Biomedical subjects

H Shimokawa

Publications and source records attributed to H Shimokawa.

At least 19 recordsLinked to original sources

PubMed2000

Inhibition of myosin phosphatase by upregulated rho-kinase plays a key role for coronary artery spasm in a porcine model with interleukin-1beta.

BACKGROUND: We recently demonstrated that the Rho-kinase-mediated pathway plays an important role for coronary artery spasm in our porcine model with interleukin-1beta (IL-1beta). In this study, we examined whether or not Rho-kinase is upregulated at the spastic site and if so, how it induces vascular smooth muscle hypercontraction. METHODS AND RESULTS: Segments of the left porcine coronary artery were chronically treated from the adventitia with IL-1beta-bound microbeads. Two weeks after the operation, as reported previously, intracoronary serotonin repeatedly induced coronary hypercontractions at the IL-1beta-treated site both in vivo and in vitro, which were markedly inhibited by Y-27632, one of the specific inhibitors of Rho-kinase. Reverse transcription-polymerase chain reaction analysis demonstrated that the expression of Rho-kinase mRNA was significantly increased in the spastic compared with the control segment. Western blot analysis showed that during the serotonin-induced contractions, the extent of phosphorylation of the myosin-binding subunit of myosin phosphatase (MBS), one of the major substrates of Rho-kinase, was significantly greater in the spastic than in the control segment and that the increase in MBS phosphorylations was also markedly inhibited by Y-27632. There was a highly significant correlation between the extent of MBS phosphorylations and that of contractions. CONCLUSIONS: These results indicate that Rho-kinase is upregulated at the spastic site and plays a key role in inducing vascular smooth muscle hypercontraction by inhibiting myosin phosphatase through the phosphorylation of MBS in our porcine model.

Animals↗

PubMed2000

Identification of human MutY homolog (hMYH) as a repair enzyme for 2-hydroxyadenine in DNA and detection of multiple forms of hMYH located in nuclei and mitochondria.

An enzyme activity introducing an alkali-labile site at 2-hydroxyadenine (2-OH-A) in double-stranded oligonucleotides was detected in nuclear extracts of Jurkat cells. This activity co-eluted with activities toward adenine paired with guanine and 8-oxo-7,8-dihydroguanine (8-oxoG) as a single peak corresponding to a 55 kDa molecular mass on gel filtration chromatography. Further co-purification was then done. Western blotting revealed that these activities also co-purified with a 52 kDa polypeptide which reacted with antibodies against human MYH (anti-hMYH). Recombinant hMYH has essentially similar activities to the partially purified enzyme. Thus, hMYH is likely to possess both adenine and 2-OH-A DNA glycosylase activities. In nuclear extracts from Jurkat cells, a 52 kDa polypeptide was detected with a small amount of 53 kDa polypeptide, while in mitochondrial extracts a 57 kDa polypeptide was detected using anti-hMYH. With amplification of the 5'-regions of the hMYH cDNA, 10 forms of hMYH transcripts were identified and subgrouped into three types, each with a unique 5' sequence. These hMYH transcripts are likely to encode multiple authentic hMYH polypeptides including the 52, 53 and 57 kDa polypeptides detected in Jurkat cells.

Adenine↗

PubMed2000

Important role of local angiotensin II activity mediated via type 1 receptor in the pathogenesis of cardiovascular inflammatory changes induced by chronic blockade of nitric oxide synthesis in rats.

BACKGROUND: The chronic inhibition of NO synthesis by N(omega)-nitro-L-arginine methyl ester (L-NAME) upregulates the cardiovascular tissue angiotensin II (Ang II)-generating system and induces cardiovascular inflammatory changes in rats. METHODS AND RESULTS: We used a rat model to investigate the role of local Ang II activity in the pathogenesis of such inflammatory changes. Marked increases in monocyte infiltration into coronary vessels and myocardial interstitial areas, monocyte chemoattractant protein-1 (MCP-1) expression, and nuclear factor-kappaB (NF-kappaB, an important redox-sensitive transcriptional factor that induces MCP-1) activity were observed on day 3 of L-NAME administration. Along with these changes, vascular superoxide anion production was also increased. Treatment with an Ang II type 1 receptor antagonist or with a thiol-containing antioxidant, N-acetylcysteine, prevented all of these changes. CONCLUSIONS: Increased Ang II activity mediated via the type 1 receptor may thus be important in the pathogenesis of early cardiovascular inflammatory changes in this model. Endothelium-derived NO may decrease MCP-1 production and oxidative stress-sensitive signals by suppressing localized activity of Ang II.

