Release Of Endothelium-derived Relaxing Factor Research Articles

Pathogenic Mechanisms of Pulmonary Arterial Hypertension: Homeostasis Imbalance of Endothelium-Derived Relaxing and Contracting Factors.

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease. Sustained pulmonary vasoconstriction and concentric pulmonary vascular remodeling contribute to the elevated pulmonary vascular resistance and pulmonary artery pressure in PAH. Endothelial cells regulate vascular tension by producing endothelium-derived relaxing factors (EDRFs) and endothelium-derived contracting factors (EDCFs). Homeostasis of EDRF and EDCF production has been identified as a marker of the endothelium integrity. Impaired synthesis or release of EDRFs induces persistent vascular contraction and pulmonary artery remodeling, which subsequently leads to the development and progression of PAH. In this review, the authors summarize how EDRFs and EDCFs affect pulmonary vascular homeostasis, with special attention to the recently published novel mechanisms related to endothelial dysfunction in PAH and drugs associated with EDRFs and EDCFs.

Effects of Ruscus extract on muscarinic receptors: Is there a role for endothelium derived relaxing factors on macromolecular permeability protection and microvascular diameter changes?

Protective effects of Ruscus extract on macromolecular permeability depend on its capacity to stimulate muscarinic receptors on endothelial cells and induce the release of endothelium derived relaxing factors (EDRFs). To investigate if these effects depend only on activation of muscarinic receptors or if EDRFs release are also necessary. We have also investigated the participation of Ruscus extract on muscarinic-induced release of EDRFs on microvascular diameters. Hamsters were treated daily during two weeks with Ruscus extract (50, 150 and 450 mg/kg/day) and then macromolecular permeability induced by histamine and arteriolar and venular diameters after cyclooxygenase (COX) and nitric oxide synthase (NOS) inhibitors: indomethacin and Nω-Nitro-L-arginine (LNA), respectively applied topically at 10-8M, 10-6M and 10-4M were observed on the cheek pouch preparation. Ruscus extract decreased macromolecular permeability in a dose-dependent fashion and did not affect microvascular diameters. NOS and COX inhibitors enhanced its effect on microvascular permeability. NOS inhibition reduced arteriolar diameter and COX blocking decreased arteriolar and venular diameters at the lowest dose and increased them at higher doses of Ruscus extract. The protective effect of Ruscus extract on macromolecular permeability seems to be mediated only via muscarinic receptors. Muscarinic activation attenuated vasoconstrictive tone through cyclooxygenase-independent endothelium derived relaxing factors.

Contribution of Rho-kinase and Adenosine Monophosphate-Activated Protein Kinase Signaling Pathways to Endothelium-Derived Contracting Factors Responses.

Vascular tonus is controlled by endothelium-derived relaxing factor (EDRF), endothelium-derived hyperpolarizing factor (EDHF) and endothelium-derived contracting factor (EDCF) under physiological circumstances. In pathological conditions, impairment of endothelium-derived relaxation can be caused by both decrease in EDRF release and increase in EDCF release. The increase in EDCF is observed with diseases such as hypertension and diabetes. The contribution of Rho-kinase and activated protein kinase (AMPK), which have opposite effects, to the increased EDCF responses was investigated. Rho-kinases are the effectors of Rho which is one of the small guanosine triphosphate-binding proteins. They increase cytosolic Ca+2 concentration and cause vascular smooth muscle to contract, keeping myosin light chain (MLC) in phosphorylated state by affecting myosin phosphatase target subunit which dephosphorylates the MLC. The activities of Rho-kinases increase with the increase of EDCF function. AMPK is the energy sensor of the cell. It provides a vasculoprotective effect by causing endothelium-dependent and endothelium-independent relaxation in smooth muscle. In contrast to Rho-kinase pathway activity, AMPK pathway activity decreases with diseases in which the EDCF function increases. In cases such as diabetes and hypertension that endothelial function impairs toward vasocontraction, it is considered that evaluating Rho-kinase and AMPK pathways which mediate contraction and relaxation in vascular smooth muscle respectively, would provide clues on choosing therapeutic target for pathologies in which endothelial dysfunction is observed.

