Endothelium-derived relaxing factor

Biological Activities of Paeonol in Cardiovascular Diseases: A Review

Paeonol is a naturally existing bioactive compound found in the root bark of Paeonia suffruticosa and it is traditionally used in Chinese medicine for the prevention and management of cardiovascular diseases. To date, a great deal of studies has been reported on the pharmacological effects of paeonol and its mechanisms of action in various diseases and conditions. In this review, the underlying mechanism of action of paeonol in cardiovascular disease has been elucidated. Recent studies have revealed that paeonol treatment improved endothelium injury, demoted inflammation, ameliorated oxidative stress, suppressed vascular smooth muscle cell proliferation, and repressed platelet activation. Paeonol has been reported to effectively protect the cardiovascular system either employed alone or in combination with other traditional medicines, thus, signifying it could be a hypothetically alternative or complementary atherosclerosis treatment. This review summarizes the biological and pharmacological activities of paeonol in the treatment of cardiovascular diseases and its associated underlying mechanisms for a better insight for future clinical practices.

Gemfibrozil derivatives as activators of soluble guanylyl cyclase - A structure-activity study

Previous studies demonstrated that anti-hyperlipidemic drug gemfibrozil acts as NO- and heme-independent activator of NO receptor soluble guanylyl cyclase. A series of new gemfibrozil derivatives were synthesized and evaluated for sGC activation. The structure-activity relationship study identified the positions in gemfibrozil's scaffold that are detrimental for sGC activation and those that are amendable for optimizing modifications. Compared with gemfibrozil, compounds 7c and 15b were more potent activators of cGMP-forming activity of purified sGC and exhibited enhanced relaxation of preconstricted mouse thoracic aorta rings. These studies established the overall framework needed for futher improvement of sGC activators based on gemfibrozil scaffold.

Regulation of smooth muscle contractility by the epithelium in rat tracheas: role of prostaglandin E2 induced by the neurotransmitter acetylcholine

Background

Previous studies have suggested the involvement of epithelium in modulating the contractility of neighboring smooth muscle cells. However, the mechanism underlying epithelium-derived relaxation in airways remains largely unclear. This study aimed to investigate the mechanism underlying epithelium-dependent smooth muscle relaxation mediated by neurotransmitters.

Methods

The contractile tension of Sprague-Dawley (SD) rat tracheal rings were measured using a mechanical recording system. Intracellular Ca²⁺ level was measured using a Ca²⁺ fluorescent probe Fluo-3 AM, and the fluorescence signal was recorded by a laser scanning confocal imaging system. The prostaglandin E₂ (PGE₂) content was measured using an enzyme-linked immunosorbent assay kit.

Results

We observed that the neurotransmitter acetylcholine (ACh) restrained the electric field stimulation (EFS)-induced contraction in the intact but not epithelium-denuded rat tracheal rings. After inhibiting the muscarinic ACh receptor (mAChR) or cyclooxygenase (COX), a critical enzyme in prostaglandin synthesis, the relaxant effect of ACh was attenuated. Exogenous PGE₂ showed a similar inhibitory effect on the EFS-evoked contraction of tracheal rings. Moreover, ACh triggered phospholipase C (PLC)-coupled Ca²⁺ release from intracellular Ca²⁺ stores and stimulated COX-dependent PGE₂ production in primary cultured rat tracheal epithelial cells.

Conclusions

Collectively, this study demonstrated that ACh induced rat tracheal smooth muscle relaxation by promoting PGE₂ release from tracheal epithelium, which might provide valuable insights into the cross-talk among neurons, epithelial cells and neighboring smooth muscle cells in airways.

Protein disulfide isomerase regulation by nitric oxide maintains vascular quiescence and controls thrombus formation

Essentials Nitric oxide synthesis controls protein disulfide isomerase (PDI) function. Nitric oxide (NO) modulation of PDI controls endothelial thrombogenicity. S-nitrosylated PDI inhibits platelet function and thrombosis. Nitric oxide maintains vascular quiescence in part through inhibition of PDI. SUMMARY: Background Protein disulfide isomerase (PDI) plays an essential role in thrombus formation, and PDI inhibition is being evaluated clinically as a novel anticoagulant strategy. However, little is known about the regulation of PDI in the vasculature. Thiols within the catalytic motif of PDI are essential for its role in thrombosis. These same thiols bind nitric oxide (NO), which is a potent regulator of vessel function. To determine whether regulation of PDI represents a mechanism by which NO controls vascular quiescence, we evaluated the effect of NO on PDI function in endothelial cells and platelets, and thrombus formation in vivo. Aim To assess the effect of S-nitrosylation on the regulation of PDI and other thiol isomerases in the vasculature. Methods and results The role of endogenous NO in PDI activity was evaluated by incubating endothelium with an NO scavenger, which resulted in exposure of free thiols, increased thiol isomerase activity, and enhanced thrombin generation on the cell membrane. Conversely, exposure of endothelium to NO+ carriers or elevation of endogenous NO levels by induction of NO synthesis resulted in S-nitrosylation of PDI and decreased surface thiol reductase activity. S-nitrosylation of platelet PDI inhibited its reductase activity, and S-nitrosylated PDI interfered with platelet aggregation, α-granule release, and thrombin generation on platelets. S-nitrosylated PDI also blocked laser-induced thrombus formation when infused into mice. S-nitrosylated ERp5 and ERp57 were found to have similar inhibitory activity. Conclusions These studies identify NO as a critical regulator of vascular PDI, and show that regulation of PDI function is an important mechanism by which NO maintains vascular quiescence.

Inhibition of nitric oxide synthase unmasks vigorous vasoconstriction in established pulmonary arterial hypertension

It is widely accepted that impaired bioavailability of endothelial nitric oxide (NO) plays a critical role in the pathophysiology of pulmonary arterial hypertension (PAH). However, there are published data that show that relatively many PAH patients respond favorably to acetylcholine‐induced pulmonary vasodilation during their follow‐up period, when diverse stages of the disorder are included. We hypothesized that NO bioavailability varies depending on the progression of PAH. Adult rats were exposed to the VEGF receptor blocker Sugen5416 and 3 weeks of hypoxia followed by return to normoxia for various additional weeks. All rats developed increased right ventricular systolic pressure (RVSP) and occlusive lesion formation at 1, 3, 5, and 8 weeks after the Sugen5416 injection. Acute NO synthase blockade did not change the elevated RVSP at the 1‐week time point, while it further increased RVSP markedly at the 3‐, 5‐, and 8‐week time points, leading to death in all rats tested at 8 weeks. Acetylcholine caused significant reduction in RVSP at the 8‐week but not the 1‐week time point, whereas sodium nitroprusside decreased the pressure similarly at both time points. Increased NO‐mediated cGMP production was found in lungs from the 8‐week but not the 1‐week time point. In conclusion, despite its initial impairment, NO bioavailability is restored and endogenous NO plays a critical protective role by counteracting severe pulmonary vasoconstriction in established stages of PAH in the Sugen5416/hypoxia/normoxia‐exposed rats. Our results provide solid pharmacological evidence for a major contribution of a NO‐suppressed vasoconstrictor component in the pathophysiology of established PAH.

Viscoelastic dynamic arterial response

BACKGROUND

Arteries undergo large deformations under applied intraluminal pressure and may exhibit small hysteresis due to creep or relaxation process. The mechanical response of arteries depends, among others, on their topology along the arterial tree. Viscoelasticity of arterial tissues, which is the topic investigated in this study, is mainly a characteristic mechanical response of arteries that are located away from the heart and have increased smooth muscle cells content.