Angiotensin II↗

PubMed2000

Sarpogrelate, a selective 5-HT2A serotonergic receptor antagonist, inhibits serotonin-induced coronary artery spasm in a porcine model.

Serotonin is one of the most important vasoactive substances and has been implicated in the pathogenesis of coronary artery spasm and of acute coronary syndrome. We have recently demonstrated that local and long-term treatment with interleukin-1beta(IL-1beta) causes coronary arteriosclerotic changes and hyperconstrictive responses to serotonin in pigs in vivo. However, it remains to be examined which serotonergic (5-HT) receptor subtype mediates coronary spasm and whether alterations in serotonergic receptors are involved in the abnormality. In this study, we examined the inhibitory effect of sarpogrelate, a selective 5-HT2A serotonergic receptor antagonist, on the serotonin-induced coronary spasm as well as the possible alterations of serotonergic receptors in our porcine model. A segment of the porcine coronary artery was carefully dissected and aseptically wrapped with cotton mesh absorbing IL-1beta-bound microbeads from the adventitia. Two weeks after the procedure, angiographic study was performed, followed by binding assay for 5-HT1B and 5-HT2A serotonergic receptors and reverse transcription-polymerase chain reaction (RT-PCR) analysis for mRNA of those receptors. Angiographic study showed coronary vasospastic responses to serotonin at the IL-1beta-treated site. Sarpogrelate dose-dependently inhibited the serotonin-induced coronary spasm, but it did not affect the prostaglandin F2alpha-induced vasoconstriction. Radiolabeled receptor-binding assay showed that receptor affinity or receptor number of the 5-HT1B, or 5-HT2A receptors did not differ significantly between the spastic and the control sites. Furthermore, RT-PCR analysis showed that the expression of neither 5-HT2A nor 5-HT1B receptor mRNA was significantly altered at the spastic site. These results indicate that serotonin-induced coronary spasm is mediated primarily by 5-HT2A receptor in our porcine model, although the 5-HT2A receptor was not up-regulated, suggesting that alteration in the signal-transduction pathway for vascular smooth muscle contraction beyond the 5-HT2A receptor plays a primary role in the pathogenesis of coronary spasm in our porcine model.

Angiography↗

PubMed2000

Role of transforming growth factor-beta1 in cardiovascular inflammatory changes induced by chronic inhibition of nitric oxide synthesis.

We previously reported that chronic inhibition of nitric oxide (NO) synthesis with N(omega)-nitro-L-arginine methyl ester (L-NAME) induces inflammatory changes (monocyte infiltration, myofibroblast formation, and monocyte chemoattractant protein-1 [MCP-1] and transforming growth factor-beta1 [TGF-beta1] expression) in the rat heart and vessel. There is debate regarding whether TGF-beta1 exhibits proinflammatory or anti-inflammatory activities. We used the rat model to investigate the role of TGF-beta in the pathogenesis of such inflammatory changes. We show here that infiltrating monocytes and myofibroblasts in the inflammatory lesions produced TGF-beta1 on the third day of L-NAME administration. Cotreatment with a monoclonal antibody against TGF-beta1, but not with control IgG, prevented the L-NAME-induced cardiac inflammation. The antibody also significantly inhibited the gene expression of MCP-1, P-selectin, and intercellular adhesion molecule-1. In summary, the antibody against TGF-beta1 prevented inflammatory changes in rat heart and vessel induced by chronic inhibition of NO synthesis, suggesting that increased production of TGF-beta1 is involved in the inflammatory changes in this model.

Animals↗

PubMed2000

Cellular and molecular mechanisms of coronary artery spasm: lessons from animal models.

