Plasma ET-1 Levels Research Articles

Contribution of endothelin-1 to microcirculatory impairment in total hepatic ischemia and reperfusion injury.

Endothelin (ET)-1 may have a role in hepatic polymorphonuclear leukocyte infiltration as well as microcirculatory disturbance during hepatic ischemia-reperfusion (HIR) injury. This study was conducted to investigate the influence of ET-1 on the hepatic microcirculation after total HIR and to evaluate the effect of a nonselective ET receptor antagonist under these conditions. Male rats pretreated with either normal saline (NS group) or TAK-044, a nonselective ET receptor antagonist (TAK group), were subjected to 120 min of total hepatic ischemia with extracorporeal portosystemic shunting. Plasma ET-1 levels increased significantly from 1 to 6 hr after reperfusion in the NS group when compared with the nonischemic control. In the early phase of reperfusion, the NS group showed significantly narrower sinusoids, lower hepatic tissue blood flow, a lower hepatic tissue oxy-hemoglobin concentration, and more hepatic neutrophil infiltration than the TAK group (P<0.05). Pretreatment with TAK-044 improved hepatic microcirculatory derangement, and resulted in significantly better 7-day survival (61.5%) with more bile production after reperfusion when compared with the NS group (P<0.01). The present study demonstrated that ET-1 is involved in the development of HIR injury by causing deterioration of the hepatic microcirculation. A nonselective ET receptor antagonist successfully ameliorated HIR injury through improvement of hepatic oxygenation and of the microcirculation along with reduced hepatic neutrophil infiltration.

ET-1 Infusion Increases Systemic Vascular Resistance and Depresses Cardiac Output in Patients with Chronic Hypoxaemia and Pulmonary Hypertension

The pulmonary vascular effects of the endothelium-derived peptide endothelin (ET) vary depending on the existing vascular tone, modes of administration and species studied; ET can cause both pulmonary vasodilatation and vasoconstriction. Increased plasma levels of ET have been reported in hypoxic pulmonary hypertension, although it is unclear whether ET is a mediator or a marker of hypoxia-induced increase in pulmonary vascular resistance (PVR). In our study, the plasma levels of ET-1 and the functional effects of ET-1 infusion in patients (n

Formula omitted]-Arginine Reduces Right Heart Hypertrophy in Hypoxia-Induced Pulmonary Hypertension

Endothelin (Et) and nitric oxide (NO) may serve as chemical mediators of hypoxia-induced pulmonary hypertension. Plasma levels of Et1 were elevated 2-fold while levels of nitrate, a NO metabolite, decreased in rats exposed to 10 days of hypoxia (10% O2). Administration ofl-arginine, the precursor for NO, decreased Et, increased nitrate, and decreased right ventricular hypertrophy in hypoxic animals. By increasing plasma NO levels, the right ventricular hypertrophy and right heart failure seen in hypoxia-induced pulmonary hypertension in human patients may be prevented.

An imbalance in plasma prostanoids in patients with Raynaud's phenomenon and pulmonary vasospasm.

Raynaud's phenomenon has been suggested as a predisposing factor for pulmonary vasospasm which may lead to pulmonary hypertension, but the occurrence of cold stimulus-induced pulmonary vasospasm has been inconsistent. Such inconsistent pulmonary vascular responses may be caused by differences in the production of endogenous vasodilators and vasoconstrictors among patients. Fourteen patients with Raynaud's phenomenon associated with mixed connective tissue disease (n=10) or systemic sclerosis (n=4) participated in the study. Right heart catheterization was performed before and after a cold pressor test, immersing a hand in cold water (15 degrees C) for 5 min. Plasma levels of 6-keto prostaglandin (PG)F1alpha, thromboxane (TX)B2 and endothelin (ET)-1 in the mixed venous blood were measured. Mean pulmonary artery pressure increased after the cold pressor test in five of 14 patients, and the patients were divided into those with pulmonary vasospasm (responders) and those without vasospasm (nonresponders). After the cold pressor test, levels of 6-keto PGF1alpha increased significantly in nonresponders (p<0.01) and decreased significantly in responders (p<0.05). The ratios of 6-keto PGF1alpha to TXB2 significantly increased in nonresponders (p<0.01) but not in responders and the difference between responders and nonresponders after the cold pressor test was also statistically significant (p<0.05). No significant change in plasma ET-1 levels occurred in either responders or nonresponders. The results suggest that an impaired production of prostaglandin I2 and an imbalance between prostaglandin I2 and thromboxane A2 are associated with the occurrence of pulmonary vasospasm induced by Raynaud's phenomenon.

