Hypoxaemia and release of endothelin-1

Hypoxic pulmonary vasoconstriction does not limit maximal exercise capacity in healthy volunteers breathing 12% oxygen at sea level

Maximal exercise capacity is reduced at altitude or during hypoxia at sea level. It has been suggested that this might reflect increased right ventricular afterload due to hypoxic pulmonary vasoconstriction. We have shown previously that the pulmonary vascular sensitivity to hypoxia is enhanced by sustained isocapnic hypoxia, and inhibited by intravenous iron. In this study, we tested the hypothesis that elevated pulmonary artery pressure contributes to exercise limitation during acute hypoxia. Twelve healthy volunteers performed incremental exercise tests to exhaustion breathing 12% oxygen, before and after sustained (8-h) isocapnic hypoxia at sea level. Intravenous iron sucrose (n = 6) or saline placebo (n = 6) was administered immediately before the sustained hypoxia. In the placebo group, there was a substantial (12.6 ± 1.5 mmHg) rise in systolic pulmonary artery pressure (SPAP) during sustained hypoxia, but no associated fall in maximal exercise capacity breathing 12% oxygen. In the iron group, the rise in SPAP during sustained hypoxia was markedly reduced (3.4 ± 1.0 mmHg). There was a small rise in maximal exercise capacity following sustained hypoxia within the iron group, but no overall effect of iron, compared with saline. These results do not support the hypothesis that elevated SPAP inhibits maximal exercise capacity during acute hypoxia in healthy volunteers.

Endothelin-1 receptor blockade does not alter the sympathetic and hemodynamic response to acute intermittent hypoxia in men

Repeat exposures to low oxygen (intermittent hypoxia, IH), like that observed in sleep apnea, elicit increases in muscle sympathetic nerve activity (MSNA) and blood pressure (BP) in men. Endothelin (ET) receptor antagonists can attenuate the sympathetic and BP response to IH in rodents; whether these data translate to humans are unclear. We hypothesized that ET-receptor antagonism would ameliorate any rise in MSNA and BP following acute IH in humans. Twelve healthy men (31 ± 1 yr) completed two visits (control, bosentan) separated by at least 1 wk. MSNA, BP, and baroreflex sensitivity (modified Oxford) were assessed during normoxic rest before and following 30 min of IH. The midpoint (T50) for each individual's baroreflex curve was calculated. Acute IH increased plasma ET-1 (P < 0.01), MSNA burst frequency (P = 0.03), and mean BP (P < 0.01). There was no effect of IH on baroreflex sensitivity (P = 0.46), although an increase in T50 was observed (P < 0.01). MSNA burst frequency was higher (P = 0.04) and mean BP (P < 0.01) was lower following bosentan treatment compared with control. There was no effect of bosentan on baroreflex sensitivity (P = 0.53), although a lower T50 was observed on the bosentan visit (P < 0.01). There was no effect of bosentan on increases in MSNA (P = 0.81) or mean BP (P = 0.12) following acute IH. Acute IH results in an increase in ET-1, MSNA, and BP in healthy young men. The effect of IH on MSNA and BP is not attenuated following ET-receptor inhibition. Present data suggest that acute IH does not increase MSNA or BP through activation of ET-receptors in healthy young men.NEW & NOTEWORTHY Repeat exposures to low oxygen (intermittent hypoxia, IH) elicit increases in muscle sympathetic nerve activity (MSNA) and blood pressure (BP) in men. Endothelin (ET) receptor antagonists can attenuate the sympathetic and BP response to IH in rodents; whether these data translate to humans were unclear. We show acute IH results in an increase in ET-1, MSNA, and BP in healthy young men; however, the effect of IH on MSNA and BP does not occur through activation of ET-receptors in healthy young men.

Endothelin-1 as a novel target for the prevention of metabolic dysfunction with intermittent hypoxia in male participants

We examined the effect of intermittent hypoxia (IH, a hallmark feature of sleep apnea) on adipose tissue lipolysis and the role of endothelin-1 (ET-1) in this response. We hypothesized that IH can increase ET-1 secretion and plasma free fatty acid (FFA) concentrations. We further hypothesized that inhibition of ET-1 receptor activation with bosentan could prevent any IH-mediated increase in FFA. To test this hypothesis, 16 healthy male participants (32 ± 5 yr, 26 ± 2 kg/m2) were exposed to 30 min of IH in the absence (control) and presence of bosentan (62.5 mg oral twice daily for 3 days prior). Arterial blood samples for ET-1, epinephrine, and FFA concentrations, as well as abdominal subcutaneous adipose tissue biopsies (to assess transcription of cellular receptors/proteins involved in lipolysis), were collected. Additional proof-of-concept studies were conducted in vitro using primary differentiated human white preadipocytes (HWPs). We show that IH increased circulating ET-1, epinephrine, and FFA (P < 0.05). Bosentan treatment reduced plasma epinephrine concentrations and blunted IH-mediated increases in FFA (P < 0.01). In adipose tissue, bosentan had no effect on cellular receptors and proteins involved in lipolysis (P > 0.05). ET-1 treatment did not directly induce lipolysis in differentiated HWP. In conclusion, IH increases plasma ET-1 and FFA concentrations. Inhibition of ET-1 receptors with bosentan attenuates the FFA increase in response to IH. Based on a lack of a direct effect of ET-1 in HWP, we speculate the effect of bosentan on circulating FFA in vivo may be secondary to its ability to reduce sympathoadrenal tone.