METHODS

The arterial wall viscosity is simulated by adopting a generalized Maxwell model and the method of internal variables, as proposed by Bonet and Holzapfel et al. The total stresses consist of elastic long-term stresses and viscoelastic stresses, requiring an iterative procedure for their calculation. The cross-section of the artery is modeled as a circular ring, consisting of a single homogenized layer, under a time-varying blood pressure. Two different loading approximations for the aortic pressure vs time are considered. A novel numerical method is developed in order to solve the controlling integro-differential equation.

RESULTS

A large number of numerical investigations are performed and typical response time-profiles are presented in pictorial form. Results suggest that the viscoelastic arterial response is mainly affected by the ratio of the relaxation time to the characteristic time of the response and by the pressure-time approximation. Numerical examples, based on data available in the literature, are conducted.

CONCLUSIONS

The investigation presented in this study reveals the effect of each material parameter on the viscoelastic arterial response. Thus, a better understanding of the behavior of viscoelastic arteries is achieved.

Arterial Flow Enhancement by Impulse Compression

Preliminary observations of rapid relief of ischemic rest pain following appli cation of a foot impulse compression device prompted this study to quantify its immediate effects.

Blood flow was calculated by means of a duplex ultrasound imager interfaced with a Doppler spectrum analyzer.

Twelve normal subjects and 10 patients with peripheral vascular disease (mean Doppler ankle/brachial systolic pressure index = 0.62 (range 0.33-0.74) were studied. Mean resting blood flow ( SD) was not significantly different in the two groups: 55.6 24.0 in normal subjects and 48.3 29.8 in the arteriopaths (p = > 0.1). During five minutes of pump application in a 45-degree foot-down position, mean popliteal blood flow increased by 93% in normal subjects (p < 0.0001) and 84 % in peripheral vascular patients (p < 0.03); there was no change in the opposite limb. In 5 normal subjects a "placebo" device produced no significant change in flow (p >0.1).

In 4 patients with vascular disease lying supine, impulse pumping produced no significant increase in popliteal blood flow.

It is suggested that the hyperemic effect may be explained by the liberation of endothelial-derived relaxing factor (EDRF), a powerful relaxant of vascular smooth muscle, produced in response to sudden pressure changes (hemodynamic shear-stress) within the venous system.

The dependence of nitric oxide synthase inhibition caused by cigarette smoking extract on the cellular aging of bovine aortic endothelial cells

OBJECTIVES

Cigarette smoking had been recorded as the main cause of impaired endothelium- dependent vasodilation in smokers by reducing nitric oxide (NO), a production of endothelial nitric oxide synthase (eNOS). However, the mechanism of NO impairment via eNOS activity is unclear until now. In this study, cell passage is suggested to be a relevant factor to eNOS expression under cigarette smoking stress.

METHODS

Bovine aortic endothelial cells (BAECs) were chosen as the research subject with passages ranking from 6 to 9 (6P to 9P). After exposure of cigarette smoking extract (CSE) solution, MTT assay and Western blot method were performed to check the cell viability as well as eNOS protein concentration. In these experiments, four concentrations of CSE at 0.5, 1, 2, and 4% were selected for treatment.

RESULTS

Our results showed that cells almost died at 4% of CSE. Besides, eNOS protein mass had a linear decrease under the increase of CSE concentration. In addition, the effect of CSE on eNOS expression was dissimilar between different passages.

CONCLUSIONS

This study indicated that CSE had effect on both cell viability and eNOS expression. Besides, a reduction in protein mass was matched with the decrease of cell viability due to CSE tress. Last but not least, the response of eNOS protein to different concentration of CSE at different passages was disparate, making the hypothesis about cell passage related inhibition of eNOS caused by CSE solution.

Vitamin B₁₂ derivatives as activators of soluble guanylyl cyclase

Various newly prepared and previously known vitamin B₁₂ derivatives have been studied as potential soluble guanylyl cyclase (sGC) activators. All compounds tested were found to activate the sGC enzyme, although to differing extents. The best results were obtained with the derivatives synthesized from c-lactone and possessing aliphatic amides in the c- and d-positions.

Exhaled nitric oxide (FENO) in non-pulmonary diseases

Exhaled nitric oxide (F(E)NO) represents the only exhaled biomarker that has reached clinical practice even in primary care settings, due to the non-invasiveness of its assessment and ease of repeat measurements, even in patients with severe airflow obstruction. While F(E)NO has been suggested as a readily determined biomarker that can aid in the diagnosis and management of asthma, its potential role in pathophysiology of non-pulmonary diseases is less clear and therefore remains to be established. The purpose of the present review is to highlight the current literature investigating the use of F(E)NO in the diagnosis and management of non-pulmonary diseases.

Molecular mechanisms of pulmonary hypertension

The pathogenesis of pulmonary arterial hypertension (PAH) is complex, involving multiple modulating genes and environmental factors. Multifactorial impairment of the physiologic balance can lead to vasoconstriction, vascular smooth muscle cell and endothelial cell proliferation/fibrosis, inflammation, remodeling and in-situ thrombosis. These are the likely mechanisms that lead to narrowing of the vessel followed by progressive increase in pulmonary vascular resistance and the clinical manifestations of pulmonary hypertension. Subsequently, major goal of the therapy is to avoid acute pulmonary vasoconstriction, halt the progression of vascular remodeling, and reverse the early vascular remodeling if possible. Recently published data addressing certain molecular mechanisms for pathogenesis of PAH have led to the successful therapeutic interventions. This review will focus on the common and critical molecular pathways including genetic basis of the development of PAH that on the whole may be new targets for therapeutic interventions.

Effect of chronic renal failure on the purinergic responses of corpus cavernosal smooth muscle in rabbits

OBJECTIVE

To examine purinergic relaxation responses in chronic renal failure (CRF) in an experimental rabbit model, and thus evaluate the possible involvement of the purinergic system in erectile dysfunction with CRF.

MATERIALS AND METHODS

The relaxant effects of ATP were measured in strips of corpus cavernosum smooth muscle taken from control and CRF rabbits. CRF was induced in New Zealand white rabbits as previously described. Penises were excised from CRF rabbits 4 weeks after inducing uraemia. In an organ bath the strips from controls and CRF rabbit corpus cavernosum were pre-contracted with phenylephrine and increasing doses of adenosine and ATP added.

RESULTS

In the pre-contracted rabbit cavernosal tissue the relaxations induced by adenosine and ATP were unchanged in CRF.

CONCLUSION

The lack of any relaxant effect of adenosine or ATP on the relaxation of cavernosal smooth muscle in rabbits with CRF might be because the relaxant effects of these agents are endothelium-independent and the endothelial purinergic receptor density was unchanged in CRF.

The effects of intermittent pneumatic compression on the arterial and venous system of the lower limb: a review

A better understanding of lower limb haemodynamics and the effects of intermittent pneumatic compression on the lower limb has led to an increasing awareness of the potential value of intermittent pneumatic compression in both venous and arterial disease. Intermittent pneumatic compression can be used in both the primary and secondary care settings, with its advantages being further enhanced by excellent patient compliance and very low rate of complications. Intermittent pneumatic compression has a proven role in the prophylaxis of deep vein thrombosis and there is some evidence that it is a useful adjunct in the management of venous ulcer disease. With laboratory and more recent clinical studies demonstrating augmentation of arterial inflow with intermittent pneumatic compression, its use in arterial diseases is being increasingly explored. Further studies are needed to define the precise role of intermittent pneumatic compression in arterial disease but any treatment regimen which reduces the need for referral or intervention in the claudicant or critically ischaemic limb will be a valuable addition to those managing arterial disease.

Chronic ethanol consumption impairs adrenoceptor- and purinoceptor-mediated relaxations of isolated rat detrusor smooth muscle

OBJECTIVE

To investigate the effects of chronic ethanol consumption on the reactivity of detrusor smooth muscle.

