N-acetylcysteine enhances endothelium-dependent vasorelaxation in the isolated rat mesenteric artery

Coronary disease in cardiac transplant patients is a major factor in the limitation of long term survival. The aim of this study was to compare the results of angioscopy with those of coronary angiography performed systematically every 18 months in our center. Twenty-nine patients (31 angioscopies) were assessed 38 +/- 21 months after transplantation. The appearance observed by angioscopy were: 1) normal, 2) yellow pigmentation of the arterial surface, 3) elevated plaque < 50%, 4) elevated plaque > or = 50% stenosis. Angiography was: 1) normal, 2) iregularities of the lumen or < 50% stenosis, 3) > or = 50% stenosis. The films were viewed by two independent investigators. Angioscopy was performed on the left anterior descending artery (N = 35), the left circumflex (N = 24) and the right coronary artery (N = 9). One to three arterial segments were examined per vessel (total of 117 segments: average 3.8 segments per patient). Angioscopy was uniterpretable in 13/117 (11%) of cases. Of the 81 (78%) segments considered normal at coronary angiography, only 55 seemed normal at angioscopy (68%). Of the 23 segments considered to be abnormal at coronary angiography, all were also considered to be abnormal at angioscopy. The authors conclude that coronary angioscopy seems to be more sensitive than coronary angiography for the detection of coronary disease due to chronic rejection. Prospective studies are required to determine whether the infra-angiographic angioscopic lesions correspond to earlier stages of coronary disease of the cardiac graft.     

Coagulation factor Xa induces endothelium-dependent relaxations in rat aorta

The relaxing effect of coagulation factor Xa on phenylephrine-contracted rat aortic rings was compared with the effect of thrombin and trypsin. All three proteases induced a dose-dependent relaxation in the presence of an intact endothelium. EC50 values were 3 +/- 1, 24 +/- 9, and 16 +/- 1 nmol/L for thrombin, trypsin, and factor Xa, respectively. Whereas thrombin induced rapid relaxations followed by partial recontraction, trypsin and factor Xa induced slower sustained effects. Factor Xa-induced relaxations were not affected by hirudin at high concentrations (1 mumol/L) but were abolished by DX9065A, a specific inhibitor of the catalytic activity of factor Xa. Furthermore, no relaxations to factor Xa could be elicited in the presence of the NO synthase inhibitor N omega-nitro-L-arginine methyl ester (100 mumol/L), whereas relaxations were not altered in the presence of the inactive enantiomer N omega-nitro-D-arginine methyl ester (100 mumol/L). Addition of factor Xa together with thrombin induced relaxations that were larger than those induced by thrombin alone, whereas factor Xa had no additional effects on trypsin-induced relaxations. Further-more, factor Xa relaxed thrombin-desensitized aortic rings but was ineffective in trypsin-desensitized tissues. These data suggest that factor Xa acts on a cleavable endothelial receptor that induces NO release, resulting in the relaxation of precontracted rat aortic rings. Factor Xa does not act through endothelial thrombin receptors but may activate another cleavable trypsin-sensitive receptor.     

Exercise training alters endothelium-dependent vasoreactivity of rat abdominal aorta

We tested the hypothesis that adaptations in peripheral arterial vasoreactivity are induced by exercise training. Male rats were trained to run on a treadmill at 30 m/min (15 degrees incline) for 1 h/day 5 days/wk for 10-12 wk. Efficacy was indicated by a 51% increase (P < 0.05) in citrate synthase activity in soleus muscle of exercise-trained (ET) rats compared with that of sedentary (SED) control rats. Responses to vasoactive compounds were examined in vitro using rings of abdominal aorta. Maximal isometric contractile tension evoked by KCl, norepinephrine (NE), and phenylephrine were not different between groups; sensitivity to phenylephrine was also not different between groups. However, sensitivity was lower for both KCl and NE in vessels from ET animals. Endothelium removal did not influence KCl sensitivity but did abolish the difference in NE sensitivity of vessel segments between ET and SED animals. Maximal vasodilator responses induced by acetylcholine (ACh; NE or prostaglandin F2 alpha preconstriction) were greater in vessel rings from ET rats. However, dilatory responses by sodium nitroprusside (NE or prostaglandin F2 alpha preconstriction) and forskolin (NE preconstriction) were not different between groups, indicating that the augmented ACh-induced dilatory response resulted from an adaptation of the endothelium. Blockade of nitric oxide synthase activity diminished ACh-induced vasodilation by 79 and 100% in SED and ET rats, respectively. These results indicate that training alters vasomotor function in rat abdominal aortas through adaptations of both endothelium and smooth muscle.     

