Alteration in endothelial function and modulation by treatment with pioglitazone in rabbit renal artery from short-term hypercholesterolemia

The present study was undertaken to investigate endothelial function and epoxyeicosatrienoic acids (EETs), which is a cytochrome P-450 monooxygenase (CYP) metabolite and one of the candidates as an endothelium-derived hyperpolarizing factor (EDHF) in the renal artery isolated from short-term hypercholesterolemic rabbits, and also to characterize the effects of pioglitazone on it. Rabbits were fed normal, 0.5% cholesterol chow, or 0.5% cholesterol chow plus 300 ppm pioglitazone for 5 weeks. The tension of isolated renal artery rings was measured isometrically. Serum lipid levels were measured and morphometric analysis was performed. EET contents in the renal artery were also determined. The cholesterol chow diet for 5 weeks increased serum lipid levels, and pioglitazone had no influence on it. In the phenylephrine precontracted renal artery, the cholesterol chow did not affect acetylcholine-induced relaxation. The N(G)-nitro-l-arginine- and indomethacin-resistant endothelium-dependent relaxation induced by acetylcholine was significantly enhanced in rabbits receiving the cholesterol chow as compared to rabbits receiving the control diet, and pioglitazone normalized it. The resistant part of acetylcholine-induced relaxation was significantly inhibited when the renal artery was treated with charybdotoxin, an inhibitor of large- and intermediate-conductance Ca(2+)-activated K(+) channels, or N,N-di-ethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF 525a), a nonselective CYP inhibitor, and it was significantly inhibited by sulfaphenazole, a selective CYP2C9 inhibitor in rabbits receiving only the cholesterol chow. In KCl-precontracted renal artery, the cholesterol chow inhibited acetylcholine-induced relaxation and pioglitazone normalized it. The cholesterol chow increased the production of EETs and reduced nitrate/nitrite contents in the renal artery, and pioglitazone strongly suppressed them. These results suggest that the EETs may be one of the EDHFs in the rabbit renal artery and beneficial effects of pioglitazone on alterations in endothelial function induced by cholesterol feeding are due, in part, to the protective action on the nitric oxide system and/or the suppression of increased production of EETs.     

Short term hypercholesterolemia alters N(G)-nitro-L-arginine- and indomethacin-resistant endothelium-dependent relaxation by acetylcholine in rabbit renal artery

The tension of isolated rings was measured isometrically to compare the N(G)-nitro-L-arginine- and indomethacin-resistant relaxation by acetylcholine (ACh) in the renal artery from normal rabbits and short term hypercholesterolemia rabbits (0.5% cholesterol chow for 5 weeks). ACh-induced relaxation in the renal artery precontracted with phenylephrine was not influenced by cholesterol-enriched chow. However, in comparison with artery from normal rabbits, the N(G)-nitro-L-arginine- and indomethacin-resistant endothelium-dependent relaxation by ACh was significantly enhanced by the chow. The resistant part of ACh-induced relaxation was significantly inhibited when the artery was treated with tetraethylammonium or SKF 525a. Results suggest that short term hypercholesterolemia modulates endothelium-derived hyperpolarizing factor-mediated relaxation in rabbit renal artery.     

Sitagliptin ameliorates lipid profile changes and endothelium dysfunction induced by atherogenic diet in rabbits

The aim of this work was to investigate the effect of sitagliptin on lipid profile and endothelium function in rabbits. Rabbits were fed either normal chow or atherogenic diet for 10 weeks. Sitagliptin (6 mg/kg/twice daily) was given orally for 6 weeks starting from week 4. Blood samples were collected at day 0, week 4, and week 10 to measure serum lipid profile, nitrate/nitrite (NOx), lactate dehydrogenase (LDH), and malondialdehyde (MDA) levels. The aortic arch and thoracic aorta were excised and used for histological study and isolated vascular preparations, respectively. Sitagliptin treatment significantly reduced the levels of low density lipoprotein cholesterol, NOx, total cholesterol, and MDA, but not triglyceridess. Additionally, sitagliptin markedly reversed the decrease in high-density lipoprotein cholesterol level. Moreover, sitagliptin significantly improved the impaired endothelium-dependent relaxation, without affecting phenylepherine-induced contraction and sodium nitroprusside-induced endothelium-independent relaxation in isolated aortic rings. Histopathological examination revealed marked reduction of the atherosclerotic lesions by sitagliptin. Immunohistochemical analysis of nuclear factor-kappa B in aortic tissue showed marked reduction in its expression upon treatment with sitagliptin compared with atherogenic diet-fed rabbits. These results suggest that sitagliptin may be an effective pharmacological approach for preventing atherosclerotic lesion progression in rabbits.     

