Endothelium-dependent Relaxation In Rat Aorta Research Articles

Vascular Protection by Ethanol Extract of Morus alba Root Bark: Endothelium-Dependent Relaxation of Rat Aorta and Decrease of Smooth Muscle Cell Migration and Proliferation.

Morus alba (white mulberry) is native to the northern part of Korea and popularly used as a traditional medicine due to its numerous health benefits against human's disease. However, the possibility that M. alba may also affect the cardiovascular system remains unexplored. This study sought to investigate the vascular protective effects of the root bark extract of M. alba (MAE). Vascular reactivity was performed in organ baths using isolated rat thoracic aorta, while platelet derived growth factor (PDGF) induced proliferation and migration of vascular smooth muscle cells (VSMCs) were studied by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) and wound healing assay, respectively. MAE evoked a concentration dependent vasorelaxation following endothelium-dependent pathway. However, vessel relaxations in response to MAE were markedly reduced after endothelium removal; treatment of endothelial nitric oxide synthase inhibitor, guanylyl cyclase inhibitor, and nonspecific potassium channel inhibitor, however, was not altered by cyclooxygenase inhibitor. Furthermore, MAE also significantly blunted contractile response to vasoconstrictor agent, phenylephrine. Taken together, the current evidence revealed that MAE is a potent endothelium-dependent vasodilator and this effect was involved in, at least in part, nitric oxide cyclic-guanosine monophosphate (NO-cGMP) pathway in combination with potassium (K+) channel activation. Moreover, MAE inhibited proliferation and migration of VSMCs induced by PDGF. Therefore, MAE could be a promising candidate of natural medicine for preventing and controlling cardiovascular diseases linked with endothelial dysfunction.

Suppression of histamine-induced relaxation of rat aorta and calcium signaling in endothelial cells by two-pore channel blocker trans-NED19 and hydrogen peroxide

The blocker of two-pore channels trans-NED 19 and hydrogen peroxide were found to inhibit histamine-induced relaxation of rat-aorta. The degree of inhibition depended on histamine concentration. The relaxation in response to I μM histamine of rat aorta preconstricted with 30 mM KCI, serotonin, or endothelin- 1, was completely abolished by 30 μM trans-NED 19. On the other hand, trans-NED 19 decreased the relaxation of the aorta in the presence of 10 μM histamine only by 2.1-fold to 2.4-fold, and there was almost no inhibition by trans-NED 19 of the relaxationinduced by 100 ptM histamine.) Relaxation of precontracted with serotonin aorta in response to 10 and 100 μM histamine was reduced by hydrogen peroxide (200 M) by 10- and 2.5-fold, respectively. Suppression of aorta relaxation by trans-NED 19 and H202 correlated with their inhibitory effect on the histamine-induced increase in the cytoplasmic free calcium concentration in human umbilical vein endothelial cells. With the use of a fluorescent probe LysoTracker, the cis-NED19 binding sites were demonstrated to be localized in endolysosomes of the endothelial cells. These data indicate that two-pore calcium channels participate in the histamine-induced endothelium-dependent relaxation of rat aorta. Furthermore, their functional role is exhibited much more clearly at low histamine concentrations. We suggest that hydrogen peroxide evokes depletion of intracellular calcium depots thereby suppressing the response to histamine.

Induction of endothelium-dependent relaxation in rat aorta via nitric oxide production caused by the aqueous extract of Astragalus membranaceus Bunge leaves

Induction of endothelium-dependent relaxation in rat aorta via nitric oxide production caused by the aqueous extract of Astragalus membranaceus Bunge leaves

Contractions induced by phenylephrine and noradrenaline are differently affected by endothelium-dependent relaxation in rat aorta.

