Occurrence and effects of endothelin in guinea-pig cardiopulmonary tissue

Changes of endothelin levels and therapeutic effects of Danshen in lung injury induced by severe acute pancreatitis in rats

AIM: To explore the changes of endothelin (ET) levels, in serum and lung, and the therapeutic effects of labiatae on severe acute pancreatitis (SAP) with lung injury in rats.

METHODS: A total of 60 Wistar rats were randomized into sham operation group (J), model group (F), and Danshen treatment group (D). The model of SAP was established by retrograde injection of 50 g/L sodium taurocholate into the pancreatic and biliary duct. The rats in group D were intraperitoneally injected with Danshen (5 mL/kg) 1 d before and 10 min after modeling. The levels of serum and pulmonary endothelin-1 were evaluated 24 and 48 h after modeling. Meanwhile, the changes of pulmonary histopathology and lung index were observed.

RESULTS: In comparison with those in group J, the pulmonary histopathological changes in group F were significantly aggravated, and the level of serum endothelin-1 and lung index were increased markedly 24 and 48 h after modeling (endothelin-1: 75.8 ± 4.8, 70.4 ± 4.8 ng/L vs 32.0 ± 6.9, 30.3 ± 4.8 ng/L, P < 0.01; lung index: 0.62 ± 0.06, 0.73 ± 0.07 vs0.41 ± 0.08, 0.41 ± 0.07, P < 0.01). Meanwhile, the expression of pulmonary endothelin-1 (using optical density) was elevated (F group: 0.48 ± 0.09, 0.61 ± 0.10; J group: 0.05 ± 0.01, 0.05 ± 0.01, P < 0.01; for 24 and 48 h respectively). Compared with those in group F, the pulmonary pathological changes in group D were notably alleviated, and the levels of serum endothelin-1 and lung index were notably dropped 24 and 48 h after modeling (60.2 ± 7.3 ng/L, 0.52 ± 0.06, P < 0.05; 57.9 ± 5.4 ng/L, 0.58 ± 0.06, P < 0.01), and the expression of pulmonary endothelin-1 was also decreased significantly (0.23 ± 0.10, 0.36 ± 0.09, for 24 and 48 h, respectively, P < 0.01 vs group F). The expression of pulmonary endothelin-1 was correlated with the lung index both at 24 and 48 h (r = 0.736, P < 0.01; r = 0.828, P < 0.01).

CONCLUSION: Endothelin-1 plays an important role in lung injury induced by SAP. Danshen can protect lung tissues from such injury.

Equine pulmonary and systemic haemodynamic responses to endothelin-1 and a selective ET(A) receptor antagonist

Based on previous in vitro studies, we hypothesised that endothelin (ET) would induce vasoconstriction in the pulmonary circululation of the horse and that this action would be mediated via ET(A) receptors. Pulmonary and systemic haemodynamic responses to endothelin-1 (ET-1), a potent vasoactive endogenous peptide, were investigated in 6 conscious, nonsedated horses at rest. Bolus i.v. injections of exogenous ET-1 (0.1, 0.2 and 0.4 microg/kg bwt) caused significant increases in pulmonary (PAP) and carotid (CAP) artery pressures, with peak increases of 79% and 51% for mean PAP and CAP, respectively. The effect of ET-1 on PAP and CAP was rapid and transient for PAP (-10 min) but prolonged for CAP (up to 60 min). ET-1 significantly decreased cardiac output by up to 35% and significantly increased systemic vascular resistance (SVR) by up to 104%. Pulmonary vascular resistance (PVR) showed a trend (P>0.05) to increase with 0.2 and 0.4 microg/kg bwt ET-1. Infusion of a selective ET(A) receptor antagonist (TBC11251) completely inhibited the responses to a subsequent bolus of 0.2 microg/kg bwt ET-1. We conclude that exogenous ET-1 exerts a potent vasoconstrictive action on the pulmonary and systemic circulations of the horse. These effects appear to be mediated largely through ET(A) receptors in both circulations. Endothelin may play a role in hypertensive conditions in the horse.

Exaggerated endothelin release in high-altitude pulmonary edema

BACKGROUND

Exaggerated pulmonary hypertension is thought to play an important part in the pathogenesis of high-altitude pulmonary edema (HAPE). Endothelin-1 is a potent pulmonary vasoconstrictor peptide that also augments microvascular permeability.

