Crosstalk between endothelin and nitric oxide in the control of vascular tone

Arginine-NO metabolites are associated with morbidity in single ventricle infants undergoing stage 2 palliation

BACKGROUND

Infants with single ventricle heart disease (SVHD) suffer morbidity from insufficient pulmonary blood flow, which may be related to impaired arginine metabolism. No prior study has reported quantitative mapping of arginine metabolites to evaluate the relationship between circulating metabolite levels and outcomes.

METHODS

Prospective cohort study of 75 SVHD cases peri-Stage 2 and 50 healthy controls. We targeted pre- and post-op absolute serum quantification of 9 key members of the arginine metabolism pathway by tandem mass spectrometry. Primary outcomes were length of stay (LOS) and post-Stage 2 hypoxemia.

RESULTS

Pre-op cases showed alteration in 6 metabolites including decreased arginine and increased asymmetric dimethyl arginine (ADMA) levels compared to controls. Post-op cases demonstrated decreased arginine and citrulline levels persisting through 48 h. Adjusting for clinical variables, lower pre-op and 2 h post-op concentrations of multiple metabolites, including arginine and citrulline, were associated with longer post-op LOS (p < 0.01). Increased ADMA at 24 h was associated with greater post-op hypoxemia burden (p < 0.05).

CONCLUSION

Arginine metabolism is impaired in interstage SVHD infants and is further deranged following Stage 2 palliation. Patients with greater metabolite alterations experience greater post-op morbidity. Decreased arginine metabolism may be an important driver of pathology in SVHD.

IMPACT

Interstage infants with SVHD have significantly altered arginine-nitric oxide metabolism compared to healthy children with deficiency of multiple pathway intermediates persisting through 48 h post-Stage 2 palliation. After controlling for clinical covariates and classic catheterization-derived predictors of Stage 2 readiness, both lower pre-operation and lower post-operation circulating metabolite levels were associated with longer post-Stage 2 LOS while increased post-Stage 2 ADMA concentration was associated with greater post-op hypoxemia. Arginine metabolism mapping offers potential for development using personalized medicine strategies as a biomarker of Stage 2 readiness and therapeutic target to improve pulmonary vascular health in infants with SVHD.

Stable Gastric Pentadecapeptide BPC 157 as Useful Cytoprotective Peptide Therapy in the Heart Disturbances, Myocardial Infarction, Heart Failure, Pulmonary Hypertension, Arrhythmias, and Thrombosis Presentation

In heart disturbances, stable gastric pentadecapeptide BPC 157 especial therapy effects combine the therapy of myocardial infarction, heart failure, pulmonary hypertension arrhythmias, and thrombosis prevention and reversal. The shared therapy effect occurred as part of its even larger cytoprotection (cardioprotection) therapy effect (direct epithelial cell protection; direct endothelium cell protection) that BPC 157 exerts as a novel cytoprotection mediator, which is native and stable in human gastric juice, as well as easily applicable. Accordingly, there is interaction with many molecular pathways, combining maintained endothelium function and maintained thrombocytes function, which counteracted thrombocytopenia in rats that underwent major vessel occlusion and deep vein thrombosis and counteracted thrombosis in all vascular studies; the coagulation pathways were not affected. These appeared as having modulatory effects on NO-system (NO-release, NOS-inhibition, NO-over-stimulation all affected), controlling vasomotor tone and the activation of the Src-Caveolin-1-eNOS pathway and modulatory effects on the prostaglandins system (BPC 157 counteracted NSAIDs toxicity, counteracted bleeding, thrombocytopenia, and in particular, leaky gut syndrome). As an essential novelty noted in the vascular studies, there was the activation of the collateral pathways. This might be the upgrading of the minor vessel to take over the function of the disabled major vessel, competing with and counteracting the Virchow triad circumstances devastatingly present, making possible the recruitment of collateral blood vessels, compensating vessel occlusion and reestablishing the blood flow or bypassing the occluded or ruptured vessel. As a part of the counteraction of the severe vessel and multiorgan failure syndrome, counteracted were the brain, lung, liver, kidney, gastrointestinal lesions, and in particular, the counteraction of the heart arrhythmias and infarction.

Altered Mitochondrial Opa1-Related Fusion in Mouse Promotes Endothelial Cell Dysfunction and Atherosclerosis

Flow (shear stress)-mediated dilation (FMD) of resistance arteries is a rapid endothelial response involved in tissue perfusion. FMD is reduced early in cardiovascular diseases, generating a major risk factor for atherosclerosis. As alteration of mitochondrial fusion reduces endothelial cells’ (ECs) sprouting and angiogenesis, we investigated its role in ECs responses to flow. Opa1 silencing reduced ECs (HUVECs) migration and flow-mediated elongation. In isolated perfused resistance arteries, FMD was reduced in Opa1^+/− mice, a model of the human disease due to Opa1 haplo-insufficiency, and in mice with an EC specific Opa1 knock-out (EC-Opa1). Reducing mitochondrial oxidative stress restored FMD in EC-Opa1 mice. In isolated perfused kidneys from EC-Opa1 mice, flow induced a greater pressure, less ATP, and more H₂O₂ production, compared to control mice. Opa1 expression and mitochondrial length were reduced in ECs submitted in vitro to disturbed flow and in vivo in the atheroprone zone of the mouse aortic cross. Aortic lipid deposition was greater in Ldlr^−/--Opa1^+/- and in Ldlr^−/--EC-Opa1 mice than in control mice fed with a high-fat diet. In conclusion, we found that reduction in mitochondrial fusion in mouse ECs altered the dilator response to shear stress due to excessive superoxide production and induced greater atherosclerosis development.

Functional implications of vascular endothelium in regulation of endothelial nitric oxide synthesis to control blood pressure and cardiac functions

The endothelium is the innermost vascular lining performing significant roles all over the human body while maintaining the blood pressure at physiological levels. Malfunction of endothelium is thus recognized as a biomarker linked with many vascular diseases including but not limited to atherosclerosis, hypertension and thrombosis. Alternatively, prevention of endothelial malfunctioning or regulating the functions of its associated physiological partners like endothelial nitric oxide synthase can prevent the associated vascular disorders which account for the highest death toll worldwide. While many anti-hypertensive drugs are available commercially, a comprehensive description of the key physiological roles of the endothelium and its regulation by endothelial nitric oxide synthase or vice versa is the need of the hour to understand its contribution in vascular homeostasis. This, in turn, will help in designing new therapeutics targeting endothelial nitric oxide synthase or its interacting partners present in the cellular pool. This review describes the central role of vascular endothelium in the regulation of endothelial nitric oxide synthase while outlining the emerging drug targets present in the vasculature with potential to treat vascular disorders including hypertension.

CASIN and AMD3100 enhance endothelial cell proliferation, tube formation and sprouting

Endothelial dysfunction is prominent in atherosclerosis, hypertension, diabetes, peripheral and cardiovascular diseases, and stroke. Novel therapeutic approaches to these conditions often involve development of tissue-engineered veins with ex vivo expanded endothelial cells. However, high cell number requirements limit these approaches to become applicable to clinical applications and highlight the requirement of technologies that accelerate expansion of vascular-forming cells. We have previously shown that novel small molecules could induce hematopoietic stem cell expansion ex vivo. We hypothesized that various small molecules targeting hematopoietic stem cell quiescence and mobilization could be used to induce endothelial cell expansion and angiogenesis due to common origin and shared characteristics of endothelial and hematopoietic cells. Here, we have screened thirty-five small molecules and found that CASIN and AMD3100 increase endothelial cell expansion up to two-fold and induce tube formation and ex vivo sprouting. In addition, we have studied how CASIN and AMD3100 affect cell migration, apoptosis and cell cycle of endothelial cells. CASIN and AMD3100 upregulate key endothelial marker genes and downregulate a number of cyclin dependent kinase inhibitors. These findings suggest that CASIN and AMD3100 could be further tested in the development of artificial vascular systems and vascular gene editing technologies. Furthermore, these findings may have potential to contribute to the development of alternative treatment methods for diseases that cause endothelial damage.