MATERIALS AND METHODS

Eight male rats received ethanol (7.2% v/v) in a modified liquid diet for 4 weeks. Two control groups were assessed; eight rats in one group were fed sucrose and received a liquid diet, and 12 rats in the second group received standard rat chow and water for 4 weeks. The reactivity of detrusor smooth muscle strips from ethanol-fed animals and control animals was evaluated in organ chambers.

RESULTS

The relaxation response elicited by isoprenaline or adenosine was unaffected in the both control groups while it was significantly inhibited, with decreased maximum responses and pD2 values, in the ethanol-fed group. Contractile responses of detrusor smooth muscle to carbachol or 80 mmol/L KCl and relaxant responses to papaverine were similar in the control groups and the ethanol-fed group. There was no change in agonist potency among the groups.

CONCLUSION

Chronic ethanol consumption impairs beta-adrenoceptor- and purinoceptor-mediated relaxation but not cholinoceptor-mediated contraction of the rat detrusor smooth muscle. Thus, it appears that different regulatory mechanisms are involved in ethanol-induced alterations in beta-adrenergic, purinergic and muscarinic receptors in detrusor strip.

Myocardial ischemia due to coronary artery spasm during dobutamine stress echocardiography

Dobutamine stress echocardiography (DSE) is a useful and safe provocation test for myocardial ischemia. Until now, the test has been focused only on the organic lesion in the coronary artery, and positive DSE has indicated the presence of significant fixed coronary artery stenosis. The aim of the present study is to examine whether myocardial ischemia due to coronary spasm is induced by dobutamine. We performed DSE on 51 patients with coronary spastic angina but without significant fixed coronary artery stenosis. All patients had anginal attacks at rest with ST elevation on the electrocardiogram (variant angina). Coronary spasm was induced by intracoronary injection of acetylcholine, and no fixed coronary artery stenosis was documented on angiograms in all patients. DSE was performed with intravenous dobutamine infusion with an incremental doses of 5, 10, 20, 30, and 40 microg/kg/min every 5 minutes. Of the 51 patients, 7 patients showed asynergy with ST elevation. All 7 patients (13.7%) had chest pain during asynergy, and both chest pain and electrocardiographic changes were preceded by asynergy. These findings indicate that dobutamine can provoke coronary spasm in some patients with coronary spastic angina. When DSE is performed to evaluate coronary artery disease, not only fixed coronary stenosis, but also coronary spasm should be considered as a genesis of asynergy.

Effects of chronic unilateral internal pudendal arterial occlusion on reactivity of isolated corpus cavernosum strips from rabbits

An animal model was developed to elucidate the effect of chronic obstruction of the internal pudendal artery on the responsiveness of the corpus cavernosum. In male albino rabbits, the internal pudendal artery was chronically ligated unilaterally with a silk tie and the occlusion was maintained for 1 month. The control group was sham-operated. The reactivity of corpus cavernosum tissue from the ligated animals and the control animals was studied in organ chambers. Unilateral chronic ligation of the internal pudendal artery caused an impaired contractile response to alpha-adrenoceptor stimulation with decreased Em and pD2 values and an impaired relaxant response to electrical field stimulation but resulted in a marked increase in the endothelium-dependent relaxant response to carbachol with an increased pD2 value. However chronic obstruction of the pudendal artery had no effect on adenosine-, papaverine- and sodium nitroprusside-induced relaxant responses, and there was no change in agonist potency. These data indicate that altered penile hemodynamics have an effect on the reactivity of the corpus cavernosum and may contribute to the etiology of impotence.

Endothelium-dependent vasodilation in well-developed coronary collateral vessels

We examined endothelium-dependent vasodilator responses in well-developed coronary collateral vessels. Collateral vessels and size-matched normal epicardial coronary arteries were isolated from canine hearts 6 months after a hollow plug had been introduced into the left anterior descending coronary artery (LAD) to stimulate collateral vessel growth. Vessel segments were isolated and studied in organ chambers. After preconstriction with prostaglandin F2 alpha, (PGF2 alpha) responses to the endothelium-dependent vasodilators, acetylcholine (ACh), substance P, and bradykinin (BK), as well as the endothelium-independent vasodilator nitroglycerin (NTG), were measured. The maximum relaxation to ACh was greater in collateral vessels (129 +/- 3.6% of the preconstricted tension) than in normal vessels (110 +/- 6.2%, p < 0.001), although the EC50 value for ACh was not significantly different between collateral and normal vessels. Collateral vessels demonstrated sensitivity to BK similar to that of normal vessels, but the maximal vasodilation achieved was greater in collaterals (138 +/- 4.6% of preconstricted tension) than in normal vessels (108 +/- 5.0%, p < 0.05). Both substance P and NTG produced dose-related relaxation that was similar in collateral vessels and normal arteries. These findings demonstrate that endothelium-dependent relaxation is intact in well-developed coronary collateral vessels.

Exercise-induced vasodilation in forearm circulation of normal subjects and patients with congestive heart failure: role of endothelium-derived nitric oxide

OBJECTIVES

This study was undertaken to investigate the role of endothelium-derived nitric oxide in the regulation of forearm blood flow during exercise in normal subjects and patients with congestive heart failure.

BACKGROUND

Nitric oxide-mediated vasodilation in response to muscarinic stimulation is impaired in the peripheral circulation of patients with congestive heart failure. Whether nitric oxide-mediated vasodilation during exercise is also impaired in patients with congestive heart failure is unknown.

METHODS

Forearm blood flows (ml/min per 100 ml) were determined during rhythmic hand grip exercise at 15%, 30% and 45% of maximal voluntary contraction by venous occlusion plethysmography before and after regional inhibition of nitric oxide synthesis with administration of L-NG-monomethylarginine (L-NMMA) in the brachial artery of 17 patients with congestive heart failure (mean age 49 years, mean left ventricular ejection fraction 0.22) and 10 age-matched normal subjects.

RESULTS

Before administration of L-NMMA in the brachial artery, forearm blood flows in patients with congestive heart failure during rhythmic hand grip exercise at 15%, 30% and 45% of maximal voluntary contraction were slightly but not significantly lower than that of normal subjects ([mean +/- SE] 6.8 +/- 1.0, 8.5 +/- 1.0 and 12.9 +/- 1.7 ml/min per 100 ml, respectively, in patients with congestive heart failure vs. 6.6 +/- 1.2, 11.6 +/- 1.9 and 16.2 +/- 1.9 ml/min per 100 ml, respectively, in normal subjects, p = NS). After administration of L-NMMA in the brachial artery, forearm blood flows in normal subjects significantly decreased by 10% to 21% during hand grip exercise but did not change during exercise in patients with congestive heart failure.

CONCLUSIONS

Regional inhibition of nitric oxide synthase with administration of L-NMMA in the brachial artery significantly decreased forearm blood flows during rhythmic hand grip exercise in normal subjects but not in patients with congestive heart failure. These findings suggest that nitric oxide-mediated vasodilation during submaximal exercise is impaired in the forearm circulation of patients with congestive heart failure.

Provocation of coronary spasm by dobutamine stress echocardiography in a patient with angiographically minimal coronary artery disease

Dobutamine stress echocardiography (DSE) has been widely used for the noninvasive diagnosis of obstructive coronary artery disease. The ST-segment elevation during DSE has been reported as an infrequent event, caused by old myocardial infarction and/or critical coronary narrowings. The patient presented here was a 35-year-old man with a recent history of nonexertional chest pain. He had hypercholesterolemia and a history of heavy smoking as risk factors. The patient developed ST-segment elevation with chest pain during 40 mcg/min dobutamine infusion for the stress echocardiographic examination. Subsequent coronary angiograms revealed only mild coronary atherosclerosis. It is speculated that coronary spasm occurred in this patient as a paradoxical response to increased coronary blood flow with dobutamine administration.

