Dietary l-Arginine Supplementation Normalizes Platelet Aggregation in Hypercholesterolemic Humans

Objectives. The present study was designed to test the hypothesis that long-term dietary supplementation with the nitric oxide precursor l-arginine would enhance vascular or platelet-derived nitric oxide activity, or both, and thereby inhibit platelet reactivity in hypercholesterolemic humans.Background. We have shown that reduced vascular activity of nitric oxide in hypercholesterolemic rabbits can be restored by l-arginine supplementation. The improvement in nitric oxide activity is associated with an inhibition of platelet aggregation ex vivo. This effect is most likely due to increased elaboration of endothelium- or platelet-derived nitric oxide, or both, because the inhibition of platelet reactivity was associated with elevation of intraplatelet cyclic guanosine monophosphate and was reversed by the nitric oxide synthase antagonist N-methyl-arginine.Methods. In a double-blinded, randomized, placebo-controlled trial, hypercholesterolemic patients were assigned to l-arginine hydrochloride, 8.4 g/day orally, or placebo for 2 weeks. Platelet-rich plasma was obtained for aggregometry induced by collagen (1 to 10 μg/ml) at four points: baseline, after 2 weeks of treatment, after a 2-week washout and after a long-term washout of 16 weeks on average. Aggregation was quantified by light transmittance and expressed as a percent transmittance observed with platelet-poor plasma.Results. Compared with normocholesterolemic control subjects, platelets from hypercholesterolemic subjects stimulated with 5 μg/ml of collagen showed increased aggregability (68.6% in hypercholesterolemic patients vs. 54.5% in normocholesterolemic control subjects, p ≤ 0.02). After 2 weeks of treatment with l-arginine (but not placebo), platelet reactivity was modestly reduced; this effect persisted for 2 weeks after discontinuation of arginine (52.6% in arginine-treated patients vs. 65.1% in normocholesterolemic control subjects, p = 0.07). After 18 weeks (i.e., 16 weeks after discontinuing arginine treatment), the platelets of hypercholesterolemic patients once again became hyperaggregable, and the extent of platelet aggregation was significantly increased compared with the 4-week point (73.6% after vs. 52.6% during arginine treatment, p < 0.01). No significant change in platelet reactivity was seen in placebo-treated hypercholesterolemic patients throughout the study. l-Arginine treatment was well tolerated without side effects.Conclusions. This double-blinded, placebo-controlled study demonstrates that dietary supplementation with l-arginine can modestly attenuate the increased platelet reactivity seen in hypercholesterolemic patients. The data are consistent with our previous studies in hypercholesterolemic animals, demonstrating that l-arginine restores endogenous nitric oxide activity and inhibits platelet aggregation. Enhancement of endogenous nitric oxide activity is a potential novel therapeutic strategy worthy of further study.(J Am Coll Cardiol 1997;29:479–85)     

Effects of L-arginine on atherogenesis and endothelial dysfunction due to secondhand smoke.

Secondhand smoke (SHS) and hypercholesterolemia increase cardiovascular risk. We hypothesized that L-arginine, the precursor of nitric oxide (NO), might protect against atherogenesis and endothelial dysfunction caused by SHS. The effects of L-arginine supplementation (2.25% solution ad libitum) and SHS (smoking chambers for 10 weeks) were examined in 32 hypercholesterolemic rabbits. Eight normal rabbits served as controls. Acetylcholine- and nitroglycerin-induced vasorelaxation was assessed in aortic rings precontracted with norepinephrine. Hypercholesterolemia increased intimal lesion area (P=0.012), reduced endothelium-dependent relaxation (P=0.009), and reduced basal (P=0.005) and stimulated (P<0.0005) production of NOs. SHS increased intimal lesion area (P=0. 01) norepinephrine-induced contraction (P=0.001) and reduced endothelium-dependent relaxation (P=0.02). SHS-induced increase in norepinephrine contraction was abolished by the inhibition of NO synthase and removal of endothelium. L-Arginine improved endothelium-dependent relaxation (P=0.001) and attenuated SHS-induced endothelial dysfunction (P=0.007) and atherogenesis (P=0. 001). Basal production of nitrogen oxides correlated inversely with intimal lesion area (r=-0.66; P<0.0005) and stimulated production of NOs correlated with endothelium-dependent relaxation (r=-0.66; P<0. 001). SHS causes endothelial dysfunction and increased adrenergic responsiveness and atherogenesis in hypercholesterolemic rabbits. Chronic dietary supplementation with the NO precursor L-arginine mitigates these effects. The adverse vascular consequences of SHS appear to be mediated via deleterious effects on endothelial function.     