In rings of rat aorta precontracted with phenylephrine (10 microM) or noradrenaline (10 microM), addition of carbachol (10 microM) produced an endothelium-dependent relaxation. However, regardless of the concentration of agonist tested, both the intensity and duration of the relaxation were significantly less when noradrenaline, rather than phenylephrine, was used as the precontracting agent. The different responses observed do not appear to be related to destruction of endothelium-derived relaxing factor by autoxidation of noradrenaline since neither EDTA (30 microM) nor superoxide dismutase (30 units mL-1) improved the relaxation to carbachol. In addition, in endothelium-free rings, the noradrenaline (1 microM)-induced contraction was less sensitive than the phenylephrine (1 microM)-induced contraction to sodium nitroprusside (0.1 microM) or to 8-Br-cGMP (300 microM). With phenylephrine-, but not noradrenaline-, induced contraction, the relaxation triggered by carbachol was significantly reduced by pretreatment of the aortic rings with chloroethylclonidine (50 microM), which inactivates a subpopulation of alpha 1-adrenoceptors. Thus, the results confirm that both alkylation sensitive and resistant alpha 1-adrenoceptors exist in rat aorta and indicate that EDRF may discriminate between these two alpha 1-adrenoceptor subtypes which are differently affected by phenylephrine and noradrenaline.

Persistence of EDHF pathway and impairment of the nitric oxide pathway after chronic mercury chloride exposure in rats: Mechanisms of endothelial dysfunction

Chronic mercury exposure impairs vascular function, leading to the depression of endothelium-dependent vasodilatation. Loss of the nitric oxide (NO) pathway has been implicated, but little is known about effects on other endothelial mediators. This study investigated the mechanisms of endothelial dysfunction in rats subjected to chronic mercury chloride exposure. The endothelium-dependent relaxation of rat aorta evoked by acetylcholine (ACh) and isoproterenol was impaired in a dose-dependent manner by chronic mercury chloride exposure. Endothelium-independent responses to sodium nitroprusside (SNP) were not affected by chronic mercury chloride exposure. In healthy vessels, ACh-induced relaxation was inhibited by L-N-nitroarginine methyl ester (L-NAME; 10(-4) M) and partially by glybenclamide (10(-5) M), indicating the involvement of NO and endothelium-derived hyperpolarizing factor (EDHF). In vessels from mercury-exposed rats, responses to ACh were insensitive to L-NAME but were significantly reduced by glybenclamide, indicating selective loss of NO-mediated relaxation. In vessels from mercury-exposed rats, responses to ACh were partially restored after treatment with the antioxidant, superoxide dismutase (SOD) and catalase, this effect was not seen when aorta from exposed group was incubated with L-NAME along with SOD and catalase indicating selective loss of NO-mediated vasodilatation and with no affect the EDHF-mediated component of relaxation. The results imply that chronic mercury exposure selectively impairs the NO pathway as a consequence of oxidative stress, while EDHF is able to maintain endothelium-dependent relaxation at a reduced level.

Resveratrol restores lysophosphatidylcholine‐induced loss of endothelium‐dependent relaxation in rat aorta tissue coinciding with inhibition of extracellular‐signal‐regulated protein kinase activation

To investigate whether resveratrol could restore the lysophosphatidylcholine (LPC)-induced loss of endothelium-dependent relaxation in in vitro cultured rat aorta tissue, first the effect of resveratrol on the loss of EDR was examined in this preparation. The results showed that resveratrol effectively attenuated the inhibition of LPC (10 μM) on both endothelium-derived relaxing factor (EDRF) and endothelium-derived hyperpolarizing factor (EDHF) in a concentration-dependent manner (1, 10, 100 μM). In addition, resveratrol inhibited elevated K+-induced vascular contracture, but had no significant effects on ACh (1 μM)-induced endothelium-dependent relaxation (EDR). A similar tendency was also observed with PD 98059 (30 μM), a selective inhibitor of ERK. When the cells were exposed to LPC (20 μM) the mRNA expression of eNOS and COX-1 mRNA were down-regulated, followed by a local induction of iNOS and COX-2. Resveratrol and PD 98059 successfully reversed the effects of LPC on relative mRNA expressions. Both resveratrol and PD 98059 inhibited the activation of ERK induced by LPC. These findings demonstrate that resveratrol can restore the LPC-induced loss of EDR in rat aorta and protect the endothelium against LPC-induced injuries via the inhibition of the inflammation-like response.

