Endothelium-dependent Vascular Function Research Articles

Effects of fluvastatin on non-endothelium dependent vasodilatation function in hyperensives

P-290 Key Words: Hypertension, Fluvastatin, Non-Endothelium-Dependent Vasodilatation:ABS>

The emerging role of asymmetric dimethylarginine as a novel cardiovascular risk factor.

There is abundant evidence that the endothelium plays a crucial role in the maintenance of vascular tone and structure. One of the major endothelium-derived vasoactive mediators is nitric oxide (NO). Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of NO synthase. ADMA inhibits vascular NO production at concentrations found in pathophysiological conditions (i.e., 3-15 micromol/l); ADMA also causes local vasoconstriction when it is infused intraarterially. The biochemical and physiological pathways related to ADMA are now well understood: dimethylarginines are the result of the degradation of methylated proteins; the methyl group is derived from S-adenosylmethionine. Both ADMA and its regioisomer, SDMA, are eliminated from the body by renal excretion, whereas only ADMA, but not SDMA, is metabolized via hydrolytic degradation to citrulline and dimethylamine by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). DDAH activity and/or expression may therefore contribute to the pathogenesis of endothelial dysfunction in various diseases. ADMA is increased in the plasma of humans with hypercholesterolemia, atherosclerosis, hypertension, chronic renal failure, and chronic heart failure. Increased ADMA levels are associated with reduced NO synthesis as assessed by impaired endothelium-dependent vasodilation. In several prospective and cross-sectional studies, ADMA evolved as a marker of cardiovascular risk. With our increasing knowledge of the role of ADMA in the pathogenesis of cardiovascular disease, ADMA is becoming a goal for pharmacotherapeutic intervention. Among other treatments, the administration of L-arginine has been shown to improve endothelium-dependent vascular function in subjects with high ADMA levels.

Influence of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase inhibitors on endothelial nitric oxide synthase and the formation of oxidants in the vasculature

HMGCoA reductase inhibitors (statins) can have effects outside the target tissue, liver, including serious side-effects such as rhabdomyolysis as well as beneficial pleiotrophic effects. One such effect is upregulation of endothelial nitric oxide synthase (e-NOS) which generally leads to vasorelaxation. However, changing the balance between localized NO and O 2 − fluxes can also lead to oxidant stress and cellular injury through formation of reactive secondary oxidants such as peroxynitrite. We compared different statins for e-NOS subcellular localization, formation of pro-oxidants, and endothelial-dependent vascular function. Vascular relaxation in aortas of statin-dosed rats was inhibited with simvastatin (sevenfold higher EC50 for acetyl-choline induced relaxation) and atorvastatin (twofold increase) but not pravastatin. Ex vivo oxidation of the fluorescent redox probe dihydrorhodamine-123 (DHR-123) was increased in aortas from simvastatin treated rats, indicating increased reactive nitrogen and oxygen species. Human aortic endothelial cells incubated with simvastatin exhibited up to threefold higher intracellular oxidation of DHR-123 along with a twofold increase in total e-NOS protein. The elevated e-NOS was found in the Golgi/mitochondrial fraction and not in the plasma membrane, and using immunofluorescence greater e-NOS was observed proximal to Golgi and cytoskeletal structures and away from plasma membrane in simvastatin-treated cells. The data suggest that the action of lipophilic statins in endothelium can shift e-NOS localization towards intracellular domains, thereby increasing the encounter with metabolically generated O 2 − to produce peroxynitrite and related oxidants. Thus, under some conditions the direct action of lipophilic HMGCoA reductase inhibitors may unbalance NO and O 2 − fluxes and promote oxidant stress, compromising potentially beneficial vascular effects of e-NOS upregulation and increasing the potential for damage to muscle and other tissues.