Long-term combined beneficial effects of physical training and metabolic treatment on atherosclerosis in hypercholesterolemic mice

The pathogenic mechanisms by which physical exercise influences atherosclerotic lesion formation remain poorly understood. Because vigorous physical training increases oxidative stress, this study tested the hypothesis that graduated and moderate physical exercise together with metabolic intervention (l-arginine and antioxidants) may contribute to increased vascular protection. Exercise training in mice was induced by graduated swimming. In hypercholesterolemic male mice on an atherogenic high-cholesterol diet, graduated and moderate exercise lowered plasma cholesterol and decreased atherosclerotic lesions compared with sedentary control mice. Antioxidants (1.0% vitamin E added to the chow and 0.05% vitamin C added to the drinking water) and l-arginine (6% in drinking water) supplementation to exercising hypercholesterolemic mice further and synergistically reduced atherosclerosis compared with untreated exercised mice. Arterial oxidation-specific epitopes and systemic oxidative stress were reduced by metabolic intervention. Graduated chronic exercise elicited an increase in production of nitric oxide through increased endothelial nitric oxide synthase expression and ameliorated scavenger activities. Thus, metabolic intervention with l-arginine and antioxidants together with graduated and moderate exercise training reduce atherosclerotic lesion formation.     

Investigation of decreased availability of nitric oxide precursor as the mechanism responsible for impaired endothelium-dependent vasodilation in hypercholesterolemic patients

Objective. The purpose of this study was to determine whether the impaired endothelium-dependent vasodllation of hyperchoiesterolemic patients is due to decreased availability of l-arginine, the substrate for nitric oxide.Background. Patients with hypercholesterolemia have impaired endothelium-dependent vasodilation that is related to a defect in the endothelium-derived nitric oxide system. However, the precise location of this abnormality has not been determined.Methods. The study included 12 hypercholesterolemic patients (6men, 6 women; 52 ± 9 years old; serum cholesterol>240mg/dl) and 15 normal volunteers (8 men, 7 women; 50 ± 6 years old; serum cholesterol < 210 mg/dl. The forearm vascular responses to intraaterial infusion of acetylccholine, an endothelium-dependent vasodilator (7.5, 15, 30 μg/min), and sodium nitropruside, a direct smoth muscle dilator (0.8,1.6,3.2 μg/min) were studied before and during Infusion of l- or d-arginine (a stereoisomer of arginine that is not a nitric oxide precursor).Results. The response to acetylcholine was lower in hypercholesterolemic patients than in control sutjects. However, no significant difference was observed with sodium nitroprusside infusion. l-Arginine augmented the response to acetylcholine in normal subjects (maximal blood flow increased from 14.4 ± 7 to 18.9 ± 10 ml/min per 100 ml, p < 0.002). In contrast, in the hypercholesterolemic patients, only a mild but not significant improvement in the response to acetylcholine was observed with the infusion of l-arginine (maximal blood flow increased from 6.8 ± 4 to 8.4 ±5ml/min per 100ml; p = 0.161; however, a similar mild but not significant change was also observed with l-arginine (maximal blood flow increased from 6.8± 4 to 8.3 ± 4 ml/min per 100 ml, p = 0.07). l-Arginine did not modify the response to sodium nitroprusside in either group.Conclusions. The augmentation of endothelium-dependent vasodilation by l-arginine, the nitric oxide precursor, is defective in hypercholesterolemic patients. This supports the concept of an abnormal endothelium-derived nitric oxide system in hypercholesterolemia and indicates that decreased availability of nitric oxide substrate is not responsible for the impaired endothelial function in this condition.     