Intermittent calf and foot compression increases lower extremity blood flow

PURPOSE

Although foot compression increases foot skin perfusion and calf compression increases popliteal artery blood flow, these compression techniques have not been evaluated in combination. The purpose of this study was to evaluate whether calf and foot compression applied separately and simultaneously increase popliteal artery blood flow and/or foot skin perfusion, and to assess the relative merits of compression in patients with superficial femoral artery occlusion.

METHODS

Twenty-two legs from 12 normal volunteers with ankle/brachial indices (ABIs) > 0.96, and 10 legs from 7 claudicator patients with angiographically documented superficial femoral artery (SFA) occlusion and patent popliteal arteries with ABIs < 0.8 were studied in the sitting position. Calf and foot cuffs connected to a rapidly inflating and deflating timed-pressure pump (Art-Assist-AA 1000; ACI Medical Inc., San Marcos, California) were applied to the subject in the sitting position. Skin blood flow of the great toe was measured with a laser doppler (Laserflo model BPM 403A; TSI Inc., St. Paul, Minnesota), and popliteal artery blood flow was measured using duplex ultrasonography (ATL-Ultramark 9; Advanced Tech Laboratory, Bothell, Washington). Foot and calf compression was applied separately and simultaneously at 120 mm Hg pressure, with a 10-second inflation and 20-second deflation cycle. Popliteal artery blood flow and foot skin perfusion were recorded and the mean of 6 cycles calculated.

RESULTS

Precompression popliteal artery blood flow (mL/min) for volunteers was 38.86 +/- 3.94, and for patients was 86.30 +/- 14.55 (P = 0.001). Precompression foot skin perfusion (mL/min/ 100/g tissue) for volunteers was 1.67 +/- 0.29, and for patients was 4.00 +/- 0.92 (P = 0.01). With the application of calf, foot, and simultaneous calf and foot compression, the popliteal artery blood flow increased in volunteers by 124%, 54%, and 173%, respectively, and in patients by 76%, 13%, and 50%. Foot skin perfusion increased in volunteers by 260%, 500%, and 328%, respectively, and in patients by 116%, 246%, and 188%. Relative increases in popliteal artery blood flow and foot skin perfusion were higher in volunteers compared with patients during compression; however, the absolute values for foot skin perfusion and popliteal artery blood flow were consistently higher in patients.

CONCLUSIONS

Measured in the sitting position, the resting popliteal artery blood flow and foot skin perfusion are greater in patients with SFA occlusion compared with normal volunteers. Following compression, popliteal artery blood flow and foot skin perfusion increased in both groups, but relatively more in volunteers. Increases in popliteal artery blood flow are significantly higher with calf compression than with foot compression for both groups. A patent SFA allows for additive increases in popliteal artery blood flow with simultaneous foot and calf compression in normal persons, whereas this is not observed in patients. However, the increases in foot skin perfusion in patients with an occluded SFA parallel the increases shown in normal volunteers, with separate and simultaneous foot and calf compression.

Diffuse disorder of coronary artery vasomotility in patients with coronary spastic angina. Hyperreactivity to the constrictor effects of acetylcholine and the dilator effects of nitroglycerin

OBJECTIVES

We examined the vasomotility of the entire epicardial coronary artery system in patients with and without coronary spastic angina.

BACKGROUND

The coronary arteries of patients with variant angina are hyperreactive to diverse constrictor stimuli. It is unclear whether the abnormal responses to constrictive or dilative stimuli, or both, result from a localized or diffuse disorder in the coronary artery tree.

METHODS

Coronary artery diameter responses to intracoronary acetylcholine and nitroglycerin were examined at the proximal, middle and distal segments of three principal coronary arteries in 36 patients with coronary spastic angina without significant stenosis and in 12 young (< or = 30 years old) and 20 older control subjects (> 30 years old) with normal coronary arteriographic findings. In 10 patients with significant coronary stenosis, the responses of the prestenotic segments were also examined.

RESULTS

In patients with coronary spastic angina, coronary spasm was induced in 23 left anterior descending, 13 left circumflex and 17 right coronary arteries by acetylcholine. Multivessel spasm was observed in 15 patients. Acetylcholine had a dilator effect on most segments in young control subjects and a mild constrictor effect in older control subjects and in patients with significant stenosis. Comparison of the responses to acetylcholine among groups demonstrated that the constrictor response of the artery with spasm was enhanced significantly and diffusely. That of the artery without spasm also tended to be enhanced. Coronary artery diameters after nitroglycerin did not differ in any segment among patients with coronary spastic angina and both control groups. In patients with coronary spastic angina, nitroglycerin significantly enhanced dilation in all segments of the artery with spasm compared with that observed in both control groups and in most segments of the artery without spasm. Patients with significant coronary stenosis had a reduced response compared with that in control subjects.

CONCLUSIONS

Hyperreactive responses not only to the constrictor effects of acetylcholine, but also the dilator effects of nitroglycerin were detected diffusely in the epicardial coronary arteries of patients with coronary spastic angina. This finding indicates that a diffuse, not localized, disorder in vasomotility is involved in the pathogenesis of coronary spastic angina.

Isoflurane attenuates cAMP-mediated vasodilation in rat microvessels

BACKGROUND

Endothelium-dependent vasodilation mediated by cGMP is known to be attenuated by the inhalational anesthetic isoflurane. The present study examines the effect of isoflurane on beta-adrenergic and cAMP-mediated vasodilation.

METHODS AND RESULTS

Fifty-three subepicardial coronary arteries (diameter, 103 +/- 13 microns) from Wistar rats were studied in vitro in a pressurized (40 mm Hg), no-flow state with use of optical density video detection system. After preconstriction of vessels with the thromboxane A2 analogue U46619 10(-6) mol/L, concentration response curves to the nonselective beta-adrenergic agonist isoproterenol, the Gs protein activator sodium fluoride, the adenylate cyclase activator forskolin, the cAMP analogue 8-Br-cAMP, or the phosphodiesterase inhibitor RO20-1724 were obtained either in the presence of absence (control) of 2% isoflurane. Relaxations to all the agents tested were significantly reduced in the presence of isoflurane compared with controls.

CONCLUSIONS

Isoflurane attenuates cAMP-mediated vasodilation. The impairment appears to be distal to adenylate cyclase and is not due to enhancement of cAMP phosphodiesterase.

Role of nitric oxide in anaphylactic shock

Nitric oxide, synthesized from the guanidino group of L-arginine by nitric oxide synthase, has an important role in pathophysiological changes associated with anaphylaxis. Nitric oxide production due to activation of constitutive nitric oxide synthase is detected using a nitric oxide-selective electrode in anaphylactic rabbits in vivo. A nitric oxide synthase inhibitor attenuates hypotension and hemoconcentration and decreases venous return but does not improve cardiac depression. Nitric oxide functionally antagonizes the effects of vasoconstrictors released by anaphylaxis in vitro. In animals pretreated with a nitric oxide synthase inhibitor, the cardiac output falls significantly, although venous return is increased. Pulmonary resistance is significantly increased with a nitric oxide synthase inhibitor, and L-arginine attenuates the bronchospasm. These findings suggest that production of nitric oxide may reduce the pathophysiologic changes, except for vasodilatation, associated with anaphylaxis.

Quantitative assessment of coronary vasoreactivity in humans in vivo. Importance of baseline vasomotor tone in atherosclerosis

BACKGROUND

Disturbances in vasomotor tone are closely linked to the development of atherosclerosis and play an integral part in the pathophysiology of myocardial ischemia in patients with coronary artery disease. Currently, evaluation of coronary vasomotor tone relies on assessment of luminal changes in response to vasoactive stimuli by quantitative angiography. Assessment of luminal changes, however, may be misleading because of the effects of geometric magnification induced by atherosclerotic wall thickening and differences in basal tone, which may obscure potential effects of vasoactive stimuli.