METHODS AND RESULTS

We measured endothelin-1 plasma levels and pulmonary artery pressure in 16 mountaineers prone to HAPE and in 16 mountaineers resistant to this condition at low (580 m) and high (4559 m) altitudes. At high altitude, in mountaineers prone to HAPE, mean (+/-SE) endothelin-1 plasma levels were approximately 33% higher than in HAPE-resistant mountaineers (22.2+/-1.1 versus 16.8+/-1.1 pg/mL, P<0.01). There was a direct relationship between the changes from low to high altitude in endothelin-1 plasma levels and systolic pulmonary artery pressure (r=0.82, P<0.01) and between endothelin-1 plasma levels and pulmonary artery pressure measured at high altitude (r=0.35, P=0.05).

CONCLUSIONS

These findings suggest that in HAPE-susceptible mountaineers, an augmented release of the potent pulmonary vasoconstrictor peptide endothelin-1 and/or its reduced pulmonary clearance could represent one of the mechanisms contributing to exaggerated pulmonary hypertension at high altitude.

Nitric oxide and endothelin-1 in coronary and pulmonary circulation

Since the discovery of the vasorelaxant properties of nitric oxide and the vasoconstrictor effect of endothelin-1, there have been many studies of the distribution and functional significance of these agents in various vascular beds. In the coronary and pulmonary circulation nitric oxide and endothelin-1 actions have been largely investigated in terms of an imbalance between the opposing effects of these vasoactive agents leading to pathophysiological conditions. This article review functional and immunocytochemical studies with emphasis on the ultrastructural localization of nitric oxide synthase and endothelin-1 in the coronary and pulmonary vascular beds. Localization of nitric oxide synthase (type III or I or II) has been shown in endothelial cells, smooth muscle, and perivascular nerves of the coronary and pulmonary vascular beds and in the neurons, nerve fibers, and the small granule-containing cells within cardiac ganglia. Endothelin-1 was mainly localized in subpopulations of coronary and pulmonary endothelial cells. These immunocytochemical studies provide information about the sources of nitric oxide and endothelin-1 that contribute to the vasomotor control of cardiac and pulmonary circulation under normal and pathophysiological conditions.

Haemodynamic influence and endothelin-1 plasma concentrations by selective or non-selective endothelin receptor antagonists in the pig in vivo

In the present study the haemodynamical effects of endothelin (ET)-receptor antagonism was evaluated using selective and non-selective ET(A)- and ET(B)-receptor blockade in normoxic pigs in vivo. In addition, the influence of the ET-antagonists on circulating plasma ET-1 levels was determined. BMS-182874 (10 and 30 mg kg(-1) i.v.), a selective ET(A)-receptor antagonist decreased the pulmonary and systemic vascular resistances. bosentan (10 and 30 mg(-1) i.v.), a non-selective ET(A)- and ET(B)-receptor antagonist caused principally similar effects as ETA-antagonism alone. No effects were observed by selective ET(B)-blockade using BQ-788 (30 microg kg(-1) i.v.). Of the three antagonists used only bosentan increased the circulating plasma ET-1 levels. It may therefore be concluded that ET contributes to basal systemic and pulmonary vascular tone through ET(A)-receptor activation. ET(B)-receptors are likely to cause the elevated plasma levels of ET-1 observed after bosentan administration. Furthermore, circulating plasma levels of ET-1 do not reflect the physiological effects of ET-1.

The endothelin antagonist bosentan: hemodynamic effects during normoxia and hypoxic pulmonary hypertension in pigs

In this study, we investigated the hemodynamic effects and receptor-blocking properties of the nonselective endothelin antagonist bosentan in pigs during normoxia and acute hypoxia. Hypoxic pulmonary hypertension was induced by decreasing the fraction of inhaled oxygen to 0.1. In a control group of pigs, hemodynamic parameters proved to be stable through 2 hours of hypoxia. Infusions of endothelin-1, endothelin-3, and sarafotoxin 6c into the pulmonary artery resulted in pulmonary and systemic vasoconstriction during normoxia, whereas endothelin administration during hypoxic pulmonary hypertension resulted in pulmonary vasodilation. After administration of bosentan, the vasopressor effect of endothelin-1 during normoxia was significantly attenuated and the pulmonary vasodilatory effect of endothelin-1 during hypoxia was reduced. Furthermore, the development of hypoxic pulmonary hypertension was significantly reduced by bosentan. In contrast, bosentan did not influence the pulmonary vasopressor response to the thromboxane mimic U-46619. We therefore conclude that vasopressor endothelin receptors seem to be activated by endogenous endothelin released during hypoxia, leading to an increase in the pulmonary vascular tone.