Regression of atherosclerosis: role of nitric oxide and apoptosis

BACKGROUND: We have recently found that administration of L-arginine to hypercholesterolemic rabbits induces regression of preexisting lesions. Others have previously shown that activation of the L-arginine/nitric oxide (NO) synthase pathway can induce apoptosis of vascular cells in vitro. Accordingly, the current study was designed to determine if dietary supplementation of L-arginine induces apoptosis of intimal lesions and if this effect is mediated through the NO synthase pathway. METHODS AND RESULTS: Male New Zealand White rabbits were fed a 0.5% cholesterol diet for 10 weeks and subsequently placed on 2.5% L-arginine HCl in the drinking water, and the cholesterol diet was continued for 2 weeks, at which time the aortas were harvested for histological studies. L-Arginine treatment increased the number of apoptotic cells (largely macrophages) in the intimal lesions by 3-fold (11.9+/-3.9 vs 3.9+/-1. 4 apoptotic cells/mm2, P<0.01). In subsequent studies, aortas were harvested for ex vivo studies. Aortic segments were incubated in cell culture medium for 4 to 24 hours with modulators of the NO synthase pathway. The tissues were then collected for histological studies and the conditioned medium collected for measurement of nitrogen oxides by chemiluminescence. Addition of sodium nitroprusside (10(-5) mol/L) to the medium caused a time-dependent increase in apoptosis of vascular cells (largely macrophages) in the intimal lesion. L-Arginine (10(-3) mol/L) had an identical effect on apoptosis, which was associated with an increase in nitrogen oxides released into the medium. These effects were not mimicked by D-arginine, and they were antagonized by the NO synthase inhibitor L-nitro-arginine (10(-4) mol/L). The effect of L-arginine was not influenced by an antagonist of cGMP-dependent protein kinase, nor was the effect mimicked by the agonist of protein kinase G or 8-BR cGMP. CONCLUSIONS: These results indicate that supplemental L-arginine induces apoptosis of macrophages in intimal lesions by its metabolism to NO, which acts through a cGMP-independent pathway. These studies are consistent with our previous observation that supplementation of dietary arginine induces regression of atheroma in this animal model. These studies provide a rationale for further investigation of the therapeutic potential of manipulating the NO synthase pathway in atherosclerosis.     

Effects of dietary L-arginine on the reactivity of canine coronary arteries

Experiments were designed to determine the effects of supplemental dietary L-arginine on the endothelial and smooth muscle function of canine coronary arteries. One group of dogs was fed the standard laboratory chow while another group was supplemented with 250 mg/kg per day L-arginine. All dogs had undergone bilateral reversed interposition saphenous vein grafting and received 325 mg/day oral aspirin. After 5 weeks of arginine feeding, left circumflex coronary arteries were removed, cut into rings, and suspended for the measurement of isometric force in organ chambers. Concentration-response curves were obtained to L-arginine, UK-14,304 (alpha2-adrenergic agonist) and A23187 (calcium ionophore) in the absence and presence of N(G)-monomethyl-L-arginine (L-NMMA) and tetraethylammonium (TEA) alone or in combination. Serum concentrations of L-arginine increased by about 20% following 2 weeks of arginine feeding and remained elevated throughout the study. In rings with and without endothelium contracted with prostaglandin F2alpha, L-arginine caused concentration-dependent contractions in rings from control animals but no significant change in tension in rings from arginine-fed animals. Contractions to L-arginine in control animals were reduced by either L-NMMA or TEA. Endothelium-dependent relaxations to the alpha2-adrenergic agonist were decreased with arginine feeding while relaxations to the calcium ionophore and the endothelium-derived factor nitric oxide were similar among groups. Relaxations to UK-14,304 were reduced by L-NMMA in both groups but by TEA only in rings from control animals. These results suggest that dietary supplementation with L-arginine modifies reactivity of endothelium and smooth muscle by at least two mechanisms: one associated with activation of potassium channels and the other with receptor-coupled release of nitric oxide.     

Magnesium dietary intake modulates blood lipid levels and atherogenesis.