Increased expression of endothelin receptors in the vasculature of portal hypertensive rats: role in splanchnic hemodynamics.

Portal hypertension (PHT) is characterized by increased portal pressure caused in part by a reduction in mesenteric vascular resistance. The aim of this study was to evaluate the role of endothelin (ET) and specific ET receptors in maintaining the vasculopathy of PHT. PHT was created in Sprague-Dawley rats by a partial portal vein ligation. Control animals were sham-operated. ET receptor expression was determined in the superior mesenteric artery of sham and PHT rats by in situ autoradiography, radioligand binding analysis, and reverse-transcription polymerase chain reactions (RT-PCR). The pressor response to ET-1 was determined in vitro using isolated vascular rings and in vivo by measuring mean arterial pressure, splanchnic blood flow, and portal venous pressure following treatment with ET and selective ET receptor antagonists. The pressor response to ET in vitro was significantly enhanced in PHT concomitant with increased ET-A and ET-B receptor expression. There was a significant increase in the peak pressor response to ET (10 microg/kg intravenously) in portal hypertensive rats without any significant change in plasma ET-1 levels. There was no significant difference in the peak splanchnic blood flow or portal venous pressure response following ET-A receptor blockade with JKC-301 infusion (200 microg/kg intravenously). In contrast, ET-B receptor blockade with IRL-1038 (200 microg/kg intravenously) preferentially decreased splanchnic blood flow and portal venous pressure in portal hypertensive rats. These data suggest that enhanced ET-B receptor expression in portal hypertensive vessels contributes to the maintenance of elevated portal pressure in these animals.

Endothelin A receptor blockade decreases pulmonary vascular resistance in premature lambs with hyaline membrane disease.

Endothelin (ET)-1 is a potent vasoconstrictor peptide that modulates basal pulmonary vascular resistance (PVR) in the normal ovine fetus and contributes to high PVR after chronic intrauterine pulmonary hypertension. Although high PVR is present in premature lambs with severe hyaline membrane disease (HMD), whether ET-1 plays a role in the pathophysiology of experimental HMD is unknown. To test the hypothesis that ET-1 activity contributes to high PVR in the premature lamb with HMD, we studied the hemodynamic effects of a selective ET(A) receptor antagonist, BQ 123, in 10 animals (gestational age 125 d; 147 d=term). After baseline measurements, animals were intubated, treated with surfactant (Infasurf), and mechanically ventilated with a fraction of inspired oxygen of 1.00 for 8 h. Animals were treated with continuous infusions of either BQ 123 (1 mg/h; treatment group, n=5) or 1% DMSO (control; n=5). Plasma ET-1 levels progressively increased during prolonged ventilation with hyperoxia (0.8+/-0.1 pg/mL, baseline to 6.8+/-2.5 pg/mL, 8 h, p < 0.05). In comparison with control lambs, BQ 123 treatment caused a sustained reduction in pulmonary vascular resistance (0.55+/-0.04 mm Hg mL-(-1) min(-1), control versus 0.18+/-0.04 mm Hg mL(-1) min(-1), BQ 123, p < 0.05), increased left pulmonary artery blood flow (70+/-12 mL/min, control versus 194+/-28 mL/min, BQ 123, p < 0.05), and increased arterial PaO2 (53+/-14 mm Hg, control versus 174+/-71 mm Hg, BQ 123, p < 0.05) 8 h after the onset of ventilation. We conclude that circulating levels of ET-1 increase after delivery of premature lambs with severe HMD, and that selective ET(A) receptor blockade causes sustained improvement in hemodynamics in severe experimental HMD. These studies suggest that ET-1 contributes to the hemodynamic abnormalities in this model of pulmonary hypertension and severe HMD.