Luteolin inhibits inflammatory response and improves insulin sensitivity in the endothelium

Endothelial insulin resistance is tightly associated with diabetic cardiovascular complication, and it is well known that inflammation plays an important role in the development of insulin resistance. Luteolin, a flavonoid abundant in some medical and eatable plants, is a potent inhibitor of inflammation. It is also reported that luteolin exhibited some chemoprotection capability to the endothelial integrity. This study aims to clarify whether the anti-inflammatory potency of luteolin contributes to amelioration of insulin resistance in the endothelium. Palmitate (PA) stimulation markedly reduced insulin-mediated endothelium-dependent relaxation in rat aorta, while luteolin pretreatment effectively reversed the effects of palmitate in a concentration-dependent manner. PA stimulation also evoked inflammatory response in endothelial cells. When the cells were pretreated with luteolin, IKKβ phosphorylation were reduced, which, in turn, blocked the NF-κB activation through attenuating P65 phosphorylation. At the same time, it was also found that the gene over-expressions for TNF-α and IL-6 were also reduced by luteolin pretreatment. When endothelial cells were stimulated with PA, the insulin signaling cascades were impaired with reduced insulin-dependent production of NO. Again, pretreatment of luteolin could effectively reverse the effects of PA. Luteolin modulated the Ser/Thr phosphorylation of insulin receptor substrates-1 and restored downstream Akt/eNOS activation, resulting in increased NO production in the presence of insulin. In conclusion, these results suggested that luteolin ameliorated inflammation related endothelial insulin resistance in an IKKβ/IRS-1/Akt/eNOS-dependent pathway.

Relative contribution of individual oxidized components in ox-LDL to inhibition on endothelium-dependent relaxation in rat aorta

Background and Aim Oxidized low-density lipoprotein (ox-LDL) causes atherosclerosis and endothelial dysfunction. No study up to the present date has examined the relative contribution of all the oxidized components in ox-LDL to inhibition on vascular function. Our aim was to investigate the effects of individual oxidized components at concentrations similar to those in ox-LDL on the impairment of endothelium-dependent relaxation in rat aorta. Methods and Results Rat thoracic aorta was pre-treated with lysophosphatidylcholine (LPC), cholesterol oxidized products (COPs), oxidized linoleic acid (ox-18:2) and oxidized linolenic acid (ox-18:3) at concentrations similar to those in human ox-LDL. Ox-LDL as a whole caused 61% inhibition while LPC, COPs and ox-18:2 at concentrations similar to those in ox-LDL caused 12%, 24% and 19% inhibition, respectively, on endothelium-dependent relaxation, suggesting that COPs produced the most adverse effect followed by ox-18:2 and LPC in an additional way. Three COPs including 7-ketocholesterol, 7α-hydroxycholesterol and 7β-hydroxycholesterol showed inhibition on endothelium-dependent relaxation with E max being reduced to 79–87% compared with the control E max (95%). At Western blot analysis phosphorylation of eNOS at Ser1177 site and total eNOS were not altered by ox-LDL treatment, indicating that ox-LDL did not affect nitric oxide (NO) synthesis capacity. Ox-LDL might react directly with NO and lower NO bioavailability. Conclusion The present study demonstrated the relative contribution of individual oxidized components in ox-LDL in the inhibition of endothelium-dependent relaxation in rat aorta. This inhibitory effect could be caused by the reduction of NO bioactivity.

Luteolin reduces high glucose-mediated impairment of endothelium-dependent relaxation in rat aorta by reducing oxidative stress