In this study, we have examined the effects of variation in dietary Mg on the atherogenic process. Oral supplementation of rabbits fed a high cholesterol diet (1% or 2%) with the Mg salt magnesium aspartate hydrochloride (Magnesiocard) (i) lowers the level of serum cholesterol and triglycerides in normal (25-35%) as well as atherosclerotic (20-40%) animals and (ii) attenuates the atherosclerotic process markedly. In addition, we found that dietary deficiency of Mg augments atherogenesis markedly and stimulates (or activates) macrophages of the reticuloendothelial system. Evidence is presented to indicate that the hypercholesterolemic state may cause the loss of Mg from soft tissues to the serum, thereby masking an underlying Mg deficiency.     

Physical training and metabolic supplementation reduce spontaneous atherosclerotic plaque rupture and prolong survival in hypercholesterolemic mice

Moderate physical exercise (PE) combined with metabolic treatment (MT) (antioxidants and l-arginine) are well known to reduce atherosclerotic lesion formation in hypercholesterolemic mice. However, the long-term beneficial effects on unstable atheroma remain poorly understood. We started early PE training in large groups of 6-week-old hypercholesterolemic mice (by graduated swimming) alone or in combination with nutritional supplementation (1.0% vitamin E added to the chow and 0.05% vitamin C and 6% l-arginine added to the drinking water). Inactive controls did not receive PE. The spontaneous development of atherosclerotic plaque rupture (associated with advanced atherosclerosis) and survival rates were evaluated. Moderate PE elicited an increase in plasma levels of nitric oxide. Early combined treatment with PE and MT in the hypercholesterolemic mice significantly reduced lesions (also detected noninvasively at 10 months) and spontaneous atherosclerotic plaque rupture and prolonged survival more effectively than each intervention alone. Thus, early concerted actions of MT and PE improve the natural history of atherosclerotic lesions and reduce the plaque instability in hypercholesterolemic mice.     

Probucol reduces plasma and aortic wall oxysterol levels in cholesterol fed rabbits independently of its plasma cholesterol lowering effect.

To understand further the antiatherogenic mechanism of probucol, the antioxidant effect of this agent was studied on specific cholesterol oxidation products in plasma and aortic wall in equally hypercholesterolemic New Zealand white rabbits. In order to maintain equal plasma total cholesterol levels, five control rabbits (C group) received a 1% followed by a 0.5% cholesterol enriched diet, while the probucol treated rabbits (C+P group) received a graded increase in the cholesterol supplemented diet from 1% to 3%; probucol supplementation was constant at 1%. After 9 weeks of feeding, the plasma oxysterols, cholest-5-ene-3 beta,7 alpha-diol, cholest-5-ene-3 beta,7 beta-diol, 5,6 beta-epoxy-5 alpha-cholestan-3 beta-ol, 5,6 alpha-epoxy-5 alpha-cholestan-3 alpha-ol and 5 alpha-cholestane-3 beta,5,6 beta-triol significantly increased over baseline levels in both experimental groups. However, the increase in all these products in plasma was 20-60% less in the C+P group than the C group (P < 0.05). Furthermore, the C+P aortic wall cholesterol oxide concentrations were 50-90% less than the C group (P < 0.05). The oxysterol pattern of the aortic wall was similar to plasma. Additionally, the aortic wall cholesterol content in the C+P group was 50% less than the C group (P < 0.05). The plasma cholesterol levels were not significantly different at any time point during the study and the cholesterol oxide content in the diets was the same. These results are consistent with the contention that the antioxidant properties of probucol serve as the basis for its antiatherogenic effects in vivo.     

Increased ischemia-reperfusion injury to the heart associated with short-term, diet-induced hypercholesterolemia in rabbits