Impairment of endothelium-dependent vasorelaxation in experimental atherosclerosis is dependent on gender

OBJECTIVE: Nitric oxide (NO) has been suggested to have antiatherosclerotic effects. It has also been demonstrated that there is a greater basal release of endothelium derived relaxing factor (EDRF) in female as compared to male rabbit aorta, which also might have beneficial effects in atherosclerosis. We thus sought to determine if gender influences the severity of atherosclerosis. METHODS: We studied 18 female and 18 male New Zealand White rabbits that were randomly divided in two groups of 9 animals each and fed either a standard or a cholesterol diet (0.75%) for 15 weeks. RESULTS: In cholesterol-fed rabbits the percentage of atherosclerotic lesions in the aorta was identical in females and males and was inversely correlated with the maximal aortic relaxation to acetylcholine as assessed in organ chamber experiments (females: P < 0.0008, males: P < 0.0002). Importantly, the cholesterol diet induced a significantly (P < 0.025) more severe impairment of maximal vasorelaxation to acetylcholine in males from 78.4 +/- 1.2% to 29.4 +/- 10.2%) compared to females (from 84.4 +/- 1.2% to 60.7 +/- 8.5%). Both male gender (P < 0.0001) and the extent of impairment of endothelium-dependent relaxation (P < 0.0002) were associated with a reduced aortic sensitivity to S-nitroso-N-acetyl-D,L-penicillamine, which releases NO into the organ bath. In contrast, the aortic sensitivity to the organic nitrates pentaerythritol tetranitrate and isosorbide 5-nitrate, which release NO after enzymatic metabolization within the smooth muscle, was not reduced. CONCLUSIONS: These results suggest that the impairment of endothelium-dependent vasorelaxation induced by atherosclerosis is dependent on gender. This may be due to a greater degradation of extracellular NO in the vessel wall of males.     

Effects of preanesthetic and anesthetic drugs on endothelium-dependent responses in the rat aorta

1. Acetylcholine often fails to induce endothelium-dependent relaxation in human vessels in vitro. Due to the fact that most of these vessels come from surgery, we examined the influence of drugs used in anesthesia on endothelium-dependent responses in rat aorta. 2. Groups of male Wistar rats of the following treatments were utilized: P group, diazepam+promethazine+atropine; I group, pentothal+succinylcholine; IG group, halothane+nitrous oxide; M group, morphine+pancuronium; C group, untreated rats. Dose-response curves to noradrenaline and acetylcholine were determined in rat aorta in vitro, in the presence and absence of endothelium. 3. Acetylcholine induced more relaxation (P < 0.05) in the rat aorta of IG group compared with that of the C group. 4. In the rat aorta from P and IG groups, the contractions produced by several concentrations of noradrenaline were significantly smaller (P < 0.05) when the endothelium was removed. Similar effects occurred in aorta strips of animals previously treated with either atropine, promethazine, cimetidine or halothane. 5. Our results suggest that drugs currently used in anesthesia interfere with some endothelium-dependent effects on isolated rat aorta but according to these results they do not seem to be responsible for the lack of acetylcholine relaxation sometimes described in human vessels in vitro.     

