Endothelial dysfunction: implications for therapy of cardiovascular diseases

Serum Metabolomics Study Based on LC-MS and Antihypertensive Effect of Uncaria on Spontaneously Hypertensive Rats

Our previous studies have shown that Uncaria has an important role in lowering blood pressure, but its intervention mechanism has not been clarified completely in the metabolic level. Therefore, in this study, a combination method of HPLC-TOF/MS-based metabolomics and multivariate statistical analyses was employed to explore the mechanism and evaluate the antihypertensive effect of Uncaria. Serum samples were analyzed and identified by HPLC-TOF/MS, while the acquired data was further processed by partial least squares discriminant analysis (PLS-DA) and orthogonal partial least squares discriminant analysis (OPLS-DA) to discover the perturbed metabolites. A clear cluster among the different groups was obtained, and 7 significantly changed potential biomarkers were screened out. These biomarkers were mainly associated with lipid metabolism (dihydroceramide, ceramide, PC, LysoPC, and TXA2) and vitamin and amino acids metabolism (nicotinamide riboside, 5-HTP). The result indicated that Uncaria could decrease the blood pressure effectively, partially by regulating the above biomarkers and metabolic pathways. Analyzing and verifying the specific biomarkers, further understanding of the therapeutic mechanism and antihypertensive effect of Uncaria was acquired. Metabolomics provided a new insight into estimate of the therapeutic effect and dissection of the potential mechanisms of traditional Chinese medicine (TCM) in treating hypertension.

The association between metabolic syndrome and vascular endothelial dysfunction in adolescents

The aim of this study was to investigate the association between metabolic syndrome (MS) and vascular endothelial cell dysfunction (ECD) in adolescents. Sixty obese pediatric inpatients at the General Hospital of Tianjin Medical University from February 2011 to February 2012 were included. Among these, 30 patients were obese and 30 patients were diagnosed with MS. Thirty healthy subjects were randomly selected as the control group. A series of indices, including height, body weight, waist circumference, hip circumference, waist/hip circumference and body mass index (BMI), as well as total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL) and high-density lipoprotein (HDL) levels were evaluated. von Willebrand factor (vWF) and plasminogen activator inhibitor-1 (PAI-1) levels were determined using an enzyme linked immunosorbent assay (ELISA). Correlation analysis between height, body weight, waist circumference, hip circumference, waist/hip circumference, BMI, TC, TG, LDL, HDL and PAI-1, as well as vWF was performed. Significant increases of vWF and PAI-1 levels were observed in the MS group compared with the control group (P<0.05). For the adolescents in the obese group, a significant increase of PAI-1 level was observed compared with the control group (P<0.05). No significant difference was observed between the vWF levels in the obese and control groups. PAI-1 was positively associated with BMI, waist circumference, waist/hip circumference, TC, TG, LDL, fasting plasma glucose (FPG), fasting insulin (FINS), systolic blood pressure (SBP) and diastolic blood pressure (DBP), respectively (P<0.05). In addition, PAI-1 was negatively associated with HDL levels (P<0.05). PAI-1 and vWF may be used as biomarkers for the diagnosis of ECD. ECD in individuals with MS may be associated with obesity, blood fat, blood sugar and blood pressure. FPG, TC and TG may be risk factors for ECD.

Acute effects of 5-methyltetrahydrofolate on endothelial function and asymmetric dimethylarginine in patients with chronic heart failure

BACKGROUND AND AIMS

Folic acid enhances endothelial function in vascular disease states but its effects in chronic heart failure (CHF) are largely unknown. We studied the acute effects of i.v. methyltetrahydrofolate (5MTHF), the active metabolite of folic acid, on endothelial function and asymmetric dimethylarginine (ADMA) in CHF patients.