While luteolin, a flavone rich in many plants, has some cardiovascular activity, it is not clear whether luteolin has beneficial effects on the vascular endothelial impairment in hyperglycemia/high glucose. Here, we reveal the protective effect of luteolin on endothelium-dependent relaxation in isolated rat aortic rings exposed to high glucose. The thoracic aorta of male Sprague–Dawley rats was rapidly dissected out and the effect of luteolin on the tension of aortic rings pretreated with high glucose (44 mM) for 4 h was measured in an organ bath system. The levels of nitric oxide (NO), hydroxy radical (OH − ) and reactive oxygen species (ROS), and the activity of superoxide dismutase (SOD) and nitric oxide synthase (NOS) were measured in aortas. The vasorelaxation after treatment with luteolin for 8 weeks in aortic rings from diabetic rats was also determined. We found that exposure to high glucose decreased acetylcholine-induced endothelium-dependent relaxation. However, high mannitol had no effect on vasorelaxation. Luteolin evoked a concentration-dependent relaxation in aortic rings previously contracted by phenylephrine, and the pD 2 value was 5.24 ± 0.04. The EC 50 of luteolin markedly attenuated the inhibition of relaxation induced by high glucose, which was significantly weakened by pretreatment with l-NAME (0.1 mM), but not by indomethacin (0.01 mM). Luteolin significantly inhibited the increase of ROS level and OH − formation, and the decrease of NO level, NOS and SOD activity caused by high glucose. The improving effect of luteolin on endothelium-dependent vasorelaxation in diabetic rat aortic rings was reversed by pretreatment with l-NAME or methylene blue. The results indicate that the decrease of endothelium-dependent relaxation in rat aortic rings exposed to high glucose is markedly attenuated by luteolin, which may be mediated by reducing oxidative stress and enhancing activity in the NOS–NO pathway.

Apigenin protects endothelium-dependent relaxation of rat aorta against oxidative stress

Apigenin is shown to have cardiovascular effects, but the effects of apigenin on aortas injured by exogenous oxidants are unknown. The objective of this study was to investigate the effect of apigenin on endothelium-dependent vasorelaxation in isolated rat aortic rings exposed to superoxide anion produced by pyrogallol, and its mechanism. The male Sprague–Dawley rat thoracic aorta was rapidly dissected out and the effect of apigenin on tension of aortic rings pretreated with 500 μM pyrogallol, inducing oxidative stress injury, was measured. The activity of nitric oxide synthase (NOS), the level of nitric oxide (NO) and the inhibition of superoxide anion in aortic tissues were measured. We found that pretreatment with pyrogallol concentration-dependently decreased acetylcholine-induced endothelium-dependent vasorelaxation. Apigenin (0.5–72.0 μM) evoked a concentration-dependent relaxation in aortas (pD 2: 5.304 ± 0.049), which was weakened by l-NAME (the maximal relaxation fell from 87.6 ± 6.7% to 37.1 ± 8.8%, P < 0.01), but not by aminoguanidine and indomethacin. Apigenin markedly attenuated the inhibition of vasorelaxation induced by pyrogallol (the maximal relaxation elevated from 55.8% ± 6.6% to 69.5% ± 6.4%, and the pD 2 increased from 6.559 ± 0.119 to 7.057 ± 0.145, P < 0.01) and increased the inhibition of superoxide anion (from 94.6% to 74.5%), the NO level (from 77.1% to 94.4%), and the constitutive NOS activity (from 35.1% to 62.5%). These results indicate that pyrogallol decreased endothelium-dependent vasorelaxation in rat aortas via oxidative stress, which was markedly attenuated by apigenin. This may be mediated by weakening the oxidative stress and the NO reduction.

Endothelium-dependent relaxation of rat aorta induced by resveratrol

It has been noted that there are a number of biologically active phenolic compounds present in wine, particularly red wine. Such compounds include, for example, catechin, epicatechin, quercetin, rutin, trans-resveratrol and cis-resveratrol. The resveratrol isomers, in particular, have been found to promote vascular relaxation. The mechanisms by which resveratrol causes vasodilatation are uncertain. The aim of this study was to investigate the mechanism(s) of resveratrolinduced vasorelaxation in rat aorta with endothelium present. Rat aortic rings were precontracted with phenylephrine. Resveratrol induced relaxation of the rat aortic rings. L-NAME, an inhibitor of NO synthase, abolished relaxation of rat aorta, but methylene blue, an inhibitor of guanylate cyclase, did not abolish relaxation induced by resveratrol. Highly selective blocker of ATP-sensitive K+ channels, glibenclamide as well as a nonselective blocker of big Ca-sensitive K+ channels, charybdotoxin did not block resveratrol-induced relaxation of rat aorta. 4-Aminopiridine, which is a non selective blocker of voltage-gated K+ (Kv) channels, and margatoxin which inhibits Kv1 channels abolished relaxation of rat aortic rings induced by resveratrol. In conclusion, we have shown that resveratrol potently relaxed rat aortic rings with endothelium present. It seems that NO and smooth muscle KV channels are included in this relaxation. This finding is of clinical importance in both veterinary and human medicine.