Endothelial Dysfunction in Renal Failure: Current Update

Endothelial dysfunction is principally characterized by impaired endothelium- dependent transduction mechanisms related to vascular relaxation, as an outcome of decreased release of endothelium-derived relaxing factors, mainly nitric oxide, as well as augmented oxidative stress, increased inflammation and predominance of vascular action produced by endothelium-derived contracting factors. Current data strongly suggest that pathological development of different types of kidney impairment with further progression to renal failure includes notable vascular changes associated with endothelial dysfunction. In accordance, this scientific field represents an advancing area of investigation, involving different biomarkers of endothelial dysfunction linked to renal impairment, as well as clinical findings with new information that can provide a more comprehensive understanding of the role of endothelial dysfunction in kidney disease. With regards to quoted facts, the aim of this article was to review the latest data related to endothelial dysfunction and renal failure by selection of relevant articles released from 2010 to 2015.

Developmental conditioning of endothelium-derived hyperpolarizing factor-mediated vasorelaxation.

Objectives:The endothelium maintains vascular homeostasis through the release of endothelium-derived relaxing factors (EDRF) and endothelium-derived hyperpolarization (EDH). The balance in EDH : EDRF is disturbed in cardiovascular disease and may also be susceptible to developmental conditioning through exposure to an adverse uterine environment to predispose to later risk of hypertension and vascular disease.Methods:Developmentally conditioned changes in EDH : EDRF signalling pathways were investigated in cremaster arterioles (18–32 μm diameter) and third-order mesenteric arteries of adult male mice offspring of dams fed either a fat-rich (high fat, HF, 45% energy from fat) or control (C, 10% energy from fat) diet. After weaning, offspring either continued on high fat or were placed on control diets to give four dietary groups (C/C, HF/C, C/HF, and HF/HF) and studied at 15 weeks of age.Results:EDH via intermediate (IKCa) and small (SKca) conductance calcium-activated potassium channels contributed less than 10% to arteriolar acetylcholine-induced relaxation in in-situ conditioned HF/C offspring compared with ∼60% in C/C (P < 0.01). The conditioned reduction in EDH signalling in HF/C offspring was reversed in offspring exposed to a high-fat diet both before and after weaning (HF/HF, 55%, P < 0.01 vs. HF/C). EDH signalling was unaffected in arterioles from C/HF offspring. The changes in EDH : EDRF were associated with altered endothelial cell expression and localization of IKCa channels.Conclusion:This is the first evidence that EDH-mediated microvascular relaxation is susceptible to an adverse developmental environment through down-regulation of the IKCa signalling pathway. Conditioned offspring exposed to a ‘second hit’ (HF/HF) exhibit adaptive vascular mechanisms to preserve dilator function.

Endothelial dysfunction and vascular disease - a 30th anniversary update.

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H2 O2 ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive Gi (e.g. responses to α2 -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive Gq (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H2 O2 ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Abstract 642: Wy14643 and Fenofibrate Reduce Acetylcholine-induced Contractions in Spontaneously Hypertensive Rat Aortae

Introduction and hypothesis: Hypertension is associated with endothelial dysfunction, which is defined as an imbalanced release of endothelium-derived relaxing factors (EDRF) and endothelium-derived contracting factors (EDCF). Oxidative stress contributes to endothelial dysfunction by increasing the production of EDCF. Research studies have demonstrated that peroxisome proliferator-activated receptor alpha agonists, Wy14643 (WY) and fenofibrate (FF), improve endothelial function. Therefore, we assessed the hypothesis that WY and FF inhibited acetylcholine-induced endothelium-dependent contractions through reduction of oxidative stress in aortae of spontaneously hypertensive rats (SHR). Method: Thoracic aortic rings, with and without endothelium, were isolated from 40-44 weeks old male SHR and their normotensive counterparts, Wistar Kyoto rats (WKY). They were suspended in organ chambers for isometric tension recording. Responses to the endothelium-dependent vasoactive agent, acetylcholine (10 -8 - 10 -4 M), and to the oxidizing agent, hydrogen peroxide (10 -8 - 10 -4 M), were examined in the presence of N ω -nitro-L-arginine methyl ester (L-NAME, 3*10 -4 M; nitric oxide synthase inhibitor). Results: Acetylcholine caused significantly greater contractions in aortic rings, with endothelium, of SHR than in those of WKY. The contraction was significantly inhibited by the combination of Tiron (10 -3 M; intracellular superoxide anion scavenger) and DETCA (10 -4 M; superoxide dismutase inhibitor), suggesting that the reactive oxygen species, hydrogen peroxide, was involved in vascular dysfunction in hypertension. Both WY (10 -5 M) and FF (10 -5 M) significantly inhibited contractions to acetylcholine in SHR aorta, suggesting that they may reduce the amount of hydrogen peroxide or inhibit its downstream signaling. Moreover, they inhibited contractions induced by hydrogen peroxide in SHR aortic rings with, but not in those without, endothelium, indicating that their inhibitory effect was endothelium-dependent. Conclusion: The peroxisome proliferator-activated receptor alpha agonists act on the endothelium to reduce acetylcholine-induced contractions that are mediated by hydrogen peroxide in aortae of hypertensive rats.