Inhibitory effects of fluvastatin, a new HMG-CoA reductase inhibitor, on the increase in vascular ACE activity in cholesterol-fed rabbits.

1. The effects of fluvastatin, a new 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, on the vascular angiotensin converting enzyme (ACE) activity in hyperlipidaemic rabbits were compared with those of enalapril, an ACE inhibitor. 2. Rabbits were fed a 1.5% cholesterol containing diet or normal diet for 16 weeks and treated with either fluvastatin or enalapril in the diet at the respective doses of 2 and 10 mg kg-1 day-1. The total cholesterol, triglyceride and phospholipid levels in serum were significantly increased in rabbits fed the high cholesterol diet. Treatment with fluvastatin but not enalapril resulted in a decrease in serum lipids. 3. The vascular ACE activities assessed via the cleavage rate from synthetic substrate in the aortic arches and upper thoracic aortae were increased by 8 to 10 times when the rabbits were made hyperlipidaemic. Fluvastatin as well as enalapril significantly lowered the tissue ACE in the aortae. 4. The ACE activities in serum did not alter in hyperlipidaemic rabbits either in the presence or absence of fluvastatin. The serum ACE activity was lowered by enalapril. 5. The lipid peroxide in serum as well as the plaque area in the thoracic aorta was significantly increased in the cholesterol diet-fed rabbits. Treatment with fluvastatin or enalapril reduced both serum lipid peroxide and plaque formation. The relaxant responses to acetylcoholine (ACh) were significantly suppressed in the cholesterol-fed rabbits. Treatment with fluvastatin or enalapril significantly reversed the suppression of ACh-induced relaxation. 6. It seems that the reduction of vascular ACE is not coupled to lipids and ACE activity in serum, but rather to lipid peroxidation. Thus, the decrease in vascular ACE activity by fluvastatin as well as the lipid-lowering effect may reduce the risk of atherosclerosis progression in the vasculature.     

Effects of acute and chronic treatment with the sodium hydrogen exchanger 1 (NHE-1) inhibitor cariporide on myocardial infarct mass in rabbits with hypercholesterolaemia

We investigated the cardioprotective effect of acute and chronic sodium hydrogen exchanger 1 (NHE-1) inhibition with cariporide under pathological conditions in rabbits fed an atherogenic diet (0.25% cholesterol, 3% coconut oil), an experimental model of atherosclerosis. New Zealand White rabbits were fed over 4 weeks with normal diet or with atherogenic diet and randomized in 3 subgroups (n=7 in each group); placebo, acute cariporide (0.3 mg/kg, 10 min. before occlusion of left anterior descending coronary artery and chronic cariporide (4 weeks 0.1% in chow). In the final infarction experiments the animals were subjected to 30 min. of myocardial ischaemia by occlusion of a branch of the left anterior descending coronary artery followed by 2 hr of reperfusion. Infarct mass was evaluated by triphenyl-tetrazolium chloride staining and the infarct size expressed as a percentage of area at risk. Besides the assessment of aortic endothelium-dependent function aortic and cardiac vessels were inspected for atherosclerotic lesions. In cholesterol-fed rabbits, the infarct size was significantly increased when compared with normal diet animals (63+/-3% versus 41+/-3%). Acute cariporide treatment reduced the infarct size in normal diet rabbits to 14%+/-3% (66% decrease, P<0.05) as well as in atherogenic diet rabbits to 22+/-3% (65% decrease, P<0.05). Chronic treatment with cariporide also reduced the infarct size significantly: normal diet 19+/-2% (53% decrease, P<0.05), atherogenic diet 32+/-3% (49% decrease, P<0.05). Total cholesterol serum levels in rabbits with atherogenic diet were significantly higher (15.3+/-2.7 mmol/l) than those on a standard diet (0.65+/-0.08 mmol/l). Chronic cariporide treatment significantly attenuated the increase of serum cholesterol (7.9+/-1.9 mmol/l) and improved the lipoprotein pattern. Although the aortas and heart vessels of hypercholesterolaemic animals were without any histological evidence of atherosclerosis they developed endothelial dysfunction (reduced endothelium-dependent relaxation by ACh), which was prevented by chronic cariporide treatment. Acute and chronic treatment with the NHE-1 inhibitor cariporide significantly reduced infarct mass. This effect was associated with improved endothelial function.     