Epithelial Na+ channel differentially contributes to shear stress-mediated vascular responsiveness in carotid and mesenteric arteries from mice

A potential "new player" in arteries for mediating shear stress responses is the epithelial Na⁺ channel (ENaC). The contribution of ENaC as shear sensor in intact arteries, and particularly different types of arteries (conduit and resistance), is unknown. We investigated the role of ENaC in both conduit (carotid) and resistance (third-order mesenteric) arteries isolated from C57Bl/6J mice. Vessel characteristics were determined at baseline (60 mmHg, no flow) and in response to increased intraluminal pressure and shear stress using a pressure myograph. These protocols were performed in the absence and presence of the ENaC inhibitor amiloride (10 µM) and after inhibition of endothelial nitric oxide synthase (eNOS) by N^ω-nitro-l-arginine methyl ester (l-NAME; 100 µM). Under no-flow conditions, amiloride increased internal and external diameters of carotid (13 ± 2%, P < 0.05) but not mesenteric (0.5 ± 0.9%, P > 0.05) arteries. In response to increased intraluminal pressure, amiloride had no effect on the internal diameter of either type of artery. However, amiloride affected the stress-strain curves of mesenteric arteries. With increased shear stress, ENaC-dependent effects were observed in both arteries. In carotid arteries, amiloride augmented flow-mediated dilation (9.2 ± 5.3%) compared with control (no amiloride, 6.2 ± 3.3%, P < 0.05). In mesenteric arteries, amiloride induced a flow-mediated constriction (-11.5 ± 6.6%) compared with control (-2.2 ± 4.5%, P < 0.05). l-NAME mimicked the effect of ENaC inhibition and prevented further amiloride effects in both types of arteries. These observations indicate that ENaC contributes to shear sensing in conduit and resistance arteries. ENaC-mediated effects were associated with NO production but may involve different (artery-dependent) downstream signaling pathways. NEW & NOTEWORTHY The epithelial Na⁺ channel (ENaC) contributes to shear sensing in conduit and resistance arteries. In conduit arteries ENaC has a role as a vasoconstrictor, whereas in resistance arteries ENaC contributes to vasodilation. Interaction of ENaC with endothelial nitric oxide synthase/nitric oxide signaling to mediate the effects is supported; however, cross talk with other shear stress-dependent signaling pathways cannot be excluded.

Endothelin-1 Regulation of Exercise-Induced Changes in Flow: Dynamic Regulation of Vascular Tone

Although endothelin (ET)-1 is a highly potent vasoconstrictor with considerable efficacy in numerous vascular beds, the role of endogenous ET-1 in the regulation of vascular tone remains unclear. The perspective that ET-1 plays little role in the on-going regulation of vascular tone at least under physiologic conditions is supported by findings that potential ET-1 constriction is minimized by the release of the vasodilator and ET-1 synthesis inhibitor, nitric oxide (NO). Indeed, ET-1 release and constriction is self-limited by ET-1-induced, endothelial ET_B receptor-mediated release of NO. Moreover, even if the balance between ET-1 and NO were reversed as the result of lowered NO activity, as occurs in a number of pathophysiologies associated with endothelial dysfunction, the well-known resistance of ET-1 constriction to reversal (as determined with exogenous ET-1) precludes ET-1 in the dynamic, i.e., moment-to-moment, regulation of vascular tone. On the other hand, and as presently reviewed, findings of ET-1-dependent modulation of organ blood flow with exercise under physiologic conditions demonstrate the dynamic regulation of vascular tone by ET-1. We speculate that this regulation is mediated at least in part through changes in ET-1 synthesis/release caused by pulsatile flow-induced shear stress and NO.

Acute nitric oxide synthase inhibition and endothelin-1-dependent arterial pressure elevation

Key evidence that endogenous nitric oxide (NO) inhibits the continuous, endothelin (ET)-1-mediated drive to elevate arterial pressure includes demonstrations that ET-1 mediates a significant component of the pressure elevated by acute exposure to NO synthase (NOS) inhibitors. This review examines the characteristics of this pressure elevation in order to elucidate potential mechanisms associated with the negative regulation of ET-1 by NO and, thereby, provide potential insight into the vascular pathophysiology underlying NO dysregulation. We surmise that the magnitude of the ET-1-dependent component of the NOS inhibitor-elevated pressure is (1) independent of underlying arterial pressure and other pressor pathways activated by the NOS inhibitors and (2) dependent on relatively higher NOS inhibitor dose, release of stored and de novo synthesized ET-1, and ET_A receptor-mediated increased vascular resistance. Major implications of these conclusions include: (1) the marked variation of the ET-1-dependent component, i.e., from 0 to 100% of the pressure elevation, reflects the NO-ET-1 regulatory pathway. Thus, NOS inhibitor-mediated, ET-1-dependent pressure elevation in vascular pathophysiologies is an indicator of the level of compromised/enhanced function of this pathway; (2) NO is a more potent inhibitor of ET-1-mediated elevated arterial pressure than other pressor pathways, due in part to inhibition of intravascular pressure-independent release of ET-1. Thus, the ET-1-dependent component of pressure elevation in vascular pathophysiologies associated with NO dysregulation is of greater magnitude at higher levels of compromised NO.

Peripheral circulation

Blood flow (BF) increases with increasing exercise intensity in skeletal, respiratory, and cardiac muscle. In humans during maximal exercise intensities, 85% to 90% of total cardiac output is distributed to skeletal and cardiac muscle. During exercise BF increases modestly and heterogeneously to brain and decreases in gastrointestinal, reproductive, and renal tissues and shows little to no change in skin. If the duration of exercise is sufficient to increase body/core temperature, skin BF is also increased in humans. Because blood pressure changes little during exercise, changes in distribution of BF with incremental exercise result from changes in vascular conductance. These changes in distribution of BF throughout the body contribute to decreases in mixed venous oxygen content, serve to supply adequate oxygen to the active skeletal muscles, and support metabolism of other tissues while maintaining homeostasis. This review discusses the response of the peripheral circulation of humans to acute and chronic dynamic exercise and mechanisms responsible for these responses. This is accomplished in the context of leading the reader on a tour through the peripheral circulation during dynamic exercise. During this tour, we consider what is known about how each vascular bed controls BF during exercise and how these control mechanisms are modified by chronic physical activity/exercise training. The tour ends by comparing responses of the systemic circulation to those of the pulmonary circulation relative to the effects of exercise on the regional distribution of BF and mechanisms responsible for control of resistance/conductance in the systemic and pulmonary circulations.

The effect of acute administration of vitamin D on micro vascular endothelial function in Caucasians and South Asian Indians

BACKGROUND

Vitamin D is a modulator of the immune system. There is some limited evidence that it also increases local blood flow in response to stress.

MATERIAL AND METHODS

In the present study, we examined 20 age matched subjects; 10 whom were from India and 10 Caucasians from the United States. Subjects were administered 4000 IU of Vitamin D3 for 3 weeks at breakfast. The function of the endothelial cells was evaluated in 2 ways; first, the response to 4 minutes of vascular occlusion was measured with a laser Doppler flow meter and second, the blood flow response to local heat at 42°C for 6 minutes.

RESULTS

The results of the experiments showed that, as reported previously, the endothelial function in people from India was less than their Caucasian counterparts. The blood flow response to heat was reduced after 3 weeks administration of vitamin D in both groups and the response to vascular occlusion in the Caucasian group. But there was only a 20% reduction in the blood flow response to heat in the Caucasian group and a 50% reduction in the group from India.