METHODS AND RESULTS

Twenty two CHF patients and 22 controls received one of the following three-step infusions (1h per each step) in a randomized, parallel group, placebo-control study: (1) active treatment (saline, 5MTHF, and 5MTHF+the endothelial nitric oxide inhibitor N(G)-monomethyl l-arginine, LNMMA); or (2) placebo (salinex3). Endothelium-dependent vasodilatation was assessed by pulse-wave analysis (salbutamol-mediated changes in augmentation index, AIx). 5MTHF did not exert any significant effects on endothelium-dependent vasodilatation both in controls [DeltaAIx post-salbutamol baseline -7.6% (-24.8/-4.1) vs. 5MTHF -5.5% (-16.7/-3.6), medians and interquartile range, and CHF patients [-1.8% (-17.3/+1.3) vs. -2.4% (-3.8/-1.2)]. However, a significant reduction in ADMA concentrations was observed in both groups [controls baseline 0.68micromol/L (0.64/0.77) vs. 5MTHF 0.65 (0.57/0.74); CHF baseline 0.76 (0.63/0.82) vs. 5MTHF 0.69 (0.66/0.71), P=0.05 for both vs. baseline and placebo. These effects persisted during co-infusion with LNMMA.

CONCLUSION

5MTHF did not affect endothelial function but significantly reduced serum ADMA concentrations both in CHF patients and controls. This suggests a direct effect of 5MTHF on ADMA metabolism.

The metabolic syndrome and the risks of unfavourable outcome of pregnancy

A metabolikus szindróma jellemzői a hasi elhízás, a magas vérnyomás, az éhhomi glükóz és dyslipidaemia együttes előfordulása. A vizsgálat célja, hogy feltárja a metabolikus anyagcserezavar és egyes terhességi szövődmények kapcsolatát. Anyag és módszer: A releváns kódok alapján retrospektíve leválogatott digitális adatbázisból a 2005–2008 közötti vizsgált időszakban (4 év) a kórházi dokumentációkban 5869 várandós anya gondozási adataival rendelkeztek. Százhetvenkettő anya (2,9%) esetében a várandósságuk első harmadában a metabolikus tünetegyüttes jellemzői szerepeltek. Ezen betegek adatait részletesen megvizsgálták, feldolgozták és releváns adataikat a többi várandós hasonló dokumentációival összehasonlították. Eredmények: A metabolikus tünetegyüttes tüneteit mutató csoportban a koraszülési arány 15,1% (26/172) volt, míg a metabolikus szindrómától mentes esetekben az idő előtti születés csupán 11,7% volt [OR: 1,52 (95%-os CI: 0,996–2,33) p=0,051]. Az anyagcserezavarban érintettek csoportjában 32 anyánál intrauterin növekedési zavart észleltek, míg ezen tünetegyüttes nélküli esetekben ez csupán 3,6%-ban (205/5697) fordult elő [OR: 6,38 (95%-os CI: 4,24–9,61) p<0,001)]. A vizsgált csoportban 47 praeeclampsiával szövődött várandósságot észleltek (27,3%), szemben a beteganyaguk további részével, ahol a terhességi mérgezés előfordulása 4,7% volt [OR: 7,93 (95%-os CI: 5,54–11,33) p<0,001]. A metabolikus tünetegyüttesben szenvedők körében 67 (38,2%) olyan beteg volt, aki több mint egy, a betegségre jellemző szülészeti szövődményben szenvedett. A kontrollcsoportban ugyanez az arány 17,0%-nak adódott [OR: 3,11 (2,27–4,26) p<0,001]. A metabolikus szindróma által érintett csoportban csupán 47 (27,3%) olyan esetet találtak, akik várandósságuk és szülésük alatt tünetmentesek voltak, míg az 5697 anyából, akiknél az első terhességi harmadban a metabolikus tünetegyüttes jeleit nem észlelték, szignifikánsan kedvezőbb arányban (74,1%, 4220 várandós) voltak olyan anyák, akik minden szövődmény nélkül viselték várandósságukat [OR: 0,132 (0,09–0,18) p<0,001]. Következtetések: A metabolikus szindróma irodalmi adatok alapján és saját megfigyeléseik szerint is jelentős szerepet játszik a szövődményes várandósságok kialakulásában, elsősorban a gyulladásos faktorok és a fokozott trombóziskészség provokálásával. Számos irodalmi adat utal arra, hogy a metabolikus tünetegyüttes esetén a már a koncepció idején alkalmazott heparinkezelés eredményes lehet. 2007-ben prospektív vizsgálatot indítottak azzal a céllal, hogy megismerjék, vajon az alacsony molekulatömegű heparin megelőző célú kezelés, segít-e elkerülni ennek az anyagcserezavarnak a kedvezőtlen következményeit? Reményeik szerint a 2010-es évektől a heparinkezelés eredményeiről adatokkal rendelkeznek.