Association of Asymmetric Dimethylarginine and Endothelial Dysfunction

There is abundant evidence that the endothelium plays a crucial role in the maintenance of vascular tone and structure. One of the major endothelium-derived vasoactive mediators is nitric oxide (NO), which has been characterized as an "endogenous anti-atherosclerotic molecule". Synthesis of NO can be selectively inhibited by guanidino-substituted analogs of L-arginine, which act as competitive inhibitors at the active site of the enzyme. One such analog is asymmetric dimethylarginine (ADMA), a compound that has been found in human plasma and urine and exerts the activity of an endogenous inhibitor of NO synthase. In contrast to ADMA, its regioisomer symmetric dimethylarginine (SDMA) does not inhibit NO synthase. The methyl groups contained within the dimethylarginine molecules are derived from S-adenosylmethionine, an intermediate in the homocysteine/methionine pathway. There is experimental evidence that homocysteine may affect endothelium-dependent vascular function by increasing the formation of ADMA. Both ADMA and SDMA are eliminated from the body by renal excretion. In addition, the metabolism of ADMA, but not SDMA, occurs via hydrolytic degradation to citrulline and dimethylamine by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). Data from experimental studies suggest that ADMA inhibits vascular NO elaboration at concentrations found in pathophysiological conditions (i.e., 3-15 microM). ADMA likely acts as an autocrine regulator of endothelial NO synthase activity. When rabbits are placed on a diet enriched with 1% cholesterol, ADMA levels are increased within 4 weeks of dietary intervention as compared to control animals. Elevated plasma concentrations of ADMA are also present in hypercholesterolemic and hypertensive patients, in patients with chronic heart failure, and in other patient groups at high risk of developing cardiovascular disease. Elevation of ADMA induces dysfunction of the endothelium, which becomes clinically evident by impaired endothelium-dependent vasodilation, hyperaggregability of platelets, and enhanced monocyte adhesion. Recent prospective studies suggest that endothelial dysfunction indicates an increased risk of future cardiovascular events. In line with these observations, we and others found evidence that ADMA is a novel cardiovascular risk factor.

Aging induces muscle-specific impairment of endothelium-dependent dilation in skeletal muscle feed arteries.

We tested the hypothesis that aging decreases endothelium-dependent vasodilation in feed arteries perfusing rat skeletal muscle. In addition, we tested the hypothesis that attenuated vasodilator responses are associated with decreased endothelial nitric oxide synthase (eNOS) and superoxide dismutase-1 (SOD-1) expression. Soleus feed arteries (SFA) and gastrocnemius feed arteries (GFA) were isolated from young (4 mo) and old (24 mo) male Fischer 344 rats. Feed arteries from the right hindlimb were cannulated with two glass micropipettes for examination of endothelium-dependent [acetylcholine (ACh)] and endothelium-independent [adenosine (Ado) or sodium nitroprusside (SNP)] vasodilator function. Feed arteries from the left hindlimb were frozen and used to assess eNOS and SOD-1 protein and mRNA expression. In SFA, endothelium-dependent dilation to ACh was reduced in old rats (0.9 +/- 0.04 vs. 0.8 +/- 0.03), whereas dilator responses to Ado and SNP were similar in SFA of young and old rats. In GFA, vasodilator responses to ACh, Ado, and SNP were not altered by age. eNOS and SOD-1 protein expression declined with age in SFA (-71 and -54%, respectively) but not in GFA. eNOS and SOD-1 mRNA expression were not altered by age in SFA or GFA. Collectively, these data indicate aging induces muscle-specific impairment of endothelium-dependent vascular function in SFA.

Prognostic role of reversible endothelial dysfunction in hypertensive postmenopausal women

ObjectivesThe aim of the present study was to assess whether optimized antihypertensive treatment is effective in modifying endothelial function and whether an improvement in flow-mediated vasodilation (FMD) in response to treatment, as an expression of reversible endothelial dysfunction, could predict a more favorable prognosis in a population of postmenopausal women. BackgroundHypertensive postmenopausal women have been shown to have abnormal endothelium-dependent vascular function. However, FMD may change over time, according to antihypertensive treatment; the prognostic value of these changes has not been investigated. MethodsA total of 400 consecutive postmenopausal women with mild-to-moderate hypertension and impaired FMD underwent ultrasonography of the brachial artery at baseline and after six months, while optimal control of blood pressure was achieved using antihypertensive therapy. They were then followed up for a mean period of 67 months (range 57 to 78). Endothelial function was measured as FMD of the brachial artery, using high-resolution ultrasound. ResultsAfter six months of treatment, FMD had not changed (≤10% relative to baseline) in 150 (37.5%) of 400 women (group 1), whereas it had significantly improved (>10% relative to baseline) in the remaining 250 women (62.5%) (group 2). During follow-up, we noticed 32 events (3.50 per 100 person-years) in group 1 and 15 events (0.51 per 100 person-years) in group 2 (p < 0.0001). ConclusionsThis study demonstrates that a significant improvement in endothelial function may be obtained after six months of antihypertensive therapy and clearly identifies patients who possibly have a more favorable prognosis.