CONCLUSIONS

Thus acute doses of vitamin D may increase vascular tone and reduce blood flow to tissue during stressors. Dosages administered for a longer duration may have beneficial effects on endothelial function but this was not examined here.

Endothelial control of vasomotor tone: the kidney perspective

Endothelial cells are essential regulators of vascular tone. They accomplish this by sensing humoral mediators and transducing their effects to the underlying vascular smooth muscle as well as by synthesizing vasoactive molecules that act in a paracrine fashion. In the kidney, the local release of these endothelial mediators, together with the concourse of specialized endothelial cells in the glomerulus, contribute to regulate renal blood flow, glomerular filtration, and tubular function that are intimately linked to sodium balance because they mutually influence each other. Ultimately, renal circulation and tubular function have a profound influence in systemic blood pressure as a result of the overall regulation of volume homeostasis.

Nitric oxide and endothelin-1 release after one-lung ventilation during thoracoabdominal esophagectomy

One-lung ventilation (OLV) is applied during esophagectomy to improve exposure during the thoracic part of the operation. Collapse of lung tissue, shunting of pulmonary blood flow, and changes in alveolar oxygenation during and after OLV may possibly induce an ischemia-reperfusion response in the lung, which may affect the pulmonary endothelium. Such a reaction might thereby contribute to the frequently occurring respiratory complications among these patients. In this small trial, 30 patients were randomized to either OLV (n= 16) or two-lung ventilation (TLV, n= 14) during esophagectomy. Central venous and arterial plasma samples were taken before and after OLV/TLV for analysis of nitrite and a metabolite of nitric oxide (NO), and also during the 1st, 2nd, 3rd, and 10th postoperative day for analysis of endothelin, another endothelium-derived vasoactive mediator. Lung biopsies were taken before and after OLV or TLV, and analyzed regarding immunofluorescence for isoform of NO synthase, a protein upregulated during inflammatory response and also vascular congestion. No changes in lung isoform of NO synthase immunofluorescence or vascular congestion were registered after neither OLV nor TLV. Plasma nitrite and endothelin levels were similar in the two study groups. We conclude that OLV does not seem to have any influence on key regulators of pulmonary vascular tone and inflammation, i.e. NO and endothelin. From this perspective, OLV seems to be a safe method, which defends its clinical position to facilitate surgical exposure during thoracoabdominal esophagectomy.

Genistein activates endothelial nitric oxide synthase in broiler pulmonary arterial endothelial cells by an Akt-dependent mechanism

Deregulation of endothelial nitric oxide synthase (eNOS) plays an important role in the development of multiple cardiovascular diseases. Our recent study demonstrated that genistein supplementation attenuates pulmonary arterial hypertension in broilers by restoration of endothelial function. In this study, we investigated the molecular mechanism by using broiler pulmonary arterial endothelial cells (PAECs). Our results showed that genistein stimulated a rapid phosphorylation of eNOS at Ser(1179) which was associated with activation of eNOS/NO axis. Further study indicated that the activation of eNOS was not mediated through estrogen receptors or tyrosine kinase inhibition, but via a phosphatidylinositol 3-kinase (PI3K)/Akt-dependent signaling pathway, as the eNOS activity and related NO release were largely abolished by pharmacological inhibitors of PI3K or Akt. Thus, our findings revealed a critical function of Akt in mediating genistein-stimulated eNOS activity in PAECs, partially accounting for the beneficial effects of genistein on the development of cardiovascular diseases observed in animal models.

Differential vulnerability of skeletal muscle feed arteries to dysfunction in insulin resistance: impact of fiber type and daily activity

Functional and structural heterogeneity exists among skeletal muscle vascular beds related, in part, to muscle fiber type composition. This study was designed to delineate whether the vulnerability to vascular dysfunction in insulin resistance is uniformly distributed among skeletal muscle vasculatures and whether physical activity modifies this vulnerability. Obese, hyperphagic Otsuka Long-Evans Tokushima fatty rats (20 wk old) were sedentary (OSED) or physically active (OPA; access to running wheels) and compared with age-matched sedentary Long-Evans Tokushima Otsuka (LSED) rats. Vascular responses were determined in isolated, pressurized feed arteries from fast-twitch gastrocnemius (GFAs) and slow-twitch soleus (SFAs) muscles. OSED animals were obese, insulin resistant, and hypertriglyceridemic, traits absent in LSED and OPA rats. GFAs from OSED animals exhibited depressed dilation to ACh, but not sodium nitroprusside, and enhanced vasoconstriction to endothelin-1 (ET-1), but not phenylephrine, compared with those in LSED. Immunoblot analysis suggests reduced endothelial nitric oxide synthase phosphorylation at Ser1177 and endothelin subtype A receptor expression in OSED GFAs. Physical activity prevented reduced nitric oxide-dependent dilation to ACh, but not enhanced ET-1 vasoconstriction, in GFA from OPA animals. Conversely, vasoreactivity of SFAs to ACh and ET-1 were principally similar in all groups, whereas dilation to sodium nitroprusside was enhanced in OSED and OPA rats. These data demonstrate, for the first time, that SFAs from insulin-resistant rats exhibit reduced vulnerability to dysfunction versus GFAs and that physical activity largely prevents GFA dysfunction. We conclude that these results demonstrate that vascular dysfunction associated with insulin resistance is heterogeneously distributed across skeletal muscle vasculatures related, in part, to muscle fiber type and activity level.

Genistein attenuates low temperature induced pulmonary hypertension in broiler chicks by modulating endothelial function

Pulmonary arterial hypertension is characterized by high pulmonary blood pressure, vascular remodeling and right ventricular hypertrophy. In the present study, we investigated whether genistein would prevent the development of low temperature-induced pulmonary hypertension in broilers. Hemodynamic parameters, vascular remodeling, the expression of endothelial nitric oxide and endothelin-1 content in lung tissue were evaluated. The results demonstrated that genistein significantly reduced pulmonary arterial hypertension and suppressed pulmonary arterial vascular remodeling without affecting broilers' performance. The beneficial effects appeared to be mediated by restoring endothelial function especially endothelial nitric oxide and endothelin-1, two critical vasoactive molecules that associated with the development of hypertension. Genistein supplementation might be a potential therapeutic strategy for the treatment of pulmonary hypertension.

Sex differences in endothelin-1-mediated vasoconstrictor tone in middle-aged and older adults

The prevalence of cardiovascular disease is lower in middle-aged and older women than men. Increased endothelin-1-mediated vasoconstriction has been linked to the etiology of a number of cardiovascular diseases, including atherosclerosis, heart failure, and hypertension. It is unknown whether a sex difference in endothelin-1-mediated vasoconstrictor tone exists in middle-aged and older adults. Therefore, we tested the hypothesis that middle-aged and older men would demonstrate greater ET-1-mediated vasoconstrictor tone than age-matched women. Forearm blood flow in response to intra-arterial infusions of endothelin (ET)-1, BQ-123 (a selective ET(A) receptor antagonist), and BQ-788 (a selective ET(B) receptor antagonist) was assessed by venous occlusion plethysmography in 21 women (age: 58 + or - 1 yr; body mass index: 26.0 + or - 1.0 kg/m(2)) and 25 men (age: 57 + or - 2 yr; body mass index: 26.8 + or - 0.7 kg/m(2)). In response to BQ-123, the increase in forearm blood flow from baseline was significantly higher in the men than the women (24 + or - 5% vs. 9 + or - 5%; P < 0.05). In contrast, the increase in forearm blood flow in response to BQ-123 coinfused with BQ-788 was greater in the women than the men, such that the maximum vasodilation to dual endothelin receptor blockade was similar between men and women (approximately 25%). There was no difference in the vasoconstrictor response to ET-1 between the sexes. These results indicate that middle-aged and older men are under greater ET(A) receptor-mediated vasoconstrictor tone than age-matched women. Since the ET(A) receptor is the predominant receptor subtype in the coronary vasculature, this sex difference in vasoconstrictor tone may be a mechanism contributing to the sex difference in the prevalence of coronary heart disease in middle-aged and older adults.