Sex-specific differences in chromosome-dependent regulation of vascular reactivity in female consomic rat strains from a SSxBN cross

High-throughput studies in the Medical College of Wisconsin Program for Genomic Applications (Physgen) were designed to link chromosomes with physiological function in consomic strains derived from a cross between Dahl salt-sensitive SS/JrHsdMcwi (SS) and Brown Norway normotensive BN/NHsdMcwi (BN) rats. The specific goal of the vascular protocol was to characterize the responses of aortic rings from these strains to vasoconstrictor and vasodilator stimuli (phenylephrine, acetylcholine, sodium nitroprusside, and bath hypoxia) to identify chromosomes that either increase or decrease vascular reactivity to these vasoactive stimuli. Because previous studies demonstrated sex-specific quantitative trait loci (QTLs) related to regulation of cardiovascular phenotypes in an F2 cross between the parental strains, males and females of each consomic strain were included in all experiments. As there were significant sex-specific differences in aortic sensitivity to vasoconstrictor and vasodilator stimuli compared with the parental SS strain, we report the results of the females separately from the males. There were also sex-specific differences in aortic ring sensitivity to these vasoactive stimuli in consomic strains that were fed a high-salt diet (4% NaCl) for 3 wk to evaluate salt-induced changes in vascular reactivity. Differences in genetic architecture could contribute to sex-specific differences in the development and expression of cardiovascular diseases via differential regulation and expression of genes. Our findings are the first to link physiological traits with specific chromosomes in female SS rats and support the idea that sex is an important environmental variable that plays a role in the expression and regulation of genes.

Vasorelaxant effects of icariin on isolated canine coronary artery

Owing to its cardiovascular therapeutical effects, icariin, a flavonoid isolated from Epimedii herba, is considered to be the major active constituent of Epimedii herba. The aim of this study is to investigate the effect of icariin on precontracted coronary artery isolated from canine. Coronary artery segments were isolated from normal anesthetized Beagle dogs and cut into 5-mm rings. The rings were mounted in an organ chamber and contracted by either 40 mM KCl or 10 microM PGF2alpha, and vasorelaxant tone to icariin was measured. Treatment of icariin could significantly produce a relaxation of precontracted coronary arterial rings with intact endothelium in a concentration-dependent manner. Comparatively, the vasorelaxation disappeared in denuded-endothelium rings. Furthermore, the vasorelaxant effect of icariin was blocked by Nomega-Nitro- L-arginine Methyl Ester (L-NAME), 1H-[1, 2, 4]-oxadiazolo [4, 3-a] quinoxalin-1-one (ODQ) but not by indomethacin and glibenclamide, respectively. Tetraethylammonium (TEA) could partly antagonize the vasorelaxant effect triggered by icariin. There was no significant gene expression difference of the endothelial nitric oxide synthase (eNOS) gene in coronary arterial rings among the different concentrations of icariin by RT-PCR, but the activity of eNOS was increased in a concentration-dependent manner after icariin exposure. These results suggest that icariin produces NO-dependent relaxation in the isolated canine coronary artery, and the possible mechanism is involved in the activation of eNOS protein and NO-cGMP pathway.

Icariin enhances endothelial nitric-oxide synthase expression on human endothelial cells in vitro

Icariin, a flavonoid isolated from Epimedii herba, is considered to be the major therapeutical constituent of E. herba. The aim of this study was to investigate the possible protective effects and to clarify the mechanism of icariin on endothelial cells in vitro. Incubation of human umbilical vein endothelial cells (HUVEC) derived EA. hy926 cells with icariin(0.1, 1, 10 micromol l(-1)) from 6 h to 72 h, then the production of NO was measured to evaluate the protective effects of icariin. RT-PCR was employed to confirm the mRNA expression of endothelial nitric oxide synthase (eNOS). Western blotting was used to evaluate the protein expression of eNOS. NO production was enhanced in a time- and concentration-dependent manner (P<0.05), which was well matched with the expression of eNOS mRNA (up to 2.4-fold) and protein (up to 2.5-fold) after long-term incubation with icariin in endothelial cells (P<0.05). Moreover, activated NF-kappaB was increased in EA. hy926 cells incubated with icariin for 24 h, in association with an increase in the expression of eNOS gene. In addition to its long-term effects on eNOS expression, icariin also enhanced the production of bioactive NO in the short-term (after a 5 min incubation, P<0.05). In concert with other effects, the protective effects of icariin on endothelial cells may contribute to the cardiovascular protective effects.