17B-estradiol and hypercholesterolemia: involvement of nitric oxide

The mechanisms of the protective effect of 17B-estradiol were investigated in the middle cerebral artery (MCA) and aorta isolated from cholesterol-fed rabbits. Three groups were assigned: control group (standard chow), cholesterol group (standard chow+1% cholesterol) and estradiol group (1% cholesterol+17B-estradiol). The MCA and the aorta were isolated, precontracted respectively with high K(+) solution or with phenylephrine and exposed to cumulative acetylcholine concentrations. In the control group, acetylcholine induced a concentration-dependent relaxation in the aorta and the MCA. Cholesterol diet for eight months reduced significantly the maximal response to acetylcholine by about 50% in the aorta and by about 30% in the MCA. The chronic treatment with 17B-estradiol restored this impaired relaxations to acetylcholine. Incubation of arteries from estradiol group with N(omega)-nitro L-arginine methyl-ester (L-NAME), a potent inhibitor of constitutive nitric oxide synthase, entirely abolished the relaxation to acetylcholine while aminoguanidine, a potent inhibitor of inducible nitric oxide synthase, did not affect this relaxation. These observations suggest that the protective effect of 17B-estradiol against hypercholesterolemia is mediated via a release of endothelial nitric oxide.     

吡格列酮对高脂饮食兔主动脉血管内皮细胞黏附分子-1表达的影响

目的探讨吡格列酮对高脂饮食下兔主动脉血管内皮细胞黏附分子(VCAM)-1表达的影响。方法设立正常饮食、高脂饮食及高脂饮食加吡格列酮干预3组,通过比较主动脉病理形态学改变、血脂的变化、VCAM-1分子的表达进行研究,采用苏木素-伊红染色用于主动脉病理形态学观察,采用免疫组织化学检测兔主动脉上VCAM-1的表达。结果吡格列酮能减轻高脂饮食所致的内膜增厚和平滑肌增生。吡格列酮还能明显升高高密度脂蛋白胆固醇(HDL),对总胆固醇(TC)、低密度脂蛋白胆固醇(LDL)、甘油三酯(TG)无明显影响。高脂饮食刺激兔主动脉VCAM-1的表达增加,吡格列酮能显著减轻这种作用(0.78±0.16vs0.42±0.11,P<0.01)。结论吡格列酮能减轻高脂饮食兔主动脉VCAM-1的表达,其作用的机制可能与其干扰核转录因子有关。     

The changes in the endothelial expression of cell adhesion molecules and iNOS in the vessel wall after the short-term administration of simvastatin in rabbit model of atherosclerosis