Amphetamine and environmentally induced hyperthermia differentially alter the expression of genes regulating vascular tone and angiogenesis in the meninges and associated vasculature

An amphetamine (AMPH) regimen that does not produce a prominent blood-brain barrier breakdown was shown to significantly alter the expression of genes regulating vascular tone, immune function, and angiogenesis in vasculature associated with arachnoid and pia membranes of the forebrain. Adult-male Sprague-Dawley rats were given either saline injections during environmentally-induced hyperthermia (EIH) or four doses of AMPH with 2 h between each dose (5, 7.5, 10, and 10 mg/kg d-AMPH, s.c.) that produced hyperthermia. Rats were sacrificed either 3 h or 1 day after dosing, and total RNA and protein was isolated from the meninges, arachnoid and pia membranes, and associated vasculature (MAV) that surround the forebrain. Vip, eNos, Drd1a, and Edn1 (genes regulating vascular tone) were increased by either EIH or AMPH to varying degrees in MAV, indicating that EIH and AMPH produce differential responses to enhance vasodilatation. AMPH, and EIH to a lesser extent, elicited a significant inflammatory response at 3 h as indicated by an increased MAV expression of cytokines Il1b, Il6, Ccl-2, Cxcl1, and Cxcl2. Also, genes related to heat shock/stress and disruption of vascular homeostasis such as Icam1 and Hsp72 were also observed. The increased expression of Ctgf and Timp1 and the decreased expression of Akt1, Anpep, and Mmp2 and Tek (genes involved in stimulating angiogenesis) from AMPH exposure suggest that angiogenesis was arrested or disrupted in MAV to a greater extent by AMPH compared to EIH. Alterations in vascular-related gene expression in the parietal cortex and striatum after AMPH were less in magnitude than in MAV, indicating less of a disruption of vascular homeostasis in these two regions. Changes in the levels of insulin-like growth factor binding proteins Igfbp1, 2, and 5 in MAV, compared to those in striatum and parietal cortex, imply an interaction between these regions to regulate the levels of insulin-like growth factor after AMPH damage. Thus, the vasculature and meninges surrounding the surface of the forebrain may be an important region in which AMPHs can disrupt vascular homeostasis.

Inhibition of methyldigoxin-induced arrhythmias by pentadecapeptide BPC 157: a relation with NO-system

Pentadecapeptide BPC 157 (GEPPPGKPADDAGLV, MW 1419) reversed congestive heart failure and various arrhythmias, influenced the NO-system and showed no proarrhythmic effect. In therapy analogy, we challenged rats with digitalis, to show attenuation by BPC 157 and the relation between the NO-system and digitalis toxicity. (i). BPC 157 prophylactic effect. Development of cumulative intravenous digitalis toxicity, BPC 157 (50 microg, 10 microg, 10 ng/kg applied intravenously immediately before a methyldigoxin increment regimen (2.0/1.5/1.5/1.0 mg/kg at 15 min-intervals, total dose 6.0 mg/kg/45 min)) reduced the number of ventricular premature beats, prolonged the time before onset of ventricular tachycardia, reduced ventricular tachycardia and AV-block duration (microg-regimes) or reduced mainly the AV-block duration (ng-regimen). (ii). BPC 157 therapy. Advanced methyldigoxin toxicity (6.0 mg/kg i.v. bolus). BPC 157 applied at the 20th second of the grade 3 AV-block shortened AV-blocks, mitigated a further digitalis toxicity course. Ventricular tachycardias were either avoided (50 microg), or markedly reduced (10 microg, 10 ng). Fatal outcome was either avoided (50 microg), reduced (10 microg), or only delayed (10 ng) (iii) BPC 157, L-NAME, l-arginine, L-NAME+l-arginine application. L-NAME-application (5 mg/kg i.p.) aggravated methyldigoxin-arrhythmias. l-arginine (200 mg/kg i.p.) alone had no effect but blunted L-NAME-exaggeration (L-NAME+l-arginine). In this respect, BPC 157 (50 microg/kg i.p.) was prophylactically and therapeutically more effective: the antagonism of L-NAME with BPC 157 produced an effect similar to BPC 157 alone. In conclusion, digitalis-induced arrhythmias in rats could be prevented and counteracted by pentadecapeptide BPC 157, mainly through an interaction with the NO-system.

Endothelin-1, aging and hypertension

PURPOSE OF REVIEW

Endothelin-1 system activation plays an important role in the etiology of atherosclerotic vascular disease. Aging and hypertension are two independent cardiovascular risk factors that have been shown to exhibit increased endothelin-1 system activation. This review focuses on the cardiovascular effects of the endothelin system, its relation to aging and hypertension, as well as potential treatment options.

RECENT FINDINGS

Many of the cardiovascular complications associated with both aging and hypertension are attributable, in part, to endothelial dysfunction, particularly vasomotor dysregulation. To date most studies have focused on the effects of aging and hypertension on endothelium-dependent nitric oxide-mediated vasodilation. However, endothelin-1-mediated vasoconstrictor tone increases with age and contributes to the pathogenesis of hypertension. Pharmacologic approaches to reduce endothelin-1 system activation have produced limited results and are largely disease-specific. In contrast, regular aerobic exercise has been shown to be extremely effective at reducing endothelin-1 system activity.

SUMMARY

Both aging and hypertension represent important cardiovascular disease risk factors that are characterized by increased endothelin-1-mediated vasoconstrictor tone. Future studies are needed to elucidate pharmacologic options for reducing endothelin-1 system activity especially in older hypertensive adults, though regular aerobic exercise must continue to be a point of emphasis for maintaining/improving vascular health.

Control of pulmonary vascular tone during exercise in health and pulmonary hypertension

Despite the importance of the pulmonary circulation as a determinant of exercise capacity in health and disease, studies into the regulation of pulmonary vascular tone in the healthy lung during exercise are scarce. This review describes the current knowledge of the role of various endogenous vasoactive mechanisms in the control of pulmonary vascular tone at rest and during exercise. Recent studies demonstrate an important role for endothelial factors (NO and endothelin) and neurohumoral factors (noradrenaline, acetylcholine). Moreover, there is evidence that natriuretic peptides, reactive oxygen species and phosphodiesterase activity can influence resting pulmonary vascular tone, but their role in the control of pulmonary vascular tone during exercise remains to be determined. K-channels are purported end-effectors in control of pulmonary vascular tone. However, K(ATP) channels do not contribute to regulation of pulmonary vascular tone, while the role of K(V) and K(Ca) channels at rest and during exercise remains to be determined. Pulmonary hypertension is associated with alterations in pulmonary vascular function and structure, resulting in blunted pulmonary vasodilatation during exercise and impaired exercise capacity. Although there is a paucity of studies pertaining to the regulation of pulmonary vascular tone during exercise in idiopathic pulmonary hypertension, the few studies that have been performed in models of pulmonary hypertension secondary to left ventricular dysfunction suggest altered control of pulmonary vascular tone during exercise. Since the increased pulmonary vascular tone during exercise limits exercise capacity, future studies are needed to investigate the vasomotor mechanisms that are responsible for the blunted exercise-induced pulmonary vasodilatation in pulmonary hypertension.

The role of shear stress on ET-1, KLF2, and NOS-3 expression in the developing cardiovascular system of chicken embryos in a venous ligation model

In this review, the role of wall shear stress in the chicken embryonic heart is analyzed to determine its effect on cardiac development through regulating gene expression. Therefore, background information is provided for fluid dynamics, normal chicken and human heart development, cardiac malformations, cardiac and vitelline blood flow, and a chicken model to induce cardiovascular anomalies. A set of endothelial shear stress-responsive genes coding for endothelin-1 (ET-1), lung Krüppel-like factor (LKLF/KLF2), and endothelial nitric oxide synthase (eNOS/NOS-3) are active in development and are specifically addressed.