Elevated plasma endothelin-1 levels in sickle cell anemia: relationships to oxygen saturation and left ventricular hypertrophy.

Endothelin-1 (Et-1) is a vasoconstrictor produced by endothelial and vascular smooth muscle cells in response to hypoxia, which induces hypertrophy in cultured cardiac myocytes. We measured plasma Et-1 levels and left ventricular dimensions in 13 patients with sickle cell anemia (SCD) and in 12 African-American controls ages 16-29 years. Endothelin-1 concentrations are significantly higher in SCD subjects than controls (10.6 +/- 1.9 vs. 3.0 +/- 1.3 pmol/L). There was a negative correlation between oxygen saturation and Et-1 levels in SCD patients (r = -0.71, P = 0.01). SCD subjects have more dilated and hypertrophied hearts corrected for body surface area than controls as evidenced by significant increases in left ventricular end diastolic dimension (31 +/- 0.8 vs. 24 +/- 0.9 mm/m2, P < 0.001), left ventricular end systolic dimension (20 +/- 0.9 vs. 16 +/- 0.8 mm/m2, P = 0.002), left ventricular posterior wall thickness (5.0 +/- 0.1 vs. 4.0 +/- 0.1 mm/m2, P < 0.001), and left ventricular mass (125 +/- 7.2 vs. 69 +/- 5.1 g/m2, P < 0.001). The index of left ventricular function, the shortening fraction, was not different between groups (34 +/- 1.2% in SCD vs. 35 +/- 1.5% in controls). The correlation between left ventricular mass and levels of Et-1 in SCD subjects was not significant (r = 0.47, P = 0.121).

Biochemical and molecular endothelin responses to morphine sulfate infusion in conscious newborn piglets

The biochemical and molecular endothelin-1 (ET-1)responses to high dose morphine sulfate infusion were studied in conscious newborn piglets(n = 6) that received a loading dose of 100 µg/kg over 5 min followed by acontinuous i.v. infusion dose of 100 µg·kg–1·h–1 for 4 h. The controlgroup (n = 6) received equivalent volume loading and infusion doses of 5% dextrose.Blood samples were drawn serially from the femoral artery and sagittal sinus vein before (0),during (30 min, 1, 2, 3, and 4 h), and post (1 and 2 h) infusion. Five micrograms oftotal RNA obtained from brainstem tissue homogenates was analyzed by reverse transcriptase –polymerase chain reaction (RT-PCR). The amounts of mRNA encoding ET-1, and endothelinreceptor subtypes ETA and ETB, were semiquantitated using densitometricscanning. Morphine infusion resulted in elevated respiratory rate and mean arterial bloodpressure, with no effect on arterial pH, PO2, and O2saturation. Compared with the control group, morphine induced significant elevations in plasmaET-1 levels following the bolus dose (systemic: 13.2 ± 3.6 vs. 8.6 ± 2.2 pg/mL, p &lt; 0.05;sagittal sinus vein: 13.7 ± 3.4 vs. 8.2 ± 0.9 pg/mL, p &lt; 0.01). These effects lasted up to2 h after discontinuation of morphine infusion (systemic: 14.5 ± 3.4 to 18.7 ± 5.7 pg/mL vs.7.5 ± 0.8 to 9.4 ± 3.2 pg/mL, p &lt; 0.05 to p &lt; 0.01; sagittal sinus vein: 14.8 ± 2.7to 17.6 ± 2.8 pg/mL vs. 7.5 ± 1.4 to 9.4 ± 3.4 pg/mL, p &lt; 0.05 to p &lt; 0.01). TheRT-PCR assay showed a twofold (p &lt; 0.02) upregulation in ET-1 and a threefold(p &lt; 0.007) upregulation in ETA receptor mRNA expression in the brainstemof morphine-treated animals. In contrast, there was a threefold (p &lt; 0.0001)downregulation of the ETB receptor mRNA expression. The rapid and sustainedelevations in systemic arterial and sagittal sinus venous ET-1 levels suggest a role for ET-1 in themorphine-induced excitatory responses observed in newborn piglets. Upregulation ofETA receptors and downregulation of ETB receptors in the brainstem withhigh doses of morphine may indicate possible effects on cerebral vascular tone. Key words: morphine sulfate, endothelin-1, reverse transcriptase –polymerase chain reaction.