Cell adhesion molecules P-selectin, VCAM-1 and ICAM-1 play an important role in the pathogenesis of atherosclerosis. High levels of nitric oxide (NO) produced by inducible NO synthase (iNOS) have been associated with atherosclerotic processes. Simvastatin is an HMG-CoA reductase inhibitor responsible for many clinical benefits. The aim of this study was to detect and quantify changes in endothelial expression of P-selectin, VCAM-1, ICAM-1 and iNOS in the vessel wall after the shortterm administration of simvastatin in a rabbit model of atherosclerosis. Eighteen New Zealand White rabbits were randomly divided into three groups (n=6). In the cholesterol group, rabbits consumed an atherogenic diet (0.4% cholesterol) for eight weeks. In the simvastatin group, rabbits consumed an atherogenic diet for six weeks and then consumed an atherogenic diet supplemented with simvastatin (10 mg kg(-1)) for two weeks. Biochemical analysis showed that administration of simvastatin led to an almost two-fold lowering of the total serum cholesterol, VLDL, LDL and HDL, but not triglycerides, compared with the cholesterol-fed rabbits only. Stereological analysis of the immunohistochemical staining revealed that administration of simvastatin (10 mg kg(-1) daily) in an atherogenic diet decreased the endothelial expression of P-selectin, ICAM-1 and iNOS in both aortic arch and carotid artery compared with the cholesterol fed-rabbits only. We conclude that simvastatin has beneficial effects on endothelial function by decreasing expression of P-selectin, ICAM-1 and iNOS in endothelial cells in the very early stages of atherogenesis.     

吡格列酮对高胆固醇模型大鼠脂肪组织细胞中肿瘤坏死因子-α分泌及其mRNA表达的影响

目的:研究吡格列酮对高胆固醇模型大鼠脂肪组织细胞中肿瘤坏死因子-α(TNF-α)分泌及其mRNA表达的影响。方法:将30只高胆固醇饮食8周的大鼠随机分为高胆固醇组(n=15)和吡格列酮组(n=15),前者继续给予高胆固醇饮食,后者在此基础上加吡格列酮3mg.kg-1.d-1,连续4周;另设喂普通饲料12周的对照组(n=15)。处死大鼠并检测血脂、血清TNF-α水平及其mRNA表达等指标。另取正常脂肪细胞加入脂多糖和不同浓度的吡格列酮(0.1、1.0、10.0μmol.L-1)中,测定脂肪组织细胞中的TNF-α水平及其mRNA表达。结果:与高胆固醇组比较,吡格列酮组可明显降低血清TNF-α水平及减弱其mRNA表达,但对血糖和血脂水平几乎无影响。上述吡格列酮各浓度组可呈浓度依赖性抑制脂多糖诱导TNF-α分泌及其mRNA表达。结论:吡格列酮可降低高胆固醇模型大鼠血清和脂肪组织中TNF-α水平。     

Effects of Doxazosin on Functional Alterations of Isolated Coronary Arteries from Cholesterol-fed Rabbits

Anti-hypertensive treatment is much less successful at reducing coronary artery disease than at reducing mortality from stroke and congestive heart failure. The effects of the α-adrenergic antagonist doxazosin on progression of atheromatous lesions and functional responses of isolated coronary arteries from cholesterol-fed rabbits have been investigated. Normotensive rabbits were fed either a standard chow (control, n = 8) or a 1% cholesterol-rich diet (n = 16) for 20 weeks. After 3 weeks the cholesterol-fed animals were assigned randomly to two groups either given placebo capsules (n = 8) or treated with doxazosin (5 mg kg^?1 day^?1; n = 8). Doxazosin reduced the mean arterial blood pressure by 10% that of the control and placebo-treated cholesterol-fed rabbits, but did not affect the plasma cholesterol, triacylglycerol and phospholipid levels, which were, after 20 weeks, severalfold increased in the cholesterol-fed rabbits compared with controls. Histological examination showed atheromatous lesions in proximal (but not distal) coronary arteries from both groups of cholesterol-fed rabbits. Doxazosin either had no effect on reduced contractions to 125 mmol L^?1 potassium saline solution or increased contractions to 5-hydroxytryptamine in proximal isolated coronary arteries from the cholesterol-fed rabbits. It did, however, abolish the hyper-responsiveness of the large atheromatous coronary arteries to noradrenaline. In both vehicle-and doxazosin-treated cholesterol-fed rabbits the maximum relaxation and sensitivity to acetylcholine were significantly reduced in proximal segments compared with the control group, whereas responses to acetylcholine in distal coronary segments were not significantly different. The relaxation to sodium nitroprusside, adenosine diphosphate and isoprenaline in proximal and distal coronary arteries were similar in the three experimental groups. These results indicate that treatment of normotensive cholesterol-fed rabbits with doxazosin prevents the hyper-responsiveness to noradrenaline of proximal coronary arteries, although it does not prevent the progression of other functional alterations observed in the coronary circulation.     