METHODS AND RESULTS

Combining angiographic measurements of luminal changes with measurements of coronary wall architecture determined by intracoronary ultrasound, we calculated absolute coronary arterial vasomotor tone in 34 patients with angiographically normal or "minimally diseased" coronary arteries. Epicardial artery vasodilator capacity in response to intracoronary nitroglycerin decreased significantly with increasing atherosclerotic wall thickening. An inverse relation existed between local atherosclerotic plaque load and nitroglycerin-induced changes in vasomotor tone (r = -.65, P < .0001) regardless of potential systematically operative factors. At the same time, basal vasomotor tone significantly decreased with increasing local atherosclerotic wall thickening (r = -.38, P = .004). The vasomotor effects of acetylcholine, an endothelium-dependent vasodilator, were inversely related to wall thickening only in segments with very minor degrees of atherosclerosis, whereas no such relation was observed for epicardial artery segments with more advanced atherosclerotic wall thickening. In these segments, however, vasoreactivity to acetylcholine was closely correlated with basal vasomotor tone (r = -.62, P = .0002).

CONCLUSIONS

Atherosclerosis is associated with impairment of the vasodilator response to both nitroglycerin and acetylcholine in epicardial arteries in vivo. Basal vasomotor tone appears to be the primary determinant of the altered coronary vasoreactivity in response to vasoactive stimuli.

Long-term cigarette smoking impairs endothelium-dependent coronary arterial vasodilator function

BACKGROUND

Smoking is a primary risk factor for coronary and peripheral vascular disease. Because the endothelium is a principal target for the effects of risk factors early in the pathogenesis of atherosclerosis, we investigated whether long-term smoking is associated with impaired endothelial vasodilator function of epicardial conductance vessels regardless of the presence or absence of atherosclerotic lesions.

METHODS AND RESULTS

Using quantitative coronary angiography, we measured epicardial artery diameter at baseline, after maximal increases in coronary blood flow that caused flow-mediated dilation (which is strictly endothelium dependent), and after intracoronary injection of nitroglycerin (an endothelium-independent dilator) in 96 patients. Endothelium-dependent, flow-mediated dilation was significantly (P < .0001) blunted in smokers (n = 46) compared with non-smokers (n = 50). The ratio of flow-dependent dilation to nitroglycerin-induced dilation was significantly (P < .001) lower in smokers (0.34 +/- 0.32) compared with nonsmokers (0.59 +/- 0.23), indicating that the blunted dilator response to increased blood flow was out of proportion to the mildly impaired dilator response to nitroglycerin in smokers. In the presence of angiographically visible atherosclerosis, flow-dependent dilation was essentially absent (3.0 +/- 6.5%) in smokers. Multivariate analysis revealed that luminal irregularities by angiography (P < .0001) and smoking (P < .001) were the only variables to be independently associated with a reduced flow-dependent dilator response of epicardial arteries. Intracoronary ultrasound demonstrated that flow-dependent dilation progressively decreased with increasing atherosclerotic plaque load (r = -.82, P < .0001; n = 24). However, over the entire range of wall thickening, segments from smokers exhibited a significantly (P < .01) impaired flow-dependent dilator response compared with those of nonsmokers.

CONCLUSIONS

Long-term cigarette smoking is associated with impaired endothelium-dependent coronary vasodilation regardless of the presence or absence of coronary atherosclerotic lesions.

Nitric oxide: its identity and role in blood pressure control

In response to biochemical factors like catecholamines, bradykinins, histamine and physical factors like shear stress, endothelial cells release a non prostanoid factor, called endothelium derived relaxing factor (EDRF), which relaxes vascular smooth muscle. Since this discovery in 1980, many additional agents have been shown to stimulate release of EDRF from endothelium. Biological and chemical evidence has supported the proposal that EDRF is actually nitric oxide (NO). Research on the synthesis, inhibition and physiological roles of nitric oxide (NO) has led to studies of its involvement in blood pressure homeostasis and immune functions.

Reduced expression of endothelial nitric oxide synthase in the lungs of patients with pulmonary hypertension

BACKGROUND

Pulmonary hypertension is characterized by abnormal thickening of the pulmonary arteries and increased pulmonary vascular resistance. Nitric oxide is a potent endothelium-derived vasorelaxant substance and an inhibitor of smooth-muscle-cell growth. Nitric oxide is produced in various cell types by the action of an enzyme, nitric oxide synthase. We compared the expression of endothelial nitric oxide synthase in the lungs of control subjects with that in the lungs of patients with pulmonary hypertension.

METHODS

We investigated the expression of endothelial nitric oxide synthase by histochemical and immunohistochemical analysis, in situ hybridization, and Northern blot analysis in the lungs of 22 patients with plexogenic pulmonary arteriopathy (arteriopathy of grades 4 through 6), 24 patients with secondary pulmonary hypertension (arteriopathy of grades 1 through 3), and 23 control subjects.

RESULTS

In the lungs of the control subjects, nitric oxide synthase was expressed at a high level in the vascular endothelium of all types of vessels and in the pulmonary epithelium. In contrast, little or no expression of the enzyme was found in the vascular endothelium of pulmonary arteries with severe histologic abnormalities (i.e., plexiform lesions) in patients with pulmonary hypertension. The intensity of the enzyme immunoreactivity correlated inversely with the severity of histologic changes. There was an inverse correlation between the arterial expression of the enzyme and total pulmonary resistance in patients with plexogenic pulmonary arteriopathy (r = -0.766, P = 0.004).

CONCLUSIONS

Pulmonary hypertension is associated with diminished expression of endothelial nitric oxide synthase. It is possible that decreased expression of nitric oxide synthase may contribute to pulmonary vasoconstriction and to the excessive growth of the tunica media observed in this disease.

The role of endothelium-derived vasoactive substances in the pathophysiology of exercise intolerance in patients with congestive heart failure

The vascular endothelium releases vasoactive substances that appear to play an important role in the normal regulation of peripheral vasomotor tone. Nitric oxide, endothelins, prostaglandins, and other endothelium-derived vasodilating and vasoconstricting factors are released by the vascular endothelium in response to a diverse array of hormonal, pharmacologic, chemical, and physical stimuli. Shear stress, produced by pulsatile blood flow at the endothelial cell luminal surface, alters endothelial production of several endothelium-derived vasoactive substances, which may contribute to regional regulation of skeletal muscle blood flow during exercise. Abnormal vascular endothelium function has been shown in both experimental and clinical heart failure. Preliminary data suggest that abnormalities of endothelial function may contribute to increased peripheral vasomotor tone during exercise in patients with congestive heart failure.

Effects of non-insulin dependent diabetes mellitus on the reactivity of human internal mammary artery and human saphenous vein

The effects of non-insulin-dependent diabetes mellitus (NIDDM) were investigated on the reactivity of human internal mammary artery (IMA) and saphenous vein (SV) rings obtained from coronary artery patients (CAP) undergoing coronary artery bypass surgery. In the presence of endothelium, the maximal contractile response and sensitivity (pD2) of IMA or SV to NA and ET-1 significantly increased in CAP with NIDDM relative to CAP only (controls). Removal of the endothelium markedly and significantly enhanced the maximal contractile response and sensitivity of IMA or SV to NA in CAP only, but did not induce a significant alteration in CAP with NIDDM compared to that in the presence of endothelium. The maximal contractile response and sensitivity of diabetic vessels with or without endothelium to NA were similar to values of corresponding vessels without endothelium obtained from nondiabetic CAP. The maximum contractions developed by NA or ET-1 were much greater in SV than that determinated in the IMA. Acetylcholine (ACh) and histamine produced endothelium-dependent relaxations in precontracted IMA and these effects of ACh and histamine significantly decreased in CAP with NIDDM. Endothelium-dependent relaxations stimulated by ACh were more pronounced in IMA than that determinated in the SV. In precontracted SV, histamine induced marked contractions that were significantly greater in CAP with NIDDM relative to CAP only. Endothelium-independent relaxations of vessels to sodium nitroprusside (SNP) were not influenced by NIDDM. Data indicate that NIDDM causes a deficit in the vasorelaxant activity of endothelium, leading to an increase in contractility of human IMA and SV. Data also suggest that IMA can be a better choice of graft for coronary occlusive disease than SV, specially in patients with NIDDM.