A selective somatostatin type-2 receptor agonist inhibits neointimal thickening and enhances endothelial cell growth and morphology following aortic balloon injury in the rabbit.

Somatostatin analogs have been shown to inhibit vascular smooth muscle cell (VSMC) proliferation and attenuate neointimal thickening following experimental balloon catheter injury. In this study, the effects of a selective agonist for the somatostatin receptor subtype 2, PRL-2486, on neointimal thickening and endothelial cell regrowth 2 weeks following balloon catheterization of male New Zealand White rabbits were determined. Rabbits treated 2 days prior to and 2 weeks after catheter injury with 10 microg/kg/day PRL-2486 (PRL-tx) had decreased I/M ratios (intimal area/medial area x 100; p < 0.05) but had no effect at lower (5 microg/kg/day) or higher (20 microg/kg/day) doses. PRL-tx had significantly decreased VSMC proliferation compared to untreated animals. PRL-tx increased endothelial regrowth by over 2-fold (p < 0.002) and improved endothelial cell morphology. Endothelial-dependent relaxation responses to acetylcholine were attenuated by catheter injury, and were not improved with PRL-tx. These data suggest that the PRL-2486-mediated inhibition of neointimal thickening exhibits a bell-shaped dose-response curve. This inhibition may be due in part to decreased VSMC proliferation, which may be a function of enhanced endothelial regrowth, but not the return of endothelium-dependent vascular function.

Evidence of an Increase in Baseline Brachial Artery Lumen Diameter Independent of Body Mass Index (BMI) among Women with Polycystic Ovary Syndrome (PCOS)Compared to Age-Matched Control Women

P29 PCOS is a reproductive endocrine disorder, characterized by chronic anovulation, androgen excess, and insulin resistance, affecting approximately 5% of the female population. PCOS is associated with an increase in CHD risk factors, including LDL cholesterol,triglycerides, obesity,and hypertension. Endothelial dysfunction has been implicated in the development and progression of atherosclerosis and has been shown to be adversely affected in males with high free testosterone levels and in men and women with increased insulin resistance. We recruited 83 women with PCOS (42.3 ± 5.8 years) from our Pittsburgh cohort and 91 controls of similar age (43.4 ± 5.4 years) to evaluate endothelium-dependent vascular function using brachial artery ultrasonography. Women on hormone replacement or oral contraceptives were excluded from the analysis. The mean BMI ± SD was 31.7 ± 8.7 and 27.1 ± 6.4 kg/m 2 in cases and controls, respectively. The groups were also similar with respect to smoking status. No difference was observed in BMI-adjusted flow mediated vasodilation (FMD) between PCOS cases and controls (p=.630). However, baseline brachial lumen diameter (LD) was significantly higher among women with PCOS compared to controls (Mean ± SE = 3.30 ± .06 vs. 3.12 ± .05) after adjustment(p=.023). Further adjustment for LDLc, HDLc, triglycerides, systolic blood pressure (SBP), or insulin did not alter the PCOS-brachial lumen diameter association. Independently of case status and BMI, HDLc was significantly associated with baseline LD(p=.001); DBP was of borderline significance(p=.099). These findings suggested that PCOS may be associated with a compensatory enlargement of the arteries in response to accelerated arterial wall thickening and/or arterial stiffening. Further analyses within PCOS cases suggested that testosterone and insulin may mediate endothelial function (FMD). Future studies are needed to futher explore vascular changes and the implication for cardio- and cerebrovascular events in this high risk population.