Possible role of nitric oxide in the pathogenesis of pulmonary hypertension in broilers: a synopsis

Nitric oxide (NO) produced by vascular endothelial cells is an important determinant of the basal tone of small arteries and arterioles. Impaired endothelial NO production has been implicated in the pathophysiology of pulmonary hypertension in humans. Available data suggest that reduction of endothelial NO synthesis, with evidence of reduced endothelial NO synthase expression in pulmonary arterioles, is associated with increased pulmonary vasomotor tone and vascular remodelling in hypertensive broilers. Supplemental l-arginine, a precursor of NO, has been shown to induce flow-dependent pulmonary vasodilation, to prevent reduced endothelial NO synthase expression and to inhibit vascular remodelling in broilers with pulmonary hypertension. Nevertheless, its effect on pulmonary hypertension syndrome incidence is limited. It appears that impaired production of NO is a secondary rather than a causative factor in the pathogenesis of pulmonary hypertension in broilers.

Alterations in endothelial control of the pulmonary circulation in exercising swine with secondary pulmonary hypertension after myocardial infarction

Secondary pulmonary hypertension after myocardial infarction (MI) has been associated with endothelial dysfunction and activation of the endothelin (ET) system. Here, we investigated whether an increased ET-mediated pulmonary vasoconstrictor influence contributes to pulmonary hypertension after MI, and whether this increased ET vasoconstriction is caused by impaired nitric oxide (NO) and prostanoid production. For this purpose, chronically instrumented swine with and without MI ran on a treadmill at 0-4 km h(-1). Mixed ET(A)/ET(B) receptor blockade (tezosentan) was performed in the absence and presence of single or combined inhibition of endothelial NO synthase (eNOS, with N(omega)-nitro-l-arginine) and cyclo-oxygenase (COX, with indometacin). In normal swine, mixed ET(A)/ET(B) blockade decreased pulmonary vascular resistance, but only during exercise. In MI swine, an increased ET-mediated vasoconstrictor influence was observed in the pulmonary circulation both at rest and during exercise. Inhibition of COX resulted in pulmonary vasoconstriction at rest in MI, but not in normal swine; this vasoconstriction in MI swine was normalized by ET(A)/ET(B) receptor blockade. Inhibition of eNOS enhanced the vasodilator response to ET(A)/ET(B) blockade, indicating that NO blunts the pulmonary vasoconstrictor influence of ET. However, this vasodilator response was enhanced to a similar degree in MI and normal swine. In summary, swine with a recent MI are characterized by an exaggerated pulmonary vasoconstrictor influence of ET. This increased ET-mediated pulmonary vasoconstrictor influence is not caused by a loss of NO bioavailability, and is blunted by an increased prostanoid-mediated vasodilatation. In conclusion, an increased ET-mediated vasoconstriction, which does not appear to be the result of loss of endothelial vasodilators, contributes to pulmonary hypertension after MI.

Big endothelin-1 is not a predictor in aortic stenosis, but is related to arterial blood pressure

BACKGROUND

In aortic stenosis, natriuretic peptides have recently been shown to correlate with ventricular function and to predict symptom-free survival and outcome. Elevated big endothelin-1 (bigET) is associated with poor prognosis in chronic heart failure, but little is known about its role in severe aortic stenosis.

METHODS

In 61 patients with aortic stenosis (71+/-10 years, mean gradient 65+/-20 mm Hg, valve area 0.63+/-0.15 cm2), plasma bigET was determined by radioimmunoassay and related to echocardiographic parameters, symptoms and survival. Patients were followed for 1 year.

RESULTS

BigET (mean 2.3+/-1.5, range 0.1-7.5 fmol/ml) was elevated > or = 1.9 fmol/ml in 54% of patients, but was not correlated to the transvalvular gradients or valve area. BigET did not differ significantly between 14 asymptomatic (2.4+/-1.0 fmol/ml) and 47 symptomatic patients (2.3+/-1.6 fmol/ml), although the highest levels were observed in 5 patients in NYHA class III-IV (4.2+/-2.2 fmol/ml, p=0.035). No significant difference in bigET was observed between 51 survivors and 10 patients who died during follow-up (2.2+/-1.4 vs 2.7+/-1.6 fmol/ml). BigET did not differ between 7 asymptomatic patients developing symptoms and those remaining asymptomatic during follow-up. BigET was significantly related to the systolic blood pressure and left ventricular systolic pressure (r=0.389, p=0.0025 and r=0.401, p=0.0018, respectively), but not to the diastolic blood pressure or interventricular septal wall thickness. BigET was inversely related to the left ventricular ejection fraction (r=0.327, p=0.01) and fractional shortening (r=0.391, p=0.044).

CONCLUSION

Although frequently elevated, bigET-1 is not a useful predictor of symptoms or outcome in patients with severe aortic stenosis. BigET increases inversely with left ventricular function and directly with systolic left ventricular and blood pressure, but is not related to transvalvular gradients or valve area.

Vasospasm in Glaucoma: Clinical and Laboratory Aspects

During the last decade, the presumed etiology of glaucoma has moved from a pure pressure concept to a combined mechanical and vascular theory. Evidence of a localized vascular insufficiency leading to perfusion deficits of ocular structures, including the optic nerve head, the retina, the choroid, and the retrobulbar vessels, is now clear. This article evaluates the role of vasospasm as the primary cause of such a vascular failure. The role of both ocular and systemic vasospasms and their clinical correlations are discussed. At a cellular level, the function of the modulating role of the vascular endothelium is reviewed. Evidence of abnormalities of the vascular endothelium and its vasoactive peptides as a conduit for vasospasm is mounting. Herein lies exciting prospects for potential pharmacologic targets in future glaucoma management.

Role of endothelin receptor activation in secondary pulmonary hypertension in awake swine after myocardial infarction

We previously observed that pulmonary hypertension secondary to myocardial infarction (MI) in swine is characterized by elevated plasma endothelin (ET) levels and pulmonary vascular resistance (PVR). Consequently, we tested the hypothesis that an increased ET-mediated vasoconstrictor influence contributes to secondary pulmonary hypertension after MI and investigated the involvement of ET(A) and ET(B) receptor subtypes. Chronically instrumented swine with (MI swine; n = 25) or without (normal swine; n = 19) MI were studied at rest and during treadmill exercise (up to 4 km h(-1)), in the absence and presence of the ET(A) antagonist EMD 122946 or the mixed ET(A)/ET(B) antagonist tezosentan. In normal swine, exercise caused a small decrease in PVR. ET(A) blockade had no effect on PVR at rest or during exercise. Conversely, ET(A)/ET(B) blockade decreased PVR but only during exercise (at 4 km h(-1), from 3.0 +/- 0.1 to 2.3 +/- 0.1 mmHg min l(-1); P <or= 0.05). MI increased pulmonary arterial pressure and PVR both at rest and during exercise (both P <or= 0.05). The increased pulmonary arterial pressure correlated with the increased plasma ET levels in resting MI swine (r = 0.71; P <or= 0.01). Furthermore, the pulmonary vasoconstrictor response to ET-1 infusion was enhanced after MI (P <or= 0.05). ET(A)/ET(B) blockade decreased PVR in MI swine from 3.6 +/- 0.3 to 3.1 +/- 0.5 mmHg min l(-1) at rest and from 3.4 +/- 0.3 to 2.4 +/- 0.2 mmHg min l(-1) during exercise at 4 km h(-1) (both P <or= 0.05). This increased response to mixed ET(A)/ET(B) blockade in MI compared to normal swine appeared to be the result of an increased ET(A)-mediated vasoconstriction, as ET(A) blockade decreased PVR in MI swine from 3.4 +/- 0.4 to 2.8 +/- 0.2 mmHg min l(-1) at rest and from 3.1 +/- 0.3 to 2.6 +/- 0.2 mmHg min l(-1) at 4 km h(-1) (both P <or= 0.05). In conclusion, increased plasma ET levels together with increased pulmonary resistance vessel responsiveness to ET result in an exaggerated pulmonary vasoconstrictor influence of ET in swine with a recent MI. This vasoconstrictor influence is the result of an emergent tonic ET(A)-mediated vasoconstriction in addition to the exercise-induced ET(B)-mediated vasoconstriction that is already present in normal swine.