Control of coronary blood flow by autacoids

Coronary flow and thus myocardial perfusion is regulated by myogenic, metabolic, humoral and neuro-hormonal factors which closely interact with local autacoids released from the endothelial lining of the coronary bed. In a number of disease states an impaired synthesis and release of autacoids decisively limit the overall capacity of coronary regulation and adaptation of myocardial perfusion to increased metabolic demands. The important factors for these control mechanisms are analyzed and reviewed in this article.

Endothelium, coronary vasodilation, and organic nitrates

Recent investigations have suggested that the vascular endothelium is an active participant in the regulation of arterial tone and blood flow. In a state of health, the endothelium contributes to hemodynamic equilibrium; however, it rapidly becomes dysfunctional in hypercholesterolemia and diabetes mellitus or with exposure to the stress of hypertension or long-term smoking. Among the deficits observed during endothelial dysfunction is a reduction in the synthesis and release or an excessive degradation of EDRF. This potent vasorelaxant is derived from the amino acid L-arginine and has been characterized as NO or a closely related substance. EDRF relaxes vascular smooth muscle by activating guanylate cyclase. A deficiency in the activity of EDRF may be the mechanism of diminished coronary vasodilation in patients with ischemic heart disease. Organic nitrates, which are metabolized to NO or S-nitrosothiol at the cellular level, are often used in the management of myocardial ischemia; they also induce vasodilation by activating guanylate cyclase. The similarities between organic nitrates and endogenous EDRF and their interactions are discussed in this review.

Lack of role for nitric oxide (NO) in the selective destabilization of endothelial NO synthase mRNA by tumor necrosis factor-alpha

The constitutive expression of endothelial nitric oxide (NO) synthase (cNOS) is essential for the physiological regulation of vascular tone and structure. The mechanism of downregulation of steady state cNOS mRNA in human umbilical vein endothelial cells exposed to tumor necrosis factor-alpha (TNF-alpha) was investigated by using Northern blot analysis of total cellular RNA. TNF-alpha produced a dose- and time-dependent decrease in cNOS mRNA expression that was near maximal at 10 U/mL and 6 hours of exposure, respectively. In contrast, steady state expression of endothelin-1 and plasminogen activator inhibitor-1 (PAI-1) mRNA was upregulated by TNF-alpha. The pharmacological generation of NO using sodium nitroprusside (10 mumol/L) and S-nitroso-acetylpenicillamine (100 to 400 mumol/L) had no effect on cNOS mRNA levels, and TNF-alpha-induced downregulation of cNOS was not prevented by coincubation with the inhibitors of NO synthesis N omega-nitro-L-arginine methyl ester (1 mmol/L) and NG-monomethyl L-arginine (10 mmol/L). Under control conditions, cNOS and PAI-1 mRNA were stable after treatment with actinomycin D for periods greater than 24 hours, whereas endothelin-1 message was rapidly degraded (half-life, < 1 hour). Pretreatment with TNF-alpha (30 U/mL) selectively reduced that half-life of cNOS mRNA to less than 12 hours without altering the stability of PAI-1 message. TNF-alpha-induced destabilization of cNOS mRNA could be partially prevented by coincubation with cycloheximide (1 mumol/L) but was not reproduced by addition of sodium nitroprusside.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelium-dependent vasodilation of peripheral conduit arteries in patients with heart failure

Endothelium-dependent vasodilation of peripheral resistance vessels is abnormal in patients with heart failure, but there are little in vivo data on endothelium-dependent vasodilation of peripheral conduit vessels. This study assessed endothelium-dependent vasodilation of forearm conduit and resistance vessels in normal subjects and patients with heart failure. The effects of intraarterial endothelium-dependent and endothelium-independent vasodilators on both forearm conduit (brachial artery) and resistance vessels were assessed in 9 patients with New York Heart Association class II-III heart failure and 11 normal subjects of similar age. Brachial artery diameter was measured by two-dimensional, moderate-frequency (8 MHz) ultrasound, and forearm blood flow was measured by strain gauge plethysmography. The endothelium-dependent vasodilator, methacholine (0.3 and 1.5 micrograms/min), increased brachial artery diameter by 7.6 +/- 1.3% and 12.2 +/- 1.5% in normal subjects as compared to 6.9 +/- 2.1% and 10.4 +/- 2.4% in patients with heart failure (P = NS, normal vs heart failure). The endothelium-independent vasodilator, nitroglycerin (0.15 microgram), also produced similar increases in brachial artery diameter in the two groups (8.2 +/- 1.3% in normal subjects vs 11.1 +/- 1.4% in patients with heart failure, P = NS). In contrast, forearm blood flow responses to methacholine were significantly (P < .05) greater in normal subjects (4.1 +/- 0.5 and 9.2 +/- 1.4 mL/min/100 mL forearm volume) than in patients with heart failure (2.0 +/- 0.8 and 5.1 +/- 1.3 mL/min/100 mL forearm volume). Forearm blood flow responses to the endothelium-independent vasodilator, sodium nitroprusside, were similar between the two groups. This study suggests that endothelium-dependent and endothelium-independent vasodilation of the brachial artery is not impaired in patients with class II-III heart failure. This finding contrasts with abnormal endothelium-dependent vasodilation of forearm resistance vessels. These data suggest that there are regional differences in endothelial function in patients with heart failure.

Enhancement of endothelium-dependent vasodilation by low-dose nitroglycerin in patients with congestive heart failure

BACKGROUND

Since organic nitroesters and endothelium-derived nitric oxide mediate vasodilation through a final common pathway, that is, by activation of soluble guanylate cyclase in vascular smooth muscle, nitroglycerin (NTG) could specifically enhance the endothelium-dependent vasodilatory response to acetylcholine (Ach) in patients with congestive heart failure (CHF) and endothelial cell dysfunction. Accordingly, the net effects of an intra-arterial infusion of NTG (10(-9) mol/L) on endothelium-dependent and endothelium-independent vasodilation were assessed in the forearm circulation of patients with CHF.

METHODS AND RESULTS

The forearm blood flow responses to intra-arterial administration of graded concentrations of Ach (10(-7) to 10(-5) mol/L) were determined by venous occlusion plethysmography (mL/min per 100 mL) in 18 patients with CHF and 5 age-matched normal subjects before and during intra-arterial infusion of NTG (10(-9) mol/L) for 20 minutes. In eight patients, the duration of the infusion of NTG (n = 5) or vehicle control solution (n = 3) was extended to 12 hours with measurement of the forearm blood flow responses to Ach at 20 minutes, 4 hours, and 12 hours. In five additional patients, forearm blood flow response to intra-arterial administration of two doses of phentolamine (0.05 and 0.5 mg) were determined before and during a 20-minute NTG infusion. Regional administration of NTG 10(-9) mol/L did not change resting forearm blood flow in either normal subjects or patients with CHF. Before administration of NTG 10(-9) mol/L, intra-arterial infusions of Ach 10(-7), 10(-5) and 10(-5) mol/L increased forearm blood flow to 14.7 +/- 6.2, 20.2 +/- 4.7, and 38.4 +/- 7.9 mL/min per 100 mL in normal subjects and to 4.1 +/- 0.8, 5.0 +/- 1.1, and 10.6 +/- 2.3 mL/min per 100 mL in patients with CHF. After administration of NTG 10(-9) mol/L for 20 minutes, the vasodilatory response to Ach significantly increased to 5.6 +/- 1.0, 6.9 +/- 1.6, and 17.7 +/- 3.4 mL/min per 100 mL in patients with CHF but did not change in normal subjects. The enhanced forearm blood flow responses to administration of Ach observed after 20 minutes of NTG administration in patients with CHF were sustained throughout a 12-hour NTG infusion. In contrast, regional administration of NTG did not change the vasodilatory responses to phentolamine.