Vascular Effects of ACE Inhibition Independent of the Renin-Angiotensin System in Hypertensive Renovascular Disease

-To evaluate whether ACE inhibition and angiotensin II type 1 blockade exert beneficial effects on NO availability independent of their blood pressure-lowering effect, we used a double-blind crossover design to study vascular function in 18 patients with hypertensive renovascular disease during 6 weeks of therapy with enalapril (Ena) and valsartan (Val) compared with non-renin-angiotensin system-mediated treatment with the alpha(1)-blocker doxazosin (Dox). Control measurements were performed in 13 age-matched volunteers. Forearm blood flow was assessed with venous occlusion plethysmography, and serotonin and nitroprusside were used as endothelium-dependent and -independent vasodilators, respectively. Blood pressure was similar during all treatment periods. Serotonin-induced vasodilation was decreased in patients during Dox treatment (n=12) compared with control subjects (n=13) (increase 42+/-20% versus 107+/-65%, P:<0.05). Crossover from Dox to Val (n=6) had no effect on serotonin response (increase 50+/-14%), but crossover to Ena (n=6) caused a significant improvement (increase 79+/-39%, P:<0.05 versus Dox). In an assessment of all patients, serotonin-induced vasodilation during Ena (n=12, increase 75+/-31%) was increased compared with both Val and Dox (43+/-14% and 42+/-20%, respectively; both P:<0.05 versus Ena). The nitroprusside response remained unaltered during all treatment periods. In conclusion, ACE inhibition improves the impaired endothelium-dependent vascular function in patients with hypertensive renovascular disease. This effect is unrelated to blood pressure-lowering or angiotensin II-mediated effects.

Relation of inflammation to vascular function in patients with coronary heart disease

Endothelium plays a pivotal role in the regulation of vascular relaxation. Inflammation may in turn induce endothelial dysfunction and thus increase the risk of atherothrombosis. We investigated 31 men with angiographically verified coronary heart disease, aged 57.7±5.3 years, in regard to endothelium-dependent, acetylcholine-induced, and to endothelium-independent, sodium nitroprusside-induced vasodilatation in the forearm vasculature by strain-gauge plethysmography. Logistic regression analysis served to determine the relation between forearm vascular function and the inflammatory factors measured, concentration of C-reactive protein, subtypes of peripheral blood T-lymphocytes, and other factors potentially affecting endothelial function (lipoprotein and glucose levels). Concentration of C-reactive protein was an independent determinant of endothelium-dependent vascular function ( P<0.001 for low dose acetylcholine, P=0.01 for high dose acetylcholine). Other determinants of endothelium-dependent vascular dysfunction were CD8-lymphocytes expressing ICAM-1 ( P=0.001), antibodies to oxidized low-density lipoprotein ( P<0.001), and body weight ( P=0.007). The present data showed an association between inflammatory risk factors linked to atherothrombosis and endothelial dysfunction in coronary heart disease patients. It is possible that endothelial dysfunction in coronary heart disease patients is related to the chronic inflammation or infection coexisting with atherosclerosis.

Homocyst(e)ine impairs endocardial endothelial function

Homocyst(e)ine injured vascular endothelium and modulated endothelial-dependent vascular function. Endothelium plays an analogous role in both the vessel and the endocardium. Therefore, we hypothesized that homocyst(e)ine modulated endocardial endothelium (EE) dependent cardiac function. The ex vivo cardiac rings from normal male Wistar-Kyoto rats were prepared. The contractile responses of left and right ventricular rings were measured in an isometric myobath, using different concentrations of CaCl2. The response was higher in the left ventricle than right ventricle and was elevated in endocardium without endothelium. The half effective concentration (EC50) and maximum tension generated by homocyst(e)ine were 106 and 5-fold lower than endothelin (ET) and angiotensin II (AII), respectively. However, in endothelial-denuded endocardium, homocyst(e)ine response was significantly increased (p &lt; 0.005, compared with intact endothelium) and equal to the response to ET and AII. To determine the physiological significance of ET, AII, homocyst(e)ine, and endothelial nitric oxide in EE function, cardiac rings were pretreated with AII (10-10 M) or ET (10-13 M) and then treated with homocyst(e)ine (10-8 M). Results suggested that at these concentrations AII, ET, or homocyst(e)ine alone had no effect on cardiac contraction. However, in the presence of 10-10 M AII or 10-13 M ET, the cardiac contraction to homocyst(e)ine (10-8 M) was significantly enhanced (p &lt; 0.01, compared with without pretreatment) and further increased in the endocardium without endothelium. The pretreatment of cardiac ring with the inhibitor of nitric oxide, Nω-nitro-L-arginine methyl ester (L-NAME), increased contractile response to homocyst(e)ine. These results suggested that homocyst(e)ine impaired EE-dependent cardiac function and acted synergistically with AII and ET in enhancing the cardiac contraction.Key words: endocardial remodeling, homocyst(e)ine, contraction, endothelin, angiotensin, endothelial-derived relaxing factor (EDRF), Nω-nitro-L-arginine methyl ester (L-NAME), endothelial dysfunction, ex vivo cardiac function, heart failure.