Endothelin-1 Serum Concentration in Pediatric Chronic Idiopathic Uveitis

Purpose

The aim of our study was to determine endothelin-1 (ET-1) concentration in chronic idiopathic uveitis in children and adolescents depending on anatomical location and grade of inflammation.

Methods

The cross-sectional study was conducted among 17 patients with chronic idiopathic uveitis and 22 healthy controls. Concentration of ET-1 in serum was determined using a commercially available ELISA kit. The concentration of C reactive protein (CRP) in serum was determined by immunoturbidimetric method using CRP4 reagent kit (Roche Diagnostics GmbH, Mannheim, Germany).

Results

Statistically significant difference between ET-1 concentration in patients with chronic idiopathic uveitis and controls was found 1.33 (1.22; 1.48) vs 1.93 (1.1; 3.11), p = 0.008). No correlations were found between ET-1 concentration and age, either in chronic idiopathic uveitis patients or controls. Nine out of 17 patients presented with anterior uveitis, 5 with posterior and 3 with panuveitis. There were no differences in ET-1 concentration between anterior, posterior and panuveitis (p = 0.634), and in terms of grade of inflammation.

Conclusion

ET-1 expression is disturbed in pediatric chronic idiopathic uveitis irrespective of the anatomical location and grade of inflammation. Lower expression of ET-1 plays a crucial role in disturbed vascular tone control and can result in permanent visual impairment in chronic non-infectious uveitis.

Effect of different high altitudes on vascular endothelial function in healthy people

BACKGROUND

The aim of the study was to provide a theoretical basis for the early diagnosis and prediction of acute altitude sickness, to provide a better entry mode for healthy people from plain areas to plateau areas, and to preliminarily clarify the possible mechanism of this approach.

METHODS

We measured endothelin-1 (ET-1), asymmetric dimethylarginine (ADMA), vascular endothelial growth factor (VEGF), nitric oxide (NO), and hypoxia-inducible factor 1 (HIF-1) levels in each sample and determined flow-mediated dilation (FMD) values using a portable OMRON color Doppler with a 7.0- to 12.0-MHz linear array probe. We used the Lewis Lake score to diagnose acute mountain sickness (AMS) and to stratify the disease severity.

RESULTS

We found no cases of AMS at any of the studied elevation gradients. We found significant differences in FMD values between individuals when at 400 m above sea level and when at 2200, 3200, and 4200 m above sea level (P < .05) but found no significant differences among those at 2200, 3200, and 4200 m. Our variance analysis showed that serum ET-1, VEGF, ADMA, NO, and HIF-1 levels in individuals at ≥3000 m and those at subplateau and plain areas (<3000 m) significantly differed (P < .05). The level of these factors also significantly differed between individuals at elevation gradients of plateau areas (3260 m vs 4270 m) (P < .05). We found no significant differences in serum ET-1, VEGF, and ADMA levels between individuals at the plateau (2260 m) and plain (400 m) areas (P > .05). NO and HIF-1 levels were significantly different in serum samples from individuals between the plateau (2260 m) and plain (400 m) areas (P < .05). However, with increasing altitude, the NO level gradually increased, whereas ET-1, ADMA, VEGF, and HIF-1 levels showed a decreasing trend. With the increase of altitude, there is no correlation between the trend of FMD and hematologic-related factors such as VEGF, NO, and HIF-1.

CONCLUSION

A healthy young male population ascending to a high-altitude area experiences a low incidence of AMS. Entering an acute plateau exposure environment from different altitude gradients may weaken the effect of acute highland exposure on vascular endothelial dysfunction in healthy individuals. Changes in serum ET-1, VEGF, ADMA, NO, and HIF-1 levels in healthy young men may be related to the body's self-regulation and protect healthy individuals from AMS. A short stay in a subplateau region may initiate an oxygen-free preconditioning process in healthy individuals, thereby protecting them from AMS. Noninvasive brachial artery endothelial function test instead of the detection of invasive hematologic-related factors for early diagnosis and prediction of the occurrence and severity of acute high-altitude disease is still lack of sufficient theoretical basis.

Endogenous ET-1 promotes ANP secretion through activation of COX2-L-PGDS-PPARγ signaling in hypoxic beating rat atria

Endothelin-1 (ET-1) is a potent stimulus for the secretion of atrial natriuretic peptide (ANP) and hypoxia stimulates the release of ET-1, which is involved in the regulation of atrial ANP secretion. However, the precise mechanism of endogenous ET-1 in the regulation of hypoxia-induced ANP secretion is unclear. Therefore, this study aimed to investigate the mechanism of hypoxia-induced endogenous ET-1 regulation of ANP secretion in isolated perfused hypoxic beating rat atria. The results of this study showed that acute hypoxia significantly stimulated ET-1 release and upregulated the expression of its type A as well as type B receptors (ETA and ETB receptors). Endogenous ET-1 induced by hypoxia markedly upregulated the expression of cyclooxygenase 2 (COX2) through activation of its two receptors, leading to an increase in lipocalin-type prostaglandin D synthase (L-PGDS) expression and prostaglandin D2 (PGD2) production. L-PGDS-derived PGD2 activated peroxisome proliferator-activated receptor γ (PPARγ), ultimately promoting hypoxia-induced ANP secretion. Conversely, L-PGDS-derived PGD2 may in turn regulate L-PGDS expression by a nuclear factor erythroid-2-related factor 2 (NRF2)-mediated feedback mechanism. These results indicate that endogenous ET-1 induced by hypoxia promotes hypoxia-induced ANP secretion by activation of COX2-L-PGDS-PPARγ signaling in beating rat atria. In addition, the positive feedback loop between L-PGDS-derived PGD2 and L-PGDS expression induced by hypoxia is part of the mechanism of hypoxia-induced ANP secretion by endogenous ET-1.