Nitric oxide blunts the endothelin-mediated pulmonary vasoconstriction in exercising swine

We have previously shown that vasodilators and vasoconstrictors that are produced by the vascular endothelium, including nitric oxide (NO), prostanoids and endothelin (ET), contribute to the regulation of systemic and pulmonary vascular tone in swine, in particular during treadmill exercise. Since NO and prostanoids can modulate the release of ET, and vice versa, we investigated the integrated endothelial control of pulmonary vascular resistance in exercising swine. Specifically, we tested the hypothesis that increased NO and prostanoid production during exercise limits the vasoconstrictor influence of ET, so that loss of these vasodilators results in exaggerated ET-mediated vasoconstriction during exercise. Fifteen instrumented swine were exercised on a treadmill at 0-5 km h(-1) before and during ET(A)/ET(B) receptor blockade (tezosentan, 3 mg kg(-1) I.V.) in the presence and absence of inhibition of NO synthase (N(omega)-nitro-L-arginine, 20 mg kg(-1) I.V.) and/or cyclo-oxygenase (indometacin, 10 mg kg(-1) I.V.). In the systemic circulation, ET receptor blockade decreased vascular resistance at rest, which waned with increasing exercise intensity. Prior inhibition of either NO or prostanoid production augmented the vasodilator effect of ET receptor blockade, and these effects were additive. In contrast, in the pulmonary bed, ET receptor blockade had no effect under resting conditions, but decreased pulmonary vascular resistance during exercise. Prior inhibition of NO synthase enhanced the pulmonary vasodilator effect of ET receptor blockade, particularly during exercise, whereas inhibition of prostanoids had no effect, even after prior NO synthase inhibition. In conclusion, endogenous endothelin limits pulmonary vasodilatation in response to treadmill exercise. This vasoconstrictor influence is blunted by NO but not by prostanoids.

The endothelium in intensive care

This article reviews the major role that the vascular endothelium plays in pathophysiological processes related to metabolism, vascular function, and blood coagulation. Normally an antithrombotic surface, inflammation activates endothelium to become a prothrombotic and pro-inflammatory interface that is critically involved in multi-organ failure in patients with severe systemic diseases including sepsis. Improving endothelial functions in sepsis is a major therapeutic challenge.

Nitric oxide inhibition unmasks ischemic myocardium-derived vasoconstrictor signals activating endothelin type A receptor of coronary microvessels

NO plays an important role in the compensatory increase in coronary flow conductance against myocardial ischemia, and NO bioavailability is impaired in various diseases. We tested the hypothesis that, when NO production is inhibited, vasoconstrictor signals from the ischemic myocardium are unmasked. We investigated the involvement of endothelin type A (ETA) receptors in the transduction of the constrictor signal. To detect coronary vasoactive signals derived from ischemic myocardium, we used a bioassay system in which an isolated rabbit coronary microvessel (detector vessel, DV) was placed on beating myocardium perfused by the left anterior descending coronary artery (LAD) of an anesthetized open-chest dog ( n = 38). The DV was pressurized to 60 cmH2O throughout the experiment and observed with an intravital microscope equipped with a floating objective. After the intrinsic tone of the DV was established, vehicle ( n = 7), Nω-nitro-l-arginine (l-NNA, 100 μmol/l; n = 13), l-NNA + BQ-123 (a selective ETAreceptor blocker, 1 μmol/l; n = 7), or BQ-123 alone (1 μmol/l; n = 7) was superfused onto the DV. Thereafter, the LAD of the beating heart was occluded. Coronary occlusion produced significant dilation of the DV by 10 ± 4%. When l-NNA was applied, the DV significantly constricted by 12 ± 5% in response to LAD occlusion, and BQ-123 abolished the vasoconstriction. Pretreatment with BQ-123 alone produced an enhancement of the ischemia-induced dilation. We conclude that ischemic myocardium releases transferable vasomotor signals that produce coronary microvascular constriction during the blockade of NO production and the constrictor signal is mediated by ETAreceptors.

A selective endothelin ETA receptor antagonist, SB 234551, improves cerebral perfusion following permanent focal cerebral ischemia in rats

In recent experimental studies, a selective antagonist of endothelin ET(A) receptors, SB 234551, improved neurological and histological outcome in both head trauma and transient focal cerebral ischemia. The present study was conducted to ascertain the degree to which hemodynamic alterations are responsible for this therapeutic effect in a model of permanent middle cerebral artery occlusion (MCAo) in rats. Anesthetized Sprague-Dawley rats were subjected to permanent MCAo by insertion of an intraluminal nylon suture coated with poly-L-lysine. The agent (SB 234551, 30 microg/kg/min = 1.8 mg/kg/h) or vehicle (PBS; 0.6 ml/h) was administered by i.v. infusion beginning 15 min after onset of MCAo and lasting for 23.75 h. Autoradiographic measurement of local cerebral blood flow (lCBF) was performed at 24 h. Physiological data were similar among groups. SB 234551 augmented perfusion by 1.7- to 1.8-fold in both the ischemic hemisphere and in the contralateral (non-ischemic) hemisphere when compared to vehicle-treated ischemic animals. In the ischemic hemisphere, the brain regions significantly benefited were those lying outside the zone of most dense ischemia (i.e., paramedian cortex and thalamus), while in the non-ischemic hemisphere all regions measured showed significant lCBF augmentation. This study demonstrates that SB 234551 therapy results in significant improvement of local cerebral perfusion in the ischemic as well as in the non-ischemic hemispheres after permanent MCAo.

Role of endothelin in α-adrenoceptor coronary vasoconstriction

It has been proposed that α-adrenoceptor vasoconstriction in coronary resistance vessels results not from α-adrenoceptors on coronary smooth muscle but from α-adrenoceptors on cardiac myocytes that stimulate endothelin (ET) release. The present experiments tested the hypothesis that the α-adrenoceptor-mediated coronary vasoconstriction that normally occurs during exercise is due to endothelin. In conscious dogs ( n = 10), the endothelin ETA/ETB receptor antagonist tezosentan (1 mg/kg iv) increased coronary venous oxygen tension at rest but not during treadmill exercise. This result indicates that basal endothelin levels produce a coronary vasoconstriction at rest that is not observed during the coronary vasodilation during exercise. In contrast, the α-adrenoceptor antagonist phentolamine increased coronary venous oxygen tension during exercise but not at rest. The difference between the endothelin blockade and α-adrenoceptor blockade results indicates that α-adrenoceptor coronary vasoconstriction during exercise is not due to endothelin. However, in anesthetized dogs, bolus intracoronary injections of the α-adrenoceptor agonist phenylephrine produced reductions in coronary blood flow that were partially antagonized by endothelin receptor blockade with tezosentan. These results are best explained if α-adrenoceptor-induced endothelin release requires high pharmacological concentrations of catecholamines that are not reached during exercise.

