Endothelin and calcium antagonists in the skin microcirculation of patients with coronary artery disease

Perioperative diltiazem or nitroglycerin in on-pump coronary artery bypass: A systematic review and network meta-analysis

Background

Arterial graft spasm is a severe complication after coronary artery bypass graft (CABG). Among numerous potential antispasmodic agents, systemic application of diltiazem and nitroglycerin had been investigated most frequently over the past three decades. However, it remains inconclusive if either or both agents could improve patient outcomes by preventing graft spasm when applied perioperatively, and, if so, which one would be a better choice. The current systematic review and network meta-analysis aims to summarize the data from all available randomized clinical trials of perioperative continuous intravenous infusion of diltiazem and/or nitroglycerin in patients undergoing on-pump CABG in order to define and compare their roles in graft spasm prevention and their impacts on perioperative outcomes.

Methods

We searched Ovid Medline, PubMed, CINAHL, Google Scholar and Cochrane Center for randomized controlled trials that reported outcome effects of perioperative continuous intravenous infusion of diltiazem and/or nitroglycerin in patients undergoing elective on-pump CABG. Conventional meta-analyses were conducted to evaluate the pairwise comparisons (diltiazem vs. placebo; nitroglycerin vs. placebo; diltiazem vs. nitroglycerin) on perioperative outcomes. Network meta-analyses were implemented to compare the three regimens through direct and indirect comparison.

Results

Twenty-seven studies involving 1,660 patients were included. Pairwise and network meta-analyses found no significant difference in mortality among the groups. There are four studies that reported blood flow measurements of internal mammary artery grafts intraoperatively after dissecting or immediately after distal anastomosis while patients were on continuous intravenous infusion of diltiazem and nitroglycerin. Although insufficient for data synthesis, the measured results from all four studies suggest that both diltiazem and nitroglycerin significantly increased blood flow of arterial grafts compared to placebo. For other perioperative outcomes, compared to diltiazem, patients that received nitroglycerin had higher odds of postoperative atrial fibrillation (OR = 2.67, 95% CI: 1.15 to 6.24) and higher peak serum cardiac enzymes. Patients that received placebo had higher odds of atrial fibrillation (OR = 3.00, 95% CI: 1.18 to 7.63) and lower odds of requiring inotrope support (OR = 0.19, 95% CI: 0.04 to 0.73) compared to diltiazem. Data from the network meta-analysis indicated that diltiazem had significantly lower odds of postoperative atrial fibrillation compared to nitroglycerin (OR = 0.39, 95% CI: 0.18 to 0.85). In fact, the rank from highest to lowest rates of postoperative atrial fibrillation was placebo>nitroglycerin>diltiazem. The rank from highest to lowest odds of requiring inotropic support is nitroglycerin> diltiazem>placebo. However, placebo had significantly higher odds of postoperative myocardial infarction than diltiazem (OR = 4.51, 95% CI: 1.34 to 15.25). The rank from highest to lowest odds of postoperative myocardial infarction, transient cardiac ischemic event and atrial fibrillation is placebo>nitroglycerin>diltiazem.

Conclusion

Compared to nitroglycerin and placebo, perioperative continuous intravenous infusion of diltiazem had stronger protective effects against postoperative ischemic cardiac injuries and atrial fibrillation although patients may need more inotropic support. The increased blood flow from diltiazem use in arterial grafts may potentially contribute to the drug’s outcome benefits.

The effect of nitric oxide synthase and cyclooxygenase inhibition on cutaneous microvascular reactivity

The role of nitric oxide (NO)- and prostacyclin (PGI(2))-independent mechanism, potentially attributable to endothelium-derived hyperpolarizing factor (EDHF), has not been extensively studied in human skin microcirculation. The aim of our study was to elucidate the contribution of the NO- and PGI(2)-independent mechanism to microvascular reactivity of cutaneous microcirculation. Skin perfusion was measured on the volar aspect of the forearm in 12 healthy male subjects (mean age 25.0 +/- 1.5), using laser Doppler (LD) fluxmetry. Combined endothelial nitric oxide synthase (eNOS) and cyclooxygenase (COX) inhibition was achieved by an intradermal injection (10 microl) of the eNOS inhibitor, L(omega)-monomethyl L-arginine (L-NMMA, 10 mM) and the COX inhibitor, diclofenac (10 mM); saline was injected as a control. LD flux was assessed at rest and after an iontophoretical application of acetylcholine (ACh, 1%), an endothelial agonist and sodium nitroprusside (SNP, 1%), an endothelium-independent agonist, respectively. Combined eNOS and COX inhibition had no effect on the baseline LDF (12.5 +/- 2.3 PU (perfusion units) in control vs. 10.9 +/- 1.8 PU in the treated site). On the other hand, the ACh-stimulated increase in LDF was significantly attenuated after eNOS and COX inhibition (390.5 +/- 43.5%), compared to the control (643.7 +/- 80.3% increase, t-test, P < 0.05). Nevertheless, at least 60% of ACh-mediated vasodilatation was preserved after combined eNOS and COX inhibition. eNOS and COX inhibition had no impact on the SNP-stimulated increase in LDF (768.8 +/- 70.5% in control vs. 733.5 +/- 54.6% in the treated site). These findings indicate that NO- and PGI(2)-independent mechanism plays an important role in the regulation of blood flow in the human skin microcirculation.

Laser Doppler imager (LDI) scanner and intradermal injection for in vivo pharmacology in human skin microcirculation: responses to acetylcholine, endothelin-1 and their repeatability

AIMS

The purpose of this study was to evaluate the repeatability of forearm skin blood flow responses to intradermal injections of acetylcholine (ACh) and endothelin-1 (ET-1) using a double injection technique (DIT) and a laser Doppler imager (LDI) scanner in the human skin microcirculation.

METHODS

We used a laser Doppler imager (Moor LDI V3.01) to continuously monitor the change in skin blood flow during intradermal administration of physiological saline (0.9% NaCl), acetylcholine (ACh 10(-7), 10(-8), 10(-9) M) and endothelin-1 (ET-1 10(-14), 10(-16), 10(-18) M) in 10 healthy male subjects. Subjects were examined on 3 different days for assessment of interday and interobserver repeatability. Injections of either drug were randomly placed on different sites of the forearm. Laser Doppler images were collected before and after injection at 2.5 min intervals for 30 min. Data were analysed after the completion of each experiment using Moor Software V.3.01. Results are expressed as changes from baseline in arbitrary perfusion units (PU).

RESULTS

ACh caused a significant vasodilation (P < 0.0001 anova, mean +/- SE: 766 +/- 152 PU, ACh 10(-9) M; 1868 +/- 360 PU, ACh 10(-8) M; 4188 +/- 848 PU, ACh 10(-7) M; mean of days 1 and 2, n = 10), and ET-1 induced a significant vasoconstrictive response (P < 0.0001 anova, -421 +/- 83 PU, ET-1 10(-18) M; -553 +/- 66 PU, ET-1 10(-16) M; -936 +/- 90 PU, ET-1 10(-14) M; mean of days 1 and 2, n = 10). There was no difference on the response to either drug on repeated days. Bland-Altman analyses showed a close agreement of responses between days with repeatability coefficients of 1625.4 PU for ACh, and 386.0 PU for ET-1 (95% CI: ACh, -1438 to 1747 PU, ET-1, -399 to 358 PU) and between observers with repeatability coefficients of 1057.2 PU for ACh and 255.8 PU for ET-1 (95% CI: ACh, -1024 to 1048 PU, ET-1, -252 to 249 PU). The variability between these responses was independent of average flux values for both ACh and ET-1. There was a significant correlation between responses measured in the same site, in the same individual on two different days by the same observer (ACh, r = 0.94, P < 0.0001; ET-1, r = 0.90, P < 0.0006), and between responses measured by two different observers (ACh, r = 0.94, P < 0.0001; ET-1, r = 0.91, P < 0.0003).