Contribution of endothelin to the acute pressor response of L-NAME in stroke-prone spontaneously hypertensive rats.

In this study, we examined whether endothelin (ET) plays a role in the short-term increase in mean arterial pressure (MAP) after nitric oxide synthase (NOS) inhibition with N(omega)-nitro-L-arginine methyl ester (L-NAME) in stroke-prone spontaneously hypertensive rats (SHRSPs). Experiments were performed by using Inactin-anesthetized male SHRSPs that were pretreated with chlorisondamine to block reflex autonomic cardiovascular effects. Injection of L-NAME (10 mg/kg, i.v.), but not D-NAME, produced rapid and marked increases (74 +/- 3 mm Hg) in MAP that were sustained for >1 h. In SHRSPs that were treated with the ET(A/B) receptor antagonist, L-754,142 (15 mg/kg + 15 mg/kg/h), L-NAME increased MAP by 45 +/- 4 mm Hg (p < 0.0001 compared with L-NAME alone). L-754,142 blocked pressor responses to big ET-1 by >90% but was without effect on pressor responses to norepinephrine. Plasma levels of ET-1 averaged 5 +/- 1 pg/ml in animals given vehicle and were slightly increased in animals given either L-NAME alone (7 +/- 2 pg/ml) or L-754,142 alone (7 +/- 2 pg/ml) but increased markedly when L-NAME and L-754,142 were given together (114 +/- 18 pg/ml). This may relate to an effect of L-754,142 to block ET-receptor-mediated clearance of ET-1. We conclude that ET plays a role in the short-term pressor response after NOS inhibition in SHRSPs.

Pharmacologic characterization of the novel, orally available endothelin-A--selective antagonist SB 247083.

Competition radioligand binding with [125I]ET-1 at human cloned ETA and ETB receptors demonstrated ET-A selective affinity by SB 247083 (Ki 0.41 and 467 nM, respectively). Accordingly, similar competitive, functional ETA receptor antagonism was observed. In vitro, SB 247083 exhibited a Kb of 3.5 +/- 0.3 nM (ET-1--induced rat aortic contraction). SB 247083 was significantly less potent as a functional ETB antagonist (Kb 0.34 +/- 0.01 microM; S6c-induced rabbit pulmonary artery contraction). In contrast to ETB-selective and mixed ETA/B antagonists, and consistent with its ETA-selective profile, in vivo administration of SB 247083 was not associated with an elevation in plasma ET-1 levels. Pharmacodynamic and pharmacokinetic studies revealed that SB 247083 was effectively absorbed from the gastrointestinal tract. A single bolus dose inhibited the hemodynamic actions of ET-1 for up to 8 h, consistent with a molecule shown to be 46% bioavailable. Therefore, the present study demonstrates that SB 247083, a unique chemical entity, represents a potent class of nonpeptide, orally active ETA-selective antagonists.

Influence of Vascular Load on Plasma Endothelin-1, Cytokines and Catecholamine Levels in Essential Hypertensives

In vitro studies demonstrated a relationship between ET-1 and basic Fibroblast Growth Factor (bFGF), and of bFGF with Platelet Derived Growth Factor (PDGF). The present study was carried out to investigate in vivo the behaviour after vascular stress of circulating ET-1, bFGF and PDGF, and catecholamines, and their relationship. In 12 healthy normotensives (NTs) and 15 essential hypertensives (Ehs) venous blood samples to determine circulating ET-1, bFGF and PDGF, and catecholamine (EPI and NE) levels were drawn before and at the third minute of a handgrip test. Blood pressures (BP) and heart rate were automatically recorded before starting, and at 1, 2, and 3 minutes during the test. The NTs showed, in basal condition, lower values than the EHs of all the examined parameters; later, the handgrip test induced significant increases in circulating levels of ET-1, bFGF and catecholamine. In the EHs at the third minute of the exercise significant increases in plasma ET-1 (p < 0.002), bFGF (p < 0.006), and EPI and NE (p < 0.0005) levels were observed. Systolic and diastolic BP significantly increased after handgrip test in NTs and EHs. Plasma ET-1 correlated with bFGF both before (p < 0.01) and at the acme (p < 0.05) of the isometric exercise. Our results show that in EHs plasma ET-1 and bFGF correlate each other, indicating that in human hypertension a linkage between ET-1 and bFGF exists.