Lapaquistat acetate, a squalene synthase inhibitor, changes macrophage/lipid-rich coronary plaques of hypercholesterolaemic rabbits into fibrous lesions

BACKGROUND AND PURPOSE: Inhibition of squalene synthesis could transform unstable, macrophage/lipid-rich coronary plaques into stable, fibromuscular plaques. We have here treated WHHLMI rabbits, a model for coronary atherosclerosis and myocardial infarction, with a novel squalene synthase inhibitor, lapaquistat acetate (TAK-475). EXPERIMENTAL APPROACH: Young male WHHLMI rabbits were fed a diet supplemented with lapaquistat acetate (100 or 200 mg per kg body weight per day) for 32 weeks. Serum lipid levels were monitored every 4 weeks. After the treatment, lipoprotein lipid and coenzyme Q10 levels were assayed, and coronary atherosclerosis and xanthomas were examined histopathologically or immunohistochemically. From histopathological and immunohistochemical sections, the composition of the plaque was analysed quantitatively with computer-assisted image analysis. Xanthoma was evaluated grossly. KEY RESULTS: Lapaquistat acetate decreased plasma cholesterol and triglyceride levels, by lowering lipoproteins containing apoB100. Development of atherosclerosis and xanthomatosis was suppressed. Accumulation of oxidized lipoproteins, macrophages and extracellular lipid was decreased in coronary plaques of treated animals. Treatment with lapaquistat acetate increased collagen concentration and transformed coronary plaques into fibromuscular plaques. Lapaquistat acetate also suppressed the expression of matrix metalloproteinase-1 and plasminogen activator inhibitor-1 in the plaque and increased peripheral coenzyme Q10 levels. Increased coenzyme Q10 levels and decreased very low-density lipoprotein cholesterol levels were correlated with improvement of coronary plaque composition. CONCLUSION AND IMPLICATIONS: Inhibition of squalene synthase by lapaquistat acetate delayed progression of coronary atherosclerosis and changed coronary atheromatous plaques from unstable, macrophage/lipid accumulation-rich, lesions to stable fibromuscular lesions.     

The effect of hypercholesterolaemia and atherosclerosis on alpha-adrenoceptor-mediated vasoconstriction in conscious rabbits and rabbit aorta.

Rabbits were fed a diet containing 1% cholesterol for 4 or 8 weeks and the constrictor responses to alpha-adrenoceptor agonists, as well as endothelium-dependent and endothelium-independent dilatation, were examined both in vivo and in vitro. The high cholesterol diet caused a significant elevation of plasma cholesterol concentration but no macroscopic evidence of atherosclerosis after 4 weeks whereas after 8 weeks there was a significant development of atherosclerotic lesions in the thoracic and abdominal aorta. In conscious rabbits pressor responses to the non-selective alpha-adrenoceptor agonist noradrenaline and the selective alpha 1-adrenoceptor agonist phenylephrine were enhanced after 4 weeks but returned to control levels after 8 weeks on the diet. The pressor responses to the alpha 2-adrenoceptor agonist B-HT 920 were reduced by the development of atherosclerosis. In the isolated thoracic aorta from these rabbits contractile responses to noradrenaline were impaired by hypercholesterolaemia whereas responses to phenylephrine were unaffected. Endothelium-dependent relaxation was impaired by hypercholesterolaemia both in vivo and in vitro after 4 and 8 weeks on the diet whereas endothelium-independent relaxation was not affected. These results indicate that the effect of hypercholesterolaemia on alpha-adrenoceptor-mediated constriction is dependent on: (1) the absence or presence of atherosclerotic lesions, (2) the size of the artery and (3) the subtype of alpha-adrenoceptor involved in the response. There does not appear to be any relationship between the loss of endothelium-dependent relaxation in hypercholesterolaemia and the observed changes in adrenergic vasoconstriction.     