Safety and Ergogenic Properties of Combined Aminophylline and Ambrisentan in Hypoxia

We hypothesized that concomitant pharmacological inhibition of the endothelin and adenosine pathway is safe and improves exercise performance in hypoxic humans, via a mechanism that does not involve augmentation of blood oxygenation. To test this hypothesis, we established safety and drug interactions for aminophylline (500 mg) plus ambrisentan (5 mg) in normoxic volunteers. Subsequently, a placebo-controlled study was employed to test the combination in healthy resting and exercising volunteers at simulated altitude (4,267 m). No serious adverse events occurred. Drug interaction was minimal or absent. Aminophylline alleviated hypoxia-induced headaches. Aminophylline, ambrisentan, and their combination all significantly (P < 0.05 vs. placebo) improved submaximal hypoxic exercise performance (19.5, 20.6, and 19.1% >placebo). Single-dose ambrisentan increased blood oxygenation in resting, hypoxic subjects. We conclude that combined aminophylline and ambrisentan offer promise to safely increase exercise capacity in hypoxemic humans without relying on increasing blood oxygen availability.

The principal pathways involved in the in vivo modulation of hypoxic pulmonary vasoconstriction, pulmonary arterial remodelling and pulmonary hypertension

Hypoxic pulmonary vasoconstriction (HPV) serves to optimize ventilation-perfusion matching in focal hypoxia and thereby enhances pulmonary gas exchange. During global hypoxia, however, HPV induces general pulmonary vasoconstriction, which may lead to pulmonary hypertension (PH), impaired exercise capacity, right-heart failure and pulmonary oedema at high altitude. In chronic hypoxia, generalized HPV together with hypoxic pulmonary arterial remodelling, contribute to the development of PH. The present article reviews the principal pathways in the in vivo modulation of HPV, hypoxic pulmonary arterial remodelling and PH with primary focus on the endothelin-1, nitric oxide, cyclooxygenase and adenine nucleotide pathways. In summary, endothelin-1 and thromboxane A₂ may enhance, whereas nitric oxide and prostacyclin may moderate, HPV as well as hypoxic pulmonary arterial remodelling and PH. The production of prostacyclin seems to be coupled primarily to cyclooxygenase-1 in acute hypoxia, but to cyclooxygenase-2 in chronic hypoxia. The potential role of adenine nucleotides in modulating HPV is unclear, but warrants further study. Additional modulators of the pulmonary vascular responses to hypoxia may include angiotensin II, histamine, serotonin/5-hydroxytryptamine, leukotrienes and epoxyeicosatrienoic acids. Drugs targeting these pathways may reduce acute and/or chronic hypoxic PH. Endothelin receptor antagonists and phosphodiesterase-5 inhibitors may additionally improve exercise capacity in hypoxia. Importantly, the modulation of the pulmonary vascular responses to hypoxia varies between species and individuals, with hypoxic duration and age. The review also define how drugs targeting the endothelin-1, nitric oxide, cyclooxygenase and adenine nucleotide pathways may improve pulmonary haemodynamics, but also impair pulmonary gas exchange by interference with HPV in chronic lung diseases.

Hypoxic Pulmonary Vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Loss of the aryl hydrocarbon receptor induces hypoxemia, endothelin-1, and systemic hypertension at modest altitude

The aryl hydrocarbon receptor (AHR) is a basic helix-loop-helix Per-Arnt-Sim transcription factor that mediates induction of metabolic enzymes and toxicity of certain environmental pollutants. Although AHR knockout (KO) mice develop cardiac hypertrophy, conflicting reports associate this pathology with hypotension or endothelin (ET)-1-dependent hypertension. Because hypertension occurred at modest altitude, we tested the hypothesis that loss of AHR increases the sensitivity to hypoxia-induced ET-1, contributing to systemic hypertension. We found that AHR KO mice were hypertensive at modest altitude (1632 m) but hypotensive at low altitude (225 m). When AHR KO mice residing at 1632 m were exposed to the partial pressure of inspired oxygen (PIO(2)) at sea level for 11 days, blood pressure declined to levels measured at 225 m. Although plasma ET-1 in AHR KO mice was significantly elevated at 1632 m and decreased at 225 m and sea level PIO(2), pulmonary prepro-ET-1 mRNA was significantly reduced at 1632 m and decreased further at 225 m and sea level PIO(2). Blood gas analysis revealed that AHR KO mice were hypoxemic, hypercapnic, and acidotic at 1632 m, values that were attenuated and normalized after 24 hours and 11 days under sea level PIO(2), respectively. Lastly, AHR inactivation in endothelial cells by small interfering RNA significantly reduced basal prepro-ET-1 mRNA but did not alter hypoxia-induced expression. Our studies establish the AHR KO mouse as a model in which modest decreases in PIO(2) lead to hypoxemia, increased plasma ET-1, and systemic hypertension without increased pulmonary prepro-ET-1 mRNA expression.