Role of lipid-derived mediators in tumor necrosis factor-induced endothelin-1 release in vivo.

We hypothesized that endothelin (ET) may be released in response to tumor necrosis factor-alpha (TNF) and that platelet-activating factor (PAF) and cyclooxygenase products modulate TNF-induced ET-1 release in vivo. Anesthetized and instrumented pigs were randomly assigned to receive: 1) saline + TNF (n = 8); 2) saline + heat-inactivated TNF (control group, n = 5); 3) WEB 2086 (PAF receptor antagonist) + TNF (n = 7); or 4) indomethacin + TNF (n = 6). Infusion of TNF was associated with increases in mean aortic, mean pulmonary artery, and intratracheal pressures, increases in systemic and pulmonary vascular resistances, and elevated plasma thromboxane B2 concentration. Plasma ET-1 concentrations were unchanged in controls and significantly increased in TNF-treated pigs at 2 to 4 h. WEB 2086 did not modify plasma levels of ET-1 during exogenous infusion of TNF. In contrast, the cyclooxygenase inhibitor, indomethacin, mildly, but not significantly, reduced plasma ET-1 levels. In addition, indomethacin (but not WEB 2086) blocked or attenuated the TNF-induced increases in mean aortic pressure, systemic vascular resistance, mean pulmonary artery pressure, pulmonary vascular resistance, and intratracheal pressure. We conclude that in the pig, cyclooxygenase products modulate some of the cardiovascular responses to TNF and may mildly affect ET-1 biosynthesis. On the other hand, PAF neither significantly influences TNF-induced biosynthesis of ET-1 nor its associated cardiovascular responses.

Endothelin-1 expression in hearts of transgenic hypertensive mice overexpressing angiotensin II.

Cardiac myocytes and vascular endothelial cells produce endothelin (ET)-1, which has potent hypertrophic effects on cardiac myocytes. Although in cultured cardiomyocytes, angiotensin II (Ang II) was reported to enhance ET-1 production in vitro, it is not known whether ET-1 production is enhanced by Ang II in vivo. We investigated the production and pathophysiologic roles of ET-1 in 20-week-old male transgenic hypertensive mice (THM), in which the renin-angiotensin system (RAS) was markedly activated because of the presence of both human renin and angiotensinogen genes. Systolic blood pressure and the ratio of left ventricular weight to body weight were significantly higher in the THM than in control mice, indicating that THM developed cardiac hypertrophy. ET-1 production was significantly increased in the heart of THM because both ET-1 mRNA expression and peptide levels were significantly higher than in controls. However, circulating plasma ET-1 levels did not differ between the groups, and blood pressure did not change after i.v. injection with a high dose (3 mg/kg) of the ETA/B-nonselective receptor antagonist SB209670. These findings suggest that increased cardiac ET-1 production may contribute to the progression of cardiac hypertrophy and that endogenous ET-1 may not be involved in the short-term modulation of blood pressure in THM of this age.

Efficacy of CI-1020, an endothelin-A receptor antagonist, in hypoxic pulmonary hypertension.

