Vasoactive mediators released by endothelins

Endothelin A receptor-like immunoreactivity on the basal infoldings of rat renal tubules and collecting ducts

We investigated the distribution of endothelin A (ET(A)) receptor-like immunoreactivity in the rat kidney using affinity-purified antibodies against amino acid residues 403-417 of the rat ET(A) receptor modified by the multiple antigen peptide complex system. Western blot analysis using the affinity-purified anti-ET(A) antibody detected bands of approximately 47.3 and 64.5 kDa in the rat kidney. By light microscopy, ET(A) receptor-like immunoreactivity was seen in the basal side of the renal tubules and collecting ducts. The most intense immunoreactivity was present in the distal renal tubules and inner medullary collecting ducts. In addition to the basal infoldings, immunoreactive puncta were scattered in the epithelial cells of the renal tubules and collecting ducts. Specimens prepared using the pre-embedding method were examined by electron microscopy, and some immunopositive signals were seen on the basal infodings of the renal tubules and collecting ducts. The lengths of immunopositive cytoplasmic membrane were far longer in the distal tubules and inner medullary collecting ducts than in the proximal tubules and outer medullary collecting ducts. Immunopositive signals were also sometimes observed in the thick portion of Henle's loop, but never in the thin portion. We have not previously detected immunopositive signals on the renal vascular systems with the antibody used here. These results suggest that endothelin acts on the basal infoldings through the ET(A) receptor, particularly in the distal tubules and inner medullary collecting ducts, although involvement of the ET(B) receptor cannot be excluded.

Distribution of endothelin receptor subtypes ETA and ETB in the rat kidney

The endothelin (ET) receptor system is markedly involved in the regulation of renal function under both physiological and pathophysiological conditions. The present study determined the detailed cellular localization of both ET receptor subtypes, ET(A) and ET(B), in the vascular and tubular system of the rat kidney by immunofluorescence microscopy. In the vascular system we observed both ET(A) and ET(B) receptors in the media of interlobular arteries and afferent and efferent arterioles. In interlobar and arcuate arteries, only ET(A) receptors were present on vascular smooth muscle cells. ET(B) receptor immunoreactivity was sparse on endothelial cells of renal arteries, whereas there was strong labeling of peritubular and glomerular capillaries as well as vasa recta endothelium. ET(A) receptors were evident on glomerular mesangial cells and pericytes of descending vasa recta bundles. In the renal tubular system, ET(B) receptors were located in epithelial cells of proximal tubules and inner medullary collecting ducts, whereas ET(A) receptors were found in distal tubules and cortical collecting ducts. Distribution of ET(A) and ET(B) receptors in the vascular and tubular system of the rat kidney reported in the present study supports the concept that both ET receptor subtypes cooperate in mediating renal cortical vasoconstriction but exert differential and partially antagonistic effects on renal medullary function.

The endothelin receptor antagonist TAK-044 in the treatment of reperfusion injury in organ transplantation

Ischaemia and reperfusion are complex interrelated events that involve the vascular endothelium. The endothelium produces endothelin (ET), the most potent vasoconstrictor identified to date. During ischaemia, endothelial transcription of ET is increased, leading to strong and sustained vasoconstriction. Ischaemia and reperfusion are indispensable parts of solid organ transplantation. Various experimental data discussed in this review show an efficacy of the mixed ET(A/B) antagonist TAK-044 in the treatment of reperfusion injury. The overall safety and tolerability of TAK-044 in humans seems to be excellent. Large clinical randomised trials on the use of TAK-044 in the treatment of reperfusion injury in different clinical situations are missing, nevertheless, the future for ET antagonists is promising.

Endothelin and the regulation of uterine and placental perfusion in hypoxia-induced fetal growth restriction

OBJECTIVE

Normal placental function is dependent on maintenance of uteroplacental perfusion. Endothelin, a potent vasoconstrictor, is produced in and is active in the uteroplacental vasculature. The purpose of this study was to determine the role of endothelin in the regulation of uteroplacental perfusion under normal conditions, and in hypoxia-induced fetal growth restriction.

METHODS

Timed-pregnant Sprague-Dawley rats, outfitted with arterial catheters, were maintained in either a normoxic or a normobaric hypoxic (12% oxygen) atmosphere from day 18 to 21 of gestation. During this time, the endothelin receptor A antagonist, A-127722, or its vehicle was administered. Regional blood flow was determined on gestational day 21 using 57Co-labeled microspheres. Data were analyzed by analysis of variance with statistical significance accepted at P<.05.