Cardiovascular Therapeutics Targets on the NO–sGC–cGMP Signaling Pathway: A Critical Overview

In a brief overview, in NO-sGC-cGMP signaling in a blood vessel, l-arginine is converted in the endothelium monolayer by the endothelial nitric oxide synthase (eNOS) to NO which diffuses into both the vessel lumen and the vessel wall, thereby activating soluble guanylate cyclase (sGC). Heme-dependent sGC stimulators and hem-independent sGC activators increase the cellular cGMP concentration via the direct activation of sGC, which results in both vasorelaxation and inhibition of platelet aggregation. Studies of the 90's definitively established the role of endothelium in all cardiovascular diseases, which were associated with endothelial dysfunction by impaired release of endothelium-derived relaxing factors with consequent risk of spasm and thrombosis. The rationale of this review is based on the fact that the discovery of NO changed the concepts of cardiovascular disease mechanisms. However, considering the jargon "from the bench to clinical practice" we concluded that a potential therapeutic revolution did not follow the pathophysiological revolution. The review is focused on general aspects without regard for advanced research aspects, and designed in two main groups: the NO/cGMP positive stimulators and blockers as "future and encouraging" new therapeutic drugs. The potential vasodilators include 1) NOS uncoupling; 2) NOS enhancers (AVE compounds); 3) NO donors (nitrovasodilators); 4) NO-independent activators (BAY compounds), and; 5) PDE5 inhibitors. The potential vasoconstrictors include 1) NOS-blockers (L-NAME, L-NMMA); 2) sGC-blockers (methylene blue), and; 3) PDEs. Few texts, selected by excellence and relevance, were crucial and considerably facilitated the elaboration of this text, in addition to our own experimental and clinical experience working on vasoplegic endothelium dysfunction.

Endothelium-dependent relaxation in response to ethanol in the porcine isolated pulmonary artery.

Many drugs cannot be dissolved in distilled water and so other solvents such as ethanol, dimethylsulphoxide and methanol are used. Because very little is known about the direct effects of these three solvents on the cardiovascular system, we have examined their effects on isolated pulmonary and coronary arteries from the pig. Increasing concentrations of ethanol, dimethylsulphoxide and methanol induced relaxation in porcine pulmonary (at 1.2% v/v, 59.9+/-9.0% (n =9), 55.9+/-9.0% (n =6) and 12.3+/-6.4% (n = 8), respectively, of U46619-induced tone) and coronary arteries (at 1.2% v/v, 69.9+/-7.1% (n = 10), 78.9+/-6.1% (n = 7) and 12.9+/-8.2% (n = 6) respectively, of U46619-induced tone). In the pulmonary arteries the relaxation in response to ethanol was found to be endothelium-dependent whereas the responses to dimethylsulphoxide and methanol were unaffected by removal of the endothelium. In the coronary arteries the relaxation to all three solvents was independent of the presence of the endothelium. Comparison of the sensitivity of the tissues to the solvents showed that ethanol and dimethylsulphoxide produced comparative responses in both the pulmonary and coronary arteries, whereas methanol was much less potent. The endothelium-dependent response to ethanol in the porcine pulmonary artery (maximum response, Emax, 67.1+/-9.3% of U46619-induced tone, n = 7) was attenuated by the cyclooxygenase inhibitor, flurbiprofen (Emax 31.9 +/- 12.0%, n=7), the nitric oxide synthase inhibitor, L-NAME (NG-nitro-L-arginine methyl ester; Emax 23.5+/-10.2%, n = 7)) and the combination of both inhibitors (Emax 18.3+/-7.8%, n = 7). The residual relaxatory response to ethanol was abolished, and converted into a contractile response, both by removal of the endothelium (at 1.7% v/v ethanol 27.3+/-11.5% of U46619-induced tone, n=7) and by the addition of a low concentration of KC1 (49.9-/+10.3%, n=6), suggesting the release of a non-prostanoid, non-nitric oxide factor from the endothelium. This response, however, was not attenuated by the cannabinoid receptor-antagonist SR141716A (N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-me thyl-1H-pyrazole-3-carboxamide HCL; 52.5-/+4.3% relaxation, n =8), suggesting that the factor released in this preparation by ethanol is not a cannabinoid. The results of this study indicate that many solvents commonly used in pharmacological experiments have pronounced vasoactive properties. Methanol might be the vehicle of choice, because it was the least active solvent, whereas high concentrations of ethanol might influence vascular function at both the level of the smooth muscle and the endothelium, with the action on the endothelium involving the release of endothelium-derived relaxing factors.