CONCLUSION

We have shown that interday and intraobserver responses to intradermal injections of ET-1 and ACh, assessed using the DIT in combination with an LDI scanner, exhibited good reproducibility and may be a useful tool for studying the skin microcirculation in vivo.

Ischemic heart disease down-regulates angiotensin type 1 receptor mRNA in human coronary arteries

Angiotensin II is important in the development of cardiovascular disease. In the present study, angiotensin II receptor mRNA levels were quantified by real-time polymerase chain reaction (real-time PCR) in human coronary arteries from patients with ischemic heart disease and controls. Furthermore, the suitability of artery culture for studying angiotensin receptor changes was evaluated by in vitro pharmacology and real-time PCR. The angiotensin type 1 (AT1) receptor mRNA levels were down-regulated in human coronary arteries from patients with ischemic heart disease as compared to controls (P<0.05). Culture of coronary arteries for 48 h induced down-regulation of the angiotensin AT1 and AT2 receptor mRNA levels and also a less efficacious angiotensin II-induced vasoconstriction (Emax=103+/-2% before and 23+/-7% after artery culture, P<0.001). Artery culture may thus be a suitable method for studying angiotensin receptor regulation.

Endothelin-B-receptor-selective antagonist inhibits endothelin-1 induced potentiation on the vasoconstriction to noradrenaline and angiotensin II

OBJECTIVE

Endothelin-A-receptor-antagonists inhibit angiotensin II- and noradrenaline-induced vasoconstriction. Whether functional constrictive endothelin-B-receptors play a role in the endothelin-1-mediated potentiation of vasoconstriction to angiotensin II and noradrenaline is thus far unknown.

METHODS

We studied the effects of noradrenaline and angiotensin II (10 mol/l) in the presence of exogenous endothelin-1 (10 mol/l) with and without selective endothelin-B-receptor-blockade by BQ-788 (10 mol/l) and dual receptor blockade with BQ-788 and the endothelin-A-selective antagonist BQ-123 (10 mol/l) in 14 healthy male volunteers (aged 20-28). Studies were performed in the human skin microcirculation under in vivo conditions using laser-Doppler flowmetry and double injection technique. The area under the time-response curve of all doses was calculated.

RESULTS

Endothelin-1 potentiated the effects of angiotensin II and noradrenaline (-944 +/- 139 perfusion units (PU), P < 0.01; -926 +/- 117 PU, P < 0.05, respectively). In the presence of BQ-788, the potentiating effect of endothelin-1 was significantly blunted (-624 +/- 132 PU, P < 0.01; -549 +/- 136 PU, P < 0.01, respectively). In the presence of BQ-123 and BQ-788 the vasoconstriction was fully inhibited (431 +/- 108 PU, P < 0.001 and 421 +/- 86 PU, P < 0.001, respectively).

CONCLUSIONS

These data suggest that functional vasoconstrictive endothelin-B receptors on vascular smooth muscle cells may contribute to the potentiating effects of high local concentrations of endothelin-1 on the vasoconstriction to noradrenaline and angiotensin II in human microcirculation.

Increased plasma endothelin-1 levels in patients with progressive open angle glaucoma

AIM

To compare the plasma levels of endothelin-1 (ET-1) between patients with primary open angle glaucoma with visual field progression despite normal or normalised intraocular pressure and patients with stabile visual fields in a retrospective study.

METHODS

The progressive group consisted of 16 primary open angle glaucoma patients and the group with stable visual field consisted of 15 patients. After a 30 minute rest in a supine position, venous blood was obtained for ET-1 dosing. Difference in the plasma level of ET-1 between two groups was compared by means of analysis of covariance (ANCOVA), including age, sex, and mean arterial blood pressure as covariates.

RESULTS

ET-1 plasma levels were found to be significantly increased in patients with deteriorating (3.47 (SD 0.75) pg/ml) glaucoma when compared to those with stable (2.59 (SD 0.54) pg/ml) visual fields (p = 0.0007).

CONCLUSIONS

Glaucoma patients with visual field progression in spite of normal or normalised intraocular pressure have been found to have increased plasma endothelin-1 levels. It remains to be determined if this is a secondary phenomenon or whether it may have a role in the progression of glaucomatous damage.

Endothelins and their inhibition in the human skin microcirculation: ET[1-31], a new vasoconstrictor peptide

AIMS

Endothelin-1 (ET-1([1-21])) is an extremely potent vasoconstrictor in the human skin microcirculation and is generated from larger precursor peptides. The aims of the present study were to assess the vasoactive effects of these precursors as well as endothelin blockade in the human skin microcirculation, in vivo.

METHODS

Six healthy volunteers received intradermal injections of a range of doses of big ET-1([1-38]), ET-1([1-31]), ET-1([1-21]), BQ-123 (ET(A) receptor antagonist), BQ-788 (ET(B) receptor antagonist), phosphoramidon [endothelin converting enzyme (ECE) inhibitor] or saline control (0.9%). Skin blood flow (SBF) was measured using standard laser Doppler flowmetry.

RESULTS

Big ET-1([1-38]), ET-1([1-31]) and ET-1([1-21]) reduced SBF when compared with saline control (P < 0.01 for all). Big ET-1([1-38]) and ET-1([1-31]) were less potent than ET-1([1-21]) as defined by skin vasoconstriction. Phosphoramidon, BQ-123 and BQ-788, given alone, all caused vasodilatation in the human skin microcirculation (P < 0.01 for all).

CONCLUSIONS

In the human skin microcirculation, big ET-1([1-38]) and ET-1([1-31]) are less potent vasoconstrictors than ET-1([1-21]). The effects of big ET-1([1-38]) and phosphoramidon suggest the presence of endogenous ECE activity in the skin. In contrast to skeletal muscle resistance vessels, ET-1([1-21]) contributes to the maintenance of skin microvascular tone through both ET(A) and ET(B) receptor-mediated vasoconstriction.

Effects of a topical enamel matrix derivative on skin wound healing

Enamel matrix derivative, obtained from developing porcine teeth, is composed mainly of amelogenin proteins and used topically in periodontal surgery for advanced periodontitis to regenerate lost connective tissues. The primary objective of this study was to investigate the effects of enamel matrix derivative on skin wound healing. Secondly, in vitro effects of enamel matrix derivative on dermal fibroblasts and microvascular endothelial cells were examined. Full-thickness, circular 2-cm skin wounds in white 16-week-old rabbits were treated thrice weekly with enamel matrix derivative (30 mg/ml) in the vehicle propylene glycol alginate or with vehicle alone. Enamel matrix derivative treatment increased the amount of granulation tissue and accelerated time to complete epithelialization by 3 days (p < 0.001) compared to vehicle treatment. In cultured fibroblasts, vascular endothelial growth factor levels in conditioned media were increased more than fivefold (p < 0.001) with enamel matrix derivative treatment (0.1mg/ml) over control, measured by specific enzyme-linked immunosorbent assay. Enamel matrix derivative also increased release of matrix metalloproteinase-2 more than threefold from fibroblasts (p < 0.001) and from endothelial cells (p < 0.001). Thus, enamel matrix derivative significantly accelerated wound closure in rabbits, possibly by increasing levels of growth factors and proteinases important for granulation tissue formation and remodeling.