Endothelium-dependent effect of perindopril and enalaprilat in rat thoracic aorta

AIM: To study the effect of the angiotensin-converting enzyme (ACE) inhibitors perindopril (Per) and enalaprilat (Ena) on the reactivity of the endothelium in normal rats. METHODS: Male rats were treated intragastrically with Per (2 mg.kg-1.d-1) or placebo (n = 18) for 6 wk. Aorta was isolated for experiment. Another set of isolated aortic rings with and without endothelium were incubated with Ena (0.1 mumol.L-1) for 30 min. Responses to acetylcholine, serotonin, phenylephrine, sodium nitroprusside (SN), and nitroglycerin (Nit) were observed. RESULTS: Endothelium-dependent relaxation to acetylcholine was augmented in aortic rings from rats treated with Per in comparison with control. The IC50 value (95% confidence limits) decreased from 3.8 (0.56-26.1) mumol.L-1 (control group) to 0.98 (0.28-3.41) mumol.L-1 (Per-treated group). The maximal relaxation was augmented from 62 +/- 9% to 78 +/- 10% (P < 0.01). However, the responses to the endothelium-independent vasodilators, SN and Nit, were similar. Serotonin- and phenylephrine-induced contractions were decreased, which were influenced by basal release of endothelium-derived relaxing factor (EDRF). EC50 values was 6.1 (2.6-14.4) nmol.L-1 vs 8.3 (3.6-18.8) nmol.L-1 in comparison with control group and Per-treated group. The maximal contraction was decreased from 2.42 +/- 0.29 g (control group) to 1.96 +/- 0.25 g (treated group) (P < 0.01). Similar results were found in incubation with Ena. CONCLUSION: Ena and Per enhanced the basic release of EDRF from vascular endothelium.     

Effects of chylomicrons and chylomicron remnants on endothelium-dependent relaxation of rat aorta

The effects of chylomicrons and chylomicron remnants on endothelium-dependent relaxation of rat aorta were studied in vitro. Chylomicrons and chylomicron remnants were prepared in vivo. Aortic rings were incubated with the lipoproteins for 45 min before the vessels were constricted with phenylephrine and concentration relaxation response curves constructed to carbachol, ATP, A23187 and S-nitroso-N-acetylpenicillamine. Maximum % relaxations to carbachol were significantly reduced by both chylomicrons and chylomicron remnants but responses to ATP and S-nitroso-N-acetylpenicillamine were unaffected. In addition, chylomicrons significantly inhibited A23187-induced relaxation, causing an increase in the EC50 value. Chylomicron remnants cause selective inhibition of carbachol-induced relaxation suggesting an action at the receptor or G protein-coupled component of the receptor-mediated activation of the L-arginine-nitric oxide pathway. Chylomicrons appear to be less selective in their inhibition of the endothelium-dependent relaxation. This study demonstrates that lipoprotein particles of dietary origin may cause endothelial cell dysfunction.     

Vasorelaxation of rat thoracic aorta caused by 14-deoxyandrographolide

1. The pharmacological effects of 14-deoxyandrographolide on rat isolated thoracic aorta were examined. 2. 14-Deoxyandrographolide (2.5-120 mumol/L) inhibited contractions induced by phenylephrine (PE; 0.1 mumol/L) and high K+ (80 mmol/L) in a concentration-dependent manner in endothelium-intact aorta. The effect was attenuated in endothelium-denuded aorta without modifying the maximal response. Like verapamil, 14-deoxyandrographolide produced a much greater vasorelaxant effect in aorta precontracted by KCl than by PE. 14-Deoxyandrographolide (20-60 mumol/L) also inhibited responses of the rat aorta to PE. 3. In Ca(2+)-free medium (KCl 55 mmol/L), 14-deoxyandrographolide (20-80 mumol/L) antagonized Ca(2+)-induced vasocontraction in a concentration-dependent manner and transient contractions induced by both caffeine (10 mmol/L) and nor-adrenaline (1 mumol/L) were suppressed or almost abolished by 14-deoxyandrographolide. 4. The vasorelaxant effect of 14-deoxyandrographolide was partially antagonized by NG-nitro-L-arginine methyl ester (25 mumol/L), a specific and competitive nitric oxide synthase (NOS) inhibitor, and methylene blue (10 mumol/L), a soluble guanylate cyclase inhibitor, but was not affected by indomethacin (20 mumol/L), a cyclo-oxygenase inhibitor, or glibenclamide (10 mumol/L), an ATP-sensitive K(+)-channel blocker. 5. These results suggest that the vasorelaxant activity of 14-deoxyandrographolide may be mediated via the activation of NOS and guanylate cyclase, as well as the blockade of Ca2+ influx through both voltage- and receptor-operated Ca2+ channels.     