CONCLUSIONS

NTG, when administered intra-arterially for 20 minutes at a dose that does not affect resting forearm blood flow, specifically increased the vasodilatory response to intra-arterial administration of Ach in patients with CHF but not in normal subjects. The vasodilatory response to Ach was consistently enhanced by low-dose NTG throughout a 12-hour period. The vasodilating effects of organic nitroesters on the peripheral vasculature of patients with CHF may result in part from an interaction with the vascular endothelium.

Assessment of endothelial modulation of coronary vasomotor tone: insights into a fundamental functional disturbance in vascular biology of atherosclerosis

The endothelium plays a major role in modulating vascular smooth muscle tone by synthesizing and metabolizing a number of vasoactive substances. Since the endothelium is both a target for and a mediator of vascular disease, functional alterations in coronary vascular reactivity due to endothelial dysfunction might play an important integral part in the clinical presentation of coronary artery disease. Recent advances in interventional techniques including intracoronary instrumentation by Doppler catheters to measure blood flow velocities and 2-D-ultrasound catheters to evaluate arterial wall architecture during coronary angiography provided the diagnostic tools to assess endothelial vasodilator function and its relation to atherosclerotic disease. The current weight of evidence suggests that disturbances of vasomotor function of epicardial conductance vessels are fundamental to the development of atherosclerosis, and impaired endothelial vasodilation is the predominant mechanism underlying inappropriate vasoconstriction in atherosclerosis. However, endothelial vasodilator dysfunction is not only confined to atherosclerotic epicardial vessels, but may also extend into the coronary microcirculation, which does not develop overt atherosclerotic lesions, but determines coronary blood flow in the absence of hemodynamically significant stenoses. The most important factors associated with impaired endothelium-mediated dilation of the coronary microcirculation are hypercholesterolemia and advanced age. With respect to the clinical presentation of coronary artery disease, endothelial vasodilator dysfunction appears to play a causative role for triggering myocardial ischemia in stable angina pectoris, to aggravate the sequelae of acute ischemic syndromes, and might be the primary underlying mechanism in some patients with syndrome X, whereas variant angina appears to be related to a hyperreactivity of the vascular smooth muscle layer. Thus, the assessment of endothelium-mediated modulation of coronary vasomotor tone in the clinical setting offers unique and important insights into mechanisms leading to ischemic manifestations of coronary artery disease.

Expression of endothelin-1 in the lungs of patients with pulmonary hypertension

BACKGROUND

Pulmonary hypertension is characterized by an increase in vascular tone or an abnormal proliferation of muscle cells in the walls of small pulmonary arteries. Endothelin-1 is a potent endothelium-derived vasoconstrictor peptide with important mitogenic properties. It has therefore been suggested that endothelin-1 may contribute to increases in pulmonary arterial tone or smooth-muscle proliferation in patients with pulmonary hypertension. We studied the sites and magnitude of endothelin-1 production in the lungs of patients with various causes of pulmonary hypertension.

METHODS

We studied the distribution of endothelin-1-like immunoreactivity (by immunocytochemical analysis) and endothelin-1 messenger RNA (by in situ hybridization) in lung specimens from 15 control subjects, 11 patients with plexogenic pulmonary arteriopathy (grades 4 through 6), and 17 patients with secondary pulmonary hypertension and pulmonary arteriopathy of grades 1 through 3.

RESULTS

In the controls, endothelin-1-like immunoreactivity was rarely seen in vascular endothelial cells. In the patients with pulmonary hypertension, endothelin-1-like immunoreactivity was abundant, predominantly in endothelial cells of pulmonary arteries with medial thickening and intimal fibrosis. Likewise, endothelin-1 messenger RNA was increased in the patients with pulmonary hypertension and was expressed primarily at sites of endothelin-1-like immunoreactivity. There was a strong correlation between the intensity of endothelin-1-like immunoreactivity and pulmonary vascular resistance in the patients with plexogenic pulmonary arteriopathy, but not in those with secondary pulmonary hypertension.

CONCLUSIONS

Pulmonary hypertension is associated with the increased expression of endothelin-1 in vascular endothelial cells, suggesting that the local production of endothelin-1 may contribute to the vascular abnormalities associated with this disorder.

SIN-1 reduces platelet adhesion and platelet thrombus formation in a porcine model of balloon angioplasty

BACKGROUND

Nitric oxide inhibits platelet adhesion and platelet aggregation in vivo. In this study, we investigated the effects of the nitric oxide donor SIN-1 on platelet adhesion and platelet-thrombus formation following experimental angioplasty.

METHODS AND RESULTS

Bilateral carotid angioplasty was performed in 20 anesthetized pigs. Animals received either SIN-1 (3-morpholino-sydnonimine; 10 micrograms/kg/min; n = 8) or placebo (n = 8) before and during angioplasty. An additional control group of pigs received trimetaphan (n = 4), which induced hemodynamic changes similar to those that followed treatment with SIN-1. Platelet deposition was quantified by the injection of autologous 111In-labeled platelets. SIN-1 reduced platelet deposition after deep arterial injury compared with placebo (mean +/- SEM, 10.870 +/- 2.415 versus 40.326 +/- 9.889 platelets x 10(6)/cm2, p < 0.05). SIN-1 reduced platelet adhesion after superficial injury compared with both placebo and trimetaphan (2.231 +/- 0.333 versus 5.278 +/- 0.606 versus 5.022 +/- 1.136 platelets x 10(6)/cm2, respectively; p < 0.005). Scanning electron microscopy confirmed that platelets were deposited in the form of an adherent monolayer following superficial endothelial denudation and were reduced in number following treatment with SIN-1. The effects of SIN-1 on platelet function were associated with a significant increase in platelet cyclic GMP concentration from baseline (3.15 +/- 0.88 versus 1.58 +/- 0.73 pmol/10(9) platelets, p < 0.005).

CONCLUSIONS

SIN-1 reduces platelet adhesion and platelet-thrombus formation following experimental angioplasty. The antiadhesive effects of SIN-1 are independent of changes in systemic hemodynamics. These results imply that the administration of a nitric oxide donor may prove effective in modifying the pathophysiological response to angioplasty injury.

Effects of adenosine on canine penile erection

We investigated the hemodynamic effects of intracavernous injection of adenosine on canine penile erection. In all ten dogs studied, adenosine induced a dose-dependent increase of intracavernous pressure (ICP). Adenosine (0.67 to 15 micrograms/kg., B.W.) increased arterial blood flow by 83 to 325 percent above baseline levels and also increased venous resistance, which resulted in a full erection (ICP = 80 to 140 cm. H2O) for one to 7 minutes. The repeatability of the adenosine effect was confirmed in eight dogs. We found that adenosine, by virtue of its smooth muscle relaxation properties, can induce a dose-dependent increase of ICP and cause a full erection in dogs.