The Preservation of Functional Activity of Smooth Muscle and Endothelium in Pig Coronary Arteries after Storage at −190°C

Pig coronary arteries have been investigated in-vitro using fresh tissue or after storage at -190 C in foetal calf serum containing 1.8 M dimethyl sulphoxide. Attention was paid to modulation of contractile activity and endothelium-dependent relaxation. After cryopreservation of the arteries maximal contractile responses to both 5-hydroxytryptamine (5-HT) and prostaglandin F2 alpha (PGF2 alpha) were markedly reduced and the pD2 values for both agonists were slightly, but significantly, diminished. Nevertheless, 5-HT antagonism by ketanserin and pizotifen was unchanged. Endothelium-independent relaxant responses of precontracted arteries to isoprenaline, forskolin, 3-isobutyl-1-methylxanthine, nitroprusside, atriopeptin III and cromakalim were generally unchanged after storage. Mechanical removal of the endothelium by rubbing enhanced the contractile response to PGF2 alpha in both fresh and stored arteries to a similar extent. In addition, endothelium-dependent relaxant responses to both 5-HT and substance P were well maintained, suggesting release of endothelium-derived relaxing factor by the stored arteries. The evidence suggests that after cryopreservation of pig coronary arteries at -190 degrees C mechanisms of relaxation, in particular those which are endothelium-dependent, are well maintained.

New Molecular Mechanisms for Cardiovascular Disease: Contribution of Endothelium-Derived Hyperpolarizing Factor in the Regulation of Vasoconstriction in Peripheral Resistance Arteries

Endothelium regulates vascular tone via release of endothelium-derived relaxing factors (EDRF) including nitric oxide (NO), prostaglandin I₂ (PGI₂), and endothelium-derived hyperpolarizing factor (EDHF). The mesenteric vascular bed produces vascular resistance to develop blood pressure and regulate tissue blood flow that plays an important role in maintenance of systemic blood pressure. There is now strong evidence that in these small resistance arteries, EDHF plays a major role in the response to vasoactive substances and regulation of vascular tone. Pharmacological analysis to investigate the role of the vascular endothelium in the regulation of α₁-adrenoceptor agonist (methoxamine)-induced vasoconstriction in rat mesenteric vascular beds showed that vasoconstriction induced by continuous perfusion of methoxamine (7 µM), but not high KCl (60 mM), time-dependently decreased to 20% of the initial constriction. The time-dependent reduction of methoxamine-induced vasoconstriction was inhibited by endothelium removal, inhibitor of EDHF (30 mM KCl, K+-channel blockers), and gap-junction inhibitor, but not NO synthase inhibitor and cyclooxygenase inhibitor and ageing. These results suggest that vascular endothelium counteracts to normalize excess vasoconstriction of the mesenteric resistance arteries by releasing EDHF, which is associated with activation of multiple K+-channels and gap junction involvement and markedly decreases with ageing.

Endoplasmic Reticulum Stress and Microvascular Endothelial Dysfunction in Diabetes.