Tissue concentrations of endothelins and functional effects of endothelin-receptor activation in human arteries and veins

In the present study, the tissue content and functional effects of endothelin-1 and endothelin-3 were examined in human vessels of importance in coronary bypass operations. Human coronary arteries (i.e., the left anterior descending coronary artery) were obtained from eight cardiac valve donors within 6 hours after death, pulmonary arteries were perioperatively obtained from 15 patients operated on because of lung tumors, and internal thoracic arteries and great saphenous and cephalic veins were obtained at coronary bypass operations from a total of 28 patients. Endothelin-1 and endothelin-3 content was quantified by radioimmunoassay. For functional experiments, the vessels were mounted in organ baths for recordings of isometric contractions in response to endothelin-1, endothelin-3, and the endothelinA-receptor agonist sarafotoxin 6c. In all vessels investigated, the endothelin-1 content was higher than that of endothelin-3. The highest levels were found in the left anterior descending coronary artery, followed in declining order by the internal thoracic artery, pulmonary artery, saphenous vein, and cephalic vein. Endothelin-1 contracted all vessels in a concentration-dependent fashion. This effect was enhanced in the left anterior descending and internal thoracic arteries by inhibition of nitric oxide and prostaglandin formation. The contractile effect was attenuated in a concentration-dependent fashion in all vessels by incubation with the endothelinA-receptor blocker BQ-123. Furthermore, contractions evoked by endothelin-1 in the left anterior descending coronary and pulmonary arteries were antagonized by the combined endothelinA- and endothelinB-receptor blocker bosentan. Endothelin-3 contracted the left anterior descending coronary and pulmonary arteries and the saphenous vein, but not the internal thoracic artery, in a BQ-123-sensitive fashion. However, after inhibition with nitric oxide or prostaglandin, endothelin-3 also contracted the internal thoracic artery, and the response in the left anterior descending coronary artery was enhanced. Sarafotoxin 6c evoked a BQ-123-sensitive contraction of the left anterior descending coronary artery. It is concluded that endothelinA receptors mediate the major portion of the vasoconstriction observed on exposure to endothelin-1, endothelin-3, and sarafotoxin 6c in the left anterior descending coronary, pulmonary, and internal thoracic arteries and the saphenous vein. Furthermore, endothelinB-receptor activation, with subsequent formation of nitric oxide or prostaglandin (or both), counteracts the vasoconstrictor response to endothelin in the left anterior descending coronary and internal thoracic arteries, but not in the pulmonary artery or saphenous vein. The present findings therefore suggest that endothelinA-receptor antagonism might prove beneficial in preventing possible endothelin-induced coronary graft spasm.

Effects of nitric oxide on hyperinflation-induced pulmonary hypertension in the isolated-perfused lung

OBJECTIVE

To determine if nitric oxide decreases pulmonary vascular resistance in hyperinflation-induced pulmonary hypertension.

DESIGN

Isolated-perfused lamb lung model.

SETTING

Experimental animal laboratory in a university setting.

SUBJECTS

Ten isolated-perfused lamb lungs harvested from subjects with a mean age of 29 days.

INTERVENTIONS

After induction of anesthesia, endotracheal intubation, and mechanical ventilation, lungs were perfused via an extracorporeal circuit. Ventilatory pressures were set to provide tidal volumes of 10 mL/kg and ventilatory rates were adjusted to maintain a Paco2 of 40 +/- 5 torr (3.5 +/- 0.7 kPa). The perfusion system consisted of a blood reservoir, a membrane oxygenator, and a nonocclusive roller pump. Blood flow was increased progressively to 50 mL/kg/min, maintaining a pulmonary arterial pressure of < 25 mm Hg and a left atrial pressure between 2 and 5 mm Hg. End-expiratory lung volume was measured using a nitrogen washout method. Baseline data were collected after a 1-hr stabilization period. Lung volume was increased to achieve 25% (moderate hyperinflation) and 50% (severe hyperinflation) increments in pulmonary vascular resistance. Nitric oxide (80 parts per million) was administered to the preparation after each increment in lung volume.