RESULTS

Both placental and uterine placental bed perfusion were significantly decreased by hypoxia and returned to normal values with the endothelin antagonist (P<.01 and P<.05, respectively). Fetal weights were significantly lower in the hypoxic group (P<.001) and restored to control levels by the antagonist.

CONCLUSION

In the rat, endothelin contributes little to the regulation of uteroplacental perfusion under normal conditions. Hypoxia results in a decrease in perfusion of the uteroplacental bed and of the placenta, and perfusion in both of these beds is normalized by endothelin A receptor antagonism. We conclude that endothelin plays a primary role in the pathophysiology of hypoxia-induced fetal growth restriction by reducing uteroplacental perfusion.

Plasma levels of endothelin-1, big endothelin-1 and thromboxane following acute pulmonary air embolism

Acute pulmonary air embolism (APAE) was induced in nine piglets by repeated intravenous bolus injection of room air into a large bore central venous catheter at time=0 min so that the mean pulmonary artery pressure (MPAP) was maintained at two times the baseline value for 4 h. Another five animals served as controls. At time=0, 30, 60, 120, 240 min, circulating arterial plasma levels of endothelin-1 (ET-1), its precursor big ET-1, and thromboxane (Tx), were measured by RIA and EIA, respectively, along with hemodynamics and blood gases. The data showed that following APAE, there was a rapid increase in MPAP and a persistent decrease in Pa(O(2)), while the mean arterial blood pressure and cardiac output remained comparable. Plasma levels of ET-1, big ET-1 and Tx were also increased steadily in these first 4 h. These results showed that during APAE, the resulted changes in the pulmonary vascular and airway tones mediated by these potent mediators could explain the observed pulmonary hypertension and the deterioration of gas exchange.

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

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

Elevated levels of endothelin-1 and prostaglandin E2 and their effect on nitric oxide generation in placental tissue from neonatal streptozotocin-induced diabetic rats

Endothelin-1 (ET-1), nitric oxide (NO) and prostaglandin E(2) (PGE(2)) are regulators of feto-placental hemodynamics. In this study we explore the inter-regulatory pathways that modulate the levels of these vasoactive agents in control and neonatal streptozotocin-induced (n-stz) diabetic rat placenta. ET-1 levels are increased in diabetic placenta when compared to controls (P<0.001), and are strongly reduced by an NO synthase inhibitor (P<0.001). PGE(2) production is increased in diabetic placenta when compared to controls (P<0.01), but these levels are not modulated by ET-1. NO levels, similar in control and in diabetic placenta, are not influenced by PGE(2), but they are negatively modulated by ET-1 in both control (P<0.05) and diabetic (P<0.01) placenta. We conclude that rat placental ET-1 inhibits NO levels but does not modify PGE(2) concentrations. The elevated levels of ET-1 and PGE(2) in diabetic placenta, potent vasoconstrictors of placental vasculature, are probably related to the induction of placental insufficiency and fetal hypoxia in this pathology.

Simultaneous changes in intracellular calcium and tension induced by endothelin-1 and sarafotoxin S6c in guinea pig isolated gallbladder: influence of indomethacin

The relationships between changes in intracellular Ca2+ and smooth muscle tension triggered by endothelin-1 and the selective endothelin ETB receptor agonist sarafotoxin S6c, as well as their susceptibility to modification by the nonselective cyclooxygenase blocker indomethacin, were assessed in guinea pig isolated gallbladder strips. Cumulative additions of either agonist (1, 10, and 100 nM) induced simultaneous graded, strongly correlated, slowly developing, and sustained changes in tension and intracellular Ca+2 (Fura-2 technique). Sarafotoxin S6c was more effective than endothelin-1 in raising intracellular Ca2+ at 1 or 10 nM, but their abilities to cause contractions were similar at all concentrations. Indomethacin (5.6 microM) markedly inhibited the changes in both intracellular Ca2+ and tension caused by all concentrations of sarafotoxin S6c (in response to 100 nM, increases in Ca2+ fluorescence intensity and tension were inhib ited from 7.7 +/- 0.7 to 4.0 +/- 0.4% and from 460 +/- 100 to 160 +/- 40 mg, respectively) but only reduced the contraction triggered by 100 nM endothelin-1 (from 560 +/- 100 to 230 +/- 70 mg). Endothelin-1 caused greater prostacyclin release from gallbladder than sarafotoxin S6c (at 100 nM, 6-keto-PGF1alpha levels in the medium rose 4.8- and 2.8-fold, respectively; P < 0.05) and slightly increased thromboxane A2 release (1.6-fold; P < 0.05). Thus, gallbladder contractions triggered by combined ETA/ETB or selective ETB receptor stimulation (with endothelin-1 or sarafotoxin S6c, respectively) are strongly correlated with increases in intracellular Ca2+ but differentially affected by indomethacin. It remains to be assessed if this difference is because endothelin-1 triggers greater prostacyclin release than sarafotoxin S6c and (or) is due to the coupling of ETA and ETB receptors to distinct patterns of generation of cyclooxygenase-derived eicosanoids.