A randomized, double blind study of the prophylactic effect of hyperbaric oxygen therapy on migraine

In a double blind, placebo-controlled study to assess the prophylactic effect of hyperbaric oxygen therapy on migraine, 40 patients were randomly assigned to a treatment group receiving three sessions of hyperbaric oxygen, or a control group receiving three hyperbaric air treatments. The patients were instructed to keep a standardized migraine diary for eight weeks before and after the treatment. Thirty-four patients completed the study. Our primary measure of efficacy was the difference between pre- and post-treatment hours of headache per week. The results show a nonsignificant reduction in hours of headache for the hyperbaric oxygen group compared to the control group. Levels of endothelin-1 in venous blood before and after treatment did not reveal any difference between the hyperbaric oxygen and control groups. We conclude that the tested protocol does not show a significant prophylactic effect on migraine and does not influence the level of endothelin-1 in venous blood.

Prognostic power of neurohumoral parameters in chronic heart failure depends on clinical stage and observation period

BACKGROUND

Endothelin (ET) and natriuretic peptides have prognostic significance in chronic heart failure (CHF). Because stimuli for forming these neurohormones differ, this study investigates whether their prognostic power depends on clinical stage and on length of the observation period.

METHODS

Plasma big ET, B-type natriuretic peptide (BNP), N-terminal BNP (N-BNP), and N-terminal atrial natriuretic peptide (N-ANP), in addition to 11 clinical and hemodynamic variables, were obtained from 452 patients with left ventricular ejection fraction (LVEF) </=35%. According to their New York Heart Association class and LVEF, patients were stratified into Group A, mild CHF (n = 114); Group B, moderate CHF (n = 210); and Group C, severe CHF (n = 128). To predict the combined end-point of death or urgent heart transplantation, a multivariate analysis was performed after an observation period of up to 1, 2, and 3 years in all patients and in each sub-group.

RESULTS

Best independents predictors were as follows: All patients: up to 1 year, big ET (p < 0.0001, chi-square = 59); and 2 and 3 years, log N-ANP (p < 0.0001, chi-square = 68; p < 0.0001, chi-square = 89). Group A: up to 2 and 3 years, log N-ANP (p < 0.001, chi-square = 12; p < 0.0001, chi-square = 25). Group B: up to 1 and 3 years, log N-ANP (p < 0.0001, chi-square = 16; p < 0.0001, chi-square = 22); and 2 years, log N-BNP (p < 0.0001, chi-square = 19). Group C: up to 1, 2, and 3 years, big ET (p < 0.0001, chi-square = 23; p < 0.0001, chi-square = 22; p < 0.0001, chi-square = 20).

CONCLUSION

Big ET was the best independent marker for 1-year prognosis in severe CHF, whereas natriuretic peptides (especially N-ANP) were better markers for 2- and 3-year prognoses in mild and moderate CHF.

Endothelin-1 levels in the pathophysiology of chronic obstructive pulmonary disease and bronchial asthma

BACKGROUND

Endothelin-1 (ET-1) has been implicated in the pathogenesis of asthma and chronic obstructive pulmonary disease (COPD). The ET-1 levels are elevated during exacerbations of asthma and COPD in bronchoalveolar lavage, serum, and sputum and fails with treatment of the exacerbations. Hypoxemia stimulates ET-1 secretion.

OBJECTIVE

The aim of this study was to examine the serum ET-1 levels in stable asthmatic and COPD patients.

MATERIALS AND METHODS

We examined 48 COPD and 26 asthmatic patients and 34 normal subjects. We collected arterial samples to measure baseline ET-1 levels in all patients and in the control group, during the day. All the patients underwent formal polysomnography (EEG, ECG, airflow, respiratory muscle movement, oximeter) to detect the presence of nocturnal, nonapneic, and oxyhemoglobin desaturation. Twelve of the COPD patients and six of the asthmatic patients were disqualified because of inadequate sleep or sleep apnea syndrome. Nineteen of the COPD patients desaturated below a baseline sleep saturation of 90% for 5 min or more, reaching a nadir saturation of at least 85%. We collected arterial samples to measure ET-1 levels, 5 min after the first period of desaturation in each of the 19 desaturators COPD patients. None of the 20 asthmatic patients exhibited oxyhemoglobin desaturation during sleep.

RESULTS

Baseline arterial ET-1 levels during the day were significantly higher in "desaturators" COPD patients (2.08+/-0.28 pg/ml) compared to "non-desaturators" COPD patients (1.38+/-0.16 pg/ml) (P<0.001) and to asthmatics (0.7+/-0.85 pg/ml) (P<0.001). ET-1 Levels in normal subjects were 1.221+/-0.02 pg/ml. In "desaturators" COPD patients ET-1 levels during the night, 5 min after the first oxyhemoglobin desaturation, were significantly higher (4.28+/-1.10 pg/ml) compared to those during the day (2.08+/-0.28 pg/ml) (P<0.001). A significant negative correlation was observed between ET-1 levels and degree of desaturation during the day (P=0.005, r=0.632) and during the night (P<0.001, r=0.930) in "desaturators" COPD patients.

CONCLUSION

According to our results: (1) ET-1 levels were significantly higher in "desaturators" COPD patients than in "non-desaturators" COPD and in asthmatics; (2) ET-1 levels were significantly higher during the night than during the day in "desaturators" COPD patients; (3) the degree of desaturation correlated negatively with the ET-1 levels in "desaturators" COPD patients, both during daytime and nighttime. These findings are consistent with the hypothesis that ET-1 is implicated in the pathophysiology of asthma and COPD, especially if nocturnal, nonapneic, oxyhemoglobin desaturation exists.