We previously showed that CI-1020, an endothelin (ET)-A-selective receptor antagonist, dose-dependently blocked acute hypoxic pulmonary hypertension (PH) in rats. In this study we show that CI-1020 can reverse existing PH and prevent progression of right ventricular hypertrophy (RVH) in rats exposed to chronic hypoxia. Male Sprague-Dawley rats were exposed to 20 days of hypoxia (10% O2) with CI-1020 treatment (20 or 40 mg/kg/day) starting on day 10. On day 20 of hypoxia, the rats were instrumented under anesthesia with a pulmonary artery cannula and allowed to recover to consciousness before measurement of mean pulmonary arterial pressure (MPAP). Blood samples were then collected for plasma ET-1 measurements, the rats killed, and their hearts dissected, dried, and weighed. RV/LV + septum ratio (g/g) was used as an index of RVH (RVHi). Normoxic rats and rats exposed to hypoxia for only 10 days were also evaluated as controls. Normoxic rats had MPAPs of 13 +/- 1 mm Hg, plasma ET-1 levels of 2.1 +/- 0.1 pg/ml, and an average RVHi of 0.29 +/- 0.03. Rats exposed to 10 or 20 days of hypoxia had MPAPs of 33 +/- 2 and 44 +/- 0 mm Hg, plasma ET-1 levels of 4.2 +/- 0.8 and 4.6 +/- 0.8 pg/ml, and average RVHis of 0.47 +/- 0.05 and 0.52 +/- 0.03, respectively. In comparison, rats treated with CI-1020 had MPAPs that were 37% (20 mg/kg/day) and 44% (40 mg/kg/day) lower than untreated 20-day hypoxic rats. Furthermore, rats dosed with 40 mg/kg/day of CI-1020 had MPAPs that were significantly lower (24%) than control 10-day hypoxic rats, indicating a significant reversal of PH. Along with this reversal in PH, their average RVHi was 23% lower (p < 0.05) relative to untreated 20-day hypoxic rats.

DOWN-REGULATION OF ET b RECEPTOR, BUT NOT ET a RECEPTOR, IN CONGESTIVE LUNG SECONDARY TO HEART FAILURE. ARE MARKED INCREASES IN CIRCULATING ENDOTHELIN-1 PARTLY ATTRIBUTABLE TO DECREASES IN LUNG ET b RECEPTOR-MEDIATED CLEARANCE OF ENDOTHELIN-1?

Receptors for endothelin (ET)-1, a potent vasoconstrictor peptide, have two isoforms, i.e. ET a receptors and ET b receptors. We previously reported that an ET a receptor antagonist greatly ameliorated pulmonary hypertension due to congestive heart failure (CHF) in rats. In the present study of rats with pulmonary congestion secondary to CHF, we determined not only ET a receptor mRNA expression but also ET b receptor mRNA expression in the congestive lung because lung ET b receptors are reported to be important for the clearance of circulating ET-1. We also measured lung ET-1 and circulating ET-1 levels. The expression of ET b receptor mRNA in the lung was significantly lower in rats with CHF than in age-matched control rats, while the expression of ET a receptor mRNA did not differ between the two groups. The protein level of ET b receptor, determined by Western blot, in the lung was lower in the rats with CHF than in the control rats, while the protein level of ET a receptor did not differ between the two groups. The lung ET-1 level and plasma ET-1 level were significantly higher in the rats with CHF than in the controls by 1.4-fold and 5.3-fold, respectively. Thus, in the rats with CHF, ET-1 was increased to a much greater extent in plasma than in the lung. The present findings suggest that selective down-regulation of ET b receptor, but not ET a receptor, occurs in the congestive lung. Since lung ET b receptors play a role in the clearance of circulating ET-1, we propose that down-regulation of lung ET b receptors partly contributes to marked increases in circulating ET-1 and that increased ET-1 in the circulating plasma as well as in the lung is involved in the progression of pulmonary hypertension in CHF.

Endothelin in cerebrospinal fluid and plasma of patients in the early stage of ischemic stroke.