Coronary artery spasm plays an important role in the pathogenesis of a wide variety of ischemic heart diseases, especially in the Japanese population. Because coronary artery spasm can be induced by a variety of stimuli with different mechanisms of action, the occurrence of the spasm appears to be due to the local hyperreactivity of the coronary artery rather than to an enhanced stimulation with a single mechanism of action. Several lines of evidence indicate that coronary artery spasm is caused primarily by smooth muscle hypercontraction whereas the contribution of endothelial dysfunction may be minimal. In order to elucidate the cellular and molecular mechanisms of the spasm, porcine models of the spasm were developed. In the first model with balloon injury and high-cholesterol feeding, a close topological correlation between the early atherosclerotic lesions and the spastic sites was noted, whereas in the second model with an inflammatory cytokine the potential importance of coronary inflammatory changes, especially at the adventitia, was noted. Subsequent studies in vivo and in vitro demonstrated that protein kinase C (PKC) and Rho-kinase are substantially involved in the intracellular mechanism of the spasm, resulting in increases in the mono- and diphosphorylations of myosin light chain (MLC). Furthermore, molecular biological analyses demonstrated that Rho-kinase is upregulated at the spastic site (at all levels, including mRNA, protein, and activity), resulting in the inhibition of MLC phosphatase through the phosphorylation of its myosin binding subunit and thereby causing the increase in MLC phosphorylations. Preliminary results also suggest that the long-term inhibition of Rho-kinase is effective in inhibiting the development of arteriosclerotic vascular lesions in several porcine models. Thus, Rho-kinase could be regarded as a novel therapeutic target for coronary arteriosclerosis in general and coronary artery spasm in particular.

Animals↗

PubMed1999

Functional significance of the conserved residues for the 23-residue module among MTH1 and MutT family proteins.

Human MTH1 and Escherichia coli MutT proteins hydrolyze 7, 8-dihydro-8-oxo-dGTP (8-oxo-dGTP) to monophosphate, thus avoiding the incorporation of 8-oxo-7,8-dihydroguanine into nascent DNA. Although only 30 amino acid residues (23%) are identical between MTH1 and MutT, there is a highly conserved region consisting of 23 residues (MTH1, Gly(36)-Gly(58)) with 14 identical residues. A chimeric protein MTH1-Ec, in which the 23-residue sequence of MTH1 was replaced with that of MutT, retains its capability to hydrolyze 8-oxo-dGTP, thereby indicating that the 23-residue sequences of MTH1 and MutT are functionally and structurally equivalent and constitute functional modules. By saturation mutagenesis of the module in MTH1, 14 of the 23 residues proved to be essential to exert 8-oxo-dGTPase activity. For the other 9 residues (40, 42, 44, 46, 47, 49, 50, 54, and 58), positive mutants were obtained, and Arg(50) can be replaced with hydrophobic residues (Val, Leu, or Ile), with a greater stability and higher specific activity of the enzyme. Indispensabilities of Val(39), Ile(45), and Leu(53) indicate that an amphipathic property of alpha-helix I consisting of 14 residues of the module (Thr(44)-Gly(58)) is essential to maintain the stable catalytic surface for 8-oxo-dGTPase.

Adaptor Proteins, Signal Transducing↗

PubMed1999

Endothelial vasodilator function is preserved at the spastic/inflammatory coronary lesions in pigs.

BACKGROUND: The question of whether or not endothelial vasodilator function in the spastic coronary artery is preserved is still controversial. We recently developed a porcine model in which long-term and local treatment with interleukin-1beta (IL-1beta) from the adventitial site causes coronary arteriosclerotic changes and vasospastic responses to autacoids. The aim of this study was to examine the endothelial vasodilator function in our new porcine model of the spasm both in vivo and in vitro. METHODS AND RESULTS: A segment of the porcine coronary artery was aseptically wrapped with cotton mesh that held absorbed IL-1beta-bound microbeads. Two weeks after the procedure, intracoronary administration of serotonin caused coronary vasospasm at the IL-1beta-treated site (n = 10). Coronary vasodilatation to bradykinin, substance P, or an increase in coronary blood flow was preserved at the spastic site. Vasodilator responses to 3-morpholinosydnonimine (an NO donor) and nitroglycerin also were comparable between the 2 sites. The vasoconstricting response to N(G)-monomethyl-L-arginine and the extent of the augmentation of the serotonin-induced vasoconstriction were comparable between the 2 sites. Organ chamber experiments showed that endothelium-dependent relaxations to bradykinin, the calcium ionophore A23187, and even the vasospastic agonist serotonin were preserved at the spastic site, whereas contractions to serotonin were augmented at the spastic site regardless of the presence or absence of the endothelium (n = 6). Endothelium-independent relaxations to sodium nitroprusside were also preserved at the spastic site. CONCLUSIONS: These results indicate that endothelial vasodilator function is preserved at the spastic site and that the spasm is caused primarily by smooth muscle hypercontraction in our porcine model.