Hemodynamic and proinflammatory actions of endothelin-1 in guinea pig small intestine submucosal microcirculation

The hemodynamic and proinflammatory effects of endothelin-1 (ET-1) in proximal (1st/2nd order) and terminal (3rd/4th order) arterioles and venules were examined in small intestine submucosa of anesthetized guinea pigs. Vessel diameter (D), red blood cell velocity, and blood flow (Q) were determined in eight proximal and eight terminal microvessels before and at 20 min of ET-1 suffusion (10(-10), 10(-9), and 10(-8) M) and then with endothelin-A (ET(A))-receptor blockade with BQ-123 (10(-5) M). This protocol was repeated with platelet-activating factor (PAF) inhibition (WEB-2086, 1.0 mg/kg iv; n = 16). The ET-1-mediated microvascular responses were also examined with endothelin-B (ET(B))-receptor blockade using BQ-788 (10(-5) M; n = 11) alone or with ET(A+B)-receptor blockade with BQ-123 + BQ-788 (n = 10). Microvascular permeability was assessed by FITC-albumin (25 mg/kg iv) extravasation in seven series: 1) buffered modified Krebs solution suffusion (n = 6), 2) histamine suffusion (HIS; 10(-3) M, n = 5), 3) ET-1 suffusion (10(-8) M, n = 5), 4) BQ-123 (10(-5) M) plus ET-1 suffusion (n = 5), 5) PAF inhibition before ET-1 suffusion (n = 5), 6) histamine-1 (H1)-receptor blockade (diphenhydramine, 20 mg/kg iv) before ET-1 suffusion (n = 5), and 7) ET(B)-receptor blockade before (BQ-788 10(-5) M; n = 3) or with ET-1 suffusion (n = 3). D and Q decreased at 10(-8) M ET-1 and returned to control values with BQ-123 and BQ-123+BQ788 but not with BQ-788 in proximal microvessels. D did not change in terminal microvessels with ET-1 (10(-8) M) but decreased with BQ-788 and increased with BQ-123. PAF inhibition did not affect the D and Q responses of proximal microvessels to ET-1 but prevented the fall in Q in terminal microvessels with ET-1. ET-1 increased vascular permeability to approximately 1/3 of that with HIS; this response was prevented with BQ-123 and WEB-2086 but not with H1-receptor blockade. This is the first evidence that submucosal terminal microvessel flow is reduced with ET-1 independent of vessel diameter changes and that this response is associated with increased microvascular permeability mediated via ET(A)-receptor stimulation and PAF activation.

Renal function in hypoxaemic chronic obstructive pulmonary disease: effects of long-term oxygen treatment

Impaired renal function is an important cause for the oedema formation, which often occurs in severe chronic obstructive pulmonary disease (COPD). In the present study, the importance of nocturnal hypoxaemia (measured by a nocturnal pulse oximetry) for the renal function was determined in 19 COPD patients, with normal levels of serum creatinine. The effects on kidney function of alleviating the nocturnal hypoxaemia [using 6 months of long-term oxygen treatment (LTOT)], was assessed in 12 patients. Renal function was assessed by determining the clearances of intravenously administered inulin (C(In)) and para-amino-hippurate (C(PAH)) and orally supplemented lithium (C(Li)) and of circulating sodium (C(Na)). The 19 patients had a mean PaO2 of 7.63 +/- 1.08 kPa, a PaCO2 of 5.98 +/- 0.85 kPa, a mean nocturnal oxygen saturation (MnSaO2) of 87.7 +/- 2.8% and an FEV1 in %P of 25.6 +/- 14.6%. C(In) and C(PAH) were 35 and 45% lower than normal, respectively, whereas C(In)/C(PAH)=filtration fraction (FF) was 31% higher than normal. Six months of LTOT in 12 of the patients was not followed by any significant change in renal function in the entire study group. However, low pretreatment MnSaO2 correlated with reductions in post-treatment (FF) (r=0.73, P<0.05). Post-treatment PaCO2 did not change significantly in patients treated with oral diuretics, but increased (P<0.05) in patients without diuretics. C(Na) decreased after LTOT in six patients with an increase in PaCO2>6%, but C(Na) increased in four patients with unchanged or decreased PaCO2 following LTOT.

CONCLUSIONS

Renal function (including filtration fraction) is impaired in hypoxaemic COPD. Filtration fraction is decreased following 6 months of LTOT solely in patients with severe pretreatment hypoxaemia and sodium clearance seems to be increased if improved oxygenation is not accompanied by increased PaCO2.