MEASUREMENTS AND MAIN RESULTS

Mean pulmonary arterial pressure, mean left atrial pressure, pulmonary vascular resistance, and static lung compliance were measured at baseline and after moderate and severe hyperinflation, both before and after nitric oxide administration. Significant decreases in pulmonary vascular resistance were found when the preparation was ventilated with nitric oxide at baseline (43% decrease) and during hyperinflation induced pulmonary hypertension at both moderate (31% decrease) and severe (23% decrease) levels of hyperinflation.

CONCLUSIONS

Inhaled nitric oxide significantly reduces pulmonary vascular resistance, even when pulmonary hypertension is induced by airway hyperinflation and supraphysiologic lung volumes. These data suggest that the use of nitric oxide following lung transplantation may allow for effective management of pulmonary hypertension in patients who receive allografts from undersized donors. Further clinical experience will be crucial in precisely defining the range of donor-recipient size mismatch that can be adequately managed and the time course over which nitric oxide can be administered safely and effectively to these patients.

Effects of endothelins 1, 2 and 3 on mucosal blood flow in the upper airways

The three endothlins 1, 2 and 3 (ET-1, ET-2 and ET-3) are 21-amino-acid peptides which in a previous study in the rabbit have been shown to increase both mucociliary activity in the maxillary sinus in vivo and ciliary beat frequency (CBF) in sinus and tracheal samples in vitro. We have also demonstrated positive immunohistochemical staining for endothelin in the epithelium of samples from both maxillary sinus and trachea. The aims of the present investigation were to study the effects of the three endothlins on mucosal blood flow in the maxillary sinus of rabbits and the nasal mucosa of humans. ET-1, ET-2 and ET-3 decreased mucosal blood flow in the maxillary sinus of rabbits measured in vivo with laser Doppler flowmetry (LDF). Significant dose-response relationships were established for all endothelins. A comparison of the regression lines of the dose-response relationships for ET-1 and ET-2 did not show any difference, whereas the regression line of the dose-response relationships for ET-3 differed significantly. Maximum effect was seen at 50.0 pmol/kg ET-1, which reduced blood flow by -74.4 +/- 7.0%. Vasoconstriction became evident 30 s after administration of the endothelins, reached its maximum after 1 min and lasted 10 to 20 min. ET-1 induced stronger vasconstriction than ET-2 and ET-3 at equal dosage, except at 100.0 pmol/kg, where ET-2 had the same effect as ET-1. No tachyphylaxis was observed after repeated 10.0 pmol/kg-dose of ET-1. Similarly, there was no tachyphylactic effect on mucociliary activity in vivo in the maxillary sinus of rabbits after repeated challenges with ET-1 at 10.0 pmol/kg. Pretreatment with the cyclooxygenase inhibitors diclofenac had no inhibitory effect on the vasoconstriction induced by ET-1 at 10.0 and 50.0 pmol/kg. In 6 human volunteers the peak blood flow in the nasal septum decreased by -41.8 +/- 11.6% (p < 0.05) and AUC (area under curve) values decreased by -612.0 +/- 322.4% (p < 0.05) after challenge with 0.1 nmol ET-1, delivered in aerosol form into the nose. The effects of the endothelins on the blood flow in the upper airways of rabbit and man indicate that they have a functional role in the regulation of the mucosal vasculature of the upper airways.