The effects of increased dietary cholesterol content on coronary vascular hemodynamics and endothelial cell transport function were assessed in isolated rabbit hearts during 3.5 hours of reperfusion after 30 minutes of global, no-flow ischemia. In control hearts from rabbits fed normal chow, perfusion pressure, left ventricular end-diastolic pressure, maximum +dP/dt, and the rate of intravascular clearance of radiolabelled albumin remained constant during 5 hours of continuous perfusion, while the mean transit time of radiolabelled albumin increased 1.6 X baseline. In ischemic hearts from rabbits fed normal chow, perfusion pressure increased 59% during reperfusion while left ventricular end-diastolic pressure and maximum +dP/dt returned toward control levels. The rate of intravascular clearance of radiolabelled albumin decreased 36%, and the mean transit time of albumin increased approximately 3 X baseline. Ischemia-reperfusion injury to the cardiac vasculature and musculature was markedly increased in hearts of rabbits fed chow supplemented with 2% cholesterol for 2-3 weeks compared to rabbits fed the same diet for a longer duration (5-16 weeks) or rabbits fed normal chow. Prior to ischemia, permeation of the coronary vasculature by albumin was increased twofold in rabbits fed cholesterol for 2-3 weeks while myocyte contractile function was normal relative to chow-fed controls or the group fed cholesterol for 5-16 weeks. These effects of acute cholesterol feeding precede occlusive atherosclerotic coronary artery disease and occur at plasma cholesterol concentrations one third of those in rabbits fed cholesterol for the longer duration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Suppression of atherogenesis in cholesterol-fed rabbits treated with nilvadipine, a new vasoselective calcium entry blocker

We examined the effects of nilvadipine, a new dihydropyridine calcium entry blocker, on atherogenesis in rabbits fed a 1% cholesterol diet. The drug was given subcutaneously to the animals in hypotensive doses of 1.0 or 3.2 mg/kg/day for 10 weeks, and was well tolerated. Plasma total cholesterol increased markedly in all the cholesterol-fed rabbits, and nilvadipine had no effect on this, or on HDL-cholesterol and triglyceride levels. However, the area of Sudan IV positive intimal lesions (one of the parameters of atherosclerosis) in the aorta decreased significantly in the nilvadipine treated animals, and in addition, cholesterol and calcium content in the thoracic aorta were reduced. The reference drugs, nifedipine and nicardipine given subcutaneously in doses of 10.0 mg/kg/day either had no effect or were weaker in antiatherogenic effect than nilvadipine. The findings suggest that nilvadipine has more potent antiatherogenic activity than nicardipine or nifedipine.     

Endothelial nitric oxide synthase activity in aorta of normocholesterolemic rabbits: regional variation and the effect of estrogen

OBJECTIVE: Several animal studies suggest that nitric oxide (NO) produced by the endothelium attenuates arterial cholesterol accumulation. In the present study we have asked the following questions: (1) is the regional variation in aortic cholesterol accumulation in hypercholesterolemic rabbits preceded by a regional variation in endothelial NO synthase (eNOS) activity in normocholesterolemic rabbits, and (2) is the antiatherogenic effect of estrogen in hypercholesterolemic rabbits preceded by a higher eNOS activity in normocholesterolemic rabbits. METHODS: The eNOS activity was determined by conversion of 14C-L-arginine to 14C-L-citrulline in freshly isolated endothelial cells of aorta in normocholesterolemic rabbits. In the regional variation study, 16 male and eight female rabbits were used. In the estrogen study, ovariectomized female rabbits were subcutaneously injected three times weekly with either 17beta-estradiol (n=7) or vehicle (n=7) for 18 weeks. RESULTS: In the regional variation study, the atherosclerosis prone aortic arch showed a significant lower eNOS activity than the more resistant abdominal aorta in both male (P<0.0001) and female (P<0.05) rabbits. In the estrogen study, the eNOS activity in the aortic arch and upper thoracic aorta was significantly higher in the estrogen than in the vehicle rabbits (P<0.05). In the lower thoracic aorta, however, the eNOS activity was the same. CONCLUSION: The findings suggest that a high NO production in the luminal endothelium of the arterial wall precedes a low cholesterol accumulation during a subsequent period of hypercholesterolemia.     