四氢普伐他汀钠对高血脂模型新西兰兔脂质代谢的影响

目的通过高脂饮食兔高血脂模型考察四氢普伐他汀钠(H4PV-Na)的降血脂和调节脂质代谢的作用。方法新西兰白兔,雄性,100只,适应性饲养2周后,随机分为空白对照组、高脂模型组、阳性对照组P(普伐他汀钠组2.5mg·kg~(-1))、阳性对照组A(阿托伐他汀钙组2.5mg·kg~(-1))和给药组(低剂量1.25mg·kg~(-1)、中剂量2.5mg·kg~(-1)、高剂量5mg·kg~(-1))。高脂饲料喂饲2周形成高脂模型后,阳性药物和供试药物强制经口灌胃给药,10mL·kg~(-1),每天上午给药1次,每周给药6d,连续10周。最后1次给药后24h,禁食过夜,取血和肝脏组织,进行血脂和肝脂相关指标检测:血清总胆固醇(TC)、三酰甘油(TG)、低密度脂蛋白胆固醇(LDL-C)、高密度脂蛋白胆固醇(HDL-C)、全血超氧化物歧化酶(SOD)活力和血清丙二醛(MDA)含量。横纹肌溶解毒性检测指标:测定血清磷酸肌酸激酶(CK)含量。取心脏、肝脏、脾脏、肺脏、肾脏、肾上腺等器官经HE染色检测脂肪组织的病理学变化。结果新西兰兔用高脂饲料喂养10周后,TC,TG和LDL-C水平升高,HDL-C水平降低,给予H4PV-Na后,TC、TG和LDL-C水平降低,HDL-C水平升高。结论 H4PV-Na具有明确的降血脂和胆固醇作用,在肝脏组织中降低胆固醇能力高于在血液中,无横纹肌溶解毒性,但在同等剂量下,H4PV-Na降脂效果稍弱于普伐他汀钠和阿托伐他汀钙。     

Etofibrate treatment alters low density lipoprotein susceptibility to lipid peroxidation.

The effect of the lipid lowering drug etofibrate was investigated on lipid peroxidation as well as on cholesterol level. Rabbits were given a 0.1% cholesterol containing diet. Total cholesterol, LDL-cholesterol, triglycerides and lipid peroxidation, expressed as thiobarbituric acid reactive products, were determined. Treatment with etofibrate led to a marked decrease in total cholesterol and LDL-cholesterol. Furthermore, Cu(2+)-induced lipid peroxide formation was reduced in etofibrate treated rabbits. These results could be confirmed in a human study when patients with moderate hypercholesterolaemia were treated with etofibrate (2 x 500 mg/day) for a period of eight weeks. It could be shown that the onset of lipid peroxidation was remarkably increased, an effect which was completely reversible. Thus, etofibrate is effective not only in lowering plasma cholesterol but also in rendering LDL less susceptible to oxidation.     

DIFFERENCES IN ENDOTHELIUM-DEPENDENT RELAXATION IN VARIOUS ARTERIES FROM WATANABE HERITABLE HYPERLIPIDAEMIC RABBITS WITH INCREASING AGE

1. Endothelium-dependent relaxation in response to acetylcholine (ACh) and the calcium ionophore A 23187 was examined in aorta, coronary, basilar and renal arteries isolated from Watanabe heritable hyperlipidaemic (WHHL) rabbits of 2, 6 and 12 months of age, with normolipidaemic heterozygous WHHL rabbits as controls. 2. In the rings of WHHL rabbit aortae and coronary arteries preconstricted with vasoconstrictors, endothelium-dependent relaxation in response to ACh was attenuated with age compared to the heterozygous WHHL rabbits. A significant negative correlation was found between the total cholesterol content and the relaxation response to ACh in the aortae or coronary arteries from 6 and 12 month old WHHL rabbits. 3. In the rings of basilar arteries, endothelium-dependent relaxations to ACh were not modified with age. Similarly, in the rings of renal arteries, the relaxation response to ACh was not changed with age, but in the 6 and 12 month preparations, after the age of 6 months, a contraction following the relaxation appeared at higher concentrations of ACh (10^?7 to 10^?6 mol/L). The contraction was endothelium-dependent and inhibited by indomethacin. 4. A 23187-induced endothelium-dependent relaxations were also markedly attenuated in the aorta and significantly in the coronary artery with age. 5. Endothelium-independent relaxation to sodium nitroprusside was not changed in all arteries from WHHL rabbits of different ages. 6. These findings indicate that in the aorta and coronary artery of the WHHL rabbit, the endothelium-dependent relaxation to ACh and A 23187 becomes impaired with increasing age (i.e., with the progression of cholesterol deposition in the arterial wall) but is preserved in the basilar and renal artery.     