Ischemic heart disease induce upregulation of endothelin receptor mRNA in human coronary arteries

Endothelin has been implicated in the pathogenesis of ischemic heart disease and congestive heart failure. The aims were to quantify endothelin type A (ETA) and type B (ETB) receptor mRNA levels in human coronary arteries from patients with ischemic heart disease, congestive heart failure and controls using real-time polymerase chain reaction (real-time PCR). In addition, the suitability of organ culture as a model mimicking endothelin receptor changes in cardiovascular disease was evaluated by in vitro pharmacology and real-time PCR. Endothelin ETA and ETB receptor mRNA levels were significantly higher in arteries from patients with ischemic heart disease (0.23+/-0.04 and 0.35+/-0.06) as compared to congestive heart failure (0.09+/-0.02 and 0.07+/-0.01) and controls (0.08+/-0.02 and 0.08+/-0.01). After organ culture, the endothelin ETB receptor mRNA levels were elevated, and the sarafotoxin 6c-induced vasoconstriction was more efficacious. Increased endothelin receptor activity may contribute to the increased vascular tone and development of atherosclerotic disease in ischemic heart disease in man.

Statins enhance postischemic hyperemia in the skin circulation of hypercholesterolemic patients: a monitoring test of endothelial dysfunction for clinical practice?

OBJECTIVES

The present study aims to investigate whether laser Doppler flowmetry can be used to monitor improvements in vascular function during statin therapy.

BACKGROUND

Endothelial dysfunction is an early feature of atherosclerosis in hypercholesterolemic patients and can be improved by statins. There are several methods to assess endothelial function in vivo, none of them being feasible in everyday practice.

METHODS

Skin perfusion, measured by laser Doppler flowmetry, was assessed at rest and during reactive hyperemia. Nineteen hypercholesterolemic patients (age 42 to 73 years, total cholesterol 5.4 to 9.6 mmol/l) were studied before and during statin therapy. To further investigate the mechanisms, postischemic skin hyperemia was measured before and after intradermal injection of the nitric oxide synthase inhibitor L-NAME and its inactive isoform D-NAME (0.5 micromol/10 microl each). On a separate day, the healthy volunteers were reexamined before and 2 h after 1,000 mg aspirin.

RESULTS

Postischemic skin blood flow was markedly reduced in hypercholesterolemic patients (45 +/- 11%) compared with healthy controls (238 +/- 20%, p < 0.0001) and improved after statin therapy (113 +/- 15%, p = 0.0005 vs. pre-treatment). In the healthy volunteers, the hyperemic responses were not significantly different after L-NAME and D-NAME. Aspirin reduced hyperemia from 274 +/- 49% to 197 +/- 40% (p = 0.025).

CONCLUSIONS

Reactive hyperemia of the skin microcirculation can be easily and reproducibly assessed by laser Doppler flowmetry. Vasodilator prostaglandins are the major mediators of postischemic skin hyperemia, which is impaired in hypercholesterolemic patients and can be enhanced by cholesterol-lowering therapy. Thus, laser Doppler flowmetry may represent a tool to assess and monitor vascular function during therapy in everyday practice.

Validation of laser Doppler flowmetry coupled with intra-dermal injection for investigating effects of vasoactive agents on the skin microcirculation in man

OBJECTIVE

To determine the reproducibility of laser Doppler flowmetry coupled with intra-dermal saline delivery.

METHODS

Delivery of saline was judged visually by two operators ( n=100), using a graduated syringe (Becton-Dickinson), by expelling saline onto a weighing boat. Volume was assessed by weight. Skin blood flow following intra-dermal injection of saline was assessed in 18 healthy volunteers; 10 attended twice to assess between-day reproducibility, and 8 attended once to assess between-site reproducibility. Results are expressed as mean value+/-SEM and 95% confidence interval for mean differences.

RESULTS

There was no difference between operators in mean injection weight, both weights being 10.3+/-0.1 mg (mean difference 0.08, 95% confidence interval, CI -0.23 to 0.39 mg; n=100, P=0.9). Intra-dermal saline caused a nine-fold increase in blood flow (0.03+/-0.003 to 0.27+/-0.02 perfusion units, PU; n=18, P<0.001). This response had a rapid onset, with the maximal effect seen at 4 min and a duration of greater than 30 min. There was no difference in the magnitude of the response between the dominant and non-dominant arms, AUC was 2.9+/-0.4 and 2.9+/-0.4, respectively (mean difference -0.05, 95% CI -0.8 to 0.73 PU; n=18, P=0.93). However, there was a trend towards differences between study visits 1 and 2: AUC was 3.2+/-0.6 and 2.0+/-0.5, respectively (mean difference 1.2, 95% CI -0.03 to 2.43 PU; n=10, P=0.7). There was no difference in the magnitude of responses between different sites on the forearm ( n=64, P=0.6).

CONCLUSIONS

These studies demonstrate that the technique of laser Doppler flowmetry coupled with intra-dermal injection is a safe, well-tolerated technique with good reproducibility. A trend towards reduced between-day reproducibility emphasizes the importance of vehicle control sites when investigating the effects of vasoactive compounds. This technique provides a reliable method for the intra-dermal delivery of drugs, despite the direct effect of injection of saline on blood flow.

Will endothelin receptor antagonists have a role in heart failure?

Mixed ET(A/B) and selective ET(A) receptor antagonists showed promising hemodynamic and symptomatic improvements in patients with heart failure. Randomized, clinical trials to investigate the effects of ET receptor antagonists on survival in patients with heart failure still need to be conducted. Also, the effects of selective ET(A) and mixed ET(A/B) receptor antagonists on the clinical outcome of patients with CHF will have to be assessed.

Endothelin receptors in endothelium-denuded human coronary artery bypass grafts and coronary arteries

BACKGROUND

Coronary artery bypass graft (CABG) surgery is hampered by deleterious vasospasm in the vessel wall, especially in vein grafts. Endothelin (ET) is a strong vasoconstrictor that can be observed in increasing concentrations during CABG surgery.

METHODS

Endothelin-induced vasoconstriction was evaluated in isolated, endothelium-denuded vessel segments of the human saphenous vein (SV), left internal mammary artery (LIMA), and coronary arteries. The ET(A) and ET(B) receptor mRNA levels were quantified by real-time polymerase chain reaction (PCR) analysis.

RESULTS

The ET(A) and ET(B) receptor mRNA levels were significantly higher in the SV than in the LIMA and the coronary arteries. ET-1 induced a more efficacious contraction in the SV and LIMA as compared with in the coronary arteries. The ET(B) receptor agonist, Sarafotoxin 6c (S6c) stimulated constriction of the LIMA and SV, while inactive in the coronary arteries. The concentration-response curve for S6c was biphasic, suggesting activation of ET(A) receptors at high concentrations as this response could be inhibited by FR139317 (10 micromol/L), and ET(B) at low concentrations as this response could be inhibited by BQ788 (0.1 micromol/L).