Pravastatin Restores DDAH Activity and Endothelium-Dependent Relaxation of Rat Aorta After Exposure to Glycated Protein

This study was designed to investigate whether glycated bovine serum albumin (AGE-BSA) inhibits dimethylarginine dimethylaminohydrolase (DDAH) activity to contribute to its adverse effect on endothelium-dependent relaxation in rat aorta, and whether pravastatin reverses the inhibition of DDAH activity and endothelial dysfunction induced by AGE-BSA. Endothelium-dependent relaxation of aortic rings was measured by isometric tension recording, and DDAH activity, and the contents of nitrite/nitrate as well as malondialdehyde (MDA) in aortic tissue were determined after exposure of Sprague-Dawley rat aorta to AGE-BSA (1.70 mmol/L) for 60 minutes in the presence or absence of pravastatin. In comparison with control, both endothelium-dependent relaxation and DDAH activity (0.032 +/- 0.002 versus 0.095 +/- 0.003 U/g protein, n = 5, P < 0.01) were significantly inhibited in isolated rat aorta after exposure to AGE-BSA, which was accompanied by decreases of nitrite/nitrate contents and elevations of MDA levels in aorta. Treatment with pravastatin (1 mmol/L) not only prevented the inhibition of endothelial function but also reversed the decrease of DDAH activity induced by AGE-BSA and normalized the alterations in nitrite/nitrate and MDA contents. Similar effects were observed when rat aorta exposed to AGE-BSA in the presence of antioxidant pyrrolidine dithiocharbamate (PDTC, 30 micromol/L) or protein kinase C inhibitor chelerythrine (1 micromol/L). These results suggested that decreased DDAH activity may be involved in endothelial dysfunction of rat aorta induced by AGE-BSA, and that pravastatin restores DDAH activity and endothelium-dependent relaxation after aorta exposure to AGE-BSA, which may be secondary to its antioxidative effects.

Images in cardiovascular medicine. Avoiding papillary muscle infarction with myocardial contrast echocardiographic guidance of nonsurgical septal reduction therapy for hypertrophic obstructive cardiomyopathy.

Intracoronary myocardial contrast echocardiography (MCE) can be used to guide the delivery of ethanol during nonsurgical septal reduction therapy for hypertrophic obstructive cardiomyopathy. The echocardiographic contrast agent is injected immediately before the injection of ethanol, down the lumen of the inflated balloon that resides in the target septal coronary artery. This is the artery that supplies the area of the septum involved with the mitral leaflet(s) in causing dynamic outflow tract obstruction. MCE provides a direct visualization of the myocardial territory that should receive ethanol and consequently undergo infarction. In rare instances, the cannulated vessel does not supply the culprit septal segment(s) but supplies instead …

The epoxy group of pramanicin is required for the optimal endothelium-dependent relaxation of rat aorta.