Endothelin infusion reduces hypoxic pulmonary hypertension in pigs in vivo

Previous work has shown that the plasma levels of the potent vasoactive peptide endothelin (ET) are increased in pathophysiological conditions with increased pulmonary vascular resistance and it has been speculated that ET may play some part in hypoxic pulmonary hypertension. We have therefore evaluated the effects of ET-infusion in the porcine pulmonary circulation after hypoxia-induced hypertension. Pits under general anaesthesia were artificially ventilated through an endotracheal tube and hypoxia was induced by decreasing the fraction inhaled O2 from 0.21 to 0.10. Haemodynamic parameters were continuously recorded using a Swan-Ganz catheter in combination with thermodilution for cardiac output measurements. ET-1 or ET-3 was given as an i.v. infusion through the Swan-Ganz catheter in the right ventricle. Hypoxia induced a reproducible increase in pulmonary vascular resistance (PVR), mean pulmonary artery pressure (MPAP) and right ventricular stroke work (RVSW) while the systemic vascular resistance (SVR) slightly decreased. Cumulative infusion of ET-1 (10, 25 and 50 ng kg-1 min-1) dose-dependently decreased MPAP and PVR; at a higher dose (100 ng kg-1 min-1), the PVR returned to the level observed at hypoxia. ET-infusions at 50 and 100 ng kg-1 min-1 evoked an increase in SVR and a decrease in cardiac output (CO) and stroke volume (SV). RVSW also gradually decreased during ET-1 infusion. Infusion of ET-3 evoked effects similar to those of ET-1 infusions, although the response to ET-3 was not that rapid in onset. In a second series of animals, repeated 15 min periods of hypoxia evoked a stable, reproducible response with a consistent increase in PVR, MPAP and RVSW which returned to baseline values during normoxia. Infusion of ET-1 (25 ng kg-1 min-1) evoked a rapidly developing decrease in PVR and MPAP which was quickly normalized upon cessation of the ET-infusion. ET-1 infusion at this concentration did not per se influence the haemodynamic parameters during normoxia. It is concluded that in the pig, short-term ET-infusion reduces the pulmonary hypertension associated with acute hypoxia.

Acute alveolar hypoxia increases endothelin-1 release but decreases release of calcitonin gene-related peptide in isolated perfused rat lungs

The release and vascular effects of calcitonin gene-related peptide (CGRP) and endothelin-1 (ET-1) during acute alveolar hypoxia (O2 2%) were examined in isolated blood-perfused rat lungs. In 10 lungs, repeatedly ventilated with hypoxic gas for 5 min, samples from effluent blood were taken during hypoxia and analysed for plasma levels of CGRP-like immunoreactivity (-LI) and ET-1-LI. The plasma levels of ET-1-LI were significantly (p < 0.05) increased in hypoxic lungs (5.5 +/- 0.5 pmol l-1) compared with normoxic controls (3.7 +/- 0.56 pmol l-1). Plasma levels of CGRP-LI were significantly (p < 0.01) lower in hypoxic lungs (43.9 +/- 2.9 pmol l-1) than in normoxic controls (55.5 +/- 4.0 pmol l-1). No significant correlation was seen between perfusate peptide levels and pulmonary artery pressure (Ppa) during ventilation with normoxic or hypoxic gas. Infusion of the CGRP receptor blocker, CGRP, did not influence either the baseline Ppa or the development of the hypoxic pulmonary vasoconstriction response (HPV). In lungs undergoing HPV, 2 nmol l-1 ET-1 added to the perfusate, significantly reduced the hypoxic pressor response by 14 +/- 3% (p < 0.05), while addition of 200 nmol l-1 ET-1 caused no significant changes in HPV. CGRP 2 nmol l-1 caused no significant attenuation of HPV (8.9%), while 200 nmol l-1 CGRP significantly reduced HPV by 16 +/- 5% (p < 0.05). To conclude: acute alveolar hypoxia changes release of CGRP and ET-1 to the perfusate in isolated rat lungs. The results further suggest that CGRP and ET-1 are not involved in the development and regulation of the hypoxic pulmonary vasoconstriction response.

Endothelin-A receptor mediates cardiac inhibition by regulating calcium and potassium currents

Voltage-sensitive ion channels play fundamental roles in the regulation of cardiac function by various neurotransmitters. Endothelins have strong positive inotropic and chronotropic effects, for which recent studies have implicated various intracellular mechanisms. However, very little is known about the underlying ion-channel regulation by the peptide. We report here that endothelin-1 consistently hyperpolarizes the membrane and shortens the duration of the action potential in mammalian atrial myocytes, leading to suppression of electrical excitability of the heart. Endothelin-1, but not endothelin-3, inhibited the L-type calcium current by decreasing cyclic AMP accumulation and activated the muscarinic potassium current by stimulating a pertussis toxin-sensitive GTP-binding protein. Consistent with these results, endothelin-1 strongly reduced the heart rate when it was increased by beta-adrenoceptor stimulation. These effects were blocked by an ETA (endothelin-1-selective) receptor-selective antagonist, BQ123 (refs 8-11). The ETA receptor-mediated regulation of cardiac ion channels gives new insight into our understanding of the physiological and pathophysiological roles of endothelins in the control of cardiac function.