Sex-specific effects of dual ET-1/ANG II receptor (Dear) variants in Dahl salt-sensitive/resistant hypertension rat model

Essential (polygenic) hypertension is a complex genetic disorder that remains a major risk factor for cardiovascular disease despite clinical advances, reiterating the need to elucidate molecular genetic mechanisms. Elucidation of susceptibility genes remains a challenge, however. Blood pressure (BP) regulatory pathways through angiotensin II (ANG II) and endothelin-1 (ET-1) receptor systems comprise a priori candidate susceptibility pathways. Here we report that the dual ET-1/ANG II receptor gene ( Dear) is structurally and functionally distinct between Dahl salt-sensitive, hypertensive (S) and salt-resistant, normotensive (R) rats. The Dahl S S44/M74 variant is identical to the previously reported Dear cDNA with equivalent affinities for both ET-1 and ANG II, in contrast to Dahl R S44P/M74T variant, which exhibits absent ANG II binding but effective ET-1 binding. The S44P substitution localizes to the ANG II-binding domain predicted by the molecular recognition theory, providing compelling support of this theory. The Dear gene maps to rat chromosome 2 and cosegregates with BP in female F2(R×S) intercross rats with highly significant linkage (LOD 3.61) accounting for 14% of BP variance, but not in male F2(R×S) intercross rats. Altogether, the data suggest the hypothesis that modification of the critical balance between ANG II and ET-1 systems through variant Dear contributes to hypertension susceptibility in female F2(R×S) intercross rats. Further investigations are necessary to corroborate genetic linkage through congenic rat studies, to investigate putative gene interactions, and to show causality by transgenesis and/or intervention. More importantly, the data reiterate the importance of sex-specific factors in hypertension susceptibility.

Attenuation of iNOS mRNA exacerbates hypoperfusion and upregulates endothelin-1 expression in hippocampus and cortex after brain trauma

Nitric oxide (NO, a vasodilator) and endothelin-1 (ET-1, a powerful vasoconstrictor) participate in the regulation of brain's microcirculation influencing each other's expression and synthesis. Following injury to the brain, NO is derived largely from the inducible form of nitric oxide synthase (iNOS). We used Marmarou's model of traumatic brain injury (TBI) to study the cerebral blood flow and expression (mRNA) of ET-1 in rats that were pretreated with antisense iNOS oligodeoxynucleotides (ODNs). Intracerebroventricular application of iNOS ODNs resulted in reduced synthesis of iNOS as detected by Western blot analysis. The cerebral blood flow (measured by laser Doppler flowmetry), generally decreased after TBI, was further markedly reduced in the treated animals and remained at low levels up to 48 h post-TBI. The expression of ET-1 (detected by in situ hybridization in cortex and hippocampus) was increased 2-3-fold following TBI alone and this increase reached 5-6-fold in animals pretreated with antisense iNOS ODNs. The results indicate that most likely, NO, generated primarily by iNOS, suppresses ET-1 production and that a decrease of NO results in upregulation of ET-1 via transcriptional and translational mechanisms. Increased availability of ET-1 at the vascular bed and the neuropil may contribute to the altered microvascular reactivity and reduced perfusion of the brain following TBI.

Doxorubicine-congestive heart failure-increased big endothelin-1 plasma concentration: reversal by amlodipine, losartan, and gastric pentadecapeptide BPC157 in rat and mouse

Overall, doxorubicine-congestive heart failure (CHF) (male Wistar rats and NMRI mice; 6 challenges with doxorubicine (2.5 mg/kg, i.p.) throughout 15 days and then a 4-week-rest period) is consistently deteriorating throughout next 14 days, if not reversed or ameliorated by therapy (/kg per day): a stable gastric pentadecapeptide BPC157 (GEPPPGKPADDAGLV, MW 1419, promisingly studied for inflammatory bowel disease (Pliva; PL 10, PLD-116, PL 14736)) (10 microg, 10 ng), losartan (0.7 mg), amlodipine (0.07 mg), given intragastrically (i.g.) (once daily, rats) or in drinking water (mice). Assessed were big endothelin-1 (BET-1) and plasma enzyme levels (CK, MBCK, LDH, AST, ALT) before and after 14 days of therapy and clinical status (hypotension, increased heart rate and respiratory rate, and ascites) every 2 days. Controls (distilled water (5 ml/kg, i.g., once daily) or drinking water (2 ml/mouse per day) given throughout 14 days) exhibited additionally increased BET-1 and aggravated clinical status, while enzyme values maintained their initial increase. BPC157 (10 microg/kg) and amlodipine treatment reversed the increased BET-1 (rats, mice), AST, ALT, CK (rats, mice), and LDH (mice) values. BPC157 (10 ng/kg) and losartan opposed further increase of BET-1 (rats, mice). Losartan reduces AST, ALT, CK, and LDH serum values. BPC157 (10 ng/kg) reduces AST and ALT serum values. Clinical status of CHF-rats and -mice is accordingly improved by the BPC157 regimens and amlodipine.

Cardiac myocytes control release of endothelin-1 in coronary vasculature

Alpha-adrenergic vasoconstriction in the coronary circulation is mediated through alpha-adrenoceptors on cardiac myocytes and subsequent release of endothelin, a very potent, long-lasting vasoconstrictor. Recent studies found that adult cardiac myocytes do not express the preproendothelin gene. Thus we hypothesized that alpha-adrenoceptor stimulation on the cardiac myocytes results in the production of an endothelin-releasing factor, which stimulates the coronary vasculature to produce endothelin. We tested this hypothesis by using an in vitro model in which isolated adult rat cardiac myocytes can be stimulated with an alpha-adrenoceptor agonist (phenylephrine). Their bathing fluid is then transferred to isolated coronary arterioles, and vasoactive responses are measured. To identify the source of endothelin, the endothelin-converting enzyme inhibitor phosphoramidon was added to either the myocytes or the isolated arterioles. Phenylephrine enhanced the vasoconstrictor properties of the myocyte bathing fluid. Administration of phosphoramidon (in either the presence or the absence of phenylephrine) to the myocytes had no effect on the vasoactive properties of the bathing fluid. In contrast, administration of phosphoramidon to the isolated arteriole before administration of the bathing fluid converted vasoconstriction to vasodilation, similar to the effect of the endothelin A receptor antagonist JKC-301, indicating that the endothelin is indeed produced by the coronary vasculature. Administration of the angiotensin type 1 receptor antagonist losartan to the vessel bath enhanced vasodilation to the bathing fluid of the phenylephrine-treated but not control myocytes. In conclusion, during alpha-adrenergic activation cardiac myocytes release a factor, probably angiotensin II, that stimulates the vascular production of endothelin. Although the physiological implications of this mechanism are not obvious, this may represent a protective mechanism that integrates neuronal vasoconstrictor mechanisms with myocardial metabolism, which minimizes periods of both coronary underperfusion and overperfusion.

Nitric oxide, angiotensin II, and hypertension

Although initially adaptive, the changes that accompany hypertension, namely, cell growth, endothelial dysfunction, and extracellular matrix deposition, eventually can become maladaptive and lead to end-organ disease such as heart failure, coronary artery disease, and renal failure. A functional imbalance between angiotensin II (Ang II) and nitric oxide (NO) plays an important pathogenetic role in hypertensive end-organ injury. NO, an endogenous vasodilator, inhibitor of vascular smooth muscle and mesangial cell growth, and natriuretic agent, is synthesized in the endothelium by a constitutive NO synthase. NO antagonizes the effects of Ang II on vascular tone, cell growth, and renal sodium excretion, and also down-regulates the synthesis of angiotensin-converting enzyme (ACE) and Ang II type 1 receptors. On the other hand, Ang II decreases NO bioavailability by promoting oxidative stress. A better understanding of the pathophysiologic mechanisms involved in hypertensive end-organ damage may aid in identifying markers of cardiovascular susceptibility to injury and in developing therapeutic interventions. We propose that those antihypertensive agents that lower blood pressure and concomitantly restore the homeostatic balance of vasoactive agents such as Ang II and NO within the vessel wall would be more effective in preventing or arresting end-organ disease.