The vascular effects of a newly discovered anti-fungal agent, pramanicin (PMC), and its two analogues, PMC-A, in which the epoxy group is replaced by a - HC = CH - bond, and PMC-B, on which the diene is converted to the saturated (CH(2))(4)-derivative, respectively, were investigated in rat aorta. All three compounds caused an initial endothelial-dependent relaxation, which is prevented either by removal of endothelium or inclusion of the nitric oxide synthase inhibitor L-NAME. Upon prolonged incubation with the aortic rings, they also caused endothelial cell dysfunction characterized as reduced relaxation to carbachol (CCh). These effects were the strongest for PMC, being completely inhibitory at 20 microM after 30 min incubation, whereas those of PMC-A and PMC-B were smaller and comparable with each other, causing 30 - 40% inhibition at 20 micro M. PMC and its analogues had no effect on KCl-induced contraction and also had no effect on relaxation induced by sodium nitroprusside, suggesting that these compounds had no effect on the basic mechanisms of the contractile elements. Phenylephrine (PE)-induced contraction, however, was significantly reduced in the presence of these compounds, the inhibitory effect being strongest with PMC, but this inhibitory action was rapidly reversible and not of the competitive mode with respect to PE. We conclude that the epoxy group in PMC is required for the optimal vascular effects. We have discussed and speculated upon the possible mechanisms of action of PMC. The potent, selective, and irreversible inhibitory effect of PMC on the endothelial function points to its potential development into an anti-angiogenic drug.

Differential role of endothelium in hawthorn fruit extract-induced relaxation of rat cerebral, coronary, carotid, and aorta

The present study was aimed to examine the role of endothelium in the relaxant effect of hawthorn fruit extract of Crataegus pinnatifida in four different types of rat arteries, posterior cerebral communicating artery, right descending coronary artery, common carotid artery, and aorta. In <TEX>$9,11-dideoxy-11{\alpha}$</TEX>, <TEX>$9{\alpha}-epoxy-methanoprostaglandin$</TEX> <TEX>$F_{2{\alpha}}$</TEX> (U46619)-preconstricted arterial rings except for aorta, the extract produced endothelium-independent relaxations with similar potency. This relaxation was unaffected by pretreatment with <TEX>$100\;{\mu}M\;N^G-nitro-L-arginine$</TEX> methylester (L-NAME, the nitric oxide synthase inhibitor), <TEX>$3\;{\mu}M$</TEX> 1H-[l,2,4]oxadiazolo<TEX>$[4,2-{\alpha}]$</TEX>quinoxalin-1-one (ODQ, the guanylate cyclase inhibitor), or <TEX>$10\;{\mu}M$</TEX> indomethacin (the cyclooxygenase inhibitor). Putative <TEX>$K^+$</TEX> channel blockers (charybdotoxin plus apamin or glibenclamide) did not affect the extract-induced relaxation in cerebral or coronary artery rings. In contrast, in rat aortic rings the extract produced significantly smaller relaxant response in endothelium-denuded rings than that in endothelium-intact rings. Pretreatment with L-NAME or ODQ abolished the extractinduced endothelium-dependent aortic relaxation, whilst indomethacin <TEX>$(3\;{\mu}M)$</TEX> had no effect. The present results indicate that hawthorn fruit extract possesses a vasorelaxing effect in cerebral, coronary and carotid arteries and this effect is independent of the presence of a functional endothelium. However, the extract-induced endothelium-dependent relaxation in rat aorta was mediated through endothelial nitric oxide and cyclic GMP-dependent mechanisms, suggesting that active components in the extract may act on endothelium to stimulate release of nitric oxide in large conduit arteries of the rats.

Aprotinin impairs endothelium-dependent relaxation in rat aorta and inhibits nitric oxide release from rat coronary endothelial cells.