Modulation of matrix metalloproteinase-1, its tissue inhibitor, and nuclear factor-kappa B by losartan in hypercholesterolemic rabbits

Upregulation of angiotensin II receptor, may be involved in the initiation and progression of atherosclerosis. To examine the contribution of AT1 receptor in the expression of matrix metalloproteinase-1 (MMP-1) and its tissue inhibitor (TIMP-2) in lipid-deposited arterial tissues, New Zealand white rabbits were given high-cholesterol chow (with losartan 25 mg/d or vehicle) for 10 weeks. Losartan reduced the areas of sudanophilia in the aorta of rabbits fed high-cholesterol diet (p < 0.01 vs. control). Losartan also significantly decreased the enhanced mRNA expression of MMP-1 and TIMP-2 in aortas of rabbits with high-cholesterol diet. Losartan-treated rabbits revealed a reduction in immunohistochemical expression of MMP-1, whereas TIMP-2 expression became localized to the intima. In addition, losartan treatment reduced the activation of NF-kappa B by inhibiting the degradation of its inhibitor I kappa-B alpha. These observations demonstrate that AT1 receptor blockade with losartan reduces lipid deposition and exerts potent inhibitory effects on NF-kappa B activation and modulates the expression of MMP-1 and TIMP-2 in hypercholesterolemic rabbits.     

Protective effects of propolis and thymoquinone on development of atherosclerosis in cholesterol-fed rabbits

Hypercholesterolemia, cholesterol-enriched diet and oxidative stress have been shown to increase serum total cholesterol (TC) and low density lipoprotein-cholesterol (LDL-C) levels resulting in development of atherosclerosis. Antioxidants play an important role in inhibiting and scavenging free radicals, thus providing protection to humans against infectious and degenerative diseases. The present study was undertaken to examine the possible protective effects of propolis (a resinous hive product collected by honeybees from various plant sources) and thymoquinone (TQ, active constituent of Nigella. Sativa seeds oil) on serum lipid levels and early atherosclerotic lesions in hypercholestrolemic rabbits. New Zealand rabbits were fed on either standard chow or atherogenic diet during four weeks and concomitantly received either propolis or TQ. At the end of experiment period, serum samples were collected to determine lipid profile, kidney functions and antioxidant status. Tissues from aorta, pulmonary artery and kidney were taken for histopathological examination. The cholesterol-enriched diet induced a significant increase in serum TC, triglycerides, LDL-C, thiobarbituric acid-reactive substances concentrations and a significant decrease in high density lipoprotein-cholesterol and in reduced glutathione levels compared to control group. Administration of propolis or TQ with cholesterol-enriched diet significantly (p < 0.05) reduced TC, LDL-C, triglycerides and thiobarbituric acid-reactive substances concentrations, while increased high density lipoprotein-cholesterol concentration, as well as glutathione content compared to high cholesterol (HC) control group. Kidney function parameters were significantly affected by cholesterol diet and both propolis and TQ counterregulated the cholesterol-induced changes. Histopathologically, early athersclerotic changes were observed in HC control group represented by endothelial damage and thickened foam cells while propolis or TQ provided protection against the HC-induced damage. In conclusion, the present study suggests the potential beneficial effects of both propolis and TQ in diminishing the risk of atherosclerosis via antioxidant mechanism.     

Effects of dicentrine on haemodynamic, plasma lipid, lipoprotein level and vascular reactivity in hyperlipidaemic rats.