Pharmacological identification of P2X1, P2X4 and P2X7 nucleotide receptors in the smooth muscles of human umbilical cord and chorionic blood vessels

To ascertain the role of extracellular adenosine 5'-triphosphate (ATP) receptors in human placenta circulation, we identified and pharmacologically characterized the P2X receptor population in its superficial vessels. Total RNA was extracted from segments of chorionic and umbilical arteries and veins of terminal placentae delivered by vaginal or Caesarian births. Polymerase chain reaction (PCR), followed by sequencing of the products, identified the presence of P2X 1, 4, 5, 6, and 7mRNAs in smooth muscle from chorionic and umbilical arteries and veins. Umbilical vessels proximal to the fetus expressed the same population of P2X subtypes, except for the P2X(5), but additionally expressed the P2X(2). Rings of chorionic vessels contracted upon addition of nucleotides and analogs with the following relative rank order of potencies in arteries and veins: alpha,beta-methyleneATP>beta,gamma-methyleneATP>PNP>ATP=diBzATP>2-MeSATP>ADP>AMP; in umbilical vessels alpha,beta-methyleneATP was at least 100-fold more potent than ATP. Nucleotide potency was less than that of PGF(2alpha) or endothelin-2, but had the same magnitude as serotonin. ATP-desensitized receptors evidenced cross desensitization to alpha,beta-methyleneATP, 2-MeSATP and diBzATP, effect not observed when desensitization was elicited by alpha,beta-methyleneATP, confirming the presence of various P2X receptor subtypes in the smooth muscles of these vessels. The vasocontractile efficacy of alpha,beta-methyleneATP was unaltered by endothelium removal, while that of ATP was significantly attenuated and those elicited by 2-MeSATP were blunted, indicating the presence of additional endothelial nucleotide receptors. These results suggest that P2X receptors participate in the humoral regulation of placental blood flow.

Prolonged hypobaric hypoxemia attenuates vasopressin secretion and renal response to osmostimulation in men

Effects of hypobaric hypoxemia on endocrine and renal parameters of body fluid homeostasis were investigated in eight normal men during a sojourn of 8 days at an altitude of 4,559 m. Endocrine and renal responses to an osmotic stimulus (5% hypertonic saline, 3.6 ml/kg over 1 h) were investigated at sea level and on day 6 at altitude. Several days of hypobaric hypoxemia reduced body weight (-2.1 +/- 0.4 kg), increased plasma osmolality (+5.3 +/- 1.4 mosmol/kgH(2)O), elevated blood pressure (+12 +/- 1 mmHg), reduced creatinine clearance (122 +/- 6 to 96 +/- 10 ml/min), inhibited the renin system (19.5 +/- 2.0 to 10.9 +/- 0.9 mU/l) and plasma vasopressin (1.14 +/- 0.16 to 0.38 +/- 0.06 pg/ml), and doubled circulating levels of norepinephrine (103 +/- 16 to 191 +/- 35 pg/ml) and endothelin-1 (3.0 +/- 0.2 to 6.3 +/- 0.6 pg/ml), whereas urodilatin excretion rate decreased from day 2 (all changes P < 0.05 compared with sea level). Plasma arginine vasopressin response and the antidiuretic response to hypertonic saline loading were unchanged, but the natriuretic response was attenuated. In conclusion, chronic hypobaric hypoxemia 1) elevates the set point of plasma osmolality-to-plasma vasopressin relationship, possibly because of concurrent hypertension, thereby causing hypovolemia and hyperosmolality, and 2) blunts the natriuretic response to hypertonic volume expansion, possibly because of elevated circulating levels of norepinephrine and endothelin, reduced urodilatin synthesis, or attenuated inhibition of the renin system.

Abnormalities of renal endothelin during acute exacerbation in chronic obstructive pulmonary disease

Circulating and urinary levels of endothelin (ET), an endothelium-derived vasoconstrictive and mitogenic peptide have been reported to increase in patients with chronic obstructive pulmonary disease (COPD), but the mechanisms of these abnormalities are not fully understood. Our study objectives were to evaluate pulmonary and renal ET clearance in COPD patients during an acute exacerbation. Our participants included nine consecutive patients with moderate to severe COPD without signs of right heart failure admitted for acute exacerbation and ten healthy volunteers (HV) as controls. ET was detected by radioimmunoassay in venous and arterial blood as well as in a timed urine specimen. For each subject, arterial/venous immunoreactive ET ratio (ir-ETart/ir-ETven) was evaluated as an index of its pulmonary clearance. Creatinine clearance was employed in each case to obtain a corrected renal ir-ET clearance. Glomerular filtration rate (GFR) was also assessed by dynamic(99m)Tc-diethylenetriamine pentaacetic acid renal scintigraphy in six COPD patients during acute exacerbation and at recovery. The ratio ir-ETart/ir-ETven was comparable in COPD patients (0.75+/-0.12) and in HV (0.82+/-0.09). A significant difference was found with respect to 24 h ir-ET urinary excretion between COPD patients during exacerbation as well as at recovery (respectively 142.1+/-12.8 ng/24 h and 89.0+/-15.1 ng/24 h) and HV (65.1+/-10.1 ng/24 h). ET renal clearance was higher in COPD patients than in HV (29.2+/-5.2 ml min(-1)in COPD during exacerbation; 17.5+/-3.9 ml min(-1)at recovery and 13.6+/-2.4 ml min(-1)in HV, P<0.001). GFR was 69.4+/-10.0 ml min(-1)in COPD patients during exacerbation and it significantly increased at the recovery (95.5+/-20.9 ml min(-1)P<0.001). Corrected renal clearance of the peptide was significantly correlated to GFR values during the exacerbation (r=-0.81, P<0.05). Furthermore change in renal ET production resulted associated with changes in paCO(2)(r=0.83, P<0.001) and in paO(2)(r=-0.73, P<0.05). Acute exacerbation in COPD patients causes an increase in renal ET production which is partially reversible at the recovery, in the absence of significant changes in ET-1 circulating levels. ET might contribute to the renal response to hypoxaemia and hypercapnia in COPD.