Homocyst(e)ine impairs endocardial endothelial function

Homocyst(e)ine injured vascular endothelium and modulated endothelial-dependent vascular function. Endothelium plays an analogous role in both the vessel and the endocardium. Therefore, we hypothesized that homocyst(e)ine modulated endocardial endothelium (EE) dependent cardiac function. The ex vivo cardiac rings from normal male Wistar-Kyoto rats were prepared. The contractile responses of left and right ventricular rings were measured in an isometric myobath, using different concentrations of CaCl2. The response was higher in the left ventricle than right ventricle and was elevated in endocardium without endothelium. The half effective concentration (EC50) and maximum tension generated by homocyst(e)ine were 10(6) and 5-fold lower than endothelin (ET) and angiotensin II (AII), respectively. However, in endothelial-denuded endocardium, homocyst(e)ine response was significantly increased (p<0.005, compared with intact endothelium) and equal to the response to ET and AII. To determine the physiological significance of ET, AII, homocyst(e)ine, and endothelial nitric oxide in EE function, cardiac rings were pretreated with AII (10(-10) M) or ET (10(-13) M) and then treated with homocyst(e)ine (10(-8) M). Results suggested that at these concentrations AII, ET, or homocyst(e)ine alone had no effect on cardiac contraction. However, in the presence of 10(-10) M AII or 10(-13) M ET, the cardiac contraction to homocyst(e)ine (10(-8) M) was significantly enhanced (p<0.01, compared with without pretreatment) and further increased in the endocardium without endothelium. The pretreatment of cardiac ring with the inhibitor of nitric oxide, Nomega-nitro-L-arginine methyl ester (L-NAME), increased contractile response to homocyst(e)ine. These results suggested that homocyst(e)ine impaired EE-dependent cardiac function and acted synergistically with AII and ET in enhancing the cardiac contraction.

Regulation of 6-pyruvoyltetrahydropterin synthase activity and messenger RNA abundance in human vascular endothelial cells.

The nitric oxide synthase cofactor tetrahydrobiopterin (BH4) is involved in the regulation of endothelium-dependent vascular functions mediated by nitric oxide. Vascular endothelial cells synthesize and secrete large amounts of BH4 on cytokine activation. There is scant knowledge about molecular mechanisms of cytokine-triggered BH4 production in endothelial cells. Pteridine production, mRNA expression of GTP cyclohydrolase (GTPCH) and 6-pyruvoyltetrahydropterin synthase (PTPS) (both key enzymes of BH4 biosynthesis), and PTPS activity were studied in human umbilical vein endothelial cells (HUVECs) exposed to inflammatory cytokines. BH4 levels were </=140-fold enhanced on treatment of HUVECs with combined interferon-gamma/tumor necrosis factor-alpha/interleukin-1 (IFN/TNF/IL-1). Specific PTPS activity was approximately 3-fold higher in cytokine-treated HUVECs than in untreated cells. Reverse-transcription/limiting-dilution polymerase chain reaction analysis showed that in response to IFN/TNF/IL-1, mRNA abundance of GTPCH and PTPS was increased approximately 64-fold and 10-fold, respectively. The present study demonstrates for the first time the cytokine-dependent regulation of PTPS, the second enzyme in BH4 synthesis. Although GTPCH is believed to be the rate-limiting step, control of endothelial PTPS expression by cytokines may play an important role in regulating BH4-dependent nitric oxide production in the vascular system.

Impairment of vascular function is associated with an age-related increase of lipid peroxidation in rats.