CONCLUSIONS

Endothelin-induced vasoconstriction is mediated by ET(A) receptors alone in coronary arteries, while a combination of ET(A) and ET(B) receptors are of importance in SV and LIMA. Expression of contractile ET(B) receptors may be a pharmacologic disadvantage that contributes to the vasospasm during CABG surgery. The lower levels of ET(A) and ET(B) receptor mRNA in the LIMA and coronary arteries as compared with in the SV may provide one explanation for the better long- and short-term patency of LIMA as compared with SV grafts.

Protein kinase C inhibitors decrease endothelin ET(B) receptor mRNA expression and contraction during organ culture of rat mesenteric artery

The effect of protein kinase C (PKC) inhibitors on the induction of endothelin ET(B) receptors during organ culture was examined in isolated segments of the rat mesenteric artery. After 24 h of organ culture, the endothelin ET(B) receptor agonist sarafotoxin 6c (S6c) induced a strong contraction compared to fresh segments. The contractile response after 24-h organ culture to S6c was studied in presence (30-min preincubation) or absence, after 24-h treatment, of the PKC inhibitors staurosporine, K252a and Ro31-7549. Exposure to staurosporine or K252a in presence and after 24-h treatment reduced the S6c contraction. In contrast, presence of 2-1[1-3(aminopropyl)indol-3-yl]-3(1-methyl-1H-indol-3-yl)maleimide (Ro31-7549), did not affect the S6c-induced contraction, whereas 24-h treatment abolished the increase of contraction. The PKA inhibitor N-(2-[bromocinnamylamino]-ethyl)-5-isoquinolinesulfonamide (H89) did not affect the S6c responses. The mRNA expressions of endothelin ET(B) receptors (analysed with real-time PCR) were abolished after 24-h treatment with the PKC inhibitors. These results suggest that PKC is involved in the endothelin ET(B) receptor upregulation following organ culture.

Enhanced vasoconstriction to endothelin-1, angiotensin II and noradrenaline in carriers of the GNB3 825T allele in the skin microcirculation

Hypertension is associated with enhanced peripheral vascular resistance, which may be mediated by enhanced vasoconstriction. The impact of the recently detected G-protein beta3-subunit gene C825T polymorphism on the response to the major pressor mediators has been studied in vivo in the human microcirculation. We assessed the effects of endothelin-1 (ET-1), angiotensin II (AT), endothelin-antagonists (BQ-123 and BQ-788) and noradrenaline (NA, each 10-16-10-8 mol) on vasoconstriction in the human skin microcirculation in vivo in 25 healthy male volunteers (13 with CC genotype, 12 TC/TT genotype) using laser Doppler flowmetry. The effects of endothelium-derived vasodilation on NA-induced effects were studied using the NO-synthase inhibitor l-nitro-monomethyl-arginine (L-NMMA) and the alpha2-adrenoceptor-antagonist yohimbine (YO). ET-1, AT and NA caused a dose-dependent vasoconstriction (P < 0.001). In carriers of the 825T allele the response to ET-1, AT and NA was significantly enhanced leading to a shift to the left of the dose-response curve of up to two log units (ET-1: P < 0.001 vs. CC; AT: P < 0.01 vs. CC; NA: P < 0.05 vs. CC). After pretreatment with L-NMMA or YO, NA induced vasoconstriction was no longer different between subjects with the CC- and CT/TT genotypes. However, following combined pretreatment with both L-NMMA and YO, vasoconstriction to NA was significantly potentiated in carriers of the T-allele. Vasodilatation to an ETA-antagonist (BQ-123) was more pronounced in the CT/TT genotype, while ETB-antagonism (BQ-788) led to a more pronounced vasoconstriction in the CT/TT genotype (not significant vs. CC). Healthy, normotensive carriers of the 825T-allele have enhanced vasoconstriction to ET-1, AT and NA in the skin microcirculation. This enhanced vasoconstriction appears to be partially antagonized by an enhanced release of endothelium derived vasodilators mediated by the stimulation of endothelial alpha2-adrenoceptors. The GNB3 C825T polymorphism is potentially an attractive pharmacogenetic marker to predict hormone-mediated responses in humans.

Role of infection in atherosclerosis and coronary artery disease: a new therapeutic target?

There is growing evidence that inflammatory processes may be involved in the development of atherosclerosis and its complications. Viral and bacterial pathogens have been implicated as possible causative factors in the pathogenesis of coronary artery disease and postangioplasty restenosis. Antibiotic trials have been completed examining which treatment of infection can prevent the complications of coronary artery disease. In high-risk patients, the results of these most recent studies have not revealed any benefit of treatment.

Organ culture: a new model for vascular endothelium dysfunction

BACKGROUND

Endothelium dysfunction is believed to play a role in the development of cardiovascular disease. The aim of the present study was to evaluate the suitability of organ culture as a model for endothelium dysfunction.

METHODS

The isometric tension was recorded in isolated segments of the rat mesenteric artery branch, before and after organ culture for 20 h. Vasodilatation was expressed as % of preconstriction with U46619. The acetylcholine (ACh) induced nitric oxide (NO) mediated dilatation was studied in the presence of 10 microM indomethacin, 50 nM charybdotoxin and 1 microM apamin. Endothelium-derived hyperpolarising factor (EDHF) was studied in the presence of 0.1 mM L-NOARG and indomethacin. Prostaglandins were studied in the presence of L-NOARG, charybdotoxin and apamin.

RESULTS

The ACh-induced NO and prostaglandin-mediated dilatations decreased significantly during organ culture (NO: 84% in control and 36% in cultured; prostaglandins: 48% in control and 16% in cultured). Notably, the total ACh-dilatation was not changed. This might be explained by the finding that EDHF alone stimulated a full dilatation even after organ culture (83% in control and 80% in cultured). EDHF may thereby compensate for the loss in NO and prostaglandin-mediated dilatation. Dilatations induced by forskolin or sodium nitroprusside did not change after organ culture, indicating intact smooth muscle cell function.

CONCLUSIONS

Organ culture induces a loss in NO and prostaglandin-mediated dilatation, which is compensated for by EDHF. This shift in mediator profile resembles that in endothelium dysfunction. Organ culture provides an easily accessible model where the molecular changes that take place, when endothelium dysfunction is developed, can be examined over time.

Endothelin receptor antagonists in cardiology clinical trials

Endothelin-1 (ET-1) is enhanced and has been demonstrated to be a prognostic marker in patients with advanced stages of heart failure, acute ischaemic syndromes, myocardial infarction and pulmonary hypertension. Activation of the endothelin (ET) system is associated with adverse haemodynamic consequences in patients with congestive heart failure and results in coronary vasoconstriction in patients with coronary artery disease (CAD). Moreover, ET-1 raises blood pressure, induces vascular and myocardial hypertrophy and acts as the natural counterpart of nitric oxide (NO), which exerts vasodilating, antithrombotic and antiproliferative effects. This article reviews recently completed and ongoing clinical trials examining the effects of ET receptor antagonists in patients with heart failure, CAD, arterial hypertension and pulmonary hypertension.

