Dysfunction of endothelial and smooth muscle cells in small arteries of a mouse model of Marfan syndrome

Background and purpose:

Marfan syndrome, a connective tissue disorder caused by mutations in FBN1 encoding fibrillin-1, results in life-threatening complications in the aorta, but little is known about its effects in resistance vasculature.

Experimental approach:

Second-order mesenteric arteries from mice at 3, 6 and 10 months of age (n= 30) heterozygous for the Fbn1 allele encoding a cysteine substitution (Fbn1^C1039G/+) were compared with those from age-matched control littermates.

Key results:

Stress–strain curves indicated that arterial stiffness was increased at 6 and 10 months of age in Marfan vessels. Isometric force measurement revealed that contraction in response to potassium (60 mM)-induced membrane depolarization was decreased by at least 28% in Marfan vessels at all ages, while phenylephrine (3 µM)-induced contraction was reduced by at least 40% from 6 months. Acetylcholine-induced relaxation in Marfan vessels was reduced to 70% and 45% of control values, respectively, at 6 and 10 months. Sensitivity to sodium nitroprusside was reduced at 6 months (pEC₅₀= 5.64 ± 0.11, control pEC₅₀= 7.34 ± 0.04) and 10 months (pEC₅₀= 5.99 ± 0.07, control pEC₅₀= 6.99 ± 0.14). Pretreatment with N_ω-Nitro-L-arginine methyl ester (200 µM) had no effect on acetylcholine-induced relaxation in Marfan vessels, but reduced vasorelaxation in control vessels to 57% of control values. Addition of indomethacin (10 µM) and catalase (1000 U·mL⁻¹) further inhibited vasorelaxation in Marfan vessels to a greater degree compared with control vessels.

Conclusions and implications:

Pathogenesis of Marfan syndrome in resistance-sized arteries increases stiffness and impairs vasomotor function.     

Combination of fluvastatin and losartan relieves atherosclerosis and macrophage infiltration in atherosclerotic plaques in rabbits

Aim:

To investigate whether the combination of fluvastatin and losartan synergistically relieve atherosclerosis and plaque inflammation induced by a high-cholesterol diet in rabbits.

Methods:

Atherosclerosis was induced with a high-cholesterol diet for 3 months in 36 New Zealand white rabbits. The animals were randomly divided into model group, fluvastatin (10 mg·kg^-1·d^-1) group, losartan (25 mg·kg^-1·d^-1) group, and fluvastatin plus losartan group. After the 16-week treatments, the blood samples the animals were collected, and the thoracic aortas were examined immunohistochemically. The mRNA and protein expression levels of monocyte chemotactic protein-1 (MCP-1) were measured using RT-PCR and Western blot.

Results:

Compared to the treatment with losartan or fluvastatin alone, the combined treatment did not produce higher efficacy in reduction of blood cholesterol level. However, the combination did synergistically decrease the intimal and media thickness of thoracic aortas with significantly reduced macrophage infiltration and MCP-1 expression in the plaques.

Conclusion:

The combined treatment with losartan and fluvastatin significantly inhibited atherosclerotic progress and reduced inflammation associated with atherosclerotic plaques.     

Association of the polymorphisms of MMP-9 and TIMP-3 genes with thoracic aortic dissection in Chinese Han population

Aim： Thoracic aortic dissection （TAD） is the most common life-threatening disorder, and a shifted balance of matrix metalloproteinases （MMPs） and tissue inhibitors of metalloproteinases （TIMPs） is involved in TAD pathogenesis. The aim of this study was to evaluate the association of 4 single-nucleotide polymorphisms （SNPs） in MMP-9 and TIMP-3 genes with TAD risk in Chinese Han population. Methods： A total of 206 Chinese patients with TAD and 180 controls were included in this study. Four SNPs （rs3918249, rs2274756, rs9609643 and rs8136803） were genotyped using high-throughput MALDI-TOF mass spectrometry. Allele and genotype association analyses were conducted using PLINK. Results： All the 4 SNPs resulted in Hardy-Weinbergl equilibrium in patients and controls. The G allele frequency for the MMP-9 SNP rs2274756 was significantly higher in female TAD patients than in female controls （P=0.0099）. Moreover, after adjusting for traditional cardiovascular risk factors （sex, age, hypertension, dyslipidemia, diabetes and smoking habit）, the rs2274756 polymorphism （odds ratio： 0.30; 95% confidence interval： 0.11 to 0.79, P--0.015） resulted in an independent susceptibility factor for TAD in females. No associations were found between the other SNPs and TAD. Conclusion： The results provide strong evidence for an association between MMP-9 SNP rs2274756 and female TAD risk in Chinese Han population.     