Amelioration of severity of myocardial injury by a nitric oxide donor in rabbits fed a cholesterol-rich diet

Objectives. This study compared the effect of a nitric oxide donor on limiting the size of infarct resulting from myocardial ischemia-reperfusion between atherosclerotic and nonatherosclerotic models.Background. Endothelial-derived relaxation in coronary arteries affected by ischemia is substantially impaired after reperfusion, and this impairment may exacerbate the myocardial ischemia-reperfusion injury. In animals with experimental atherosclerosis, release of endothelial-derived relaxing factor is also decreased, and the propagation of myocardial infarction could be exacerbated.Methods. We examined the extent of myocardial injury induced by ischemia (30 min) and reperfusion (48 hr) in rabbits fed a cholesterol-rich (1%) or normal diet for 10 weeks. We also evaluated the effect of a nitric oxide donor (S-nitroso-N-acetylpenicillamine [SNAP]), a nitric oxide precursor (l-arginine) or a degradation product of SNAP (N-acetylpenicillamine) on infarct size in these models.Results. Severity of myocardial injury was significantly exacerbated in cholesterol-fed rabbits (75.2 ± 4.4% [mean ± SEM]) compared with that in non-cholesterol-fed rabbits (53.2 ± 5.2%). This exacerbation was prevented by treatment with SNAP (50.2 ± 6.4%) but not with l-arginine (70.5 ± 6.0%) or N-acetylpenicillamine (70.4 ± 4.8%) in cholesterol-fed rabbits. However, SNAP did not limit infarct size in non-cholesterol-fed rabbits (60.8 ± 4.2%). The rate-pressure product was similar during the course of the experiment in all the groups.Conclusions. Myocardial damage induced by ischemia-reperfusion was significantly exacerbated in rabbits fed a long-term cholesterol-rich diet but was effectively reversed by treatment with a nitric oxide donor. However, this agent did not limit infarct size in normal rabbits. Thus, a nitric oxide donor reduces myocardial infarct size in atherosclerotic but not in nonatherosclerotic rabbits.     

Suppression of experimental atherosclerosis in rabbits by interferon-inducing agents

The effects of two chemically different interferon inducers on the suppression of atherosclerosis were studied in rabbits fed an atherogenic chow diet. One group (10 rabbits per group) was fed normal rabbit chow, and three groups were fed an atherogenic chow. One of the latter groups received the atherogenic feeding alone; the other two were treated with either polyinosinic-polycytidylic acid (poly I:C) or 2-amino-5-bromo-6-phenyl-4-pyrimidinone (ABPP). Neither of the drugs reduced significantly the hypercholesterolemia induced by the feeding. However, both poly I:C and ABPP treatment significantly reduced the percent area of the aortic intimal surface lesions, stained for lipid with Sudan IV, compared with that in untreated rabbits fed atherogenic chow. Microscopic sections of typical aortic plaques showed that both drug treatments significantly reduced the size and number of intimal lipid deposits compared with those observed in the aortas of untreated animals. Chemical analysis for cholesterol and collagen content revealed that interferon-inducing agents significantly reduced cholesterol deposits in the aorta, with little effect on fibrous protein deposition. The results indicate that two unrelated interferon-inducing drugs suppressed atherogenesis without reducing serum cholesterol and low density lipoprotein levels. Whether the protection against atherosclerosis is exerted by endogenous interferon production remains to be determined.     

Dietary L-aspartate and L-glutamate inhibit fatty streak initiation in cholesterol-fed rabbit

BACKGROUND AND AIM: Low-density lipoprotein (LDL) oxidation is a potential atherogenic agent, and protecting LDL from oxidation prevents atherogenesis. It has been shown that L-aspartate and L-glutamate decrease lipid peroxidation after reoxygenation by means of the initiation of the cardiopulmonary bypass circuit (CPB), when supplemented to the CPB prime, and so they may protect against atherogenesis. The aim of this study was to evaluate the effect of the dietary administration of L-aspartate and L-glutamate on fatty streak onset in cholesterol-fed rabbit. METHODS AND RESULTS: Male New Zealand white rabbits were fed for four weeks with either a high-cholesterol plus corn oil diet (control group) or the same diet supplemented with 12.5 mM L-aspartate and 12.5 mM L-glutamate in drinking water (Asp + Glu group). The mononuclear cells adhering to the endothelium and the intimal foam cells of the thoracic aorta were used to quantify the extent of atherosclerosis. Total serum cholesterol and lipid peroxidation activity, measured as thiobarbituric acid reactive substances (TBARS), were determined 0, 1 and 4 weeks after a 2-week adaptation period. There were no between-group differences in body weight or food intake during the intervention. Serum TBARS were significantly increased in both groups during the experimental period but without any statistical difference between groups. At the end of the dietary intervention, there was a ten-fold increase in total serum cholesterol concentration in both groups vs baseline. The numbers of adherent mononuclear cells and intimal foam cells were both significantly lower in the Asp + Glu group. CONCLUSIONS: Our results suggest that dietary supplementation with L-aspartate and L-glutamate seems to protect the arterial wall from atherogenesis in an experimental animal.     