Identification of elastin peptides with vasorelaxant activity on rat thoracic aorta

Different Epstein-Barr-virus(EBV) variants were found to be associated with nasopharyngeal carcinoma (NPC). The type-C variant lacks the BamHI site between the BamHI W1* and I* regions and the type-f variant has an extra BamHI site in the BamHI F fragment. The BNLF1 gene (which encodes the LMP1 protein) from a nude-mouse-passaged CAO strain and from NPC biopsies from Taiwanese patients also exhibits variations resulting in structural and functional differences in the protein. The BZLF1 gene encodes the ZEBRA protein which triggers the EBV lytic cycle. A difference has been observed in 8 amino acids in the ZEBRA sequence in B95-8 (Z95) and P3HR1 (ZP3) cell lines. EBV found in NPC biopsies and peripheral-blood cells from Asians was predominantly of the ZP3 type (72%), while 81% of samples from different EBV-associated diseases and peripheral-blood cells from North Africa or Europe were of the Z95 type. We found that an alanine 206 had been replaced by a serine in the Z95 sequence in 72% of the NPC biopsies from European and North African patients. The Zser206 variant is found in a significantly lower percentage (p < 0.001) of other EBV-positive tissues from individuals in the same region (10-33%). In contrast, a 30-bp deletion is observed near the 3' end of the LMP1 gene in the majority of EBV (86%) from NPC and peripheral-blood cells from Asians, whereas a significantly lower percentage (p < 0.001) of NPC biopsies from European and North African patients (56%) have this deletion, as do lymphocytes from control individuals from the same region (36 and 55% respectively).     

Vibrio vulnificus hemolysin dilates rat thoracic aorta by activating guanylate cyclase

Hemolysin produced by Vibrio vulnificus caused hypotension and tachycardia in rats and dilated rat thoracic aorta. Hemolysin-induced vasodilatation of the aorta was not affected by N omega-nitro-L-arginine methyl ester and aminoguanidine, NO synthase inhibitors, whereas the vasodilatation was inhibited by LY 83,583, a guanylate cyclase inhibitor. Hemolysin elevated cGMP levels, and the elevation was abolished by LY 83,583. These results suggest that V. vulnificus hemolysin activates guanylate cyclase independently of NO synthase, and the subsequent increase in cGMP levels results in vasodilatation.     

Possible mechanism of captopril induced endothelium-dependent relaxation in isolated rabbit aorta

Natural resistance-associated macrophage protein 1 (NRAMP1) is a putative membrane protein that dominates natural resistance to infection. An NRAMP1-glutathione S-transferase fusion protein was used to test the ability of the NRAMP1 NH2-terminal domain to bind to taxol-stabilized microtubules. Co-sedimentation analysis showed that the fusion protein binds to microtubules. Although the NH2-terminal domain of the NRAMP1 molecule has structural homology with the Pro-rich region of microtubule-associated protein 4 (MAP4), the presence of the MAP4 microtubule-binding domain fragment had little effect on the binding of the fusion protein to microtubules.     

Mechanisms of the enhanced contractile response to phenylephrine in thoracic aorta isolated from rats with dietary magnesium deficiency

The mechanisms underlying the enhanced contractile response to phenylephrine (PE) and increased susceptibility to nifedipine of de-endothelialized thoracic aorta isolated from rats with dietary magnesium deficiency (Mg-deficient rats) were examined by functional and radioligand binding studies. Enhanced PE-induced contractions and increased susceptibility to nifedipine in Mg-deficient rats were not observed in the presence of 10 microM H7. PE significantly decreased the KD value without changing Bmax in the binding of [3H]PN200-110 to de-endothelialized aortic strips. The KD value obtained in the Mg-deficient rats was significantly smaller than that in the controls. Nifedipine displaced the binding of [3H]PN200-110 concentration-dependently, and the pKi value in Mg-deficient rats was significantly larger than that in the controls. A combination of PE and H7 abolished this difference. These results indicate that the modulation of L-type Ca2+ channels via the stimulation of alpha 1-adrenoceptors may be involved in the enhancement of vasoconstriction and increased susceptibility to nifedipine in aortas isolated from Mg-deficient rats. The H7-sensitive mechanisms may play an important role in these phenomena.     