Effects of ticlopidine on pharmacokinetics of losartan and its main metabolite EXP-3174 in rats

Aim:

Losartan and antiplatelet agent ticlopidine can be prescribed concomitantly for prevention or therapy of cardiovascular diseases. Hence, the effects of ticlopidine on the pharmacokinetics of losartan and its active metabolite EXP-3174 were evaluated in rats.

Methods:

Ticlopidine (4 or 10 mg/kg po) was administered 30 min before administration of losartan (9 mg/kg po or 3 mg/kg iv). The activity of human CYP2C9 and 3A4 were measured using the CYP inhibition assay kit. The activity of P-gp was evaluated using rhodamine-123 retention assay in MCF-7/ADR cells.

Results:

Ticlopidine (10 mg/kg) significantly increased the areas under the plasma concentration-time curves (AUCs) and peak plasma concentration (C_max) of oral losartan (9 mg/kg), as well as the AUCs of the active metabolite EXP-3174. Ticlopidine (10 mg/kg) did not significantly change the pharmacokinetics of intravenous losartan (3 mg/kg). Ticlopidine inhibited CYP2C9 and 3A4 with IC₅₀ values of 26.0 and 32.3 μmol/L, respectively. The relative cellular uptake of rhodamine-123 was unchanged.

Conclusion:

The significant increase in the AUC of losartan (9 mg/kg) by ticlopidine (10 mg/kg) could be attributed to the inhibition of CYP2C9- and 3A4-mediated losartan metabolism in small intestine and/or in liver. The inhibition of P-gp in small intestine and reduction of renal elimination of losartan by ticlopidine are unlikely to be causal factors.     

Losartan protects liver against ischaemia/reperfusion injury through PPAR-γ activation and receptor for advanced glycation end-products down-regulation

Background and Purpose

PPAR-γ has been reported to be a protective regulator in ischaemia/reperfusion (I/R) injury. The receptor for advanced glycation end-products (RAGE) plays a major role in the innate immune response, and its expression is associated with PPAR-γ activation. Several angiotensin receptor blockers possess partial agonist activities towards PPAR-γ. Therefore, this study investigated the action of losartan, particularly with regard to PPAR-γ activation and RAGE signalling pathways during hepatic I/R.

Experimental Approach

Mice were subjected to 60 min of ischaemia followed by 6 h of reperfusion. Losartan (0.1, 1, 3 and 10 mg·kg⁻¹) was administered 1 h prior to ischaemia and immediately before reperfusion. GW9662, a PPAR-γ antagonist, was administered 30 min prior to first pretreatment with losartan.

Key Results

Losartan enhanced the DNA-binding activity of PPAR-γ in I/R. Losartan attenuated the increased serum alanine aminotransferase activity, TNF-α and IL-6 levels, and nuclear concentrations of NF-κB in I/R. GW9662 reversed these beneficial effects. Losartan caused a decrease in apoptosis as assessed by TUNEL assay, in release of cytochrome c and in cleavage of caspase-3, and these effects were abolished by GW9662 administration. Losartan attenuated not only I/R-induced RAGE overexpression, but also its downstream early growth response protein-1-dependent macrophage inflammatory protein 2 level; phosphorylation of p38, ERK and JNK; and subsequent c-Jun phosphorylation. GW9662 reversed these effects of losartan administration.

Conclusions and Implications

Our findings suggest that losartan ameliorates I/R-induced liver damage through PPAR-γ activation and down-regulation of the RAGE signalling pathway.     