Vascular effects of newer cardiovascular drugs: focus on nebivolol and ACE-inhibitors

Alterations in the function and structure of the blood vessel wall account for most clinical events in the coronary and cerebrovascular circulation such as myocardial infarction and stroke. Cardiovascular drugs may exert beneficial effects on the vascular wall both at the level of the endothelium and vascular smooth muscle cells. Therefore, endothelial mediators, in particular nitric oxide (NO) and endothelin (ET), are of special interest. Drugs can modulate the expression and actions of NO, a vasodilator with antiproliferative and antithrombotic properties, and of ET, a potent vasoconstrictor and proliferative mitogenic agent. The most successful drugs in this context are statins and angiotensin-converting enzyme (ACE)-inhibitors. While statins increase the expression of NO synthase. ACE-inhibitors increase the release of NO via bradykinin-mediated mechanisms. Antioxidant properties of drugs are also important, as oxidative stress is crucial in atherosclerotic vascular disease. These properties may explain part of the effects of calcium antagonists and ACE-inhibitors. Indeed, angiotensin II stimulates NAD(P)H oxidases responsible for the formation of superoxide, which inactivates NO. ACE-Inhibitors thus increase the bioavailability of NO. Newer cardiovascular drugs such as nebivolol are able to directly stimulate NO release from the endothelium both in isolated arteries and in the human forearm circulation. ET receptor antagonists may exert beneficial effects in the vessel wall by preventing the effects of ET at its receptors and by reducing ET production. In summary, cardiovascular drugs have important effects on the vessel wall, which may be clinically relevant for the prevention and treatment of cardiovascular disease.

Endothelin A receptor antagonists in congestive heart failure: blocking the beast while leaving the beauty untouched?

Congestive heart failure (CHF) is a disease process characterized by impaired left ventricular function, increased peripheral and pulmonary vascular resistance and reduced exercise tolerance and dyspnea. Thus, mediators involved in the control of myocardial function and vascular tone may be involved in its pathophysiology. The family of endothelins (ET) consists of four closely related peptides, ET-1, ET-2, ET-3, and ET-4, which cause vasoconstriction, cell proliferation, and myocardial effects through activation of ET(A) receptors. In contrast, endothelial ET(B) receptors mediate vasodilation via release of nitric oxide and prostacyclin. In addition, ET(B) receptors in the lung are a major pathway for the clearance of ET-1 from plasma. Thus, infusion of an ET(A) receptor antagonist into the brachial artery in healthy humans leads to vasodilation whereas infusion of an ET(B) receptor antagonist causes vasoconstriction. ET-1 plasma levels are elevated in CHF and correlate both with the hemodynamic severity and with symptoms. Plasma levels of ET-1 and its precursor, big ET-1, are strong independent predictors of death in patients after myocardial infarction and with CHF. ET-1 contributes to increased systemic and pulmonary vascular resistance, vascular dysfunction, myocardial ischemia, and renal impairment in CHF. Selective ET(A) as well as combined ET(A/B) receptor antagonists have been studied in patients with CHF showing impressive hemodynamic improvements (i.e. reduced peripheral vascular and pulmonary resistance as well as increased cardiac output). These results indicate that ET receptor antagonists indeed have a potential to improve hemodynamics, symptoms, and potentially prognosis of CHF which still carries a high mortality.

Endothelin-A receptor antagonist inhibits angiotensin II and noradrenaline in man

AIMS

Endothelin-1 (ET-1) is a potent vasoconstrictor produced by the vascular endothelium. The interactions of ET with the mediators of the sympathetic nervous system and the renin-angiotensin-system in humans are unclear.

METHODS

We studied the effects of the ETA-selective antagonist BQ-123 and the ETB-selective antagonist BQ-788 (both 10(-10)-10(-8) M) on ET-1 (10(-16)-10(-10) M), angiotensin II (AT, 10(-16)-10(-10) M) and noradrenaline (NA, 10(-16)-10(-10) M) induced vasoconstriction in the human skin microcirculation in vivo in 25 healthy male volunteers using laser Doppler flowmetry and double injection technique.

RESULTS

BQ-123 caused a dose-dependent vasodilatation (maximum effect: + 949 +/- 84 AUC-PU, P < 0.001), whereas BQ-788 induced mild vasoconstriction (maximum effect: -388 +/- 96 AUC-PU, P < 0.01). In the presence of BQ-123, but not BQ-788, ET-1, AT and NA caused markedly less vasoconstriction at any tested agonist dose; the effect was most pronounced on ET-1 (maximum effect at 10(-14) M: + 814 +/- 93 AUC-PU vs ET alone, P < 0.001), followed by noradrenaline (maximum effect at 10(-16) M: +580 +/- 107 AUC-PU vs NA alone, P < 0.01) and angiotensin II (maximum effect at 10(-14) M: + 493 +/- 111 AUC-PU vs AT alone, P < 0.001).

CONCLUSIONS

ETA-selective antagonism inhibits vasoconstriction to AT and NA in vivo in healthy subjects. This beneficial effect may be useful for the treatment of patients with cardiovascular disease including hypertension especially in combination therapy with sympatholytic agents and inhibitors of the renin-angiotensin system.

Antihypertensive drugs and the sympathetic nervous system

The sympathetic nervous system (SNS) plays an important role in the regulation of blood pressure homeostasis and cardiac function. Furthermore, the increased SNS activity is a predictor of mortality in patients with hypertension, coronary artery disease and congestive heart failure. Experimental data and a few clinical trials suggest that there are important interactions between the main pressor systems, i.e. the SNS, the renin-angiotensin system and the vascular endothelium with the strongest vasoconstrictor, endothelin. The main methods for the assessment of SNS activity are described. Cardiovascular drugs of different classes interfere differently with the SNS and the other pressor systems. Pure vasodilators including nitrates, alpha-blockers and dihydropyridine (DHP)-calcium channel blockers increase SNS activity. Finally, central sympatholytics and possibly phenylalkylamine-type calcium channel blockers reduce SNS activity. The effects of angiotensin-II receptor antagonists on SNS activity in humans is not clear; experimental data are discussed in this review. There are important interactions between the pressor systems under experimental conditions. Recent studies in humans suggest that an activation of the SNS with pure vasodilators in parallel increases plasma endothelin. It can be assumed that, in cardiovascular diseases with already enhanced SNS activity, drugs which do not increase SNS activity or even lower it are preferable. Whether this reflects in lower mortality needs to be investigated in intervention trials.

Endothelin receptor antagonists in congestive heart failure: a new therapeutic principle for the future?

Congestive heart failure (CHF) is characterized by impaired left ventricular function, increased peripheral and pulmonary vascular resistance and reduced exercise tolerance and dyspnea. Thus, mediators involved in the control of myocardial function and vascular tone may be involved in its pathophysiology. The family of endothelins (ET) consists of four closely related peptides, ET-1, ET-2, ET-3 and ET-4, which cause vasoconstriction, cell proliferation and myocardial effects through activation of ETA receptors. In contrast, endothelial ETB receptors mediate vasodilation via release of nitric oxide and prostacyclin. In addition, ETB receptors in the lung are a major pathway for the clearance of ET-1 from plasma. Thus, infusion of an ETA-receptor antagonist into the brachial artery in healthy humans leads to vasodilation, whereas infusion of an ETB-receptor antagonist causes vasoconstriction. Endothelin-1 plasma levels are elevated in CHF and correlate both with hemodynamic severity and symptoms. Plasma levels of ET-1 and its precursor, big ET-1, are strong independent predictors of death after myocardial infarction as well as in CHF. Endothelin-1 contributes to increased systemic and pulmonary vascular resistance, vascular dysfunction, myocardial ischemia and renal impairment in CHF. Selective ETA, as well as combined ETA/B-receptor antagonists, have been studied in patients with CHF, and their use has shown impressive hemodynamic improvement (i.e., reduced peripheral vascular and pulmonary resistance as well as increased cardiac output). These results indicate that ET-receptor antagonists, indeed, have a potential to improve hemodynamics, symptoms and, potentially, prognosis in patients with CHF, which still carries a high mortality.