Aprotinin, a non-specific serine protease inhibitor, reduces postoperative bleeding after coronary artery surgery. The mechanism of action for this 'blood-sparing' effect of aprotinin is only partially clarified. We therefore aimed to investigate the effect of aprotinin on the release of nitric oxide (NO), a vasodilator and antiaggregant factor, from rat coronary microvascular endothelial cells and on the NO-mediated endothelium-dependent relaxation of rat thoracic aorta. Endothelium-intact and endothelium-denuded thoracic aortic rings from Wistar rats (250-300 g) were suspended in organ chambers. Contractile and relaxant responses in the absence and presence of aprotinin (125, 250 and 500 KIU/ml) were recorded via a mechanotransducer. Coronary microvascular endothelial cells (CMEC) were isolated on a Langendorff system by collagenase perfusion of the hearts from the same rats. Calcium ionophore- (1 microM) induced release of NO from confluent cells was determined spectrophotometrically by measuring its stable metabolites, nitrite and nitrate, via Griess reaction. Aprotinin selectively enhanced phenylephrine-induced contractions in endothelium-intact rat thoracic aortic rings, but not in the endothelium-denuded rings. The use of a nitric oxide synthesis inhibitor Nomega-nitro-L-arginine methyl ester (100 microM) on endothelium-intact rings produced a similar increase in phenylephrine-induced contractions. KCl-induced contractions remained unaltered. Aprotinin inhibited acetylcholine-, calcium ionophore- and L-arginine-induced endothelium-dependent relaxations, but not sodium nitroprusside-induced endothelium-independent relaxation. Aprotinin had no significant effect on basal nitrite-nitrate release from CMEC, while it inhibited calcium ionophore-induced total nitrite accumulation in the supernatants. Aprotinin selectively impairs endothelium-dependent relaxation as well as basal NO availability in rat thoracic aortic rings and inhibits NO release from rat CMEC. This effect of the drug may contribute to its 'blood-sparing' action and may also account for the increase in perioperative restenosis risk observed in clinical practice during aprotinin therapy.

Endothelium-dependent relaxation of rat aorta and main pulmonary artery by the phytoestrogens genistein and daidzein.

The dietary phytoestrogens genistein and daidzein have been shown to relax agonist-preconstricted arteries in vitro; the mechanisms of relaxation remain incompletely understood. This study aimed to determine whether the relaxation of phenylephrine (PE)-constricted rat aorta and main pulmonary artery by genistein and daidzein was endothelium-dependent. Effects of endothelial-denudation, and pretreatment with with 100 microM L-N(G)-nitroarginine methyl ester (L-NAME) and/or 10 microM indomethacin on relaxation of PE (1 microM)-preconstricted contractures by genistein (1-100 microM) and daidzein (3-100 microM) were assessed by measuring isometric force development by rat arterial rings. The effect of L-NAME on relaxation to 17beta-estradiol (10 microM) was also measured in aorta. Genistein and daidzein caused concentration-dependent relaxation of aorta rings preconstricted with PE (1 microM). The IC50 values were 5.7 microM (n=8, 95% confidence limits 4.3-7.7 microM) and 36.7 microM (n=12, 95% confidence limits 25.7-44.1 microM), respectively. Removal of the endothelium and pretreatment with L-NAME (100 microM) significantly inhibited relaxation at 3, 10 and 30 microM genistein and 10 and 30 microM daidzein. The contracture evoked in rat aorta by depolarization with 75 mM K+ solution was similarly relaxed by genistein in a partially endothelium-dependent manner. 17Beta-estradiol (10 microM) caused a 48.7+/-5.0% (n=11) relaxation of the PE contracture, which was significantly reduced to 25.1+/-5.3% (n=7) by L-NAME. Relaxations brought about by 17beta-estradiol, genistein, and daidzein were not significantly affected by the genomic estrogen receptor antagonist ICI 182,780 (10 microM). Similar endothelium-dependent effects of genistein were observed in the main pulmonary artery. The results show that the relaxation of these rat arteries by concentrations of genistein and daidzein which overlap those present in human plasma after ingestion of soybean-containing meals is largely endothelium dependent.

Effect of chronic lithium administration on endothelium-dependent relaxation in rat aorta.

1. The effects of chronic lithium administration on the relaxant responses of rat thoracic aortic rings in the presence of indomethacin (a cyclo-oxygenase inhibitor) and/or NG-nitro-L-arginine (L-NOARG; a nitric oxide synthase inhibitor) to acetylcholine (ACh) or sodium nitroprusside were investigated in the present study. 2. Acetylcholine produced a concentration-dependent relaxation in vessels precontracted by phenylephrine (PE), while in lithium-treated rats the maximal relaxation was significantly increased. 3. Indomethacin (20 mumol/L) significantly potentiated the ACh-induced relaxation in lithium-treated and control rats. 4. NG-Nitro-L-arginine (1 mumol/L) decreased the ACh-induced relaxation in both control and lithium-treated rats. In contrast, indomethacin (20 mumol/L) reversed the inhibitory effect of L-NOARG. 5. Sodium nitroprusside produced similar concentration-dependent relaxations of vessels from both control and lithium-treated rats, which was not affected by indomethacin. In endothelium-denuded rings, indomethacin (20 mumol/L) caused a rightward shift in the concentration-contraction curve to PE. 6. These data support evidence for a possible increase in endothelium-dependent relaxation induced by ACh during long-term administration of lithium in rat aortic rings.