We tested the hypothesis that an increase in endogenous lipid peroxidation over time is associated with an impairment of endothelium-dependent vascular function in resistance-sized mesenteric arteries that is due in part to alterations of arachidonate metabolism. Susceptibility to red blood cell hemolysis and sera levels of malondialdehyde were increased (P < 0.05) from 20 wk (n = 12) to 40 wk (n = 12) in female Sprague-Dawley rats. Arteries were studied in a myograph by examining the endothelial modification of phenylephrine vasoconstriction and the relaxation responses of the mesenteric arteries to methacholine. We observed the following. 1) An increase in sensitivity to alpha 1-adrenergic stimulation occurred between 20 and 40 wk of age. Cyclooxygenase inhibition decreased the sensitivity to phenylephrine only in the arteries from the 40-wk-old rats, indicating that a cyclooxygenase-dependent vasoconstrictor was modifying the phenylephrine response. 2) Nitric oxide synthase inhibition caused a greater increase in phenylephrine sensitivity in the arteries from the 20-wk-old rats than those from the 40-wk-old rats, indicating that nitric oxide modification of phenylephrine sensitivity decreased with age. 3) Endothelium-independent relaxations were not affected between 20 and 40 wk of age. 4) At 40 wk, the sensitivity to the methacholine-mediated relaxation response decreased without impairing the maximal relaxation response. This reduced sensitivity was removed with cyclooxygenase inhibition or thromboxane A2/prostaglandin H2 (PGH2) receptor blockade. 5) Aortas from the 40-wk-old rats had an increased expression of PGH synthase. Collectively, these observations indicate that, in the female rat, an increase in lipid peroxidation over time is associated with changes in endothelium-dependent vascular function that were due in part to a cyclooxygenase-dependent vasoconstrictor.

Attenuated endothelium-dependent vascular relaxation in patients with sleep apnoea.

To evaluate endothelium-dependent vascular function in obstructive sleep apnoea patients. Forearm blood flow and vascular resistance were studied in eight normotensives and eight obstructive sleep apnoea patients and also in eight normotensive and eight hypertensive controls after graded brachial artery infusion of acetylcholine (10-60 micrograms/min) and sodium nitroprusside (1-6 micrograms/min), respectively. Patients and controls were matched for age, sex and body weight. Forearm blood flow after acetylcholine infusion was reduced in patients compared with that in controls (peak flows were 6.0 +/- 0.7 and 9.8 +/- 1.5 ml/min for 100 g, respectively), but there was no difference between hypertensive and normotensive subjects. However, the hypertensive obstructive sleep apnoea group exhibited a reduced flow response to sodium nitroprusside compared with that of their corresponding hypertensive controls. Minimal forearm vascular resistance after acetylcholine infusion and after sodium nitroprusside infusion was higher in obstructive sleep apnoea patients than it was in controls. Endothelium-dependent vascular relaxation in patients with obstructive sleep apnoea was reduced independently of hypertension. An additional defect in endothelium-independent vascular relaxation was found in obstructive sleep apnoea patients with hypertension. These findings suggest a vascular pathogenetic link between obstructive sleep apnoea and systemic hypertension.

Effects of cardioplegia on vascular function and the “no-reflow" phenomenon after ischemia and reperfusion: Studies in the isolated blood-perfused rat heart