Animals↗

PubMed1999

Interferon-gamma inhibits the myofibroblastic phenotype of rat palatal fibroblasts induced by transforming growth factor-beta1 in vitro.

Interferon-gamma (IFN-gamma), a multifunctional cytokine, has been noted as a potential therapeutic agent for various fibrotic disorders, including excessive scar tissue formation. We previously reported that transforming growth factor-beta1 (TGF-beta1) induced the myofibroblastic phenotype in palatal fibroblasts derived from palatal mucosa, and that such effects might have a close link to palatal scar formation. In the present study, we examined the effects of IFN-gamma on TGF-beta1-pretreated palatal fibroblasts for the purpose of clarifying the suppressive potency against myofibroblastic phenotype expression in vitro. IFN-gamma significantly altered the spindle morphology of TGF-beta1-pretreated palatal fibroblasts into the polygonal one that was similar to the non-treated palatal fibroblasts. This change was parallel with a decrease in the expression of alpha-smooth muscle actin protein, a marker for myofibroblast, as determined by immunoblot analysis. Northern blot analysis showed that IFN-gamma inhibited proalpha2(I) collagen mRNA expression that was stimulated by TGF-beta1 pretreatment for 24 h. Furthermore, IFN-gamma decreased the cell contractility enhanced by TGF-beta1 pretreatment for 24 h in a three-dimensional collagen gel culture system. These results suggest that IFN-gamma may have negative effects with regard to controlling the myofibroblastic phenotype induced by TGF-beta1 in palatal fibroblasts.

Actins↗

PubMed1999

Primary endothelial dysfunction: atherosclerosis.

The endothelium synthesizes and releases several vasodilating factors, including nitric oxide, endothelium-derived hyperpolarizing factor, and prostacyclin. Under certain conditions, it also liberates vasocontracting factors. Thus, the endothelium plays an important role in regulating vascular homeostasis. Several intracellular mechanisms are involved in the synthesis of nitric oxide, including receptor-coupled G proteins, the availability of L-arginine, cofactors for endothelial nitric oxide synthase and the expression of the enzyme. Endothelial dysfunction by aging, menopause and hypercholesterolemia is involved in the development of atherosclerotic vascular lesions, and predisposes the blood vessel to several vascular disorders, such as vasospasm and thrombosis. Multiple mechanisms are apparently involved in the pathogenesis of the endothelial dysfunction in atherosclerosis. The reduced production of nitric oxide by the endothelium is caused by abnormalities in endothelial signal transduction, availability of L-arginine, cofactors for endothelial nitric oxide synthase and expression of the enzyme. Other mechanisms may also be involved in the impaired endothelium-dependent relaxations in atherosclerosis, including increased destruction of nitric oxide by superoxide anion, altered responsiveness of vascular smooth muscle, and concomitant release of vasocontracting factors. In addition to the treatment of the underlying risk factors, several pharmacological agents can improve endothelial dysfunction in atherosclerosis. Thus, the endothelium is a novel therapeutic target for the treatment of atherosclerotic cardiovascular disease.

Animals↗

PubMed1999

In situ hybridization for matrix metalloproteinase-1 and cathepsin K in rat root-resorbing tissue induced by tooth movement.

The movement of teeth during orthodontic treatment occasionally induces undesirable root resorption. Although high collagenolytic activity has been detected in resorbing tissue of deciduous teeth, the cellular origin of collagenolytic enzymes in root-resorbing tissue caused by tooth movement has not been identified. Here, rats were subject to 7 days of experimental tooth movement to induce root resorption. In situ hybridization with digoxigenin-labelled RNA probes was performed on sections of the maxillary bone to detect the mRNAs that encode matrix metalloproteinase-1 (MMP-1) and cathepsin K in root-resorbing tissue. MMP-1 mRNA was detected in fibroblastic cells, cementoblasts and osteoblasts, but not in odontoclasts nor osteoclasts. Moreover, MMP-1 mRNA was highly expressed in some cementocytes located near odontoclasts and in many osteocytes. In contrast, cathepsin K mRNA was expressed only in odontoclasts and osteoclasts. These results suggest that MMP-1 and cathepsin K are important in root resorption during tooth movement in a mode similar to bone resorption.