Hypercholesterolemia increases coronary endothelial dysfunction, lipid content, and accelerated atherosclerosis after heart transplantation

Hyperlipidemia may increase endothelial damage and promote accelerated atherogenesis in graft coronary vasculopathy. To study the effects of hypercholesterolemia on coronary endothelial dysfunction, intimal hyperplasia, and lipid content, a porcine model of heterotopic heart transplantation, allowing nonacute rejection without immunosuppressive drugs, was used. A high cholesterol diet was fed to donor and recipient swine 1 month before and after transplantation. The endothelial function of coronary arteries of native and transplanted hearts from cholesterol-fed animals was studied in organ chambers 30 days after implantation and compared with endothelial function in arteries from animals fed a normal diet. The total serum cholesterol increased 3-fold in donors and recipients. Endothelium-dependent relaxations to serotonin, to the alpha(2)-adrenergic agonist UK14,304, and to the direct G-protein activator sodium fluoride were decreased significantly in allografted hearts compared with native hearts from both groups. Relaxations to the calcium ionophore A23187 and bradykinin were decreased significantly in allografts from animals fed the high cholesterol diet. The prevalence of intimal hyperplasia was significantly increased in coronary arteries from hypercholesterolemic swine. There was a significant increase in the lipid content of allograft arteries of hypercholesterolemic recipients. Hypercholesterolemia causes a general coronary endothelial dysfunction, increases the prevalence of intimal hyperplasia, and augments the incorporation of lipids in the vascular wall after heart transplantation. Hyperlipidemia accelerates graft coronary atherosclerosis through its effects on the endothelium.     

烟酸对高脂血症兔主动脉壁脂蛋白脂肪酶与三磷酸腺苷结合盒转运体A1表达的影响

目的观察烟酸对高脂血症兔主动脉壁脂蛋白脂肪酶和三磷酸腺苷结合盒转运体A1表达的影响,探讨烟酸抗动脉粥样硬化的机制。方法10只新西兰大白兔给予高脂饮食8周后,随机分为淀粉组与烟酸组:淀粉组(n=5)饲以高脂饲料及淀粉;烟酸组(n=5)在高脂饮食基础上给予烟酸[400 mg/(kg.d)];另5只兔给予普通饮食14周作为正常对照组。14周末结束实验,采用免疫组织化学染色和半定量分析法观察烟酸对主动脉壁脂蛋白脂肪酶和三磷酸腺苷结合盒转运体A1表达的影响。结果烟酸组14周后总胆固醇、低密度脂蛋白胆固醇、甘油三酯较淀粉组分别下降43.9%、47.0%和44.3%,高密度脂蛋白胆固醇明显上升(P均<0.001);与淀粉组相比,烟酸组斑块面积减小约1.97倍,内膜厚度及内膜/中膜厚度比值分别减小约2.87倍和3.70倍;烟酸可显著下调主动脉壁脂蛋白脂肪酶的表达和上调三磷酸腺苷结合盒转运体A1的表达。结论烟酸抗动脉粥样硬化的机制可能与下调动脉壁脂蛋白脂肪酶的表达和上调三磷酸腺苷结合盒转运体A1的表达有关。     

Effects of dietary supplementation with fish oil on atherosclerosis and myocardial injury during acute coronary occlusion-reperfusion in diet-induced hypercholesterolemic rabbits.