Spontaneous echocardiographic contrast in the descending thoracic aorta

Spontaneous echocardiographic contrast (SEC) is an occasional finding observed in the atria in patients undergoing transesophageal echocardiographic studies, but has rarely been described in the descending thoracic aorta in the absence of an aortic dissection. The pathophysiology of SEC in the cardiac and vascular structures appears to be related to an interaction between red blood cells and plasma proteins in the setting of a low flow state. In this report we present three cases of SEC in the descending thoracic aorta, with one of the cases of SEC resolving with repair of his underlying cardiac disorder.     

Roles of calcium-activated and voltage-gated delayed rectifier potassium channels in endothelium-dependent vasorelaxation of the rabbit middle cerebral artery

1. The cellular mechanism(s) of action of endothelium-derived vasodilator substances in the rabbit middle cerebral artery (RMCA) were investigated. Specifically, the subtypes of potassium channels involved in the effects of endothelium-derived relaxing factors (EDRFs) in acetylcholine (ACh)-induced endothelium-dependent vasorelaxation in this vessel were systematically compared. 2. In the endothelium-intact RMCA precontracted with histamine (3 microM), ACh induced a concentration-dependent vasorelaxation, which was sensitive to indomethacin (10 microM) or N(G)-nitro-L-arginine (L-NOARG; 100 microM); pD2 values 8.36 vs 7.40 and 6.38, P < 0.01 for both, n = 6 and abolished by a combination of both agents. ACh caused relaxation in the presence of high K+ PSS (40 mM KCl), which was not affected by indomethacin, but abolished by L-NOARG and a combination of indomethacin and L-NOARG. 3. In the presence of indomethacin, relaxation to ACh in the endothelium-intact RMCA precontracted with histamine was unaffected by either glibenclamide (10 microM), an ATP-sensitive K+ channel (K[ATP]) blocker, 4-aminopyridine (4-AP, 1 mM) or dendrotoxin (DTX, 0.1 microM), delayed rectifier K channel (Kv) blockers. However, relaxation responses to ACh were significantly inhibited by either LY83583 (10 microM) and 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 10 microM), guanylyl cyclase inhibitors, or charybdotoxin (CTX; 0.1 microM), iberiotoxin (ITX, 0.1 microM) and apamin (APA, 0.1 microM), large conductance Ca2+-activated K+ channels (BK[Ca]) blocker and small conductance Ca2+-activated K+ channel (SK[Ca]) blocker, respectively. 4. In the presence of L-NOARG, relaxation to ACh was unaffected by glibenclamide or the cytochrome P450 mono-oxygenase inhibitor, clotrimazole (1 microM), but was significantly inhibited by either 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ 22,536, 10 microM) and 2',3'-dideoxyadenosine (2',3'-DDA, 30 microM), adenylyl cyclase inhibitors, or 4-AP, DTX, CTX, ITX and APA. 5. In the endothelium-denuded RMCA precontracted with histamine, authentic NO-induced relaxation was unaffected by glibenclamide, 4-AP and DTX, but significantly reduced by ODQ, ITX and APA. Authentic prostaglandin I2 (PGI2)-induced relaxation was unaffected by glibenclamide, but significantly reduced by 2',3'-DDA, 4-AP, DTX, ITX and APA. Forskolin-induced relaxation was significantly inhibited by high K+, CTX and 4-AP. 6. These results indicate that: (1) in the RMCA the EDRFs released by ACh are NO and a prostanoid (presumably PGI2), and there is no evidence for the release of a non-NO/PGI2 endothelium-derived hyperpolarizing factor (EDHF), (2) K(Ca) channels are involved in NO-mediated relaxation of the RMCA but both K(Ca) and Kv channels are involved in PGI2-mediated relaxation.     