Influence of indomethacin on effects of endothelin-1 on guinea pig isolated rings of common bile duct and sphincter of Oddi

The effects of endothelin-1 on motility of guinea pig extra-hepatic biliary tract portions were studied. Endothelin-1 (< or =100 nM) failed to contract rings of hepatic, cystic, proximal or distal common bile ducts, or choledochal or papillary halves of sphincter of Oddi. At 100 nM, endothelin-1 or sarafotoxin S6c (selective endothelin ET(B) receptor agonist) inhibited contractions of choledochal (but not papillary) sphincter of Oddi to carbachol (1 microM) by 63+/-5 and 45+/-9%, respectively. In distal common bile duct, indomethacin (5.6 microM) unmasked potent contractile effects of endothelin-1 [EC(50) 7.8 (5.5-11.1) nM; E(MAX) 80+/-6% of response to 80 mM KCl] and enhanced the contractile potency of carbachol (585-fold at EC(50) level), but not cholecystokinin C-terminal octapeptide. Inhibition of cholinergic responsiveness of the choledochal sphincter of Oddi by endothelin-1 was reduced by BQ-123 (1 microM; endothelin ET(A) receptor antagonist; cyclo[DTrp-DAsp-Pro-DVal-Leu]) and abolished by either BQ-123 plus BQ-788 (1 microM; endothelin ET(B) receptor antagonist; N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-methoxycarboyl-D-norleucine) or indomethacin. Thus, eicosanoids of the cyclo-oxygenase pathway (i.e. prostanoids) suppress endothelin-1-induced contractions of distal common bile duct and mediate endothelin ET(A) and ET(B) receptor-dependent inhibition of cholinergic responsiveness of the choledochal portion of the sphincter of Oddi.

Pathogenic role of endothelin 1 in hemodynamic dysfunction in experimental acute pulmonary thromboembolism

The plasma endothelin-1 (ET-1) level is elevated in patients with acute pulmonary thromboembolism (APE). Whether ET-1 is a pathogenic mediator or a simple marker of APE is not known. We investigated the role of ET-1 in hemodynamic dysfunction in APE through evaluating the effects of ET(A) receptor antagonist in an experimental APE model. We also examined ET-1 expression in embolized lungs. In a canine autologous blood clot pulmonary embolism model, ET(A) receptor antagonist ZD2574 (10 mg/kg, intravenous; ZD2574 group; n = 6) or vehicle (control group; n = 5) was administered. Hemodynamic and gas exchange parameters and plasma levels of ET-1 were serially measured. Prepro-ET-1 mRNA expression and the distribution of ET-1 peptide in lung tissues were also examined. With ZD2574 pulmonary arterial pressure and pulmonary vascular resistance significantly decreased, and were lower compared with the control group. The decrease in cardiac output was also less in the ZD2574 group. Plasma ET-1 levels increased after embolization. Prepro-ET-1 mRNA expression increased in embolized lungs and ET-1 peptide expression also increased in embolized lungs, particularly in the muscular pulmonary arteries, compared with normal lungs. These findings suggest that ET-1 partially contributes to hemodynamic derangements of APE, and that ET(A) receptor antagonists might constitute a useful therapeutic tool for APE.