Inhibition of iNOS protects endothelial-dependent vasodilation in aged rats

Aim:

To examine whether iNOS contributes to endothelial dysfunction in aged rats.

Methods:

Male Sprague Dawley rats were divided into three groups: young rats, aged rats treated with vehicle and aged rats treated with N-[3-(Aminomethyl) benzyl] acetamidine (1400W, 1 mg/kg, ip). Vasorelaxation was measured in isolated thoracic aorta. iNOS expression of thoracic aortic arteries was detected using immunohistochemistry and Western blot. Nitrotyrosine (a marker for peroxynitrite formation) content and expression in thoracic aortic tissue were determined using enzyme linked immunosorbent assay and immunohistochemistry.

Results:

Maximal relaxation induced by acetylcholine (10^-9 to 10^-5 mol/L) in the aged rats treated with vehicle was significantly decreased (70%±15%, P<0.01), as compared with the young rats (95%±8%). However, the maximal relaxation induced by acidified NaNO2 (an endothelium-independent vasodilator) had no significant difference between the two groups. Moreover, iNOS and nitrotyrosine expression increased in the vessels of the aged rats. In the aged rats treated with 1400W (a highly selective iNOS inhibitor) nitrotyrosine expression was reduced and acetylcholine-induced vasorelaxation was markedly improved (maximal relaxation was increased to 87%±8%, P<0.05), but the acidified NaNO₂-induced vasorelaxation had no significant change.

Conclusion:

Our study demonstrated that inhibition of iNOS by 1400W increased endothelium-dependent vasodilation in aged rats. The mechanism was related with attenuation of peroxynitrite formation.     

Dog left ventricular midmyocardial myocytes for assessment of drug-induced delayed repolarization: short-term variability and proarrhythmic potential

Background and purpose:

Increased oxidative stress and up-regulation of matrix metalloproteinases (MMPs) may cause structural and functional vascular changes in renovascular hypertension. We examined whether treatment with spironolactone (SPRL), hydrochlorothiazide (HCTZ) or both drugs together modified hypertension-induced changes in arterial blood pressure, aortic remodelling, vascular reactivity, oxidative stress and MMP levels and activity, in a model of renovascular hypertension.

Experimental approach:

We used the two-kidney,one-clip (2K1C) model of hypertension in Wistar rats. Sham-operated or hypertensive rats were treated with vehicle, SPRL (25 mg·kg⁻¹·day⁻¹), HCTZ (20 mg·kg⁻¹·day⁻¹) or a combination for 8 weeks. Systolic blood pressure was monitored weekly. Aortic rings were isolated to assess endothelium-dependent and -independent relaxations. Morphometry of the vascular wall was carried out in sections of aorta. Aortic NADPH oxidase activity and superoxide production were evaluated. Formation of reactive oxygen species was measured in plasma as thiobarbituric acid-reactive substances. Aortic MMP-2 levels and activity were determined by gelatin and in situ zymography, fluorimetry and immunohistochemistry.

Key results:

Treatment with SPRL, HCTZ or the combination attenuated 2K1C-induced hypertension, and reversed the endothelial dysfunction in 2K1C rats. Both drugs or the combination reversed vascular aortic remodelling induced by hypertension, attenuated hypertension-induced increases in oxidative stress and reduced MMP-2 levels and activity.

Conclusions and implications:

SPRL or HCTZ, alone or combined, exerted antioxidant effects, and decreased renovascular hypertension-induced MMP-2 up-regulation, thus improving the vascular dysfunction and remodelling found in this model of hypertension.     

Contractile, but not endothelial, dysfunction in early inflammatory arthritis: a possible role for matrix metalloproteinase-9

BACKGROUND AND PURPOSE

Excess morbidity/mortality in rheumatoid arthritis (RA) is associated with increased incidence of cardiovascular disease. In this ‘proof-of-concept’ study, vascular function was characterized in the murine collagen-induced arthritis (mCIA) model, the benchmark choice for evaluation of the pathological processes and assessment of new therapies.