1. The effects of dicentrine on haemodynamic, plasma lipid, lipoprotein level and vascular reactivity were investigated in Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats, fed a high fat-high cholesterol diet. 2. In high fat-high cholesterol (HF-HC) diet fed WKY and SH rats, oral administration of dicentrine (5 and 10 mg kg-1, twice a day) for 4 weeks caused significant reductions in total plasma cholesterol (CE) by reducing the low density lipoprotein (LDL) fraction, and reductions in total plasma triglyceride (TG) by reducing the very low density lipoprotein (VLDL) fraction. 3. Dicentrine therapy was associated with increased high density lipoprotein (HDL)-cholesterol levels; thus the ratio of total plasma cholesterol to HDL-cholesterol was improved. 4. In HF-HC diet fed conscious WKY and SH rats, oral administration of dicentrine (5 and 10 mg kg-1, twice a day) also evoked dose-related decreases in mean arterial pressure (MAP) which were of greater magnitude in SH rats. Neither dose of dicentrine caused a significant change in heart rate (HR). 5. The aortic arches from SH rats fed the HF-HC diet for 8 weeks were significantly more affected by the atherosclerotic lesions than the abdominal aortae and renal arteries of WKY and SH rats. Oral administration of dicentrine (5 and 10 mg kg-1) for 4 weeks did not diminish the atherosclerotic lesion areas in WKY and SH rats. 6. In aortae of the hyperlipidaemic rats, significantly attenuated EC50 values and augmented maximal responses for phenylephrine-induced contraction were obtained. Endothelium-dependent relaxation to acetylcholine was abolished, while endothelium-independent relaxation to nitroprusside was well preserved.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of chronic renal failure on phosphodiesterase inhibitor-induced relaxation responses in rabbit cavernosal strips

Erectile dysfunction is common in men with chronic renal failure. Previously nitrergic and endothelium-dependent relaxation responses have been shown to be reduced in chronic renal failure rabbits. We have therefore investigated the efficacy of phosphodiesterase inhibitors on the corpora cavernosa obtained from uremic rabbits. Uremia was induced with 5/6 nephrectomy and 4 weeks later cavernosal tissue strips were isolated. The relaxant effect of phosphodiesterase 5 inhibitors, zaprinast (1-300 microM) and sildenafil (0.01-300 microM), phosphodiesterase 3 inhibitor amrinone (1-100 microM) and non-specific phosphodiesterase inhibitor papaverine (1-300 microM) were investigated on phenylephrine (10 microM)-induced tone. We found a shift in the dose-response curve of only phosphodiesterase 5 inhibitors. These results suggest that the decreased production or availability of endogenous nitric oxide in chronic renal failure animals leads to decreased efficacy of phosphodiesterase 5 inhibitors to induce relaxation.     

Experimental hyperlipidemia and atherosclerosis induced by cholesterol diet in SPF Japanese white rabbits

Experimental hyperlipidemia and atherosclerosis induced by a cholesterol diet in SPF male and female rabbits (JW/KBL) were investigated by the determination of the lipid contents of the plasma, liver and thoracic aorta; determination of morphological changes of the aortic arch by head angiography; and computer tomography of the brain. Rabbits were fed the diet that contained 1% cholesterol for eight weeks. The plasma lipid levels began to rise from two weeks after the cholesterol diet was started, reached the peak four to six weeks later, and then fell in both males and females at eight weeks. The cholesterol of the high density lipoprotein in male rabbit plasma was slightly increased by the cholesterol diet, but not in female rabbits. An increase in the total cholesterol (TC) and triglyceride contents of the liver and an increase in the TC and phospholipid contents of the thoracic aorta were observed at the eighth week. Histological examination of the aortic arch showed marked lipid vacuoles under the endothelial cells, noticeable lipid inclusions in the smooth muscle cells of the intima and granular prominences on the internal surface of the aorta. Head angiography of rabbits fed the cholesterol diet revealed a constriction of the lumina of several arteries due to the lipid depositions. These results suggest that hyperlipidemia and atherosclerosis can be produced at the eighth week using SPF rabbits fed on a cholesterol diet.