Endothelin 1 (ET-1), a highly potent endogenous vasoactive peptide, exerts a sustained vasoconstrictive effect on cerebral vessels. Elevation of ET-1 in plasma has been reported 1 to 3 days after ischemic stroke. Since we assumed that a much faster and more intense response may be observed in the cerebrospinal fluid (CSF) and since an increase in concentration of ET-1 in the CSF may cause constriction of cerebral vessels and eventually influence the neurological outcome, we measured ET-1 values in the CSF within 18 hours of stroke onset and compared the values with those in the plasma. Twenty-six consecutive patients with acute stroke were clinically evaluated according to the modified Matthew Scale and underwent two repeat CT scans. Within 5 to 18 hours of stroke onset, lumbar puncture and blood samples were concomitantly obtained and tested; ET-1 levels in CSF and plasma of these patients were analyzed by radioimmunoassay and compared with the levels of a control group of patients with no neurological disease. The mean CSF concentration of ET-1 in the CSF of stroke patients was 16.06 +/- 4.9 pg/mL, compared with 5.51 +/- 1.47 pg/mL in the control group (P < .001). It was significantly higher in cortical infarcts (mean, 17.7 +/- 4.1 pg/mL) than in subcortical lesions (mean, 10.77 +/- 4.1 pg/mL) (P < .001) and significantly correlated with the volume of the lesion (P = .003). The correlation between ET-1 levels in the CSF and the Matthew Scale score was less significant (P = .05). Plasma ET-1 level was not elevated in any group. ET-1 is found to be significantly elevated in the CSF of stroke patients during the 18 hours after stroke. No elevation was demonstrated in plasma at this time period. ET-1 may be used as an additional indicator of ischemic vascular events in the early diagnosis of stroke. The dissimilarity between the CSF and plasma ET-1 concentrations may lead also to an hypothesis that there is a vasoconstrictive effect on the cerebral vessels or a neuronal effect caused by ET-1 in the mechanism of the progression of brain ischemia.

Anatomic heterogeneity of vascular aging: role of nitric oxide and endothelin.

We investigated the effects of aging, a cardiovascular risk factor, on vascular function with regard to endothelial nitric oxide synthase (eNOS), superoxide dismutase (SOD), and endothelin (ET-1) in aorta and femoral artery of the rat. Concentration-response curves to acetylcholine, calcium ionophore A23187, norepinephrine, ET-1, big endothelin, sodium nitroprusside, and exogenous SOD were obtained. Expression of eNOS mRNA was analyzed by reverse-transcription polymerase chain reaction, SOD activity was assessed using a chemiluminescence-based cytochrome c assay, and ET-1 plasma concentrations were measured by radioimmunoassay. In aorta of old rats, relaxations to acetylcholine and calcium ionophore A23187, basal NO release, and expression of eNOS mRNA in aortic endothelial cells were reduced (P<.05). In femoral arteries, relaxations to acetylcholine were preserved, whereas basal release of NO was attenuated (P<.05). Aging selectively increased contractions to norepinephrine and functional endothelin converting enzyme activity and attenuated contractions to ET-1 in aortas but not femoral arteries. Vascular SOD activity was higher in the femoral artery (P<.05) and unaffected by aging. Plasma ET-1 levels increased and plasma SOD activity decreased with age (P<.05). Aging was associated with an anatomic heterogeneity of endothelial dysfunction, functional endothelin converting enzyme activity, and vascular SOD activity. Vascular function was impaired in the aorta but not the femoral artery, which may be related to lower eNOS mRNA expression and SOD activity. These data suggest differential regulation of the vascular aging process that may contribute to the anatomic heterogeneity of atherosclerosis.

Endothelin-1 production during the acute chest syndrome in sickle cell disease.

To investigate the role of the endothelial-derived vasoactive mediator endothelin (ET-1) in the acute chest syndrome (ACS), we incubated bovine pulmonary artery endothelial cells (BPAEC) with red blood cells (equivalent to a hematocrit of 20%) and/or autologous plasma (1:10 dilution) from two patients during ACS and during routine clinic visits. Cellular RNA was analyzed for ET-1 transcripts by Northern analysis and ET-1 protein levels in BPAEC supernatants and in plasma measured by radioimmunoassay. ET-1 mRNA expression and protein levels increased in BPAEC exposed to plasma obtained during ACS; in contrast, exposure to plasma obtained during routine clinic visits did not alter BPAEC ET-1 mRNA expression or protein levels. Plasma ET-1 level was elevated during ACS, decreased during resolution, and remained slightly elevated during routine clinic visits. Plasma obtained from one patient 4 d prior to hospitalization for vasoocclusive crisis contained the highest ET-1 level and markedly increased BPAEC ET-1 mRNA expression and protein levels. In both patients, BPAEC ET-1 mRNA and protein expression in vitro and plasma ET-1 levels in vivo correlated with stage of disease and occurred in the absence of direct erythrocyte contact in vitro. These observations suggest that ET-1 production contributes to development of ACS.