EXPERIMENTAL APPROACH

Mice in the very early stages of arthritis development [and appropriate naïve (non-immunized) age-matched controls] were used in the study. Blood pressure was measured using tail cuff plethysmography. Vascular function in rings of isolated aorta was studied with isometric tension myography. Levels of NO metabolites (NO_x), MMP-9 protein and IL-1β in plasma and MMP-9 protein in aortic homogenates were quantified.

KEY RESULTS

Impaired vascular contractile responses in arthritis were unaffected by ex vivo inhibition of NOS (endothelial/neuronal and inducible) or COX activities. Endothelium-dependent and -independent relaxation, plasma NO_x and blood pressure were unaffected by arthritis. Plasma and aortic homogenate MMP-9 protein levels were increased significantly in arthritis. Incubation of aortic tissues from naïve control animals with exogenous MMP-9 impaired subsequent contractile responses, mirroring that observed in arthritis. A role for IL-1β in perpetuating contractile dysfunction and increasing aortic MMP-9 was excluded.

CONCLUSIONS AND IMPLICATIONS

These data identify for the first time a relationship between early arthritis and contractile dysfunction and a possible role for MMP-9 therein, in the absence of overt endothelial dysfunction or increased NO production. As such, MMP-9 may constitute a significant target for early intervention in RA patients with a view to decreasing risk of cardiovascular disease.     

Boldine improves endothelial function in diabetic db/db mice through inhibition of angiotensin II-mediated BMP4-oxidative stress cascade

BACKGROUND AND PURPOSE

Boldine is a potent natural antioxidant present in the leaves and bark of the Chilean boldo tree. Here we assessed the protective effects of boldine on endothelium in a range of models of diabetes, ex vivo and in vitro.

EXPERIMENTAL APPROACH

Vascular reactivity was studied in mouse aortas from db/db diabetic and normal mice. Reactive oxygen species (ROS) production, angiotensin AT₁ receptor localization and protein expression of oxidative stress markers in the vascular wall were evaluated by dihydroethidium fluorescence, lucigenin enhanced-chemiluminescence, immunohistochemistry and Western blot respectively. Primary cultures of mouse aortic endothelial cells, exposed to high concentrations of glucose (30 mmol L⁻¹) were also used.

KEY RESULTS

Oral treatment (20 mg kg⁻¹day⁻¹, 7 days) or incubation in vitro with boldine (1 μmol L⁻¹, 12 h) enhanced endothelium-dependent aortic relaxations of db/db mice. Boldine reversed impaired relaxations induced by high glucose or angiotensin II (Ang II) in non-diabetic mouse aortas while it reduced the overproduction of ROS and increased phosphorylation of eNOS in db/db mouse aortas. Elevated expression of oxidative stress markers (bone morphogenic protein 4 (BMP4), nitrotyrosine and AT₁ receptors) were reduced in boldine-treated db/db mouse aortas. Ang II-stimulated BMP4 expression was inhibited by boldine, tempol, noggin or losartan. Boldine inhibited high glucose-stimulated ROS production and restored the decreased phosphorylation of eNOS in mouse aortic endothelial cells in culture.

CONCLUSIONS AND IMPLICATIONS

Boldine reduced oxidative stress and improved endothelium-dependent relaxation in aortas of diabetic mice largely through inhibiting ROS overproduction associated with Ang II-mediated BMP4-dependent mechanisms.     

Angiotensin II regulates the LARG/RhoA/MYPT1 axis in rat vascular smooth muscle in vitro

Aim:

To identify a key protein that binds monomeric G protein RhoA and activates the RhoA/Rho kinase/MYPT1 axis in vascular smooth muscle cells (VSMCs) upon angiotensin II (Ang II) stimulation.

Methods:

Primary cultured VSMCs from Sprague-Dawley rats were transfected with siRNAs against leukemia-associated RhoGEF (LARG), and then treated with Ang II, losartan, PD123319, or Val⁵-Ang II. The target mRNA and protein levels were determined using qPCR and Western blot analysis, respectively. Rat aortic rings were isolated, and the isometric contraction was measured with a force transducer and recorder.