The push, the pull and the periphery

If the failing left ventricle could be given an effective push, other approaches to the treatment of heart failure would not be needed. We have inotropes only for short-term parenteral use. We have no safe inotrope for chronic oral use. The effect of digitalis is only feeble and the phosphodiesterase inhibitors seem to increase mortality from sudden death. Diuretics are dramatic for acute pulmonary oedema and the mainstay for chronic fluid retention but do not improve the pump and by reducing blood volume stimulate the renin angiotensin system to vasoconstriction, further fluid retention and hypokalaemia. Nitrates drop pre-load without reducing blood volume but tolerance is a problem and stroke volume does not increase. Reduction of afterload helps the failing ventricle to empty, the pull and output increases. The angiotensin converting enzyme inhibitors (ACEI) are now the cornerstone of heart failure treatment, reducing mortality in severe heart failure (CONSENSUS) and superior to standard vasodilator therapy (V-HeFT-2) at improving the survival of patients with mild to moderate heart failure. ACEI can reduce the incidence of ventricular ectopy and probably do this through improving left ventricular function, from decreasing sympathetic tone, reducing myocardial oxygen demand or increasing serum potassium but ACEI did not diminish the incidence of sudden death in the SOLVD trial despite reducing mortality. Disappointingly little improvement in exercise tolerance and persistence of chronic fatigue in heart failure concentrated attention on the periphery.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelial vasomotor regulation in health and disease

The purpose of this review is to provide the anaesthetists with a comprehensive update on the endothelial-cell control of local blood flow. This single cell layer was originally thought to represent only a passive barrier. It is now evident that it plays an active role in a broad variety of biological functions. Since the discovery of the endothelial-derived relaxing factor (EDRF), it has been the subject of a considerable amount of research. It is established that EDRF is secreted continuously at a basal state and that many physical stimuli as well as vasoactive substances can modulate its secretion. Evidence presented indicates that the endogenous vasodilatation produced by EDRF is similar to that of the exogenous nitrovasodilator nitroglycerin and nitroprusside (i.e., nitric oxide). Aside from EDRF, the endothelium produces other vasodilating as well as vasoconstricting factors. A review of the physiology of the endothelium regarding the local control of blood flow is provided along with its influence upon several pathophysiological states. Also included is an overview of the influence of anaesthetic agents on endothelial function. These findings linking vasomotor control to endothelial function will help to explain pathophysiological process and may lead to new therapeutic modalities.

Effect of cell density on endothelin release from endothelial cells and phosphoramidon dependent inhibition

The modulation of endothelin (ET) release from endothelial cells was investigated as a function of cell density. The present study examined the release of ET from bovine pulmonary artery endothelial cells (BPAEC) and bovine aortic endothelial cells (BAEC) at various cell densities, as well as the effects of phosphoramidon, thiorphan and pepstatin on ET release at different densities. ET release from BPAEC and BAEC decreased as cell density increased. This cell density effect was not observed with prostacyclin release from either BPAEC or BAEC. Phosphoramidon (1 mM) inhibited ET release at every density examined for both BPAEC and BAEC. Thiorphan (1 mM) inhibited ET release from BPAEC weakly at low density and had no effect on ET release from BAEC. Pepstatin (1 mM) slightly inhibited ET release in BPAEC at the lowest density and had no effect at any other cell density for either cell type. These protease inhibitors had no effect on cell viability as determined by trypan blue exclusion and a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide conversion assay. This study supports the concept that ET release is modulated by endothelial cell density. In addition, these data demonstrate that phosphoramidon, which presumably inhibits the endothelin converting enzyme, can inhibit ET release over a range of cell densities without affecting cell viability.

Impaired endothelium-dependent and independent vasodilation in patients with type 2 (non-insulin-dependent) diabetes mellitus

The endothelium plays a pivotal role in modulating the reactivity of vascular smooth muscle through the formation of several vasoactive substances. We examined the effects of endothelium-dependent and independent vasodilators on forearm blood flow in 29 patients with Type 2 (non-insulin-dependent) diabetes mellitus and in 21 control subjects, using venous occlusion plethysmography. Via a brachial artery cannula, increasing amounts of acetylcholine and glyceryl trinitrate were infused in doses of 60, 120, 180 and 240 mmol per min and 3, 6 and 9 nmol per min respectively. NG monomethyl-L-arginine, a stereospecific inhibitor of endothelium derived relaxing factor, was infused to inhibit basal and stimulated release of this dilator substance. Reactive hyperaemic forearm blood flow did not differ between groups. Forearm blood flow responses to each dose of acetylcholine were significantly greater in control than diabetic subjects (p less than 0.01 for all doses). NG monomethyl-L-arginine attenuated forearm blood flow from maximal stimulated values when responses were compared with the natural decline to acetylcholine in forearm flow in both control and diabetic subjects (p less than 0.05 for both groups), but had no effect on basal blood flow responses. Forearm blood flow responses to each dose of glyceryl trinitrate were significantly greater in control than diabetic subjects (p less than 0.05 for all). These data provide evidence for endothelial and smooth muscle dysfunction in diabetes which may have important therapeutic implications.

Endothelium-mediated relaxation in transplanted aorta

This study compares the vasodilating effect of endothelium-derived relaxing factors (EDRFs) in free arterial grafts with that in their normal control vessels. The infrarenal aorta of Sprague-Dawley rats was transplanted into the same position in other inbred recipient rats. A Krebs buffer solution (4 degrees C) served as the preservation solution. The ischemic time for the grafts (n = 8) was 42 +/- 1 minutes. Two grafts were studied after 3 days and six grafts, after 60 days. Ring segments were cut from all vessels, and isometric contractions were recorded in organ baths. The vessel segments were constricted with noradrenaline, a thromboxane A2 mimic (U-46619), or prostaglandin F2 alpha. Concentration-response curves with acetylcholine, which was used as the endothelium-stimulating substance causing release of EDRFs, were obtained. The patency of the grafts was 100%. Acetylcholine induced relaxation in all vessel segments with intact intima, whereas no relaxation was seen when the endothelium was manually removed. No significant differences were found between the grafts and the normal control vessels. Histology of the 60-day grafts showed elastomuscular arteries without intimal thickening and a media consisting of eight to ten muscle layers interrupted by five to six elastic lamellae. Scanning electron microscopy showed no major differences between normal endothelium and the endothelium of 3-day or 60-day grafts. This study indicates that free elastomuscular arterial grafts, in which the morphology of the intima is preserved, will retain their full ability to release EDRFs.

Impaired vascular reactivity following angioplasty is mainly due to endothelial injury

Vasoconstriction occurs frequently following coronary angioplasty and is implicated in the pathogenesis of abrupt closure and restenosis. Control of vasomotor tone is regulated in part directly by smooth muscle cells and indirectly through the endothelium. To study the mechanisms underlying vasoconstriction, the effect of angioplasty and endothelial denudation on endothelium-dependent and -independent relaxation was examined in 15 mongrel dogs. Percutaneous transluminal angioplasty and endothelial denudation of the right femoral artery were performed. Endothelial injury was assessed by adhesion of indium-111-labeled platelets. Endothelium-dependent and -independent relaxation were assessed using acetylcholine and nitroglycerin, respectively. Vessels precontracted with potassium chloride and exposed to acetylcholine showed impaired relaxation in both the angioplasty and denuded groups (angioplasty = 14 +/- 5%, denuded = 0 +/- 0%, normal = 73 +/- 12%; P less than 0.05 for both angioplasty and denuded compared to normal). Precontraction with phenylephrine yielded similar results (angioplasty = 16 +/- 8%, denuded = 4 +/- 2%, normal = 39 +/- 10%; P less than 0.05 only for denuded segment compared to normal). Segments precontracted with phenylephrine and exposed to nitroglycerin did not demonstrate impaired relaxation (angioplasty = 73 +/- 9%, denuded = 68 +/- 9%, normal = 71 +/- 7%, P = ns). Mean indium-111 counts were similar in both the angioplasty and denuded segments (2820 +/- 1481 and 2963 +/- 1228 counts/min/g, respectively) compared to a lower count in the normal segment (1514 +/- 956 counts/min/g). Thus, angioplasty produces significant vascular injury and impairment of vasodilator function, comparable to that caused by endothelial denudation alone. This implies that vasoconstriction seen following coronary angioplasty may be due to endothelial injury and the resultant loss of control of vasomotor tone.