The ability of cardioplegia to protect against cardiac contractile dysfunction caused by ischemia and reperfusion is well established. The effects of cardioplegia on vascular injury and the no-reflow phenomenon, however, remain controversial. We used the blood-perfused rat heart to study the effect of St. Thomas' Hospital cardioplegic solution on postischemic endothelium-dependent and endothelium-independent vascular function, the extent of the no-reflow phenomenon, and the temporal relationship between postischemic vascular and contractile function. Isolated rat hearts (16 per group) perfused with blood from a support rat at 60 mm Hg were subjected to 10, 20, 30 or 40 minutes of global ischemia and 40 minutes of reperfusion at 37° C. Eight hearts in each group also received cardioplegia (45 mm Hg for 2 minutes) before ischemia. Left ventricular developed pressure was measured with an intraventricular balloon. At the end of reperfusion, a bolus of 250 μg nitro- l-arginine methyl ester was infused to assess endothelium dependent vascular function. After a 20-minute washout, 25 μg sodium nitroprusside was infused to assess endothelium-independent vascular function. Fluorescein (1 ml, 1% weight/volume) was then infused to assess no-reflow; this involved freezing the hearts, cutting them into transverse sections (10 × 1 mm), video recording the sections under ultraviolet light, digitizing the images, and analyzing density of fluorescence. No-reflow was defined as a flow of less than 5%. Compared with nonischemic control responses, endothelium-independent vascular function was significantly decreased only after 30 and 40 minutes of ischemia (48.1% ± 3.8% and 24.3% ± 7.4%, p < 0.05), but it was significantly protected by cardioplegia (66.6% ± 3.9% and 64.5% ± 5.2%, p < 0.05). A significant reduction in endothelium-dependent vascular function was observed after 40 minutes of ischemia (-31.8% ± 6.6% vs -50.4% ± 1.6% in control hearts, p < 0.05), and again this was improved by cardioplegia (-45.0% ± 3.4%, p < 0.05 vs ischemic group). Areas of no reflow were present after 30 and 40 minutes of ischemia (11.9% ± 6.8% and 33.4% ± 14.1% of left ventricular mass), and at each time period they were significantly decreased by cardioplegia (0.7% ± 0.4% and 3.8% ± 1.6%, p < 0.05). Postischemic contractile dysfunction was observed before any vascular alteration was apparent. After only 20 minutes of ischemia, the postischemic recovery of left ventricular developed pressure fell to 56.7% ± 4.0%, but both endothelium-dependent vascular function and endothelium-independent vascular function were unaffected. In conclusion, vascular alterations are apparent only after prolonged periods of ischemia, longer than those required to observe contractile dysfunction, and cardioplegia protects against postischemic endothelium-dependent and endothelium-independent vascular dysfunction and reduces the extent of the no-reflow phenomenon. (J T horac C ardiovasc S urg 1996;111:432-42)

Lipid peroxidation increases arterial cyclooxygenase activity during pregnancy

OBJECTIVE: We tested the hypothesis that increased production of lipid peroxides (induced by a mild vitamin E deficiency) during pregnancy would alter the cyclooxygenase pathway of arachidonate metabolism, resulting in impaired endothelial-dependent vascular function. STUDY DESIGN: Mesenteric arteries from pregnant control (n = 12) and pregnant vitamin E-deprived (n = 12) Sprague-Dawley rats were studied in a myograph. RESULTS: Surprisingly, endothelial-dependent relaxations to methacholine were enhanced in arteries from the pregnant vitamin E-deprived rats compared with the pregnant control rats (mean effective concentration producing a 50% response = 0.034 vs 0.046 μmol/L, p < 0.05). In the arteries from the vitamin E-deprived rats this enhanced response was blunted and the group difference eliminated in the presence of a cyclooxygenase inhibitor (1 μmol/L meclofenamate, mean effective concentration producing a 50% response 0.057 vs 0.034 μmol/L, p < 0.05) but had no effect on the arteries from the control pregnant rats. The thromboxane A2-prostaglandin H2 receptor blocker (1 μmol/L SQ 29548) had no effect on the arteries from either group. Endothelial-independent relaxations to sodium nitroprusside were not affected by vitamin E deprivation. Arachidonic acid elicited less tension in the arteries from the vitamin E-deprived rats compared with the controls (at 10 μmol/L: 0.41 vs 0.90 mN/mm, p < 0.01). Cyclooxygenase inhibition potentiated the vasoconstrictor response only in the arteries from the vitamin E - deprived rats (at 10 μmol/L: 0.92 vs 0.41 mN/mm, p < 0.01) so that the group difference was eliminated. CONCLUSION: An elevation of lipid peroxides, mediated by a mild vitamin E deprivation, resulted in an increased cyclooxygenase-dependent vasorelaxation in the mesenteric arteries of the pregnant rat. (AM J OBSTET GYNECOL 1994;170:215-22.)