CHANGES IN PLASMA ENDOTHELIN-1 (ET-1) LEVELS DURING AND POST MORPHINE SULPHATE (MS) INFUSION IN CONCIOUS NEWBORN PIGLETS ♦ 330

MS injection into concious immature pigs have been previously shown to produce an excitatory state associated with systemic and pulmonary artery hypertension. ET-1 is a potent vasoconstrictor peptide produced by the vascular endothelium. The hypothesis that basal systemic and cerebrovascular plasma ET-1 levels are altered during MS infusion was tested in concious newborn piglets (1-3 days old). The study animals (n=6) received a bolus of 100 μg/kg of MS over 5 minutes, followed by a continuous i.v. infusion (100μg/kg/hr) for 4 hrs. The control animals (n=6) received an equivalent volume bolus and infusion of 5% dextrose. Blood samples from the carotid artery and sagittal sinus vein were collected before, during (0.5, 1, 2, 3& 4 hrs) and post (1 & 2 hrs) infusion for the determination of plasma ET-1 levels by enzyme immunoassay. In the MS group systemic ET-1 plasma levels increased by 40% (14.9±3.9 pg/ml, p<0.05) at 1 hr and by 52% (15.3±4.1 pg/ml, p<0.01) at 3 hrs compared to baseline(9.0±1.0 pg/ml). Compared to the control group, systemic ET-1 plasma levels remained significantly elevated following the bolus dose (34%, p<0.05), during (39% to 53%, p<0.01) and 2 hrs post (41%, p<0.01) MS infusion. Similarly, sagittal sinus vein plasma ET-1 levels were consistently greater after the bolus injection (13.7±3.4 pg/ml, p<0.05) and remained elevated during the MS infusion (37% to 40%, p<0.05), and at 1(43%, p<0.05) and 2 (47%, p<0.01) hrs post infusion, when compared to baseline and control. These data indicate that continuous therapeutic dosages of MS infusion in newborn piglets results in high levels of ET-1 in the systemic and cerebrovascular circulation. The systemic and pulmonary vascular responses to MS infusion in newborn piglets may be mediated in part, by increased systemic and cerebrovascular ET-1 production.

Endothelin causes portal and pulmonary hypertension in porcine endotoxemic shock

A porcine model of endotoxemic shock was used to test the hypothesis that endothelins (ET) mediate the sustained increases in portal and pulmonary vascular resistances. Anesthetized pigs (n = 18) were instrumented and pretreated with 1) saline as a control; 2) indomethacin (Idm), a cyclooxygenase (Cox) inhibitor; or 3) Idm + bosentan (Bos), a mixed ET-receptor antagonist, and then were treated with endotoxin to produce shock and followed for 240 min. Global and regional hemodynamic parameters and plasma levels of ET-1 and thromboxane B2 were measured. The results show that 1) ET is independently responsible for the sustained increase in pulmonary vascular resistance; 2) ET and Cox products combine to increase portal venous resistance; 3) ET independently reduces cardiac output and attenuates or negates global systemic arterial vasodilation (presumptively mediated by nitric oxide) and exhibits regional differences, having little if any influence on the gut arterial bed. When considered with our prior study of nitric oxide regulation of the same beds in endotoxemic shock (N. Brienza, T. Ayuse, J. P. Revelly, C. P. O'Donnell, and J. L. Robotham, J. Appl. Physiol. 78: 784-792, 1995), the similarities between the portal venous and pulmonary arterial beds suggest that these two beds reflect phenomena occurring in microvascular and/or venous beds in multiple organs. The overall results suggest that a dynamic balance exists between NO and ET regulating arterial and microvascular and/or venous vasomotor activity during the evolution of endotoxemic shock.