Diabetes mellitus is a chronic metabolic disease characterized by hyperglycemia, due to deficiency in insulin or insulin resistance, and represents a major cause of morbidity and mortality in contemporary societies [1,2]. According to the world health organization (WHO), more than 285 million people worldwide suffered from diabetes of which 4 million died in 2010. The prevalence is expected to enhance to 380 million by 2030. Genetic and environmental factors associated with life style such as unhealthy diet, physical inactivity, harmful use of alcohol and tobacco, and obesity contribute to the increasing incidence of diabetes. The situation becomes extremely critical since type 1 and type 2 diabetes compromise the cardiovascular homeostasis. Based on the report of WHO and clinical studies, the direct cause of death for 80 % of diabetic patients is cardiovascular diseases. Studies in human and experimental diabetic animal models have reported vascular dysfunction and structural arterial wall remodeling [3-5]. It is well known that endothelial dysfunction is an important risk factor of cardiovascular diseases [6,7]. Several hypothesis and mechanisms documented the relationship between diabetes and microvascular endothelial dysfunction [8,9], which include reduced endothelium-derived relaxing factor (EDRF) release and bioavailability, and enhanced endothelium-derived constricting factors release associated with augmented oxidative stress levels. Despite treatments have progressed, the development of novel effective treatments for patients with vascular complications in diabetes remains a major research goal.

ChemInform Abstract: Endothelial Modulation of Agonist‐Induced Vasoconstriction in Mesenteric Microcirculation

AbstractReview: 28 refs.

Regeneration of the Endothelium in Vascular Injury

The endothelium mediates relaxations (dilatations) of the underlying vascular smooth muscle cells. The endothelium-dependent relaxations are due to the release of non-prostanoid vasodilator substances. The best characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO). The endothelial cells also release substances (endothelium-derived hyperpolarizing factor, EDHF) that cause hyperpolarization of the cell membrane of the underlying vascular smooth muscle. The release of EDRF from the endothelium can be mediated by both pertussis toxin-sensitive G(i) (alpha(2)-adrenergic activation, serotonin, thrombin) and insensitive G(q) (adenosine diphosphate, bradykinin) coupling proteins. The ability of the endothelial cell to release relaxing factors can be upregulated by impregnation with estrogens, exercise and antioxidants, and down-regulated by oxidative stress and increased presence of oxidized LDL. Following injury or apoptotic death, the endothelium regenerates. However, in regenerated endothelial cells, there is an early selective loss of the pertussis-toxin sensitive mechanisms of EDRF-release. Functional studies suggest that abnormal handling of LDL because of increased oxidative stress play a key role in this selective loss. Genomic analysis demonstrates the emergence of fatty acid binding protein-A (A-FBP) and metalloproteinase-7 (MMP7) in regenerated endothelial cells. The reduced release of NO resulting from the endothelial dysfunction in regenerated areas creates a locus minoris resistentiae which favors the occurrence of vasospasm and thrombosis as well as the initiation of atherosclerosis.

Endothelial Modulation of Agonist-induced Vasoconstriction in Mesenteric Microcirculation

It is widely accepted that vascular endothelium regulates vasoconstriction via release of endothelium-derived relaxing factors (EDRF). The mesenteric circulation, which is the largest vascular bed, influences regulation of systemic blood pressure. However, the role of EDRF in the modulation of vascular tone in peripheral mesenteric circulation has not been extensively studied. Therefore, our recent studies investigated the role of the vascular endothelium in the regulation of methoxamine (alpha(1)-adrenoceptor agonist)-induced vasoconstriction and their age-related changes in rat mesenteric vascular beds. In mesenteric vascular beds with intact endothelium isolated from 8 week-old rats, the initial maximum vasoconstriction induced by continuous perfusion of methoxamine was time-dependently decreased during 3 hour-perfusion. Neither nitric oxide synthase inhibitor nor cyclooxygenase inhibitor altered this time-dependent reduction of methoxamine-induced vasoconstriction. Endothelium removal, K(+)-channel inhibitors and gap junction inhibitor significantly inhibited the time-dependent reduction of methoxamine-induced vasoconstriction. In the preparations with intact endothelium from 16 week-old rats, the time-dependent reduction of methoxamine-induced vasoconstriction disappeared. Furthermore, endothelium removal and treatment with cyclooxygenase inhibitor, thromboxane A(2) receptor antagonist or superoxide dismutase mimetic significantly reduced the methoxamine-induced vasoconstriction in the preparations from 16 week-old rats. These findings suggest that vascular endothelium acts to depress methoxamine-induced vasoconstriction by releasing endothelium-derived hyperpolarizing factor (EDHF), and dysfunction in this endothelial modulation develops with ageing.