Mechanisms underlying enhanced contractile response to endothelin-1 in diabetic rat basilar artery

We investigated the influence of streptozotocin-induced diabetes on the responsiveness of the rat basilar artery to endothelin-1 (ET-1) and nitric oxide (NO), which is known to counteract ET-1. In basilar arteries isolated from diabetic rats: (a) the ET-1-induced contraction was enhanced, (b) the contraction induced by N(G)-nitro-l-arginine [a nitric oxide synthase (NOS) inhibitor] was weaker, and (c) the levels of the mRNAs for ET(A)/ET(B) receptors and prepro-ET-1, but not for NOS, were significantly elevated (all versus age-matched controls). These data indicate that ET-1-induced vasoconstriction may be increased in the diabetic rat basilar artery, and that this hyper-reactivity to ET-1 may be due to an overproduction of ET-1, an up-regulation of ET(A)/ET(B) receptors, and a defect in the bioavailability of NO.

Physiology of the endothelium

In the past, the endothelium was considered to be inert, described as a 'layer of nucleated cellophane', with only non-reactive barrier properties, such as presentation of a non-thrombogenic surface for blood flow and guarding against pro-inflammatory insults. However, it is now becoming clear that endothelial cells actively and reactively participate in haemostasis and immune and inflammatory reactions. They regulate vascular tone via production of nitric oxide, endothelin and prostaglandins and are involved in the manifestations of atherogenesis, autoimmune diseases and infectious processes. They produce and react to various cytokines and adhesion molecules and it is now clear that they can mount anti- and pro-inflammatory and protective responses depending on environmental conditions and are key immunoreactive cells. Endothelial dysfunction or activation also contributes to a variety of disease states.

Role of Membrane Potential and Expression of Endothelial Factors in Restenosis After Angioplasty in SHR

We examined the roles played by impaired K + channels, diminished nitric oxide (NO) production, endothelin release, and smooth muscle membrane potential in the increased restenosis observed in spontaneously hypertensive rat (SHR) carotid arteries after angioplasty. The SHR carotid was found to be less polarized than that of normotensive Wistar rats (NWR), and it was further depolarized by the α 2 agonist UK 14,304. This response was blocked by iberiotoxin, indicating that calcium-dependent K + channels operate normally in the SHR carotid. Acetylcholine caused a hyperpolarization that was significantly smaller in SHR than in NWR carotids, indicating a deficient release of NO in the SHR. After angioplasty, SHR and NWR vessels were depolarized, returning to baseline after 10 days. In the SHR but not in the NWR the contralateral carotid was also depolarized, and this was prevented by the endothelin A/B receptor antagonist bosentan. After angioplasty, endothelin-1 plasma levels increased in both SHR and NWR, but the increase was significantly more prolonged in SHR. We found that the more pronounced restenosis observed in the SHR carotid after angioplasty is not due to impairment of calcium-dependent K + channels but is related to the relatively depolarized vascular smooth muscles, involving endothelin release caused by reduced NO levels in that strain.

Flow-induced endothelium-dependent vasoreactivity in rat mesenteric arterial bed

We studied rat mesenteric arterial beds to determine the relationship between the effects of flow-induced shear stress and agonists on mesenteric vasoreactivity. When beds were perfused at gradually increasing flow rates, perfusion pressure was flow rate-dependently increased. The flow rate-mediated increase in perfusion pressure was significantly enhanced by N(G)-nitro-L-arginine (L-NOARG) plus methylene blue (MB) and slightly enhanced by treatment with tetraethylammonium (TEA). In the presence of L-NOARG, MB, TEA, and indomethacin, the flow rate-induced increase in perfusion pressure was significantly enhanced, but this enhancement was significantly inhibited by combined treatment with BQ-123 plus BQ-788 (ET(A)- and ET(B)- receptor antagonists, respectively). The ET-1 content of the perfusate was significantly increased following combined pretreatment with L-NOARG, MB, TEA, and indomethacin at a high flow rate. The methoxamine-induced contraction was significantly enhanced by NOS inhibition in both high- and low- flow-treated groups. The released nitrite level was significantly greater in high-flow-loaded than in the low-flow-loaded beds. We conclude that in this model, the response of vascular tone to flow stimulation is subtly regulated by endothelium-derived factors (especially, NO, endothelium-derived hyperpolarizing factor, and ET-1), and that these factors interact with each other.

Expression of nitric oxide synthase isoforms in the human placenta is not altered by labor

Nitric oxide has various biological activities including smooth muscle relaxation, anti-inflammatory activity, anti-coagulatory activity. As the human placenta is known to express nitric oxide synthases, this study investigated the possible effect of labor on the expression of endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) in human placental tissues at term. Both eNOS and iNOS mRNA expression in placental tissues in labor were significantly higher than those in the amnion, chorion laeve, decidua vera and myometrium. The eNOS mRNA and protein expressions in placental tissues in labor (n = 12) were 1.6023 +/- 0.1652 (eNOS/GAPDH, mean +/- SEM) and 12.8 +/- 1.3 arbitrary units (AU), respectively, which were similar to those not in labor (n = 10), 1.5806 +/- 0.2042 (eNOS/GAPDH) and 11.4 +/- 1.8 AU. The iNOS mRNA and protein expressions in the placental tissues in labor were 1.2831 +/- 0.2436 (iNOS/GAPDH) and 10.7 +/- 2.1 AU respectively, similar to those not in labor, 1.9254 +/- 0.8004 (iNOS/GAPDH) and 13.3 +/- 1.8 AU. The guanosine 3',5'-cyclic monophosphate (cGMP) concentration in the placental tissues in labor was 23.6 +/- 1.4 fmol/g wet tissue, similar to that not in labor, 26.1 +/- 2.0 fmol/g wet tissue. These findings suggest that nitric oxide production in the human placenta is maintained during labor.

Endothelial cell functions

Endothelial cells play a wide variety of critical roles in the control of vascular function. Indeed, since the early 1980s, the accumulating knowledge of the endothelial cell structure as well as of the functional properties of the endothelial cells shifted their role from a passive membrane or barrier to a complex tissue with complex functions adaptable to needs specific in time and location. Hence, it participates to all aspects of the vascular homeostasis but also to physiological or pathological processes like thrombosis, inflammation, or vascular wall remodeling. Some of the most important endothelial functions will be described in the following review and more specifically, their role in blood vessel formation, in coagulation and fibribolysis, in the regulation of vascular tone as well as their participation in inflammatory reactions and in tumor neoangiogenesis.

Modulation and roles of the endothelins in the pathophysiology of pulmonary embolism

Recent research on the endothelins (ETs) and their pathways in acute pulmonary embolism (APE) has led to significant advances in the understanding of this disease. ETs are potent vasoconstrictors and bronchoconstrictors found abundantly in the lung and can be released by stimuli such as endothelial injury, hypoxia, or thrombin, a key product in the coagulation cascade. Many studies using different approaches and methods of inducing pulmonary embolization, both in vitro and in vivo in various species, have mostly shown that ETs play an important role in the pathophysiology of APE. These results were obtained by comparing the hemodynamic data in the presence or absence of various ETs inhibitors, but also by assessing the modulation of the ET-related elements of this system by molecular, cell biology, and pharmacological methods. Based on the current understanding, a mechanism involving the ET pathway in the pathophysiology of APE is proposed for the reader's considerations. We postulate that ETs are primary mediators in APE based on the following: (i) their source from pulmonary endothelial cells where the primary injury takes place; (ii) their direct vasconstrictive, bronchoconstrictive, and promitogenic effects via distinct ET receptors; and (iii) their indirect effects associated with the secondary release of thromboxane and other mediators, which are released from inflammatory cells and platelets, which together can potentiate the overall hemodynamic response, most specifically the pulmonary vascular bed. Such combined effects of ETs on bronchomotor and vasomotor tone in the lung can adversely affect ventilation perfusion matching and lead to severe hypoxemia without causing significant changes in the chest X-ray of these patients. Thus, we may consider ET inhibitors as future current therapeutic agents in patients with PE.