Animals↗

PubMed1999

Role of superoxide anion in the pathogenesis of cytokine-induced myocardial dysfunction in dogs in vivo.

OBJECTIVE: Although studies in vitro have implicated oxygen-derived free radicals as possible mediators of inflammatory cytokine-induced cell injury, the role of the radicals in the cytokine-induced myocardial dysfunction in vivo remains unclear. The present study was designed to address this point in our novel canine model of cytokine-induced myocardial dysfunction in vivo. METHODS: Studies were performed in mongrel dogs, in which microspheres (MS, 15 microns in diameter) with and without interleukin-1 beta (IL-1 beta) were injected into the left main coronary artery (control and IL-1 beta group). Left ventricular ejection fraction (LVEF) was evaluated by echocardiography for 1 week. RESULTS: Immediately after the intracoronary injection of MS (10(6)/kg), LVEF equally decreased to approximately 30% in both the control and IL-1 beta group. While LVEF rapidly recovered within 2 days in the control group, it remained depressed in the IL-1 beta group until day 7 (p < 0.0001 vs. control group). Pretreatment with OPC-6535 (an inhibitor of superoxide production) before (2 mg/kg i.v.) and 1 and 2 days after IL-1 beta MS application (1 mg/kg i.v.) prevented the IL-1 beta-induced myocardial dysfunction. Superoxide production in the myocardium was significantly higher in the IL-1 beta group than in the control group at day 2 (p < 0.01), and OPC-6535 significantly suppressed the IL-1 beta-induced superoxide production (p < 0.01). An HPLC assay showed that nitrotyrosine, a marker of the formation of peroxynitrite by superoxide anion and nitric oxide, was present in the myocardium treated with IL-1 beta but not in that with control MS. OPC-6535 abolished the IL-1 beta-induced formation of myocardial nitrotyrosine. CONCLUSION: These results indicate that superoxide anion and the resultant formation of peroxynitrite may substantially be involved in the pathogenesis of the cytokine-induced myocardial dysfunction in dogs in vivo.

Analysis of Variance↗

PubMed1999

Rho-kinase-mediated pathway induces enhanced myosin light chain phosphorylations in a swine model of coronary artery spasm.

OBJECTIVE: We recently demonstrated in our swine model of coronary artery spasm that enhanced myosin light chain (MLC) phosphorylations (both MLC mono- and diphosphorylations) play a central role in the pathogenesis of the spasm. However, the molecular mechanism for and the phosphorylation sites for the enhanced MLC phosphorylations were unknown. In the present study, we addressed these points using hydroxyfasudil, a novel inhibitor of protein kinases, which we found preferentially inhibits Rho-kinase. METHODS: The specificity of the inhibitory effects of hydroxyfasudil on Rho-kinase, MLCK, MRCK beta and PKC were examined by kinase assay in vitro. The left porcine coronary artery was chronically treated with interleukin-1 beta (IL-1 beta, 2.5 micrograms). Two weeks after the operation, coronary artery vasomotion was examined both in vivo and in vitro. MLC phosphorylations were examined by Western blot analysis and the sites for the phosphorylations by anti-phosphorylated MLC antibodies that identified the monophosphorylation site as Ser19 and diphophorylation sites as Ser19/Thr18 of MLC. RESULTS: Inhibitory effects of hydroxyfasudil was at least 100 times more potent for Rho-kinase as compared with other protein kinases tested. Intracoronary serotonin (10 micrograms/kg) caused coronary hyperconstriction at the IL-1 beta-treated site in vivo, which was dose-dependently inhibited by hydroxyfasudil (p < 0.01). The coronary segment taken from the spastic site also showed hypercontractions to serotonin in vitro, which were again dose-dependently inhibited by hydroxyfasudil (p < 0.01). Western blot analysis showed that MLC monophosphorylation was significantly greater in the spastic segment than in the control segment, while MLC diphosphorylation was noted only at the spastic segment (p < 0.01). The sites for the mono- and diphosphorylated MLC were identified as the monophosphorylated site Ser19 and diphosphorylated sites Ser19/Thr18 of MLC, respectively. Both types of MLC phosphorylations at the spastic segment were markedly inhibited by hydroxyfasudil (p < 0.01). CONCLUSION: These results indicate that hydroxyfasudil-sensitive Rho-kinase-mediated pathway appears to mediate the enhanced MLC phosphorylations (on Ser19 and Ser19/Thr18 residues) and plays a central role in the pathogenesis of coronary artery spasm.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1999