We studied myocardial injury during acute coronary occlusion-reperfusion and atherosclerosis in rabbits fed a high cholesterol diet with or without fish oil supplementation. New Zealand white male rabbits were divided into 3 groups. Eight control rabbits fed with laboratory standard rabbit chow were group I. In addition to the standard chow, 15 rabbits fed with a 1% cholesterol-enriched diet for 6 weeks were group II, and 10 rabbits fed with a 1% cholesterol-enriched and 10% fish oil supplemented diet for 6 weeks were group III. Acute coronary occlusion was induced by ligating the marginal branch of the left circumflex coronary artery for 1 h, followed by reperfusion for 4 h. Myocardial injury was assessed by tissue creatine kinase activities and amino-nitrogen concentrations from the ischemic (infarct) and nonischemic (normal) myocardium, and the infarct area/risk area ratios of the left ventricle. The surface area of the atherosclerotic lesions of the aorta and pulmonary artery was measured by planimeter. There was significantly more myocardial loss of creatine kinase and amino-nitrogen in the cholesterol-fed rabbits than the controls (p less than 0.01 and 0.02, respectively). The cholesterol and fish oil-treated rabbits had a nonsignificant reduction in myocardial loss of both agents as compared to their corresponding cholesterol-fed ones. The same trend was also found in the infarct area/risk area ratio. Fish oil treated rabbits had a good effect on the reduction of atherosclerotic lesions and tissue cholesterol levels in the aorta and pulmonary artery, but not in the left ventricle.(ABSTRACT TRUNCATED AT 250 WORDS)     

An experimental study of atherosclerosis as a sequela of coronary arteritis

In order to examine the effect of corticosteroids on coronary atherogenesis in collagen diseases, an experimental study of serum sickness was performed. Forty-two rabbits were divided into four groups (Groups A-D). Group B, C and D rabbits received four intravenous injections of bovine serum albumin (250 mg/Kg) at 16-day intervals. Groups A, C and D rabbits were fed ad libitum cholesterol supplemented diet (1%) 16 days after the last injection. Group D rabbits received subdermal injections of prednisolone (1 mg/Kg) three times per week in the same period. After 124 days, all rabbits were sacrificed. Serum cholesterol and phospholipid increased in Group A, C and D rabbits. Group A rabbits showed intimal foam cell proliferation. Group B rabbits showed slight fibrous intimal thickening. The coronary arteries of Group C rabbits showed fatty-proliferative intimal thickening and an increase in the incidence of vascular lesions (13.9% of the coronary arteries as compared with 11.7% for Group A and 8.4% for Group B). The coronary lesions of Group D showed the same pattern as those of Group C, but the incidence of lesions was 6.0%. It was concluded that prednisolone did not augment immunologically induced atherosclerosis.     

Endothelium-derived relaxing factor (nitric oxide) has a tonic vasodilating action on coronary collateral vessels

Objectives. We sought to determine whether endothelium-derived relaxing factor (nitrix oxide) exerts a tonic vasodilating effect on coronary collateral channels developed in response to myocardial ischemia.Background. Although the coronary collateral circulation is known to react to several vasoactive agents, the role of endogenously produced nitric oxide is unclear.Methods. Coronary collateral channels were induced in the left circumflex artery bed of 12 chronically instrumented dogs by either ameroid implantation or repeated occlusion of the left circumflex coronary artery. With the native circumflex artery occluded, aortic and circumflex pressures and microsphere flows were measured before and after systemic administration of N^G-nitro-l-arginine methyl ester, an arginine analogue known to block the synthesis of nitric oxide.Results. N^G-nitro-l-arginine methyl ester increased mean aortic pressure from a mean ± SEM of 92 ± 4 to 114 ± 4 mm Hg, whereas pressure in the occluded circumflex artery decreased from 61 ± 4 to 55 ± 4 mm Hg. The increase in aortic-circumflex pressure gradient (from 31 ± 4 to 59 ± 5 mm Hg) was accompanied by a decrease in flow in the circumflex bed (from 1.31 ± 0.14 to 1.09 ± 0.15 ml/min per g), resulting in an increase in coronary collateral resistance averaging 173 ± 37% (from 26 ± 4 to 64 ± 9 mm Hg/ml per min per g, p < 0.01). The increase in collateral resistance could be partially reversed by administration of l-arginine.Conclusions. We conclude that nitric oxide normally exerts a substantial tonic dilating effect in coronary collateral vessels. Disease-induced alterations in endothelial function may limit collateral perfusion importantly.