Results:

Stimulation with Ang II (0.1 μmol/L) for 0.5 h significantly increased the level of LARG mRNA in VSMCs. At 3, 6, and 9 h after the treatment with Ang II (0.1 μmol/L) plus AT₂ antagonist PD123319 (1 μmol/L) or with AT₁ agonist Val⁵-Ang II (1 μmol/L), the LARG protein, RhoA activity, and phosphorylation level of myosin phosphatase target subunit 1 (MYPT1) in VSMCs were significantly increased. Knockdown of LARG with siRNA reduced these effects caused by AT₁ receptor activation. In rat aortic rings pretreated with LARG siRNA, Ang II-induced contraction was diminished.

Conclusion:

Ang II upregulates LARG gene expression and activates the LARG/RhoA/MYPT1 axis via AT₁, thereby maintaining vascular tone.     

Sesamin ameliorates arterial dysfunction in spontaneously hypertensive rats via downregulation of NADPH oxidase subunits and upregulation of eNOS expression

Aim:

Sesamin is one of the major lignans in sesame seeds with antihyperlipidemic, antioxidative and antihypertensive activities. The aim of this study was to examine the effects of sesamin on arterial function in spontaneously hypertensive rats (SHRs).

Methods:

SHRs were orally administered sesamin (40, 80 and 160 mg·kg⁻¹·d⁻¹) for 16 weeks. After the rats were killed, thoracic aortas were dissected out. The vasorelaxation responses of aortic rings to ACh and nitroprusside were measured. The expression of eNOS and NADPH oxidase subunits p47^phox and p22^phox in aortas were detected using Western blotting and immunohistochemistry. Aortic nitrotyrosine was measured with ELISA. The total antioxidant capacity (T-AOC) and MDA levels in aortas were also determined.

Results:

The aortic rings of SHRs showed significantly smaller ACh-induced and nitroprusside-induced relaxation than those of control rats. Treatment of SHRs with sesamin increased both the endothelium-dependent and endothelium-independent relaxation of aortic rings in a dose-dependent manner. In aortas of SHRs, the level of T-AOC and the expression of nitrotyrosine, p22^phox and p47^phox proteins were markedly increased, while the level of MDA and the expression of eNOS protein were significantly decreased. Treatment of SHRs with sesamin dose-dependently reversed these biochemical and molecular abnormalities in aortas.

Conclusion:

Long-term treatment with sesamin improves arterial function in SHR through the upregulation of eNOS expression and downregulation of p22^phox and p47^phox expression.     

Effects of a new advanced glycation inhibitor,LR-90, on mitigating arterial stiffening and improving arterial elasticity and compliance in a diabetic rat model: aortic impedance analysis

BACKGROUND AND PURPOSE

We determined the effects of treatment with LR-90, an inhibitor of advanced glycation end products, on the mechanical properties of the arterial system in streptozotocin (STZ)-induced diabetic Sprague Dawley rats, using aortic impedance analysis, and further investigated the effects of LR-90 on the progression of aortic pathology.

EXPERIMENTAL APPROACH

STZ-induced diabetic rats were treated with or without LR-90 (50 mg L^-1 in drinking water) for 8 weeks and compared with control groups. Arterial BP measurements, various metabolic parameters, aortic histopathology, collagen cross-linking, AGE accumulation, and RAGE protein expression in aortic tissue were determined. Pulsatile parameters were evaluated using a standard Fourier series expansion technique and impulse response function of the filtered aortic input impedance spectra.

KEY RESULTS

LR-90 reduced glycated haemoglobin and triglycerides levels, although it had no effect on the glycaemic status. LR-90 did not affect arterial BP, but prevented the diabetes-induced increase in peripheral resistance and variations in aortic distensibility, as it reduced aortic characteristic impedance by 21%. LR-90 also prevented the elevation in wave reflection factor, as indicated by a 22.5% reduction and an associated increase of 23.5% in wave transit time, suggesting it prevents the augmentation of the systolic load of the left ventricle. Moreover, LR-90 inhibited collagen cross-linking and the accumulation of AGE and RAGE in the vasculature of diabetic rats.