Mechanisms of hypertension in patients with chronic obstructive pulmonary disease and acute respiratory failure

PURPOSE

To investigate the effects of hypoxemia, hypercapnia, and cardiovascular hormones (norepinephrine, endothelin-1, and atrial natriuretic factor) on blood pressure during acute respiratory failure.

PATIENTS AND METHODS

Patients with chronic obstructive pulmonary disease and acute respiratory failure were divided into four groups of 10 patients each: hypoxemia-normocapnia, hypoxemia-hypercapnia, hypoxemia-hypocapnia, and normoxemia-hypercapnia. Plasma norepinephrine levels were determined by high-performance liquid chromatography with electrochemical detection. Plasma endothelin-1 and atrial natriuretic factor levels were radioimmunoassayed after chromatographic preextraction.

RESULTS

Systolic blood pressure and cardiovascular hormone levels were greater in patients with hypercapnia (whether or not they also had hypoxemia) than in those with normocapnia and hypoxemia. For example, in patients with hypercapnia and normoxemia, the mean (+/- SD) systolic blood pressure was 183+/-31 mm Hg and the mean norepinephrine level was 494+/-107 pg/mL, as compared with 150+/- 6 mm Hg and 243+/-58 pg/mL in those with normocapnia and hypoxemia (both P<0.05). Similar results were seen for endothelin-1 and atrial natriuretic factor levels, and for the comparisons of hypoxemic patients who were hypercapnic with those who were normocapnic.

CONCLUSIONS

These results suggest that blood carbon dioxide levels, rather than oxygen levels, are responsible for hypertension during acute respiratory failure, perhaps as a result of enhanced sympatho-adrenergic activity.

Cor Pulmonale

The goals of treatment of cor pulmonale are 1) to reduce pulmonary arterial hypertension; 2) to optimize gas-exchange efficiency; and 3) to improve survival. These goals are achieved through long-term oxygen therapy, bronchodilator and vasodilator therapy, aggressive treatment of pulmonary infection, and anticoagulation. Selected patients may benefit from available surgical options.

Diuretic effect of hypoxia, hypocapnia, and hyperpnea in humans: relation to hormones and O(2) chemosensitivity

We studied the contributions of hypoxemia, hypocapnia, and hyperpnea to the acute hypoxic diuretic response (HDR) in humans and evaluated the role of peripheral O(2) chemosensitivity and renal hormones in HDR. Thirteen healthy male subjects (age 19-38 yr) were examined after sodium equilibration (intake: 120 mmol/day) during 90 min of normoxia (NO), poikilocapnic hypoxia (PH), and isocapnic hypoxia (IH) (days 1-3, random order, double blind), as well as normoxic voluntary hyperpnea (HP; day 4), matching ventilation during IH. O(2) saturation during PH and IH was kept equal to a mean level measured between 30 and 90 min of breathing 12% O(2) in a pretest. Urine flow during PH and IH (1.81 +/- 0.92 and 1.94 +/- 1.03 ml/min, respectively) but not during HP (1.64 +/- 0.96 ml/min) significantly exceeded that during NO (control, 1.38 +/- 0.71 ml/min). Urine flow increases vs. each test day's baseline were significant with PH, IH, and HP. Differences in glomerular filtration rate, fractional sodium clearance, urodilatin, systemic blood pressure, or leg venous compliance were excluded as factors of HDR. However, slight increases in plasma and urinary endothelin-1 and epinephrine with PH and IH could play a role. In conclusion, the early HDR in humans is mainly due to hypoxia and hypocapnia. It occurs without natriuresis and is unrelated to O(2) chemosensitivity (hypoxic ventilatory response).

Receptor-mediated vascular and metabolic actions of endothelin-1 in canine small intestine

The effects of endothelin-1 (ET-1) infusion on blood flow (QG) and O2 uptake (VO2G) were examined in the small intestine of anesthetized dogs (n = 10). Arterial and venous flows of a gut segment were isolated, and the segment was perfused at constant pressure. Arterial and gut venous blood samples were taken, gut perfusion pressure and QG were measured, and O2 extraction ratio (OERG) and VO2G were calculated. ET-1 was infused (0.118 microgram. kg-1. min-1 ia) throughout the experiment. In group 1 (n = 5), ETA receptors were blocked using BQ-123 (0.143 mg. kg-1. min-1 ia) followed by blockade of ETB receptors with BQ-788 (0.145 mg. kg-1. min-1 ia). The order of ETA and ETB receptor blockade was reversed in group 2 (n = 5). In group 1, the decrease in QG observed with ET-1 infusion was partially reversed with BQ-123; no further change occurred after BQ-788 administration. In group 2, addition of BQ-788 to the infusate further decreased QG, whereas addition of BQ-123 returned QG to a value not different from that with ET-1 infusion alone. These data indicated that ET-1-induced vasoconstriction in the gut was mediated via ETA receptors and that this constriction was buffered by activation of ETB receptors. VO2G decreased in proportion to the decrease in QG with ET-1, decreased further with ET-1 plus ETB receptor blockade (group 2), and increased in proportion to the increases in QG with ETA receptor blockade (both groups). No changes in OERG occurred during ETA and ETB receptor antagonism in either group. This study is the first to demonstrate that a flow-limited decrease in gut VO2G occurred with infusion of ET-1 in gut vasculature. An intriguing and novel finding was that, during O2 limitation, OERG was only 50% of that normally associated with ischemia in this tissue.