Effects of vitamin E deficiency on vasomotor activity and ultrastructural organisation of rat thoracic aorta

1. The effects of vitamin E deficiency were evaluated in aortic rings isolated from rats maintained on a diet deficient in vitamin E. 2. Endothelium-dependent vasodilator responses to acetylcholine (ACh) and calcium ionophore, A23187, were reduced in preparations from treated animals, compared to the age-matched controls. The maximal vasodilation to ACh was 66.4 +/- 9 (n = 4) and 38.8 +/- 7 (n = 4) % in control and 10 month-treated preparations, respectively. 3. The endothelium-independent vasodilator responses to sodium nitroprusside as well as the concentration-dependent contractile responses to noradrenaline, did not differ between treated and control preparations. 4. Electron microscopic examination of vascular segments and revealed that, following vitamin E deficiency, normal tissue organisation was disrupted, the endothelial monolayer either not being in contact with the underlying tissue or being absent in most of the areas analysed. 5. It is concluded that during vitamin E deficiency both morphological disruption and functional impairment of endothelium occur without observable modification of muscle cell function and morphology.     

Characterization of alpha1-adrenoceptor subtypes mediating contractions to phenylephrine in rat thoracic aorta, mesenteric artery and pulmonary artery

1. The subtype of alpha1-adrenoceptor mediating contractions to phenylephrine of the rat thoracic aorta, mesenteric artery and pulmonary artery were investigated by use of antagonists which show selectivity between the cloned alpha1-adrenoceptor subtypes in binding studies. 2. Cumulative concentration-contraction curves for phenylephrine were competitively antagonized in the rat thoracic aorta by prazosin (pA2 9.9), WB4101 (pA2 9.6), 5-methylurapidil (pA2 8.1), benoxathian (pA2 9.2) and indoramin (pA2 7.4). These compounds were also competitive antagonists in the mesenteric and pulmonary arteries (except for 5-methylurapidil in the pulmonary artery), (prazosin pA2 9.9 and 9.7; WB4101 pA2 9.8 and 9.6; 5-methylurapidil pA2 7.9 and pK(B) estimate 8.0; benoxathian pA2 8.8 and 9.3; indoramin pA2 7.2 and 7.5, respectively). 3. RS 17053 was not a competitive antagonist in any blood vessel as Schild plot slopes were greater than unity. The pK(B) estimates for RS 17053 were 7.1 in aorta, 7.0 in the mesenteric artery and 7.7 in the pulmonary artery. 4. The alpha1D-subtype selective antagonist BMY 7378 appeared to be non-competitive with shallow Schild plot slopes. The data were better fitted with two lines in all tissues, with Schild plot slopes that were no longer different from unity, except in the pulmonary artery. The higher affinity site for BMY 7378 in the aorta had a pA2 of 9.0, while it was 8.8 and 8.9 in the mesenteric and pulmonary arteries, respectively. 5. MDL73005EF acted in a non-competitive manner in all three blood vessels, with shallow Schild plot slopes. The pK(B) estimates for MDL73005EF were 8.4 in aorta, 7.5 in the mesenteric artery and 8.0 in the pulmonary artery. 6. In all three blood vessels the functionally determined antagonist affinity estimates correlated best with published pKi values for their displacement of [3H]-prazosin binding on membranes expressing cloned alpha1d-adrenoceptors compared with alpha1a- or alpha1b-adrenoceptors. The antagonist affinity estimates in the aorta, mesenteric and pulmonary arteries correlated highly with their previously published pA2 values in rat aorta (alpha1D) and less well with those for alpha1A- and alpha1B-adrenoceptors mediating contraction of the rat epididymal vas deferens and rat spleen, respectively. 7. The results of this study suggest that the contraction to phenylephrine of the rat thoracic aorta, mesenteric artery and pulmonary artery are mediated in part via the alpha1D-subtype of adrenoceptor. The data for both BMY 7378 and MDL73005EF in all three blood vessels are consistent with receptor heterogeneity. However, the identity of the second site is unclear.