Search

The participation of prostanoids, nitric oxide and non-prostanoid non-nitric oxide factors in endothelium-dependent relaxations was investigated in phenylephrine (PE)-constricted carotid and femoral arteries of C57BL6 mice. The carotid artery was more sensitive to acetylcholine as compared to the femoral artery, and cyclooxygenase inhibition did not influence the relaxation in either vessel. In the carotid artery, high doses of acetylcholine caused transient constrictions, which were abolished by indomethacin or piroxicam. In the carotid but not the femoral artery, N(omega)-nitro-L-arginine or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) enhanced PE-induced contractions enormously, suggesting that endogenous nitric oxide production is much higher in the carotid artery. While in the carotid artery all relaxation was abolished by N(omega)-nitro-L-arginine or ODQ, a residual response (34+/-5% and 74+/-4%, respectively) but with a different shape, was maintained in the femoral artery. This N(omega)-nitro-L-arginine-resistant relaxation was abolished by the combination of apamin and charybdotoxin. In both arteries, ODQ abolished relaxation to S-nitroso-N-acetyl-D-penicillamine, while N(omega)-nitro-L-arginine enhanced the sensitivity to this donor of exogenous nitric oxide. In 30 mM KCl, the relaxation to acetylcholine was abolished by N(omega)-nitro-L-arginine or ODQ in either artery. In conclusion, in the carotid artery endothelium-dependent relaxation is mediated predominantly by nitric oxide acting via cyclic GMP-dependent pathways, while in the femoral artery part of the relaxation can be attributed to a non-prostanoid non-nitric oxide factor operating via apamin/charybdotoxin-sensitive potassium channels.

Oxidized low-density lipoprotein (LDL) is currently regarded as a tentative key player in atherosclerosis by virtue of its ability to induce intracellular lipid accumulation and to modulate cell functions in the vessel wall. We previously demonstrated that inducible nitric oxide (NO) synthase activity is attenuated in lipid-laden J774 macrophages obtained by incubation with oxidized LDL 200 micrograms ml-1 for 24 h. In the present study we investigated the effect of oxidized LDL in a lower concentration (20 micrograms ml-1) or for a shorter time (6 h) and the possible mediator role of prostaglandin E2 and prostacyclin. Prostaglandins and the NO synthase metabolites citrulline and nitrite were elevated in the 24 h supernatant after immune stimulation with interferon-gamma 100 U ml-1 with or without lipopolysaccharide 10 micrograms ml-1. Pretreatment with oxidized LDL 20 micrograms ml-1 for 18 h decreased nitrite release by 31 +/- 2%, whereas prostaglandin production was not affected. A 6 h pre-exposure to 200 micrograms ml-1 had an opposite effect: it significantly potentiated interferon-gamma-stimulated prostaglandin E2 (10-fold), prostacyclin (7-fold), nitrite (1.5-fold), and citrulline (2.4-fold) release. Indomethacin 10 microM abolished the prostaglandin production and largely prevented the oxidized LDL-dependent increase in NO synthase activity. Acetylated LDL was without effect. The data show that the immune-induced release of NO is potentiated or suppressed, depending on the conditions of exposure to oxidized LDL. The potentiation due to short, high-dose exposure is partly mediated by prostaglandins since indomethacin inhibited both processes.

The aim of the present study is to investigate the effects of TRPV1 and TRPA1 receptor antagonists and their synergism on the visceromotor responses during experimental colitis in rats. Colitis was induced in rats by a TNBS/ethanol enema at day 0 and was assessed at day 3 using endoscopy, histology and a myeloperoxidase assay. The visceromotor response to colorectal distension (1080 mmHg) was evaluated in conscious rats before (control condition) and 3 days after 2,4,6-trinitrobenzene sulfonic acid (TNBS) administration (colitis condition). At day 3, visceromotor responses were assessed before and after treatment with a TRPV1 (BCTC) or TRPA1 (TCS-5861528) receptor antagonist either alone or in combination and either after intraperitoneal or intrathecal administration. Endoscopy, microscopy and myeloperoxidase activity indicated severe colonic tissue damage 3 days after TNBS administration. Colorectal distension-evoked visceromotor responses demonstrated a 2.9-fold increase during acute colitis (day 3) compared to control conditions. Intraperitoneal and intrathecal administration of BCTC or TCS-5861528 partially reversed the colitis-induced increase in visceromotor responses compared to control conditions (P

In the present study we used a new model, in which the positioning of a non-occlusive collar around the rabbit carotid artery results, within 7 days, in the generation of a neo-intima, a precursor lesion of atherosclerosis. We investigated the effects of this intimal proliferation on the responsiveness to serotonin (5-hydroxytryptamine, 5-HT) and noradrenaline (NOR) after 1, 2 and 7 days. Already after 1 day the collar-treated arteries were more sensitvie to 5-HT, but not to NOR. This sensitivity persisted over a period of 7 days. However, the development of a neo-intima diminished the maximum contractile force to NOR after 2 and 7 days, but not to 5-HT. These results demonstrate that there is a relatively selective increase in sensitivity to 5-HT during neo-intima formation, even without hypercholesterolaemia.