Lipid peroxidation increases arterial cyclooxygenase activity during pregnancy

<b>Objective:</b> We tested the hypothesis that increased production of lipid peroxides (induced by a mild vitamin E deficiency) during pregnancy would alter the cyclooxygenase pathway of arachidonate metabolism, resulting in impaired endothelial-dependent vascular function. <b>Study Design:</b> Mesenteric arteries from pregnant control (<i>n</i> = 12) and pregnant vitamin E-deprived (<i>n</i> = 12) Sprague-Dawley rats were studied in a myograph. <b>Results:</b> Surprisingly, endothelial-dependent relaxations to methacholine were enhanced in arteries from the pregnant vitamin E-deprived rats compared with the pregnant control rats (mean effective concentration producing a 50% response=0.034 vs 0.046 μmol/L, <i>p</i> < 0.05). In the arteries from the vitamin E-deprived rats this enhanced response was blunted and the group difference eliminated in the presence of a cyclooxygenase inhibitor (1 μmol/L meclofenamate, mean effective concentration producing a 50% response 0.057 vs 0.034 μmol/L, <i>p</i> < 0.05) but had no effect on the arteries from the control pregnant rats. The thromboxane A₂-prostaglandin H₂ receptor blocker (1 μmol/L SCE 29548) had no effect on the arteries from either group. Endothelial-independent relaxations to sodium nitroprusside were not affected by vitamin E deprivation. Arachidonic acid elicited less tension in the arteries from the vitamin E-deprived rats compared with the controls (at 10 μmol/L: 0.41 vs 0.90 mN/mm, <i>p</i> < 0.01). Cyclooxygenase inhibition potentiated the vasoconstrictor response only in the arteries from the vitamin E-deprived rats (at 10 wmol/L: 0.92 vs 0.41 mN/mm, <i>p</i> < 0.01) so that the group difference was eliminated. <b>Conclusions:</b> An elevation of lipid peroxides, mediated by a mild vitamin E deprivation, resulted in an increased cyclooxygenase-dependent vasorelaxation in the mesenteric arteries of the pregnant rat.

Cyclooxygenase-dependent vasoconstrictor alters vascular function in the vitamin E-deprived rat.

We tested the hypothesis that increased production of lipid peroxides, mediated by a dietary vitamin E deprivation, would alter the cyclooxygenase pathway of arachidonate metabolism, resulting in impaired endothelium-dependent vascular function. Mesenteric arteries from control (n = 12) and vitamin E-deprived (n = 12) Sprague-Dawley rats were studied in a myograph. Endothelium-dependent relaxations to methacholine were similar in the arteries from vitamin E-deprived rats compared with control arteries (EC50, 0.057 +/- 0.006 versus 0.065 +/- 0.009 microM). However, in the arteries from the vitamin E-deprived rats, this response was potentiated in the presence of a cyclooxygenase inhibitor (1 microM meclofenamate; EC50, 0.035 +/- 0.003 versus 0.057 +/- 0.006 microM; P < .05) or thromboxane A2/prostaglandin H2 receptor blocker (1 microM SQ 29548; EC50 0.029 +/- 0.002 versus 0.057 +/- 0.006 microM; P < .05) but had no effect on the arteries from the control rats. Endothelium-independent relaxations to sodium nitroprusside were not effected by vitamin E deprivation. Arachidonic acid increased tension twofold more in the arteries from the vitamin E-deprived rats compared with the control rats (at 1 microM; 0.43 +/- 0.05 versus 0.23 +/- 0.03 mN/mm; P < .05). The enhanced vasoconstriction was blunted, and the group difference was eliminated by a cyclooxygenase inhibitor (0.15 +/- 0.02 versus 0.43 +/- 0.05 mN/mm, P < .05) or a thromboxane A2/prostaglandin H2 receptor blocker (0.17 +/- 0.04 versus 0.43 +/- 0.05 mN/mm, P < .05). Prostaglandin endoperoxide synthase expression, determined by Western immunoblotting on aortas from the same rats, was increased in the vitamin E-deprived rats (3.14 +/- 0.8 versus 1.06 +/- 0.4 fmol/ng DNA, P < .05). In summary, mesenteric arteries from the vitamin E-deprived rats demonstrated altered endothelium-dependent responses that were in part due to a cyclooxygenase-dependent vasoconstrictor binding to the thromboxane A2/prostaglandin H2 receptor. In the aorta, there was an associative increase in the expression of prostaglandin endoperoxide synthase. We speculate that, in some vascular diseases, increased lipid peroxidation may influence endothelium-dependent vascular function by modulating the cyclooxygenase pathway of arachidonate metabolism.