CONCLUSIONS AND IMPLICATIONS

Treatment with LR-90 may impart significant protection against diabetes-induced aortic stiffening and cardiac hypertrophy and provides an additional therapeutic option for treatment of AGE associated diabetic complications.     

Chronic nicotine treatment enhances vascular smooth muscle relaxation in rats

Aim:

To investigate the effect of chronic nicotine treatment on vascular function and to identify the underlying mechanisms.

Methods:

Adult rats were treated with nicotine (3 mg·kg⁻¹·d⁻¹, sc) for 6 weeks. After the rats were sacrificed, aortic rings were prepared for detecting vascular reactivity, and thoracic aorta and periaortic fat samples were collected for histological and molecular biology studies.

Results:

Chronic nicotine treatment significantly reduced periaortic fat, and specifically enhanced smooth muscle relaxation without altering the aortic adventitial fat and endothelium function. Pretreatment with the soluble guanylyl cyclase inhibitor ODQ (3 μmol/L) or PKG inhibitor Rp-8-Br-PET-cGMP (30 μmol/L) abolished the nicotine-induced enhancement of smooth muscle relaxation, whereas the cGMP analogue 8-Br-cGMP could mimic the nicotine-induced enhancement of smooth muscle relaxation. However, the chronic nicotine treatment did not alter PKG protein expression and activity in aortic media.

Conclusion:

Chronic nicotine treatment enhances vascular smooth muscle relaxation of rats via activation of PKG pathway.     

Improvement of aortic valve stenosis by ApoA-I mimetic therapy is associated with decreased aortic root and valve remodelling in mice

Background and Purpose

We have shown that infusions of apolipoprotein A-I (ApoA-I) mimetic peptide induced regression of aortic valve stenosis (AVS) in rabbits. This study aimed at determining the effects of ApoA-I mimetic therapy in mice with calcific or fibrotic AVS.

Experimental Approach

Apolipoprotein E-deficient (ApoE^−/−) mice and mice with Werner progeria gene deletion (Wrn^Δhel/Δhel) received high-fat diets for 20 weeks. After developing AVS, mice were randomized to receive saline (placebo group) or ApoA-I mimetic peptide infusions (ApoA-I treated groups, 100 mg·kg⁻¹ for ApoE^−/− mice; 50 mg·kg⁻¹ for Wrn mice), three times per week for 4 weeks. We evaluated effects on AVS using serial echocardiograms and valve histology.

Key Results

Aortic valve area (AVA) increased in both ApoE^−/− and Wrn mice treated with the ApoA-I mimetic compared with placebo. Maximal sinus wall thickness was lower in ApoA-I treated ApoE^−/− mice. The type I/III collagen ratio was lower in the sinus wall of ApoA-I treated ApoE^−/− mice compared with placebo. Total collagen content was reduced in aortic valves of ApoA-I treated Wrn mice. Our 3D computer model and numerical simulations confirmed that the reduction in aortic root wall thickness resulted in improved AVA.

Conclusions and Implications

ApoA-I mimetic treatment reduced AVS by decreasing remodelling and fibrosis of the aortic root and valve in mice.     

Ramipril retards development of aortic valve stenosis in a rabbit model: mechanistic considerations

BACKGROUND AND PURPOSE

Aortic valve stenosis (AVS) is associated with significant cardiovascular morbidity and mortality. To date, no therapeutic modality has been shown to be effective in retarding AVS progression. We evaluated the effect of angiotensin-converting enzyme inhibition with ramipril on disease progression in a recently developed rabbit model of AVS.

EXPERIMENTAL APPROACH

The effects of 8 weeks of treatment with either vitamin D₂ at 25 000 IU for 4 days a week alone or in combination with ramipril (0.5 mg·kg⁻¹) on aortic valve structure and function were examined in New Zealand white rabbits. Echocardiographic aortic valve backscatter (AV_BS) and aortic valve : outflow tract flow velocity ratio were utilized to quantify changes in valve structure and function.