Nonselective endothelin-receptor antagonism attenuates hemodynamic changes after massive pulmonary air embolism in dogs

STUDY OBJECTIVES

To evaluate the effects of nonselective endothelin (ET)-receptor antagonism on the hemodynamic changes and serum thromboxane (TX)-A(2) levels after a massive pulmonary air embolism (PAE) in dogs.

DESIGN

Prospective trial.

SETTING

University laboratory.

INTERVENTIONS

Anesthetized mongrel dogs (ET-receptor antagonist group; n = 6) received a bolus injection of 1 mg of the nonselective ET-A/ET-B-receptor antagonist PD 145065 (Sigma Chemical; St. Louis, MO), and dogs in the control group (n = 6) received saline solution. Hemodynamic data were recorded 5 min after the administration of antagonist or saline solution. Subsequently, each dog received 2.5-mL air/kg via the right femoral vein (the PAE), and the hemodynamic data were recorded for up to 60 min thereafter. Arterial blood samples were drawn at baseline and 15 min after PAE for the determination of plasma TX-A(2), measured by enzyme-linked immunosorbent assay as TX-B(2) (the stable metabolite of TX-A(2)).

RESULTS

PD 145065 alone produced no hemodynamic effects. However, dogs pretreated with PD 145065 had significantly lower increases in mean pulmonary arterial pressure and in pulmonary vascular resistance after the PAE (116% and 165%, respectively) compared to the control dogs (187% and 367%, respectively). The mean arterial pressure (MAP), cardiac index (CI), and plasma TX-B(2) levels were unaltered after PAE in the presence of ET-receptor antagonist, whereas CI and MAP decreased 5 to 10 min after PAE, and TX-B(2) concentrations increased 15 min after PAE in control dogs (p < 0.05 in all cases).

CONCLUSIONS

Nonselective antagonism of ET receptors attenuates the pulmonary hypertension and blunts the TX-A(2) release caused by massive PAE in dogs.

Endothelin ET(A) receptor antagonism attenuates the pressor effects of nicotine in rats

The increased endothelin-1 levels observed after smoking may result from nicotine-stimulated endothelin-1 production by endothelial cells. In this study, we investigated the effects of selective endothelin ET(A) receptors antagonist Cycle D-a-aspartyl-L-prolyl-D-isoleucyl-D-tryptophyl (JKC 301) and of endothelin ET(B) receptors antagonist N-cis-2, 6-dimethylpiperidino-carbonyl-L-gamma-methyl-leucyl-D-L-m ethoxycarbonyl-tryptophanyl-norleucine (BQ 788) on the changes in mean arterial pressure, heart rate, and plasma thromboxane B(2) (the stable product of thromboxane A(2)) levels caused by increasing doses of nicotine (0.6, 2, 6, and 20 micromol/kg) in anesthetised rats. Nicotine (0.6, 2, and 6 micromol/kg) significantly increased the mean arterial pressure in control and BQ 788-pretreated rats, while only a nicotine dose of 2 micromol/kg) increased the mean arterial pressure in JKC 301-pretreated animals. There were no differences in the nicotine-induced changes in heart rate or in the increases in thromboxane B(2) levels among the groups treated with saline, JKC 301 and BQ 788. These results demonstrate that whereas the antagonism of endothelin ET(A) receptors attenuated the increase in blood pressure after nicotine injections, endothelin ET(B) receptor antagonism had no such effect. In addition, the antagonism of endothelin ET(A) or ET(B) receptors did not affect thromboxane A(2) production after nicotine administration. These findings suggest that endothelin-1 may have a role in the acute effects of nicotine.

The hemodynamic effects of endothelin receptor antagonism during a venous air infusion in dogs

Endothelin (ET) is involved in the humoral component of the vasoconstriction during pulmonary embolism. We examined the effects of selective ET receptor antagonists on the hemodynamic and respiratory changes and on serum thromboxane B2 (TXB2) levels, during a continuous venous air infusion (VAI) in anesthetized mongrel dogs. The VAI (0.2 mL x kg(-1) x min(-1)) was initiated 5 min after an injection of saline (controls, n = 7), 1 micromol of the selective ET(A) receptor antagonist JKC-301 (group A, n = 6), or 1 micromol of the selective ET(B) receptor antagonist BQ-788 (group B, n = 6). Hemodynamic evaluation was performed every 15 min of VAI, and blood samples were drawn for blood gas analysis and TXB2 determinations. The increase in pulmonary perfusion pressure after 30 min of VAI was attenuated in Group A compared with the controls and Group B (Group A = 7+/-1 mm Hg; Group B = 16+/-1 mm Hg; controls = 14+/-1 mm Hg; P < 0.05). Pulmonary vascular resistance showed a similar behavior. TXB2 concentrations increased after 60 min of VAI in the controls and in Group B, but not in Group A (controls = 48%; Group B = 104%; Group A = 18%; P < 0.05 for controls and Group B). Similar decreases in Pao2 and Sao2 were observed in the three groups. We conclude that antagonism of ET(A) receptors attenuates the hemodynamic changes and blunts the increase in thromboxane A2 production during a VAI in dogs.