The nitric oxide synthase inhibitor L-NMMA potentiates noradrenaline-induced vasoconstriction: effects of the alpha2-receptor antagonist yohimbine

OBJECTIVE

Alpha2-adrenoceptors can be found both on vascular smooth muscle cells and on the endothelium, where they exert opposing effects on vascular tone. In vitro, the stimulation of alpha2-adrenoceptors on endothelial cells leads to the release of vasodilating substances like nitric oxide (NO) and prostanoids. Little is known of this mechanism in vivo.

DESIGN AND METHODS

We investigated the effects of the NO-synthase inhibitor L-NMMA (10(-6) mol) and the alpha2-adrenoceptor antagonist yohimbine (YO, 10(-10)-10(-6) mol) on noradrenaline (NA, 10(-12)-10(-8) mol)-induced vasoconstriction in the forearm skin microcirculation of 16 healthy volunteers using double injection technique and laser Doppler flowmetry. Results are expressed in perfusion units (PU) as differences from baseline and control in mean +/- SEM; the area under the time-response-curve was calculated (AUC).

RESULTS

NA (10(-8)- 10(-12) mol) caused a marked, dose-dependent reduction in blood flow (mean effect -745 +/- 84 AUC PU; P< 0.001 versus saline). NA-induced vasoconstriction was enhanced by L-NMMA (mean effect -916 +/- 72 AUC PU; P< 0.001 versus NA). YO (10(-6)-10(-10) mol) induced a significant, dose-dependent vasodilation (mean effect +/- 446 +/- 110 AUC PU; P < 0.05 versus control); high doses of YO (10(-6) mol) inhibited NA constriction (P < 0.001 versus NA), whereas lower doses of YO (10(-8)/10(-10) mol) had no effect or even increased NA-induced constriction. In the presence of L-NMMA, YO (10(-8) and 10(-10) mol) further potentiated NA-induced vasoconstriction (mean effect -1165 +/- 108 AUC PU; NS versus NA).

CONCLUSION

These data demonstrate, that in humans in vivo, endogenous NO attenuates noradrenergic constriction. The effects of YO suggest that endothelial alpha2-adrenoceptors are involved in the release of NO and other vasodilating substances. Furthermore, there is an additive NO-independent vasodilation, which can be unmasked by L-NMMA.

Therapeutic potential for endothelin receptor antagonists in cardiovascular disorders

The endothelins are synthesized in vascular endothelial and smooth muscle cells, as well as in neural, renal, pulmonal, and inflammatory cells. These peptides are converted by endothelin-converting enzymes (ECE-1 and -2) from 'big endothelins' originating from large preproendothelin peptides cleaved by endopeptidases. Endothelin (ET)-1 has major influence on the function and structure of the vasculature as it favors vasoconstriction and cell proliferation through activation of specific ET(A) and ET(B) receptors on vascular smooth muscle cells. In contrast, ET(B )receptors on endothelial cells cause vasodilation via release of nitric oxide (NO) and prostacyclin. Additionally, ET(B) receptors in the lung are a major pathway for the clearance of ET-1 from plasma. Indeed, ET-1 contributes to the pathogenesis of important disorders as arterial hypertension, atherosclerosis, and heart failure. In patients with atherosclerotic vascular disease (as well as in many other disease states), ET-1 levels are elevated and correlate with the number of involved sites. In patients with acute myocardial infarction, they correlate with 1-year prognosis. ET receptor antagonists have been widely studied in experimental models of cardiovascular disease. In arterial hypertension, they prevent vascular and myocardial hypertrophy. Experimentally, ET receptor blockade also prevents endothelial dysfunction and structural vascular changes in atherosclerosis due to hypercholesterolemia. In experimental myocardial ischemia, treatment with an ET receptor antagonist reduced infarct size and prevented left ventricular remodeling after myocardial infarction. Most impressively, treatment with the selective ET(A) receptor antagonist BQ123 significantly improved survival in an experimental model of heart failure. In many clinical conditions, such as congestive heart failure, both mixed ET(A/B )as well as selective ET(A) receptor antagonism ameliorates the clinical status of patients, i.e. symptoms and hemodynamics. A randomized clinical trial showed that a mixed ET(A/B) receptor antagonist effectively lowered arterial blood pressure in patients with arterial hypertension. In patients with primary pulmonary hypertension or pulmonary hypertension related to scleroderma, treatment with a mixed ET(A/B) receptor antagonist resulted in an improvement in exercise capacity. ET receptor blockers thus hold the potential to improve the outcome in patients with various cardiovascular disorders. Randomized clinical trials are under way to evaluate the effects of ET receptor antagonism on morbidity and mortality.

Time-course changes in plasma endothelin-1 and its effects on the mesenteric arterial bed in streptozotocin-induced diabetic rats

AIM

To examine the mechanisms underlying the elevated plasma endothelin-1 (ET-1) in diabetes and its vascular effects.

RESULTS

Relationships between the plasma ET-1 level and the levels of other plasma constituents (glucose, cholesterol, and triglyceride) were found in 10-week streptozotocin (STZ)-induced diabetic rats. In contrast, at 1 week after the STZ injection only plasma ET-1 and glucose levels were elevated, suggesting that the hyperglycaemia might trigger the excess production of ET-1. Incubation with high glucose promoted the release of ET-1 from the isolated mesenteric arterial bed. In STZ-induced diabetic rats, the maximum contractile response of the mesenteric arterial bed to ET-1 was significantly reduced, and the vasoconstriction and vasodilation induced by the ET(B)-receptor agonist IRL-1620 in this bed were significantly impaired. The vascular responses induced by these ET receptor agonists were restored to normal by chronic treatment of diabetic rats with insulin for 7 or 4 weeks.

CONCLUSIONS

These results suggest: (1) that the marked increase in plasma glucose in STZ-induced diabetic rats elevates the plasma ET-1; and (2) that the decreased contractile and vasodilator responses of the mesenteric arterial bed to ET-1 receptor agonists may be due to desensitization of not only ET(A), but also ET(B) receptors, an effect secondary to the elevation of plasma ET-1.

Skin microcirculation in healthy subjects and patients with arteriosclerosis

The concept to use the human skin microcirculation as a pharmacological in-vivo test system is old; however, methods developed in the 50s have been abandoned because of side effects and/or use of radioactive substances. We describe a newly developed minimally invasive method that allows in-vivo pharmacology in the human skin microcirculation injecting very low doses of a substance of drug without any systemic effects. The double injection technique (DIT) bears the potential to predict the effects of a drug and/or the vascular reactivity or dysfunction of other less accessible areas of the circulation (e.g. the myocardium). The DIT has been applied for studies in healthy volunteers and patients with atherosclerosis; the focus of interest was endothelial (dys-)function and the effect of exogenous vasoactive drugs. Using endothelin antagonists, we investigated the role of endogenous endothelin under physiological conditions and in atherosclerosis. The NO-synthase inhibitor L-NMMA has been applied to study the L-arginine-NO-pathway and the role of endothelial adrenoceptors. Ongoing studies with the DIT comparing coronary and skin microcirculation may help to develop minimally invasive methods to predict the effects of drugs and vascular function in the heart.