Activation of J774-macrophages with lipopolysaccharide (LPS) or LPS and recombinant interferon-γ (IFN-γ) induced nitric oxide (NO) synthase activity, as measured by the production of nitrite and citrulline. NO synthase activity was suppressed by loading the cells with oxidatively modified low-density lipoprotein (ox-LDL) but not with acetylated LDL (ac-LDL), although the intracellular lipid accumulation was comparable. This suggests that the extent of activation of lipid-loaded macrophages may be influenced by the type of lipid.

Many studies have shown that loss of endothelium-derived nitric oxide is a major factor of ischemic episodes in patients with coronary artery disease and there is increasing evidence to suggest that nitric oxide might exert antiatherosclerotic actions. Based on these concepts, the results of animal studies on the effects of lipid lowering drugs, antioxidants, angiotensin converting enzyme inhibitors, Ca2+ channel blockers, estrogens and agents which modulate nitric oxide bioavailability are presented and compared to the results of patient studies and clinical trials. In spite of encouraging results obtained with antioxidants in animals, clinical trials could only show a clear positive effect of vitamin E treatment on the outcome of cardiovascular disease. Angiotensin converting enzyme inhibitors can ameliorate endothelial dysfunction in coronary heart disease, but their impact on disease progression remains unclear. There is evidence that estrogen replacement therapy in post-menopausal women may increase the bioavailability of nitric oxide. Finally, improved endothelial function and plaque stability clearly contribute to the clinical benefits of lipid lowering interventions, statins in particular. Taken together, these studies lend support to the concept that improving endothelial function and nitric oxide release might serve as valuable elements in the prevention or therapy of cardiovascular disease.

The purpose of the study was to evaluate whether balloon angioplasty is associated with changes in nitric oxide synthase (NO synthase) activity. Normal rabbit carotid arteries were examined 10 min or 1, 2, 3 or 10 weeks after angioplasty with 2 or 2.5-mm balloons. Immunohistology was used to evaluate intimal thickening and endothelial cell regeneration. The NO synthase activity was studied functionally using isolated segments in organ chambers. Immunohistochemistry of the endothelial cell markers von Willebrand factor and platelet endothelial cell adhesion molecule-1 indicated that the regeneration of endothelial cells from patchy islands that remained after angioplasty was virtually complete within 2 weeks. However, the endothelium-dependent relaxations elicited by acetylcholine remained impaired up to 10 weeks after dilatation. Contractions elicited by 5-hydroxytryptamine (5-HT) were attenuated, but were significantly augmented by the NO synthase blocker, nitro- l -arginine. Furthermore, in contrast to normal arteries, the balloon-treated arteries developed marked contractions in response to nitro- l -arginine methyl ester ( l -NAME), contractions which could be reversed by l -arginine. The latter contractions and relaxations were not influenced by endothelial removal. These results suggest that although the endothelium quickly regenerates after severe balloon injury, the endothelium-dependent release of nitric oxide remains disturbed. However, the functional data also suggest that angioplasty led to a significant induction of NO synthase in ‘non-endothelial’ cells of the artery.

Intimal thickening predisposes to atherosclerosis and is often associated with alterations of the vascular reactivity of the artery. We investigated whether dexamethasone inhibited the intimal thickening and reactivity changes induced by a silicone collar placed around the left rabbit carotid artery for 2 weeks. The sham-operated, right artery served as control. Dexamethasone (1 mg/kg/day), given in the drinking water (n = 10) or by a subcutaneous minipump (n = 10), abolished intimal thickening compared to that of both placebo groups (n = 10). Both dexamethasone and the collar suppressed the isometric force development of isolated segments elicited by KCl in organ chamber experiments. The collar raised the sensitivity to serotonin (5-hydroxytryptamine, 5-HT) and the maximum force development (Emax) after normalization for the KCl responses. Dexamethasone exerted complex effects on 5-HT contractions in sham arteries: the curves often became biphasic, and sensitivity and Emax of the first phase were depressed by dexamethasone. In contrast, dexamethasone raised the hypersensitivity of collared arteries to 5-HT even further. Collar and dexamethasone did not influence endothelium-dependent relaxations elicited by acetylcholine or the calcium ionophore A-23187. It is concluded that dexamethasone interfered with neo-intima formation in the collar model, presumably by inhibition of smooth muscle cell migration and/or proliferation, without restoring contractile behaviour. Therefore, the collar-induced alterations in the reactivity of the smooth muscle cells in the media appear to be unrelated to the process of intimal thickening.