IMPLICATIONS

We evaluated the effects of endothelin receptor antagonists during a venous air infusion in dogs. EndothelinA receptor antagonism attenuated the hemodynamic changes and blunted the increase in thromboxane A2 production in this setting.

Evolution of streptozotocin-pancreatic damage in the rat: modulatory effect of endothelins on the nitridergic and prostanoid pathway

Many lines of evidence indicate that an increased pancreatic production of nitric oxide (NO) and prostaglandins (PGs) is found in the pancreas of streptozotocin-diabetic rats and that endothelins (ETs) are closely related to the nitridergic and prostanoid pathway in several tissues. In the present study the relationship between NO, ETs, and PGs has been explored in isolated pancreatic tissue from streptozotocin-diabetic rats. Pancreatic ET levels are higher in pancreatic tissues from diabetic (D) rats compared to control (C) animals. The addition of nitric oxide synthase (NOS) inhibitors (1 mM N(G)-nitro-l-arginine methyl ester, 600 microM N(G)-monomethyl-l-arginine) in the incubating medium reduces and NO donors (SIN-1, 300 microM spermine suppress, NONOate 100 microM) increases ET levels in pancreatic slices from C and D animals. PGE(2) (10(-7) M) increases and indomethacin (10(-6) M) decreases ET pancreatic production only in D but not in C tissues when added into the incubating bath. When tissues are incubated in the presence of endothelin 1 (ET-1) (10(-7) M), NOS activity is higher in C pancreas, while the ET-receptor antagonist bosentan (B) decreases NOS levels in D but not in C tissues. When pancreatic arachidonic acid (AA) conversion to prostaglandins was explored, ET-1 increased PGF(2alpha), PGE(2), and TXB(2) levels in C but not in D tissues. B abolishes TXB(2) increment due to the diabetic state, but failed in modulating AA conversion to 6-keto PGF(1alpha), PGF2(alpha) and PGE(2) in D pancreas. Our results show an alteration in AA metabolism, ET production, and NO increment associated with pancreatic damage due to streptozotocin.

Effects of endothelin-1 on capsaicin-induced nociception in mice

The influence of endothelin-1 on nociception induced by capsaicin was assessed in the mouse hindpaw. Local endothelin-1 injection (1 to 20 pmol/paw) 30 min prior to ipsilateral injection of capsaicin (0.1 microg/paw) increased, in a graded fashion, the time spent licking the injected paw. Maximal hyperalgesia was obtained with 10 pmol/paw of endothelin-1 (capsaicin-induced hindpaw licking time increased from 43 +/- 3 s to 114 +/- 7 s, n = 6), but no hyperalgesia was evident following 30 pmol/paw of endothelin-1. The selective endothelin ET(B) receptor agonists sarafotoxin S6c (< or = 30 pmol/paw) and IRL 1620 (i.e., Suc[Glu9,Ala11,15]endothelin-1-(10-21); < or = 100 pmol/paw) failed to induce hyperalgesia. Local treatment with BQ-123 (i.e., cyclo[DTrp-DAsp-Pro-DVal-Leu] 1 nmol/paw selective endothelin ET(A) receptor antagonist), 10 min before endothelin-1 (10 pmol/paw), fully blocked the hyperalgesic response, whereas similar treatment with the selective endothelin ET(B) receptor antagonist BQ-788 (i.e., N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D- 1-methoxy-carboyl-D-norleucine) was ineffective. Intravenous injection of bosentan (17 and 52 micromol/kg a non-peptidic mixed endothelin ET(A)/ET(B) receptor antagonist) or BMS 182874 (i.e., 5-[dimethylamino]-N-[3,4-dimethyl-5-isoxazolyl]-1-naphthalenesulph onamide; 10 and 30 micromol/kg; a non-peptidic selective endothelin ET(A) receptor antagonist), 1 h before endothelin-1, inhibited its hyperalgesic effect in a graded fashion and abolished the response at the higher doses. None of the antagonists modified nociception induced by capsaicin alone or the hyperalgesia induced by local injection of 5-hydroxytryptamine (5-HT; 2 nmol/paw, 30 min before capsaicin). Hyperalgesia induced by 5-HT was abolished by simultaneous injection of endothelin-1 or the endothelin ET(B) receptor agonist IRL 1620 (each at 30 pmol/paw). Therefore, local endothelin-1 exerts a dual influence in this model: at low doses it causes endothelin ET(A) receptor-mediated hyperalgesia (i.e., it potentiates capsaicin-induced nociception), whereas at higher doses it induces an anti-hyperalgesic effect against 5-HT which seems to be mediated via distinct endothelin ET (possibly ET(B)) receptors.