Cytokines induce increased endothelin ET(B) receptor-mediated contraction

The effect of cytokines on the induction of contractile endothelin ET(B) receptors during organ culture was examined. Ring segments of rat superior mesenteric artery were used fresh or incubated for 24 h in Dulbecco's modified Eagle's medium alone, or with either interleukin-1beta, tumor necrosis factor-alpha (TNF-alpha) or interleukin-2. In fresh arterial segments there was no endothelin ET(B) receptor-induced contraction. After incubation, the selective endothelin ET(B) receptor agonist sarafotoxin 6c evoked a contraction of 22 +/- 6% relative to that induced by 60 mM K+. The endothelin ET(B) receptor-induced contraction was further increased to 125 +/- 25% and 157 +/- 29% by interleukin-1beta and TNF-alpha, respectively, while interleukin-2 did not alter the endothelin ET(B) receptor-induced contraction. The identity of the contractile receptor was confirmed as the endothelin ET(B) receptor by the use of an additional specific endothelin ET(B) receptor agonist, IRL 1620, and by antagonist experiments with FR 139317 and IRL 2500. The endothelin-1-induced contraction was not altered by either of the cytokines. Reverse transcriptase-polymerase chain reaction revealed increased levels of endothelin ET(B) mRNA, relative to endothelin ET(A) mRNA following organ culture, suggesting that contractile endothelin ET(B) receptors appear via de novo transcription. None of the cytokines changed the ratio of endothelin ET(A) and endothelin ET(B) receptor mRNA, indicating that the further increased sarafotoxin 6c-induced contraction is mediated through an enhancement of intracellular signalling mechanisms.

Endothelin in cardiovascular control: the role of endothelin antagonists

Endothelin (ET) is a potent vasoconstrictor associated with various cardiovascular diseases. ET mediates its effects through ET receptors on vascular smooth muscle cells as well as on the vascular endothelium. Furthermore, a neurotransmitter role for ET has been suggested on the basis of experimental and human in vivo studies. ET antagonists are potent tools for studying the effects of ET and its receptors. They have been widely used in vitro and in experimental models of cardiovascular disease, where ET levels are elevated and reactivity to ET is altered. Promising clinical trials in hypertension, coronary artery disease, and congestive heart failure are discussed in this review. Different forms of renal failure are associated with markedly increased ET levels, and ET antagonists experimentally improve renal function in these models. Extrapolating from experimental and first clinical experience, ET antagonists could be useful in the treatment of hypertension, coronary artery disease, congestive heart failure, and renal failure, especially in combination with other drugs, ie, angiotensin converting enzyme inhibitors. The inhibition of ET-induced stimulation of nociception allows for speculation that ET antagonists might even have analgesic properties.

Increased levels of endothelin ETB receptor mRNA in human omental arteries after organ culture: quantification by competitive reverse transcription-polymerase chain reaction

1. Using competitive reverse transcription-polymerase chain reaction (RT-PCR) and in vitro pharmacology, smooth muscle endothelin ETB receptor expression was studied in segments of human omental artery, fresh and after organ culture for 1 and 5 days. 2. The competitive RT-PCR assay used in the present study uses an internal RNA standard bearing a 69 b.p. deletion in order to control all steps of the reaction, including the RT step. Control experiments showed linearity over five subsequent 1:10 dilutions and a wide range of cycle numbers. The assay was able to quantify subattomolar concentrations in samples under 1 microgram total RNA, making it possible to measure mRNA expression even in small tissue biopsies. 3. In fresh arteries, ETB mRNA levels were 0.19 +/- 0.05 amol/microgram total RNA (range 0.03-0.42 amol/microgram; n = 8). After organ culture, an increase in ETB mRNA levels by 317 +/- 28 and 288 +/- 12% was found at days 1 and 5, compared with fresh arteries, respectively. 4. In vitro pharmacology showed that endothelin (ET)-1 induced a strong and potent contraction in fresh arteries, whereas the selective ETB receptor agonist IRL 1620 failed to induce a significant contraction. The ET-1-induced contraction was not altered in potency or Emax after organ culture for 1 and 5 days. In contrast, IRL 1620 induced a clear contraction after 1 day, which increased further in both Emax and potency after 5 days organ culture. 5. Our results indicate that a massive new transcription of ETB receptor mRNA is induced by organ culture, resulting in functional contractile ETB receptors on the smooth muscle layer.

Exercise capacity in heart transplant recipients: relation to impaired endothelium-dependent vasodilation of the peripheral microcirculation

OBJECTIVES

The aim of this study was to examine the responses to endothelium-dependent and -independent vasodilators on the peripheral microcirculation in heart transplant recipients in relation to exercise capacity compared with that in healthy controls.

BACKGROUND

Impaired endothelium-dependent vasodilation of the microcirculation may play an important role in the limitation of exercise capacity after heart transplantation.

METHODS

Microvascular perfusion responses to four graded levels of iontophoretically applied 1% acetylcholine (endothelium-dependent vasodilator) and 1% sodium nitroprusside (SNP) (endothelium-independent) in the forearm skin of 42 transplant recipients and 16 age-matched controls were determined by laser Doppler perfusion measurements. Maximal exercise capacity was assessed by peak oxygen uptake (peak VO2) during progressive, symptom-limited, upright bicycle exercise.

RESULTS

With similar baseline perfusion levels in transplant recipients and controls (4.2 +/- 0.4 vs 4.6 +/- 0.6 arbitrary units [AU]), the increases in perfusion to acetylcholine, but not to SNP, were significantly attenuated in the transplant recipients: 7.0 +/- 1.0 vs 11.0 +/- 2.0, 12.7 +/- 1.5 vs 21.0 +/- 2.8, 21.0 +/- 1.9 vs 32.7 +/- 2.4, and 28.0 +/- 1.6 vs 39.2 +/- 2.4 AU, respectively (all p < 0.01). Peak VO2 was significantly lower in the transplant recipients (22.4 +/- 1.0 vs 38.0 +/- 2.9 ml/kg/min; p < 0.01). Furthermore, acetylcholine responses of the transplant recipients correlated closely to their peak VO2, irrespective of level of application (r = 0.63; p < 0.001, all four acetylcholine responses taken together), whereas no such correlation was found for SNP responses. In the control group, no relation was observed in acetylcholine/SNP responses to peak VO2.

CONCLUSIONS

Exercise limitation in transplant recipients appears strongly associated with attenuated endothelium-dependent vasodilation of the peripheral microcirculation.