An L-arginine-dependent pathway, by which L-arginine is metabolised to citrulline and nitrogen oxides, has been recently identified in some cell types. In cultured rat lung fibroblasts the presence of L-arginine was necessary for the production of nitrite to be induced by rat recombinant interferon-gamma and synergistically enhanced by lipopolysaccharide and interleukin-1beta. Lipopolysaccharide and interleukin-1beta did not induce nitrite biosynthesis by themselves. Biosynthesis was apparently dependent on tetrahydrobiopterin, since it could be blocked by diaminohydroxypyrimidine, an inhibitor of tetrahydrobiopterin synthesis. Dexamethasone blocked nitrite production by a receptor-mediated mechanism. These data indicate that rat lung fibroblasts express an L-arginine-dependent nitric oxide synthase which can be induced by some mediators of inflammation.

The interaction between dipyridamole and nitric oxide (NO) was studied using isolated rabbit platelets and segments of the rabbit aorta. Dipyridamole potentiated the anti-aggregating activity of authentic NO when platelet aggregation was induced by the thromboxane A2 mimetic U-46619 or adenosine diphosphate (ADP). This potentiation was also seen when washed rabbit platelets were exposed to aortic effluent containing endothelium-derived NO. In the thoracic aorta dipyridamole hardly influenced the endothelium-dependent relaxations induced by acetylcholine. However, dipyridamole clearly enhanced the dilatation caused by exogenous NO from four different sources, including endothelial cells.

Rat alveolar and pleural macrophages incubated with lipopolysaccharide, opsonized zymosan or recombinant interferon-γ, but not with recombinant tumor necrosis factor-α, produced nitrite dose and time depcndently. This production depends on the presence and amount of L-arginine in the culture medium. The precursor of the nitrite was demonstrated as being nitric oxide, by bleaching of ferredoxin at 410 nm when added to the culture medium. Addition of NG-monomethyl-L-arginine, an inhibitor of nitric oxide synthesis, and cycloheximide, a protein synthesis inhibitor, to the medium resulted in a decrease of nitrite production. Glucocorticoids were able to block the induction of nitrite production in alveolar macrophages. These data indicate that pulmonary macrophages are capable of secreting L-arginine-derived nitrogen oxides.

The nature of the inhibitory non-adrenergic non-cholinergic (NANC) neurotransmitter was studied in circular muscle strips of the canine terminal ileum and ileocolonic junction. Nitric oxide (NO) induced tetrodotoxin-resistant NANC relaxation, similar to that induced by electrical stimulation or acetylcholine (ACh). Incubation with the stereospecific inhibitors of NO biosynthesis, N G -monomethyl-L-arginine (L-NMMA) and N G -nitro-L-arginine (L-NNA), resulted in an increase of basal tension in the ileocolonic junction which was partly reversed by L-arginine but not by D-arginine. Moreover, L-NMMA and L-NNA, but not D-NMMA, concentration dependently inhibited the NANC relaxation in response to electrical stimulation and ACh, but not that in response to NO or nitroglycerin. This inhibitory effect was reversed by L-arginine but not by D-arginine. Hemoglobin reduced the NANC relaxation in response to electrical stimulation, ACh and nitroglycerin, and abolished the responses to NO. Our results suggest that NO or a NO releasing substance mediates the NANC relaxation in the canine terminal ileum and ileocolonic junction. Non-adrenergic non-cholinergic (NANC) neurotransmission; Ileum (canine); Ileocolonic junction (canine); Nitric oxide

Administration of endotoxin (lipopolysaccharide W E. coli O111 B 4 , 0.5 mg/kg i.v.) induced about 20% activation of the complement system (measured as CH 50 and C3), a biphasic hypotension, thrombocytopenia and a significant rise in blood levels of 6-oxo-PGF 1α . Complement depletion (CH 50 and C3 less than 3%) with Cobra Venom Factor significantly reduced the initial fall in blood pressure and the rise in 6-oxo-PGF 1α , and abolished the second phase of hypotension and the thrombocytopenia, due to subsequent injection of endotoxin. It is concluded that activation of about 20% of the complement system by endotoxin is a prerequisite for the occurrence of thrombocytopenia and secondary hypotension, and that it is involved in the increase in blood levels of 6-oxo-PGF 1α . The results of histamine determinations in rabbit blood and plasma indicate that, besides products derived from prostaglandin endoperoxides, other vasoactive substances, possibly released during complement-mediated adherence aggregation of platelets, might contribute to the endotoxin-induced hypotension.

A sensitive high pressure liquid chromatography (HPLC) method was used to measure acetylcholine release from canine bronchial tissue in response to electrical stimulation. Indomethacin enhanced the efflux of acetylcholine, an effect that was reversed by the addition of prostaglandin E2 (PGE2). Prostaglandin D2 (PGD2) had no effect on acetylcholine output. These data suggest that prostaglandins, possibly PGE2, are involved in a negative feedback control mechanism for acetylcholine release in canine bronchi.