Endothelin receptor mRNAs in human fetal membranes, chorionic vessels, and decidua parietalis

Endothelin-1 (ET-1) is synthesized in avascular human amnion; and, immunoreactive ET-1 is present in amniotic fluid in concentrations 10 to 100 times those in blood. ET-1 acts, most commonly, in a local or paracrine manner; therefore, it is possible that amnion/amniotic fluid ET-1 acts on contiguous tissues, namely chorion laeve or placental surface (chorionic) vessels, or in an autocrine fashion on amnion cells. To address these possibilities, the levels of ET(A) and ET(B) receptor mRNAs were evaluated in amnion, chorion laeve, decidua parietalis, placenta, and chorionic vessel tissues. By Northern analysis of total RNA (20 microg), ET(A) and ET(B) receptor mRNAs were detected in decidua (n = 18), placenta (n = 14), and chorionic vessels (n = 13). In chorion laeve (n = 24), ET(B) receptor mRNA but not ET(A) receptor mRNA was detected by Northern analysis of total RNA. Northern analysis of chorion laeve poly(A)+ mRNA (1.5-2.5 microg) revealed ET(A) receptor mRNA at low levels. Neither ET(A) nor ET(B) receptor mRNAs were detected in amnion tissue by Northern analysis of total RNA (n = 30; placental and reflected amnion from 15 pregnancies) or by Northern analysis of poly(A)+ mRNA (1.5-2.5 microg). Moreover, there was no demonstrable dose-dependent effect of ET-1 on prostaglandin E2 production or DNA synthesis in amnion epithelial cells in primary culture. The findings of this investigation are indicative that ET-1 in amniotic fluid or secreted from amnion may act in a paracrine fashion on chorion laeve by way of the ET(B) receptor and on chorionic vessels by way of ET(A) and ET(B) receptors.

Endothelins in chronic liver disease

This review describes recent progress in the accumulation of knowledge about the endothelins (ETs), a family of vasoactive 21-amino acid polypeptides, in chronic liver disease. Particular prominence is given to the dynamics of ET-1 and ET-3 and their possible relation to the disturbed circulation and neurohumoral dysregulation found in cirrhosis. Recent studies have shown that the ET system is highly activated in most cirrhotic patients. Circulating ET-1 and ET-3 levels have a positive relation to the severity of the disease and fluid retention, with the highest values recorded in patients with functional renal failure. Studies on liver biopsies have revealed synthesis of ET-1 in hepatic endothelial and other cells, and recent investigations have identified the hepatosplanchnic system as a major source of ET-1 and ET-3 spillover into the circulation, with a direct relation to portal venous hypertension. In addition, marked associations with disturbance of systemic haemodynamics and with abnormal distribution of blood volume have been reported. Although the pathophysiological importance of the ET system in chronic liver disease is not completely understood, similarities to other vasopressive and antinatriuretic regulatory systems (i.e. the sympathetic nervous system, renin-angiotensin-aldosterone and vasopressin) are apparent, with respect to kinetics and haemodynamic dysregulation. Cirrhosis seems to be a pathophysiological condition with indications of the occurrence of ETs, not only as local modulators, but also as a system with potential importance for systemic regulation.