Value of cardiopulmonary exercise testing and big endothelin plasma levels to predict short-term prognosis of patients with chronic heart failure

OBJECTIVES

We tested the hypothesis that, in patients with stable heart failure, measuring big endothelin-1 (ET-1) plasma level at rest predicts short-term prognosis better than peak oxygen consumption (VO2max) at exercise.

BACKGROUND

Cardiopulmonary exercise testing and evaluation of neurohumoral plasma factors are established tools to estimate survival in patients with heart failure. No data, however, exist comparing the prognostic value of both marker categories simultaneously.

METHODS

Two hundred twenty-six heart failure patients were studied in regard to a combined end point of death and prioritization for urgent cardiac transplantation within 1 year follow-up.

RESULTS

During the study period 149 patients were without cardiac events (group A), 69 patients died or were urgently transplanted (group B) and 8 patients were alive after a nonurgent heart transplant operation. Norepinephrine (p < 0.0001), atrial natriuretic peptide (p < 0.001), big endothelin plasma levels (p < 0.0001 as well as workload, VO2max and achieved percentage of predicted peak oxygen consumption (pVO2max) (all p < 0.0001) differed significantly between groups A and B. In multivariate stepwise regression analysis, however, only big ET-1 plasma concentration (chi2=74.4, p < 0.0001), New York Heart Association function class (chi2=33.9, p < 0.0001), maximal workload (chi2=7.2, p < 0.01, and plasma atrial natriuretic peptide (ANP) concentration (chi2=4.6, p < 0.05) were independently related to outcome. Peak oxygen consumption or pVO2max did not reach statistical significance in this model. Event-free survival rates were significantly lower in patients with a big ET-1 level of 4.3 fmol/ml or more than with lower big ET-1 levels (p < 0.0001).

CONCLUSION

We conclude that in patients with chronic heart failure who are stable on oral therapy measuring big ET-1 and ANP plasma levels may be a valuable noninvasive adjunct to improve the prognostic accuracy of detecting high risk patients compared with exercise testing alone.

Nitric oxide: an important role in the maintenance of systemic and pulmonary vascular tone in man

AIMS

The aim of this study was to examine whether nitric oxide (NO) has an important role in maintaining basal vascular tone in normal man by examining the effects of nitric oxide inhibition using N(G)-monomethyl-L-arginine (L-NMMA) on systemic and pulmonary haemodynamics.

METHODS

Ten normal male volunteers 26 +/- 1.6 years were studied on two separate occasions in a double-blind, placebo controlled crossover study. They were randomised to receive either a continuous infusion of L-NMMA (4 mg kg(-1) h(-1)) with a front loaded bolus (4 mg kg(-1)) or volume matched placebo. Pulsed wave Doppler echocardiography was used to measure cardiac output (CO), mean pulmonary artery pressure (MPAP) and hence systemic vascular resistance (SVR) and total pulmonary vascular resistance (TPR). Measurements were made prior to infusion (t0) and after 4, 8, and 12 min (t1, t2 and t3).

RESULTS

Infusion of L-NMMA significantly increased mean arterial blood pressure (MAP), SVR and TPR and significantly reduced heart rate (HR), stroke volume (SV) and CO compared to placebo. These effects were observed at t1 and persisted during the entire infusion period.

CONCLUSIONS

These results are consistent with a role for basal nitric oxide generation in the maintenance of basal systemic and pulmonary vascular tone in normal man.

Endothelin as a regulator of cardiovascular function in health and disease

The endothelins are a family of endothelium-derived peptides that possess characteristically sustained vasoconstrictor properties. Endothelin-1 appears to be the predominant member of the family generated by vascular endothelial cells. In addition to its direct vascular effects, endothelin-1 has inotropic and mitogenic properties, influences homeostasis of salt and water, alters central and peripheral sympathetic activity and stimulates the renin-angiotensin-aldosterone system. Studies with endothelin receptor antagonists have indicated that endothelin-1 probably has complex opposing vascular effects mediated through vascular smooth muscle and endothelial ET(A) and ET(B)receptors. Endogenous generation of endothelin-1 appears to contribute to maintenance of basal vascular tone and blood pressure through activation of vascular smooth muscle ET(A)receptors. At the same time, endogenous endothelin-1 acts through endothelial ET(B) receptors to stimulate formation of nitric oxide tonically and to oppose vasoconstriction. In view of the multiple cardiovascular actions of endothelin-1, there has been much interest in its contribution to the pathophysiology of hypertension. Results of most studies suggest that generation of, or sensitivity to, endothelin-1 is no greater in hypertensive than it is in normotensive subjects. Nonetheless, the deleterious vascular effects of endogenous endothelin-1 may be accentuated by reduced generation of nitric oxide caused by hypertensive endothelial dysfunction. It also appears likely that endothelin participates in the adverse cardiac and vascular remodelling of hypertension, as well as in hypertensive renal damage. Irrespective of whether vascular endothelin activity is increased in hypertension, anti-endothelin agents do produce vasodilatation and lower blood pressure in hypertensive humans. There is more persuasive evidence for increased endothelin-1 activity in secondary forms of hypertension, including pre-eclampsia and renal hypertension. Endothelin-1 also appears to play an important role in pulmonary hypertension, both primary and secondary to diseases such as chronic heart failure. The hypotensive effects of endothelin converting enzyme inhibitors and endothelin receptor antagonists should be useful in the treatment of hypertension and related diseases. Development of such agents will increase knowledge of the physiological and pathological roles of the endothelins, and should generate drugs with novel benefits.