KEY RESULTS

Treatment with ramipril significantly reduced AV_BS and improved aortic valve : outflow tract flow velocity ratio. The intravalvular content of the pro-oxidant thioredoxin-interacting protein was decreased significantly with ramipril treatment. Endothelial function, as measured by asymmetric dimethylarginine concentrations and vascular responses to ACh, was improved significantly with ramipril treatment.

CONCLUSIONS AND IMPLICATIONS

Ramipril retards the development of AVS, reduces valvular thioredoxin-interacting protein accumulation and limits endothelial dysfunction in this animal model. These findings provide important insights into the mechanisms of AVS development and an impetus for future human studies of AVS retardation using an angiotensin-converting enzyme inhibitor.     

Prevention of arterial stiffening by pyridoxamine in diabetes is associated with inhibition of the pathogenic glycation on aortic collagen

Background and purpose:

Our team previously demonstrated that diabetes induces a deterioration in vascular dynamics, in parallel with the enhanced formation of advanced glycation end products. The aim of this study was to determine whether prevention of the arterial stiffening by pyridoxamine in diabetes is associated with inhibition of the pathogenic glycation on aortic collagen.

Experimental approach:

Diabetes was induced in rats by a single tail vein injection with 55 mg·kg⁻¹ steptozotocin (STZ). After induction of hyperglycaemia, animals were treated for 8 weeks with pyridoxamine (1 g·L⁻¹ in drinking water) and compared with the age-matched untreated diabetic controls. Pulse wave reflection along the vasculature was derived using the impulse response function of the filtered aortic input impedance spectra.

Key results:

Treatment of this experimental diabetes with pyridoxamine resulted in a significant increase in wave transit time and a decrease in wave reflection factor, indicating that pyridoxamine attenuates the diabetes-induced augmentation in systolic load of the left ventricle coupled to its arterial system. Meanwhile, pyridoxamine therapy ameliorated the diabetes-related cardiac hypertrophy, as evidenced by the reduction in ratio of the left ventricular weight to body weight. Glycation-derived modification of aortic collagen was also found to be attenuated by administration of pyridoxamine to the STZ-induced diabetic rats.

Conclusions and implications:

Pyridoxamine imparts significant protection against the diabetes-induced deterioration in pulsatile arterial load imposed on the heart, at least partly through inhibition of the formation of advanced glycation end products and their accumulation on aortic collagen of the STZ-treated rats.     

The prolactin family hormones regulate vascular tone through NO and prostacyclin production in isolated rat aortic rings

Aim:

Prolactin family hormones include growth hormone, placental lactogen and prolactin, which are able to regulate angiogenesis via NO and prostaglandins. However, their effects on vascular tone are not fully understood. The aim of this study was to evaluate the effects of prolactin family hormones on rat vascular tone in vitro.

Methods:

Aortic rings were prepared from adult male rats and precontracted with phenylephrine, then treated with the hormones and drugs. The tension was measured with isometric force displacement transducer connected to a polygraph. NO production and prostacyclin release in physiological solution was determined. Cultured rat aortic endothelial cells (RAECs) were treated with the hormones and drugs, and the phosphorylation of eNOS at serine 1177 was assessed using Western bolt analysis.

Results:

Administration of growth hormone or placental lactogen (0.01–100 nmol/L) induced endothelium-dependent vasodilation. Both the hormones significantly increased the phosphorylation of eNOS in RAECs and NO level in physiological solution. Preincubation with L-NAME blocked growth hormone- or placental lactogen-induced vasodilation and NO production. Preincubation with an antibody against growth hormone receptors blocked growth hormone- and placental lactogen-induced vasodilation. Addition of a single dose of prolactin (0.01 nmol/L) induced sustained vessel relaxation, whereas multiple doses of prolactin induced a biphasic contraction-relaxation effect. The vascular effects of prolactin depended on endothelium. Prolactin significantly increased the level of prostacyclin I₂ in physiological solution. Preincubation with indomethacin or an antibody against prolactin receptors blocked prolactin-induced vasodilation.

Conclusion:

The prolactin family hormones regulate rat vascular tone, selectively promoting either relaxation or contraction of vascular smooth muscle via activation of either growth hormone receptors or prolactin receptors within the endothelium.     