Endothelial dysfunction: a strategic target in the treatment of hypertension?

Endothelial dysfunction is a common feature of hypertension, and it results from the imbalanced release of endothelium-derived relaxing factors (EDRFs; in particular, nitric oxide) and endothelium-derived contracting factors (EDCFs; angiotensin II, endothelins, uridine adenosine tetraphosphate, and cyclooxygenase-derived EDCFs). Thus, drugs that increase EDRFs (using direct nitric oxide releasing compounds, tetrahydrobiopterin, or L-arginine supplementation) or decrease EDCF release or actions (using cyclooxygenase inhibitor or thromboxane A2/prostanoid receptor antagonists) would prevent the dysfunction. Many conventional antihypertensive drugs, including angiotensin-converting enzyme inhibitors, calcium channel blockers, and third-generation beta-blockers, possess the ability to reverse endothelial dysfunction. Their use is attractive, as they can address arterial blood pressure and vascular tone simultaneously. The severity of endothelial dysfunction correlates with the development of coronary artery disease and predicts future cardiovascular events. Thus, endothelial dysfunction needs to be considered as a strategic target in the treatment of hypertension.

Impact of sleep on arrhythmogenesis.

Sleep is generally considered to be a protected period, when the cardiovascular system benefits from the restorative influences of the sleeping brain. However, the dynamics of cardiovascular control during sleep can tax the capacity of the diseased coronary circulation and myocardium with surges in sleep-state–related autonomic activity and disruptions in airway function and central nervous system regulation. In this regard, sleep may constitute an autonomic stress test for the heart. The scope of sleep-related risk for atrial and ventricular arrhythmias is substantial. The major subgroups susceptible to adverse influences of surges in autonomic activity during sleep are those with ischemic heart disease, heart failure, and channelopathies (Table).1 It is significant that 20% of myocardial infarctions and 15% of sudden deaths occur at night in the United States.2 Most atrial arrhythmias in patients younger than 61 years of age have nocturnal onset.3 The young are not immune to risk, as sudden infant death syndrome (SIDS) claims 2500 lives in the United States annually.4 Cardiovascular risk is compounded by comorbid factors, most notably apnea, which affects an estimated 4% to 9% of the general population5 and is considerably more prevalent among obese individuals.6 The more common form is obstructive sleep apnea (OSA), with partial or complete collapse of the pharynx. Half of heart failure patients experience either OSA or central sleep apnea (CSA) with central nervous system–mediated periodic breathing, commonly referred to as Cheyne-Stokes respiration. Such cardiorespiratory disturbances profoundly alter autonomic nervous system activity and increase risk of arrhythmia, hypertension, and myocardial infarction. View this table: Table. Patient Groups at Potentially Increased Risk for Nocturnal Cardiac Events It is surprising, as recently underscored by Malhotra and Loscalzo,7 that the significance of cardiovascular risk during sleep may not be duly recognized within the cardiology community. The reasons are …

Adaptação de um sistema de ensaio biológico para detecção de fatores relaxantes endoteliais derivados do endocárdio atrial canino

The aim of this study was to assess the release of endothelium-derived relaxing factors from the endocardium of canine atrial appendage. To study the release of endothelium-derived relaxing factor (EDRF) from intact atrial endocardial endothelium, tube-shaped sutures of canine atrial appendages were performed and effluents from these tubes were bioassayed (isolated perfused organ chamber system) for detection of EDRF in canine coronary artery. Effluent from the right atrial appendage caused a relaxation of 58.4 +/- 10.1% and the left atrial appendage 74.9 +/- 8.5% from the initial prostagladin F2alpha contraction in coronary artery. No significant statistical difference was detected in effluent from the right and left atrial appendages. This relaxation was abolished by treating the heart tubes with Triton X-100 and reduced by treatment with LNMMA, a competitive inhibitor of nitric oxide and with indomethacin, an inhibitor of the cyclo-oxygenase pathway, also indicating the release of vasodilatory prostanoids from the endocardial endothelium. This study showed for the first time, in vitro luminal release of EDRF and prostacyclin from the canine heart atrium. The ability of the endocardial endothelium to produce these factors could play an important role in preventing thrombus formation in the cardiac chambers.

