), and mercaptopropionylglycine (MPG), a hydroxyl radical scavenger (antioxidant group). At 20 minutes of reflow, isovolumic developed pressure recovered completely in the antioxidant group, but in the stunned group it recovered by only 57%. [Ca (2+)]iand contractile force measurements in trabeculae revealed the expected depression of myofilament function in the stunned group, with no change in Ca2+transients relative to nonischemic controls. In contrast, Ca2+transients were smaller, but force was greater, in the antioxidant group relative to both the stunned group and to nonischemic controls. Steady-state [Ca2+]i-forcerelationships revealed a striking increase of maximal force and a modest shift of activation to a lower range of [Ca2+]i. The increase in maximal force was reproduced by allopurinol+MPG or by allopurinol alone under nonischemic conditions and also by oxypurinol (100 [micro sign]mol/L), a potent inhibitor of XO. We conclude that allopurinol and oxypurinol sensitize the cardiac myofilaments to Ca2+. This Ca2+-sensitizingeffect underlies the preservation of contractility observed with an allopurinol+MPG antioxidant cocktail in a model of stunned myocardium. These serendipitous findings identify allopurinol and oxypurinol as the lead compounds of a novel class of inotropic agents. (Circ Res. 1998;83:423-430.)

ISSN:0009-7330    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Myocytes overlying a zone of infarction form the primary substrate for serious reentrant ventricular arrhythmias. In vitro and in vivo studies suggest that antiarrhythmic agents affect Na+channels of cells from the epicardial border zone (EBZ) of the 5-day infarcted heart differently than they affect those of normal muscle. However, the mechanisms responsible for this difference remain unclear. Previous studies have revealed differences in Na+current (INa) density and inactivation gating kinetics in myocytes dispersed from the EBZ (IZs). Since changes in inactivation gating could influence lidocaine action, we examined the effects of lidocaine on INaor=to-100-mV) holding potentials. Consistent with a high affinity for the inactivated channel conformation, lidocaine produced more tonic block in IZs than NZs at depolarized holding potentials. Additionally, in drug-free conditions, IZ INaexhibited an enhanced rate of inactivation from closed states, a delay in recovery from inactivation, and increased use-dependent reduction in amplitude during rapid (1- to 3-Hz) pulse trains. In both IZs and NZs, lidocaine (20 to 120 [micro sign]mol/L) accelerated the rate of time-dependent loss of availability and markedly delayed recovery from availability, inducing significant use-dependent reduction of INaor=to60 [micro sign]mol/L, the difference in use-dependent current reduction between IZs and NZs was minimized. The action of lidocaine to render Na+channel inactivation in NZs more similar to that of IZs may be central to its (pro)antiarrhythmic effects. (Circ Res. 1998;83:431-440.)

ISSN:0009-7330    

出版商:OVID    

年代:1998

数据来源: OVID