Effects of estrogen replacement with and without medroxyprogesterone acetate on brachial flow-mediated vasodilator responses in postmenopausal women with coronary artery disease

BACKGROUND

Hormone therapy has been shown to have no cardioprotective effect and may, in fact, be harmful in older postmenopausal women. Estrogen has been shown to enhance endothelial-dependent flow-mediated vasodilation (FMD) in healthy and younger women. The effect of estrogen on older and less healthy postmenopausal women with atherosclerosis is unclear.

METHODS

The Estrogen Replacement and Atherosclerosis trial randomized 309 postmenopausal women with established coronary atherosclerosis (mean, 65.8 years) to unopposed estrogen (conjugated estrogen, 0.625 mg), estrogen plus 2.5 mg medroxyprogesterone actate (MPA), or placebo. After mean of 3.2 years of follow-up, brachial FMD was measured using 2-dimensional ultrasound in women available for follow-up at 4 of the 5 clinic sites (n = 198).

RESULTS

The %FMD of the brachial artery was not statistically different in the placebo arm compared with either unopposed estrogen or estrogen + MPA arm in both the adjusted and the unadjusted models. Subsequent analysis combining the estrogen arm with the estrogen + MPA arm and comparing with the placebo arm was also not significant in both the adjusted and the unadjusted models. Similar results were obtained when analyses were limited to women who took >80% of the study medication over the course of the trial (n = 133).

CONCLUSION

An average of 3.2 years of treatment with unopposed estrogen or estrogen plus progestins did not result in significant improvements in endothelial vasodilation compared with placebo. This apparent absence of an effect on brachial artery endothelial function in older postmenopausal women with established coronary heart disease may help explain the lack of benefit of estrogen for secondary prevention of coronary heart disease.

Coronary artery disease and prevention of heart failure

Coronary artery disease is a major contributor to the progression of left ventricular systolic dysfunction and heart failure (HF). Recognizing that coronary artery disease is a leading cause of HF in the United States is critical to reducing mortality resulting from this condition. Although some patients may be candidates for mechanical revascularization to improve left ventricular function, all patients are candidates for aggressive secondary prevention strategies. This review discusses the prevalence of coronary artery disease, prognostic significance and pathophysiology, risk factor modifications, pharmacologic treatments, and the role of revascularization.

Evaluation of transcutaneous Doppler ultrasonography for the measurement of blood flow in the femoral artery of pigs

OBJECTIVE

To compare measurements of blood flow in the common femoral artery obtained by duplex Doppler ultrasonography (DDU) and a reference ultrasonic transit-time flow (TTF) method and to examine the impact of Doppler spectral waveform measurement techniques on volumetric estimates.

ANIMALS

5 healthy female pigs.

PROCEDURES

Femoral arterial blood flow was measured simultaneously in anesthetized pigs by use of a TTF probe (left femoral artery) and transcutaneous DDU (right femoral artery). A range of flow states was induced pharmacologically by using xylazine, bradykinin, dobutamine, and isoflurane. Volumetric blood flow was calculated from DDU waveforms, using the product of the flow velocity integral (FVI), the cross-sectional vessel area, and heart rate. Three calculations of FVI were obtained by manually tracing the Doppler spectral envelopes at the outer envelope, the modal, and the inner envelope of the spectral dispersion pattern. Data analysis included calculation of Pearson correlation coefficients and Bland-Altman limits of agreement.

RESULTS

Blood flow measured by DDU was more closely correlated with TTF measurements when the modal or inner envelope tracing method was used (r, 0.76 and 0.78; limits of agreement, -100 to 54.2 and -48.5 to 770 mL/min, respectively). Limits of agreement for the outer envelope tracing method were -238.5 to 64 mL/min.

CONCLUSIONS AND CLINICAL RELEVANCE

Transcutaneous DDU is a reliable noninvasive technique for measuring blood flow in the femoral artery of pigs over a range of flow states. Tracing the inner envelope of the Doppler spectral dispersion pattern provided the best estimate of blood flow in this study.