Effect of the effluent released from the canine internal mammary artery after intraluminal and extraluminal perfusion of acetylcholine and adenosine diphosphate

Segments of the canine internal mammary artery (35 mm in length) were suspended in vitro in an organ chamber containing physiological salt solution (95% O2/5% CO2, pH = 7.4, 37°C). Segments were individually cannulated and perfused at 5 ml/minute using a roller pump. Vasorelaxant activity of the effluent from the perfused internal mammary arteries was bioassayed by measuring the decrease in tension induced by the effluent of the coronary artery endothelium-free ring which had been contracted with prostaglandin F2α (2 × 10-6 M). Intraluminal perfusion of adenosine diphosphate (10-5 M) induced significant increase in relaxant activity in the effluent from the perfused blood vessel. However, when adenosine diphosphate (10-5 M) was added extraluminally to the internal mammary artery, no change in relaxant activity in the effluent was noted. In contrast, acetylcholine produced significant increase in the relaxant activity on the effluent of the perfused internal mammary artery with both intraluminal and extraluminal perfusion. The intraluminal and extraluminal release of endothelium-derived relaxing factor (EDRF) by acetylcholine (10-5 M) can be inhibited by site-specific administration of atropine (10-5 M). These experiments indicate that certain agonists can induce the release of EDRF only by binding to intravascular receptors while other agonists can induce endothelium-dependent vasodilatation by acting on neural side receptors.

Extracellular acidosis suppresses endothelial function by inhibiting store-operated Ca2+ entry via non-selective cation channels

Hypoxia, ischaemia, and exogenous chemicals can induce extracellular and intracellular acidosis, but it is not clear which of these types of acidosis affects endothelial cell function. The synthesis and release of endothelium-derived relaxing factors (EDRFs) are linked to an increase in cytosolic Ca(2+) concentration, and we therefore examined the effects of extracellular and intracellular acidosis on Ca(2+) responses and EDRF production in cultured porcine aortic endothelial cells. Cytosolic pH (pH(i)) and Ca(2+) were measured using fluorescent dyes, BCECM/AM (pH-indicator) and fura-2/AM (Ca(2+)-indicator), respectively. EDRFs, nitric oxide (NO) and prostaglandin I(2) (PGI(2)) were assessed using DAF-FM/DA (NO-indicator dye) fluorometry and 6-keto PGF(1alpha) enzyme immunoassay, respectively. HEPES buffers titrated to pH 6.4, 6.9, and 7.4 were used to alter extracellular pH (pH(o)), and propionate (20 mmol/L) was applied to cause intracellular acidosis. Extracellular acidosis strongly suppressed bradykinin (BK, 10 nmol/L)- and thapsigargin (TG, 1 micromol/L)-induced Ca(2+) responses by 30 and 23% at pH(o) 6.9, and by 80 and 97% at pH(o) 6.4, respectively. During the examinations, there were no significant differences in pH(i) among the three groups at pH(o) 7.4, 6.9, and 6.4. Extracellular acidosis also inhibited BK-stimulated PGI(2) production by 55% at pH(o) 6.9 and by 77% at pH(o) 6.4, and NO production by 38% at pH(o) 6.9 and by 91% at pH(o) 6.4. The suppressive effects of extracellular acidosis on Ca(2+) responses and NO production were reversible. Propionate changed pH(i) from 7.3 to 6.9, without altering pH(o) (7.4). Intracellular acidosis had no effect on BK- and TG-induced Ca(2+) responses or NO production. These results indicate that extracellular, but not intracellular, acidosis causes endothelial dysfunction by inhibiting store-operated Ca(2+) entry, so helping to clarify the vascular pathophysiology of conditions such as ischaemia, hypoxia, acidosis, and ischaemia-reperfusion.