IN VITRO AND IN VIVO EXPERIMENTAL EFFECT OF KOREAN RED GINSENG ON ERECTION

To elucidate the efficacy of Korean red ginseng (KRG) on penile erectile tissue and erectile response, the effect of ginseng was evaluated in both in vivo and in vitro experiments in laboratory animals. Fifty milligrams of KRG per kilogram in weight was mixed in physiologic saline and given by mouth for 3 months to both rabbits and rats. In vitro experiments were performed by observing the responses to acetylcholine (ACh) and KRG of strips of rabbit corpus cavernosum. In vivo experiments were performed by measuring the cavernosal pressures after the stimulation of pelvic nerves innervating rat corpus cavernosum. On rabbit cavernosal muscle strips precontracted with phenylephrine (5x10(-6) M), increasing concentrations of ACh (10(-7), 10(-6), 10(-5), 10(-4) M) showed dose dependent relaxation in the control group (10(-7) M: 15.32%, 10(-6) M: 35.44%, 10(-5) M: 59.45%, 10(-4) M: 76.54%)(p<0.01). After 3 months of KRG administration, the relaxation responses to ACh were increased significantly (10(-7) M: 34.18%, 10(-6) M: 56.35%, 10(-5) M: 75.33%, 10(-4) M: 89.86%)(p<0.01). Relaxation effects of KRG were significantly increased after administering KRG for 3 months, as evident by the intracavernousal pressure to electrostimulation being 107.52 cm. water in the control group and significantly increased to 138.34 cm. water after 3 months administration of KRG (p<0.01). We confirmed that the long-term administration of KRG enhances erectile capacity and that its action is mediated by endothelium-derived relaxing factor and peripheral neurophysiologic enhancement.

Inhibition of endothelium-dependent vascular relaxation by lysophosphatidylcholine: impact of lysophosphatidylcholine on mechanisms involving endothelium-derived nitric oxide and endothelium derived hyperpolarizing factor.

Hyperlipidemia has been associated with an increase in the incidence of atherosclerosis. The oxidation of low density lipoprotein (LDL) plays an important role in the initiation and progression of atherosclerosis, one of its effects being the inhibition of endothelium dependent relaxation (EDR). The elevated level of lysophosphatidylcholine (LPC) in oxidatively modified LDL has been shown to be a biochemical factor responsible for the impairment of EDR in vascular ring preparations. Several endothelium-derived modulators are thought to control vascular responsiveness. The present work examined whether acetylcholine (ACh)-induced EDR in rat aorta (pre-contracted with phenylephrine, PE) involved both endothelium-derived nitric oxide (EDNO) and endothelium-dependent hyperpolarizing factor (EDHF) and whether LPC inhibited either of these selectively. Indomethacin (10(-5) M), had no significant effect on EDR, indicating that products of cyclooxygenase, including prostacyclin, are not involved. Treatment with either N(W)-nitro-L-arginine methyl ester (L-NAME, 6.8 microM) to inhibit the production of EDNO or with elevated K+ (15 mM), to block the hyperpolarizing effect of EDHF impaired EDR considerably (each of these shifting the inhibitory dose-response relationship to ACh by almost one log unit); in muscles treated with both of these agents EDR was completely inhibited. In each of L-NAME- and K-treated muscles, the addition of LPC (20 microM) further impaired EDR. LPC did not independently raise the tone of resting- or PE-contracted aorta. We conclude that the inhibition of EDR of rat aorta by LPC involves the actions of both EDNO and EDHF.