Growth hormone deficiency and vascular risk

The importance of growth hormone deficiency (GHD) in adult life has become more apparent over the last decade. As well as a distinct clinical syndrome there is a significant excess risk of cardiovascular disease. Although it is difficult to ascertain what part is played by the original pituitary disorder and the concomitant replacement hormonal therapies, there is clear evidence that GHD is associated with known cardiovascular risk factors such as body shape, lipid profile, insulin resistance, blood pressure, vessel wall morphology and haemostatic factors. Novel means of assessing vascular risk such as pulse wave velocity and flow-mediated dilatation can also estimate the risk without invasive procedures. The role of possible mediators of endothelial function such as nitric oxide and free radicals is being investigated further. Replacement of GH in GH-deficient patients leads to many effects on the above indices, some but not all of which are associated with reduced vascular risk. Long-term follow-up studies of morbidity and mortality are required for an accurate assessment of the beneficial effects of therapy.

A placebo-controlled study examining the effect of allopurinol on heart rate variability and dysrhythmia counts in chronic heart failure

AIMS

Allopurinol improves endothelial function in chronic heart failure by reducing oxidative stress. We wished to explore if such an effect would attenuate autonomic dysfunction in CHF in line with many other effective therapies in CHF.

METHODS

We performed a prospective, randomized, double-blind cross-over study in 16 patients with NYHA Class II-IV chronic heart failure (mean age 67 +/- 10 years, 13 male, comparing allopurinol (2 months) at a daily dose of 300 mg (if creatinine < 150 micromol l-1) or 100 mg (if creatinine > 150 micromol l-1) with matched placebo. Mean heart rate and dysrhythmia counts were recorded from 24 h Holter tapes at monthly intervals for 6 months. We assessed autonomic function using standard time domain heart rate variability parameters (HRV): SDNN, SDANN, SDNN index, rMSSD and TI.

RESULTS

Allopurinol had no significant effect on heart rate variability compared with placebo; the results are expressed as a difference in means +/- s.d. with 95% confidence interval (CI) between allopurinol and placebo: SDNN mean = 6.5 +/- 4.8 ms, P = 0.18 and 95% CI (-3.7, 17); TI mean = -2.1 +/- 1.4, P = 0.16 and 95% CI (-5.2, 0.8); SDANN mean = -2.8 +/- 7 ms, P = 0.68 and 95% CI (-18, 12); SDNNi mean = 2 +/- 6.6, P = 0.7 and 95% CI (-12, 16); RMSSD mean = -0.9 +/- 2, P = 0.68 and 95% CI (-5.6, 3.7). For mean heart rate the corresponding results were 0.9 +/- 1.4, P = 0.5 and 95% CI (-2, 3.8). Log 24 h ventricular ectopic counts (VEC) were 0.032 +/- 0.37, P = 0.7 and 95% CI (-0.1, 0.2). Patient compliance with study medication was good since allopurinol showed its expected effect of reducing plasma uric acid (P < 0.001).

CONCLUSIONS

Allopurinol at doses, which are known to reduce oxidative stress appear to have no significant effect on resting autonomic tone, as indicated by time domain heart rate variability or on dysrhythmia count in stable heart failure patients.

Workshop: endothelial cell dysfunction leading to diabetic nephropathy : focus on nitric oxide

Clinical manifestations of diabetic nephropathy are an expression of diabetic microangiopathy. This review revisits the previously proposed Steno hypothesis and advances our hypothesis that development of endothelial cell dysfunction represents a common pathophysiological pathway of diabetic complications. Specifically, the ability of glucose to scavenge nitric oxide is proposed as the initiation phase of endothelial dysfunction. Gradual accumulation of advanced glycated end products and induction of plasminogen activator inhibitor-1, resulting in the decreased expression of endothelial nitric oxide synthase and reduced generation of nitric oxide, are proposed to be pathophysiologically critical for the maintenance phase of endothelial dysfunction. The proposed conceptual shift toward the role of endothelial dysfunction in diabetic complications may provide new strategies for their prevention.