Relation of endothelins to volume regulating neurohumoral systems in patients with cirrhosis of the liver

The aim of the present study was to investigate the relationship between ET plasma concentrations and other hormonal systems in acute volume regulation of patients with cirrhosis. Ten healthy controls and 10 cirrhotic patients, five without and five with ascites were studied after 1 h in a sitting posture and subsequently subjected to 1 h head-out water immersion. Blood was collected for determinations of ET-1, ET-3, ANF, aldosterone, renin activity and noradrenaline. In addition, in 10 patients with compensated cirrhosis the effect of loop diuretics on ET-3, aldosterone and renin was studied. ETs in cirrhosis were significantly (P < 0.01) higher than in controls both before (ET-1, 19.6 +/- 1.3 pgmL-1 vs. 11.8 +/- 0.4 pgmL-1; ET-3, 18.5 +/- 1.4 pgmL-1 vs. 9.5 +/- 0.5 pgmL-1) and after water immersion (ET-1, 18.6 +/- 1.2 pgmL-1 vs. 12.4 +/- 0.3 pgmL-1; ET-3, 18.7 +/- 1.7 pgmL-1 vs. 10.0 +/- 0.5 pgmL-1). In cirrhotic patients, basal and immersion concentrations of ET-1 were significantly correlated to noradrenaline plasma concentrations (r = 0.79, P < 0.05). ET-3 plasma concentrations in cirrhosis were correlated to renin activity (r = 0.65, P < 0.05). Furthermore, ET-3 in cirrhosis was inversely correlated to systolic and mean arterial blood pressure (r = -0.55, P < 0.01 and r = -0.50, P < 0.05; respectively). To investigate the effect of hypovolaemia in compensated cirrhosis, 10 patients without ascites were studied before and after treatment with loop diuretics. In compensated cirrhosis ET-3 was significantly increased 6h after oral diuretic treatment (17.9 +/- 1.0 pgmL-1 vs. 15.5 +/- 0.4 pgmL-1, P < 0.001). The presented data demonstrate relations of endothelins, particularly of ET-3 to neurohumoral systems in patients with cirrhosis of the liver.

The effects and molar potency of iloprost, U46619 and sodium nitroprusside on capsular and vascular smooth muscle of the isolated perfused canine spleen

The isolated canine spleen was perfused at constant flow with continuous recording of splenic arterial perfusion pressure (SAPP) and spleen weight. Intra-arterial injections of the thromboxane A2 (TXA2) mimetic U46619 caused dose-related increases in splenic arterial perfusion pressure (SAPP) of short duration (ED50 0.31 nmol). There were very small changes in spleen weight accompanying any of the vasoconstrictor responses to U46619. The stable analogue of prostacyclin, iloprost, caused dose-dependent reductions in SAPP (ED50 1.3 nmol) indicating vasodilation. There were no changes in spleen weight to any doses of iloprost indicating a lack of action on capsular smooth muscle. Similarly, the nitric oxide (NO) mimetic sodium nitroprusside caused dose-related reductions in SAPP of short duration (ED50 5.8 nmol). No changes in spleen weight accompanied splenic vasodilator responses to any dose of sodium nitroprusside (SNP). The results indicate the potential actions and intrinsic potency of three endogenous vasoactive substances and provide information about their relative roles in the control of the splenic microcirculation in situations when they are released.

Phosphoramidon does not inhibit endogenous endothelin-1 release stimulated by hemorrhage, cytokines and hypoxia in rats

The role of phosphoramidon-sensitive endothelin converting enzyme in the release of endogenous endothelin-1 was investigated in anesthetized rats. Intravenous infusion of phosphoramidon 0.3 mg/kg/min did not suppress the release of endothelin-1 stimulated by hemorrhage or cytokines. Elevation of endothelin-1 in rats subjected to hypoxia was not modified by phosphoramidon (0.1 or 0.3 mg/kg/min for 2 h). A high dose of phosphoramidon (10 mg/kg i.v. +0.1 mg/kg/min) significantly potentiated the hypoxia-induced increases in plasma endothelin-1 levels. Increases in endothelin-1 release caused by bilateral nephrectomy were further enhanced by hypoxia. It is concluded that the release of endogenous endothelin-1 release stimulated by hemorrhage, cytokines and hypoxia is resistant to inhibition by phosphoramidon, and at high doses, phosphoramidon potentiates hemorrhage- and hypoxia-induced increases in endothelin-1 levels, most likely by preventing its degradation.