Posturally induced leg vasoconstrictive responses: relationship to standing duration, impedance and volume changes

Shifting legs to a gravity-dependent position provokes a physiological vasoconstrictive response that forms the basis of several diagnostic tests based on initial (< 5 min) blood perfusion decreases. However, it is not known if responses are maintained over longer duration and if they depend on the volume shifted to the limb during the manoeuvre. These issues were investigated by measurements of blood perfusion changes on foot and ankle (laser Doppler) and below-knee volume and impedance changes induced by 30 min of standing in 10 healthy volunteers. Initial perfusion decreases were 66.4% +/- 2.6% and 49.3% +/- 3.8% for ankle and foot dorsum, respectively, and were fully maintained during sustained standing without evidence of 'vasodilator escape'. Response magnitudes were not dependent on leg volume changes using geometric or impedance measures. A close correlation (r2 = 0.78) between impedance and volume changes suggests the former as a useful way of assessing dynamic limb volume changes. Sustained vasoconstrictive responses make it unlikely that extending the duration of such tests would offer more, diagnostic information than is currently available.

Appearance of contractile endothelin-B receptors in rat mesenteric arterial segments following organ culture

The aim of this study was to examine how different procedures for organ culture affect the expression of contractile endothelin(ET)-B receptors in a branch of the rat mesenteric artery. In fresh segments, ET-1 and ET-3 induced similar strong contractions, ET-1 being 20-fold more potent, whereas neither of the selective ETB receptor agonists, sarafotoxin 6c (S6c) nor IRL 1620, induced significant contractions. In segments cultured for 1 day, ET-3 was only 3-fold less potent as ET-1, and S6c and IRL 1620 induced concentration-dependent contractions which were about 60% of the ET-1 induced contraction. The maximum contractile response to S6c was not altered in segments cultured with foetal calf serum or in buffer solution, but was reduced to about 20% of the control value when cultured in glucose-free buffer solution. The contraction to S6c was abolished in segments placed in cold (4 degrees C) buffer solution. Removal of the endothelium had no effect on the S6c-induced contractions. Arteries cultured at isometric tension (at 2 mN) for 1 day achieved the same contractile response for ETB agonists as resting segments. Pressurized arteries (60 mmHg) did not constrict to S6c when mounted as a fresh segment but demonstrated a strong contraction after 1 day at this transmural pressure. This study suggests that the appearance of ETB receptor mediated contraction following organ culture is not dependent on specific nutrients, endothelial factors or absence of intrinsic tension, but is a metabolically active process.

Endothelin-1 induces vasodilation in human skin by nociceptor fibres and release of nitric oxide

AIMS

Endothelin is a peptide produced by endothelial cells with many biological properties. In the human skin microcirculation endothelin induces neurogenic vasodilation associated with burning pruritus. We investigated the mechanisms involved in this response.

METHODS

The effects of prolonged pretreatment with capsaicin, a specific inhibitor of polimodal nociceptor fibres, and of the nitric oxide synthase inhibitor L-NMMA on endothelin-1-induced vasodilation were studied in 15 human subjects. Furthermore, we investigated the effects of the ET(A)-selective antagonist PD147953 on bradykinin-induced vasodilation.

RESULTS

After local injection, endothelin-1 caused vasoconstriction at the injection site and a profound vasodilation in the surrounding area (flare reaction, P<0.01). This response was specific and not induced by saline, albumin, acetylcholine or an ET-antagonist. Prolonged capsaicin pretreatment inhibited endothelin-1 induced vasodilation in the area surrounding the injection site, but not the central vasoconstriction at the injection site. Bradykinin also induced a marked vasodilation in the area surrounding the injection site; this was not inhibited by an ETA-selective antagonist, while the flare reaction was. L-NMMA applied at the site of the flare reaction prevented endothelin-1-induced vasodilation.

CONCLUSIONS

Endothelin-1 in the human skin microcirculation stimulates polimodal nociceptor fibres leading to the release of nitric oxide. This response may play a pathophysiological role in inflammatory processes in the human skin.

Is there a rationale for combining angiotensin-converting enzyme inhibitors and calcium antagonists in cardiovascular disease?

Coronary artery disease and its sequelae remain the most important cause of morbidity and mortality in Western countries. Because the pathophysiologic characteristics of coronary artery disease are multifactorial, impairment of endothelial function featuring enhanced vasoconstriction, increased platelet vessel wall interaction, adherence of monocytes, migration and proliferation of vascular smooth muscle cells are crucially involved. Endothelial cells release numerous vasoactive substances regulating function of vascular smooth muscle and trafficking blood cells such as nitric oxide (NO), which is a potent vasodilator also inhibiting cellular growth and migration. In addition, NO possesses antiatherogenic and thromboresistant properties by preventing platelet aggregation and cell adhesion. These effects are counterbalanced by endothelial vasoconstrictors such as angiotensin II and endothelin-1. In the blood vessel wall, the local vascular effects of angiotensin-converting enzyme (ACE) inhibitors and calcium antagonists are synergistic. ACE inhibitors diminish the conversion of angiotensin I into angiotensin II and the inactivation of bradykinin. Calcium antagonists counteract angiotensin II and endothelin-1 at the level of vascular smooth muscle by reducing Ca2+ inflow and facilitating the vasodilator effects of NO. In hypertensive animals, long-term combination therapy with verapamil and trandolapril is particularly effective in reversing endothelial dysfunction. Further, ACE inhibitors and calcium antagonists exert beneficial vascular and complementary hemodynamic effects. Whereas ACE inhibitors inhibit the renin-angiotensin system and reduce sympathetic outflow, calcium antagonists dilate large conduit and resistance arteries. Because small vessels appear to be more dependent on extracellular Ca2+ than larger vessels, nifedipine and verapamil effectively inhibit endothelin-induced vasoconstriction in vitro and in vivo in the resistance circulation. Long-term treatment with ACE inhibitors substantially reduces morbidity and mortality rates in patients with left ventricular dysfunction after myocardial infarction; beneficial effects of verapamil in secondary prevention are confined to patients with normal left ventricular ejection fraction. In summary, long-term combination therapy of ACE inhibitors and calcium antagonists might provide beneficial effects in cardiovascular disease because they exert synergistic hemodynamic, antiproliferative, antithrombotic, and antiatherogenic properties.

Transcriptional regulated plasticity of vascular contractile endothelin ET(B) receptors after organ culture

The aim of the present study was to investigate the level of regulation of the contractile endothelin ET(B) receptor which appears spontaneously after organ culture of vascular segments. Endothelin-1 elicited a strong contraction while the selective endothelin ET(B) receptor agonist, sarafotoxin 6c, had a negligible effect on fresh ring segments of rat mesenteric artery. After organ culture in serum-free Dulbecco's modified Eagle's medium at 37 degrees C (for 1 or 2 days) the endothelin-1-induced contraction was unchanged, whereas sarafotoxin 6c induced, after 1 day, a marked contraction which was further increased at day 2. The contraction induced by sarafotoxin 6c was significantly attenuated by the transcriptional inhibitor, actinomycin D, or the translational inhibitor, cyclohexamide, while the endothelin-1-induced contraction was much less affected. mRNA for endothelin ET(A) and endothelin ET(B) receptors was present in fresh human omental arteries denuded of endothelium. However, after organ culture, endothelin ET(B) mRNA was more prominent than endothelin ET(A) mRNA. Furthermore, the mRNA for both receptors was decreased after treatment with actinomycin D but not with cyclohexamide. This suggests that the endothelin ET(A) receptor is the dominating contractile receptor in fresh arteries while organ culture induces transcription and subsequent translation of contractile endothelin ET(B) receptors.