Expression of PDGF-beta receptor, EGF receptor, and receptor adaptor protein Shc in rat osteoblasts during spaceflight.

A number of studies have indicated that microgravity induces osteopenia and modulates functions of mammalian cells. However, the molecular mechanisms underlying these effects of microgravity are still unknown. Rat osteoblasts were cultured for 4 and 5 days during Shuttle-Spacelab flight, and fixed by guanidine isothiocyanate solution on board after treatment with 1alpha, 25 (OH)2 vitamin D3. The mRNA levels for platelet-derived growth factor (PDGF)-beta receptor, epidermal growth factor (EGF) receptor, the growth factor receptor adaptor protein Shc, and c-fos were determined using the method of quantitative reverse transcription-polymerase chain reaction. The mRNA levels for EGF receptor were not altered by microgravity. However, the mRNA levels for PDGF-beta receptor, Shc, and c-fos were decreased to 62, 55 and 25% on the 4th day of flight, and 47, 40, and 43% on the 5th day, respectively, as compared to the corresponding ground controls. Expression of the growth factor receptor and the receptor adaptor protein was modulated in rat osteoblasts during spaceflight. Data suggest that signal transduction via growth factor receptors in rat osteoblasts is impaired by microgravity. Dysfunction of osteoblasts might be involved in spaceflight-induced osteopenia.

Animals↗

PubMed1999

Long-term vascular effects of Nomega-nitro-L-arginine methyl ester are not soley mediated by inhibition of endothelial nitric oxide synthesis in the rat mesenteric artery.

Nomega-nitro-L-arginine methyl ester (L-NAME), one of the synthetic L-arginine analogues with inhibitory effects of nitric oxide (NO) synthesis, is now widely used to examine the role of NO in various organs. We and others demonstrated that long-term treatment with L-NAME causes hypertension and cardiovascular lesions (perivascular fibrosis and medial thickening), especially at microvascular levels. However, convincing evidence is still lacking that these long-term cardiovascular effects of L-NAME are solely mediated by the inhibition of the synthesis of endothelium-derived NO (EDNO). This study was thus designed to better understand the effects of long-term treatment with L-NAME with special reference to EDNO synthesis. Male Wister-Kyoto rats were orally administered L-NAME for 8 weeks. Blood pressure significantly increased at 3 days and 1 and 8 weeks of the treatment. Endothelium-dependent relaxations to acetylcholine (ACh) of the aorta were reduced 3 days after the treatment, recovered at 1 week, and again reduced at 8 weeks, whereas the relaxations of the small mesenteric artery were unaltered throughout the experimental periods. At 8 weeks, indomethacin-sensitive, endothelium-dependent contractions to ACh were noted. The relative contributions of NO and endothelium-derived hyperpolarizing factor also were unchanged. Citrulline assay demonstrated that substantial levels of constitutive NO synthase activity remained in the aorta during the experiments. The long-term treatment with L-NAME caused perivascular fibrosis and medial thickening, not only in the aorta but also in the mesenteric artery. These results suggest that mechanism(s) other than simple inhibition of EDNO synthesis is involved in the long-term cardiovascular effects of L-NAME in the rat mesenteric artery.

Animals↗

PubMed1999

Long-term treatment with eicosapentaenoic acid augments both nitric oxide-mediated and non-nitric oxide-mediated endothelium-dependent forearm vasodilatation in patients with coronary artery disease.