KMUP-3 attenuates ventricular remodelling after myocardial infarction through eNOS enhancement and restoration of MMP-9/TIMP-1 balance

BACKGROUND AND PURPOSE

Previously, 7-[2-[4-(4-nitrobenzene)piperazinyl]ethyl]-1, 3-dimethylxanthine (KMUP-3) has been shown to induce aortic smooth muscle relaxation through K_ATP channel opening and endothelial nitric oxide synthase (eNOS) enhancement. We further investigated whether KMUP-3 protects against myocardial remodelling after myocardial infarction (MI), and whether KMUP-3 increases the expression of eNOS in MI rats.

EXPERIMENTAL APPROACH

Wistar rats were randomly allocated into three groups: MI (n= 10), MI + KMUP-3 group (n= 10) and sham group (n= 10). MI was induced by ligation of the left anterior descending coronary artery. After recovery, the MI + KMUP-3 group received KMUP-3 (0.3 mg·kg⁻¹·day⁻¹) infusion for 4 weeks, while the MI and sham group received vehicle only. To further confirm that the effect of KMUP-3 is dependent on eNOS, KMUP-3 was applied in the culture of transforming growth factor-β-stimulated human cardiac fibroblasts.

KEY RESULTS

KMUP-3 treatment attenuated cardiac hypertrophy post-MI and improved cardiac function. The fibrotic area was reduced by KMUP-3 both in central-, peri- and non-infarction areas. KMUP-3 enhanced the expression of eNOS and tissue inhibitor of metalloproteinase-1 (TIMP-1), but reduced matrix metalloproteinase-9 (MMP-9) expression. In vitro, the activities of KMUP-3 were blocked by pretreatment with the eNOS inhibitor N^ω-nitro-L-arginine methyl ester.

CONCLUSIONS AND IMPLICATIONS

The K_ATP channel opener KMUP-3 preserved cardiac function after MI by enhancing the expression of eNOS. In addition, KMUP-3 restored the myocardial MMP-9/TIMP-1 balance and attenuated ventricular remodelling by an eNOS-dependent mechanism.     

Diabetic state,high plasma insulin and angiotensin II combine to augment endothelin-1-induced vasoconstriction via ETA receptors and ERK

Background and purpose:

Mechanisms associated with the enhanced contractile response to endothelin-1 in hyperinsulinaemic diabetes have been examined using the rat aorta. Functions for angiotensin II, endothelin-1 receptor expression and extracellular signal-regulated kinase (ERK) have been investigated.

Experimental approach:

Streptozotocin-induced diabetic rats were infused with angiotensin II or, following insulin treatment, were treated with losartan, an angiotensin II receptor antagonist. Contractions of aortic strips with or without endothelium, in response to endothelin-1 and angiotensin II, were examined in vitro. Aortic ET_A receptors and ERK/MEK expression were measured by western blotting.

Key results:

Insulin-treated diabetic rats exhibited increases in plasma insulin, angiotensin II and endothelin-1. The systolic blood pressure and endothelin-1-induced contractile responses in aortae in vitro were enhanced in insulin-treated diabetic rats and blunted by chronic losartan administration. {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 (phosphatidylinositol 3-kinase inhibitor) and/or PD98059 (MEK inhibitor) diminished the enhanced contractile response to endothelin-1 in aortae from insulin-treated diabetic rats. ET_A and ET_B receptors, ERK-1/2 and MEK-1/2 protein expression and endothelin-1-stimulated ERK phosphorylation were all increased in aortae from insulin-treated diabetic rats. Such increases were blunted by chronic losartan administration. Endothelin-1-induced contraction was significantly higher in aortae from angiotensin II-infused diabetic rats. angiotensin II-infusion increased ERK phosphorylation, but the expression of endothelin receptors and ERK/MEK proteins remained unchanged.

Conclusions and implications:

These results suggest that the combination of high plasma angiotensin II and insulin with a diabetic state induced enhancement of endothelin-1-induced vasoconstriction, ET_A receptor expression and ERK expression/activity in the aorta. Losartan improved both the diabetes-related abnormalites and the diabetic hypertension.