Differences in vascular effects and removal of endothelin-1 in human lung, brain, and skeletal muscle

To investigate the effects and elimination of endothelin-1 in humans, an intravenous infusion of endothelin-1 (ET-1) (4 pmol kg-1 min-1 for 20 min) was given to 10 healthy volunteers. Arterial plasma endothelin-1 like immunoreactivity (ET-1-LI) increased eleven-fold. The fractional extraction of ET-1-LI was 41% and 30% across the pulmonary and skeletal muscle vascular beds, respectively. The lung eliminated almost half of the administered ET-1. No fractional extraction was found in the cerebral circulation. The pulmonary oxygen uptake (VO2) was increased slightly by endothelin-1. Across both the cerebral and skeletal muscle vascular beds the arterio-venous oxygen difference decreased (P < 0.05), suggesting vasodilation, the effect lasting up to 1 h after the end of endothelin-1 infusion in the cerebral circulation. Arterial-pulmonary artery oxygen difference increased by 20%. ET-1 infusion led to a decrease in heart rate (10%), cardiac output (14%) and stroke volume (8%) (all with P < 0.05) as well as a 7% increase in mean arterial blood pressure. Pulmonary and systemic vascular resistance increased by 67% and 25%, respectively (P < 0.05). These results demonstrate the regional differences in the removal of circulating endothelin-1, the lung being mainly responsible for the plasma elimination. Endothelin-1 seems to exert both vasoconstrictive and vasodilatory actions in humans, probably depending on differences in receptor populations and endothelium configuration in various vascular beds.

Endothelin-1 in adult respiratory distress syndrome

Endothelin-1 (ET-1), a potent vasoconstrictor peptide produced by endothelial cells and degraded predominantly in the pulmonary vasculature, has been implicated in the development of various organ dysfunctions. To determine the pathophysiologic role of ET-1 in adult respiratory distress syndrome (ARDS) and the impact of impaired lung function on transpulmonary peptide handling, we compared plasma levels and pulmonary ET-1 balance in 14 patients with ARDS and in seven healthy control subjects. To obtain comparable conditions in both groups, the ET-1 level was raised in the control group by exogenous infusion (0.4 pmol/kg/min) to 9.4 +/- 0.8 pmol/L. ARDS was accompanied by a hyperdynamic circulatory pattern with increased cardiac output and depressed total vascular resistance but, simultaneously, pulmonary hypertension. Venous ET-1 concentration was massively increased in ARDS (9.8 +/- 1.2 versus 2.1 +/- 0.2 pmol/L, p < 0.001). In control subjects, the lung cleared the major fraction of ET-1 (fractional extraction 43 +/- 8.8%, uptake 12.5 +/- 2.5 pmol/min). In contrast, in ARDS there was a pronounced pulmonary releases into the circulation (32.8 +/- 10.3 pmol/min). We conclude that ET-1 concentrations are elevated in ARDS as the result of both increased formation and decreased disposal. Lung failure affects not only gas exchange but also nonrespiratory, metabolic pulmonary functions.

Endothelin immunoreactivity of airway epithelium in asthmatic patients

There is extensive pharmacological and physiological evidence that endothelin-1 influences airway calibre. In mammals, endothelin receptor occur on airway smooth muscle, local storage and release of the peptide have been demonstrated, and inhalation of endothelin-1 induces bronchoconstriction. To investigate the relation between endothelins and asthma the expression of this peptide in endobronchial biopsy specimens was examined immunohistochemically with an antiserum against endothelin-1. Biopsy specimens from 17 asthmatic patients and 11 atopic and non-atopic healthy controls revealed striking differences, with endothelin expression being evident in airways epithelium and vascular endothelium in 11 of the 17 asthmatic patients but in only 1 of 11 controls. These results suggest that endothelins may play a part in the exaggerated bronchomotor tone of asthma.

Endothelin as a putative sensory neuropeptide in the guinea-pig: different properties in comparison with calcitonin gene-related peptide