Effects of homocysteine on endothelial nitric oxide production

Hyperhomocysteinemia (HHCy) is an independent and graded cardiovascular risk factor. HHCy is prevalent in patients with chronic renal failure, contributing to the increased mortality rate. Controversy exists as to the effects of HHCy on nitric oxide (NO) production: it has been shown that HHCy both increases and suppresses it. We addressed this problem by using amperometric electrochemical NO detection with a porphyrinic microelectrode to study responses of endothelial cells incubated with homocysteine (Hcy) to the stimulation with bradykinin, calcium ionophore, or L-arginine. Twenty-four-hour preincubation with Hcy (10, 20, and 50 microM) resulted in a gradual decline in responsiveness of endothelial cells to the above stimuli. Hcy did not affect the expression of endothelial nitric oxide synthase (eNOS), but it stimulated formation of superoxide anions, as judged by fluorescence of dichlorofluorescein, and peroxynitrite, as detected by using immunoprecipitation and immunoblotting of proteins modified by tyrosine nitration. Hcy did not directly affect the ability of recombinant eNOS to generate NO, but oxidation of sulfhydryl groups in eNOS reduced its NO-generating activity. Addition of 5-methyltetrahydrofolate restored NO responses to all agonists tested but affected neither the expression of the enzyme nor formation of nitrotyrosine-modified proteins. In addition, a scavenger of peroxynitrite or a cell-permeant superoxide dismutase mimetic reversed the Hcy-induced suppression of NO production by endothelial cells. In conclusion, electrochemical detection of NO release from cultured endothelial cells demonstrated that concentrations of Hcy >20 microM produce a significant indirect suppression of eNOS activity without any discernible effects on its expression. Folates, superoxide ions, and peroxynitrite scavengers restore the NO-generating activity to eNOS, collectively suggesting that cellular redox state plays an important role in HCy-suppressed NO-generating function of this enzyme.

A pivotal role of nitric oxide in endothelial cell dysfunction

The functional role of the vascular endothelium is a subject of growing interest and appreciation. Some of the key functions of the endothelium are modulated by the activity and expression of endothelial nitric oxide synthase (eNOS), suggesting a role for this enzyme in endothelial dysfunction. Several well-known angiogenic stimulators exert their effect only in the presence of the functional eNOS. In this setting NO production is responsible for the scalar podokinetic cell motility, which is a prerequisite for the acquisition of vectorial movement when guidance cues are applied. The mode of this NO action appears to lie in the accelerated turnover of focal adhesions through the process of activation/inactivation of protein tyrosine phosphatases. Localization of eNOS to the caveolar domains, in the proximity of clustered beta1 integrins, provides an additional level of regulatory complexity through the modulation of caveolar dynamics and the state of caveolin oligomerization. Therefore, eNOS serves various important functions in the endothelium and is a putative target for therapeutic interventions.

Prevention of suboptimal beta-blocker treatment in patients with myocardial infarction

OBJECTIVE

To review the published data and clinical guidelines on the use of beta-blockers in myocardial infarctions (MIs) and contrast that with actual clinical practice.

DATA SOURCES

A MEDLINE search (January 1970-June 1999) was performed to identify all relevant articles. References from these articles were also evaluated for review if deemed important.

DATA SYNTHESIS

Intravenous and oral beta-blockers have been proven to improve outcomes in patients with MIs in numerous clinical trials. In current clinical practice, only 15% of MI patients receive intravenous beta-blockers and long-term beta-blocker therapy is used in <40% of patients without contraindications. However, they could be safely administered to 40% and 70% of these patients, respectively. Furthermore, most of these patients are receiving doses far below those found beneficial in clinical trials. Many of the real and perceived contraindications to beta-blockers are reviewed to allow the practitioner to identify patients who are incorrectly excluded from beta-blocker therapy. Also discussed are special clinical situations in which the benefits observed during clinical trials may not apply.

CONCLUSIONS

Beta-blockers are valuable drugs in the treatment of peri- and post-MI. In clinical practice, most patients are not treated or are inadequately treated with beta-blockers. Pharmacists should ensure that such patients actually have an absolute contraindication or unusual situation where therapy is not firmly indicated. Patients without absolute contraindications warrant titration to specific target doses or a target heart rate of 55-60 beats/min.

How to assess endothelial function in human blood vessels

This brief review discusses the ways, if and when available, to examine endothelium-dependent changes diameter in human blood vessels. It stresses the problems in ensuring proper matching between arteries (and veins) from different human sources. It briefly considers the evidence in vitro supporting the role of endothelium-derived nitric oxide, hyperpolarizing factor and contracting factors (including metabolites of arachidonic acid and endothelin). It emphasizes the difficulty in extrapolating observations obtained in isolated arteries (and veins) to the intact human circulation. The overall conclusion is that the interpretations derived from animal work apply to the human vasculature.