Long-term treatment with eicosapentaenoic acid (EPA) is known to improve impaired endothelium-dependent relaxations of atherosclerotic blood vessels in animals and humans. However, it remains to be determined which mechanisms are involved in this beneficial effect of EPA. In this study, we investigated our hypothesis that EPA improves both nitric oxide (NO)-mediated and non-NO-mediated endothelium-dependent vasodilatation in patients with coronary artery disease. The study included eight patients with documented coronary artery disease. The forearm vascular responses to the endothelium-dependent vasodilator acetylcholine and substance P were examined before and after intraarterial infusion of NG-monomethyl-L-arginine (L-NMMA). Same measurements were repeated after the treatment with EPA (1,800 mg/day) for 6 weeks. The long-term treatment with EPA augmented forearm blood-flow response to both acetylcholine and substance P. Furthermore, acute administration of L-NMMA significantly inhibited the EPA-induced augmented response to acetylcholine but not that to substance P. The forearm vascular response to sodium nitroprusside was unchanged by the EPA treatment. These results indicate that long-term treatment with EPA augments both NO-dependent and non-NO-dependent endothelium-dependent forearm vasodilatation in patients with coronary artery disease. Thus the beneficial effects of EPA appear to extend to non-NO-dependent mechanism(s).

Acetylcholine↗

PubMed1999

Important role of endothelium-derived hyperpolarizing factor in shear stress--induced endothelium-dependent relaxations in the rat mesenteric artery.

Shear stress is one of the most important stimulators for the release of endothelium-derived relaxing factors. Although shear stress-induced release of nitric oxide (NO) has been extensively investigated, it remains to be elucidated whether endothelium-derived hyperpolarizing factor (EDHF) contributes to the endothelium-dependent relaxations to shear stress. This study was designed to address this point in the isolated rat mesenteric artery. Large mesenteric arteries (400-500 microm) and resistance mesenteric arteries (150-250 microm) of the rat were precontracted with phenylephrine (at 80 mm Hg of perfusion pressure), and the changes in vessel diameter in response to variable flow (0-300 microl/min) were continuously examined. The relative contributions of vasodilator prostaglandins, NO, and EDHF were analyzed by the inhibitory effects of indomethacin (10(-5) M), N(G)-nitro-L-arginine (L-NNA, 10(-4) M), and KCl (40 mM), respectively. The shear stress-induced relaxations were totally endothelium dependent in both-sized blood vessels, and the contribution of NO was more prominent in large arteries than in resistance arteries, whereas that of EDHF was noted in both-sized blood vessels. Tetrabutylammonium (a nonselective inhibitor of K channels) almost abolished, whereas the combination of charybdotoxin (an inhibitor of both large- and intermediate-conductance Ca2+ -activated K channels) and apamin (an inhibitor of small-conductance Ca2+ -activated K channels) significantly inhibited the EDHF-mediated component of the shear stress-induced relaxations. These results indicate that EDHF plays an important role in shear stress-induced endothelium-dependent relaxations, where K channels, especially calcium-activated K channels, appear to be involved.

Animals↗

PubMed1999

Pathogenic role of oxidative stress in vascular angiotensin-converting enzyme activation in long-term blockade of nitric oxide synthesis in rats.

Inhibition of nitric oxide (NO) synthesis with N(omega)-nitro-L-arginine methyl ester (L-NAME) activates vascular angiotensin-converting enzyme (ACE) and causes oxidative stress. We investigated the role of oxidative stress in the pathogenesis of ACE activation in rats. Studies involved aortas of rats receiving no treatment, L-NAME, L-NAME plus L-arginine, or L-NAME plus an antioxidant drug (N-acetylcysteine, allopurinol, or ebselen) for 7 days. L-NAME significantly increased oxidative stress (O(2)(-)) and ACE activity. The increased O(2)(-) production was normalized by removal of endothelium. Immunohistochemistry showed the increased ACE activity in the endothelial layer. Treatment with antioxidant drugs did not affect the L-NAME-induced increase in systolic arterial pressure but did prevent increases in vascular O(2)(-) production and ACE activity. These results implicate oxidative stress in the pathogenesis of vascular ACE activation in rats with long-term inhibition of NO synthesis. The observed effects of antioxidant drugs on ACE activation do not appear to involve the hypertension induced by L-NAME.

Animals↗