Both endothelin-(ET) and calcitonin gene-related peptide- (CGRP) like immunoreactivity (-LI) were present in a variety of organs and neuronal tissue of the guinea-pig as determined by radioimmunoassay (RIA). Neuronal tissues like dorsal root ganglia (DRG) contained by far the highest levels of both ET- (65 +/- 11 pmol/g) and CGRP-LI (34 +/- 5 pmol/g). The tissue levels of ET-LI remained unchanged after 6-hydroxydopamine and capsaicin-pretreatment, while CGRP-LI was markedly reduced after capsaicin. Chromatographic characterization revealed that the main portion of ET-LI in the DRG, right atrium and lung corresponded to synthetic ET-1. Immunohistochemical studies showed the presence of ET-LI in a few neurons of intact DRG and many neurons in DRG cell-cultures, partly co-existing with CGRP-LI. In the neuronal cells of DRG cultures the ratio between the ET- and CGRP-LI was 1:27 compared to 2:1 in intact DRG. 24 h after ligation of the sciatic or vagal nerves no accumulation of ET-LI was observed above the ligation, while CGRP-LI was increased 4-5-fold. Transection (10 days) of the sciatic nerve caused a 85-95% depletion of CGRP-LI in the distal skin, gastrocnemius muscle and trunk below the transection site, while in the proximal portion of the nerve CGRP-LI increased. No effects on ET-LI in these tissues were observed after sciatic nerve transfection. In release experiments on DRG cell cultures. Langendorff heart preparations or perfused guinea-pig lungs, potassium (60 mM), capsaicin or antidromic nerve stimulation evoked a clear-cut increase in the supernatant levels of CGRP-LI, suggesting release, while no effect on the ET-LI concentration was observed in the effluent. Furthermore, anoxia failed to influence the outflow of ET-LI from the heart and lung. It is concluded that ET-1-LI is present in high levels in spinal ganglia and ET-LI occurs in afferent cell-bodies, but in comparison with CGRP, ET shows remarkable inertness upon various experimental conditions including no evidence for axonal transport, loss after denervation or release. The neuronal ET-LI seems to increase under culture conditions, however. The possible function for the high content of ET-LI in the intact guinea-pig peripheral nervous system remains to be elucidated and may mainly be related to a non-neuronal pool considering the relatively low content of ET-LI compared to CGRP in cultured DRG cells.

Detection of endothelin-like immunoreactivity in epithelium and fibroblasts of the human umbilical cord

We studied tissue sections of freshly obtained full-term and premature human umbilical cords using polyclonal antibody to endothelin and immunocytochemistry. Endothelin immunoreactivity was detected in the cytoplasm of epithelial cells and primitive fibroblasts, but not in the endothelial cells of both full-term and premature umbilical cords. Immunoelectron microscopy using indirect immunogold staining technique localized endothelin immunoreactivity to the cytoplasm of the epithelial cells and fibroblasts but not confined to any particular structures. No endothelin immunoreactivity was detected in the nucleus or on the cell membrane. Pre-absorption tests with synthetic endothelin-1, -2, and -3 independently established that the immunoreactivity represented endothelin-1 and -2, but not -3. The presence of endothelin-1 and -2-like immunoreactive materials in epithelial cells and fibroblasts of human umbilical cord suggests a role of endothelin in parturition.

Occurrence, specific binding sites and functional effects of endothelin in human cardiopulmonary tissue

Endothelin (ET)-like immunoreactivity (-LI) was detected in the human cardiopulmonary system, with the highest levels being found in the left anterior descending coronary artery, followed by the lung, right atrium, pulmonary artery, bronchus, pulmonary vein and left ventricle. Chromatographic characterization showed that the ET-LI in the lung and left ventricle corresponded to synthetic ET-1. Specific, high-affinity binding sites for ET-1, with an extremely slow dissociation rate, were found in the lung, right atrium and left ventricle. Displacement studies revealed a rank order of potency of ET-1 greater than ET-2 and sarafotoxin 6b greater than ET-3 and big ET-1. Scatchard analysis indicated a single receptor population in the lung (KD 1.53 x 10(-10) M) and left ventricle (KD 3.0 x 10(-11) M). In functional experiments, ET-1 evoked concentration-dependent, long-lasting vasoconstriction of a higher potency than that evoked by ET-2 and ET-3 in epicardial coronary arteries as well as in pulmonary arteries. ET-1 and ET-2 also showed bronchoconstrictor activity at considerably lower concentrations (threshold 10(-11) M) of ET-1 than those needed to cause vasoconstriction (10(-9) M). ET-LI, mainly consisting of ET-1, occurs in human cardiopulmonary tissue. Specific, high-affinity sites with irreversible binding for ET-1 are found in both the heart and lung. ET-1 is more potent than ET-2 or ET-3 in displacing ET-1 binding and in causing vasoconstriction and bronchoconstriction. Thus, in the human heart and lung, ET-1 seems to be the most abundant and biologically active of the endothelin peptides.