Low Doses Of Endothelin-1 Research Articles

H2S mediates the vasodilator effect of endothelin-1 in the cerebral circulation.

H2S is an endogenous gasotransmitter that increases cerebral blood flow. In the cerebral vascular endothelium, H2S is produced by cystathionine δ-lyase (CSE). Endothelin-1 (ET-1) has constrictor and dilator influences on the cerebral circulation. The mechanism of the vasodilation caused by ET-1 may involve endothelium-derived factors. We hypothesize that ET-1-elicited dilation of pial arterioles requires an elevation of H2S production in the cerebral vascular endothelium. We investigated the effects of ET-1 on CSE-catalyzed brain H2S production and pial arteriolar diameter using cranial windows in newborn pigs in vivo. H2S was measured in periarachnoid cerebrospinal fluid. ET-1 (10-12-10-8 M) caused an elevation of H2S that was reduced by the CSE inhibitors propargylglycine (PPG) and β-cyano-l-alanine (BCA). Low doses of ET-1 (10-12-10-11 M) produced vasodilation of pial arterioles that was blocked PPG and BCA, suggesting the importance of H2S influences. The vasodilator effects of H2S may require activation of smooth muscle cell membrane ATP-sensitive K+ (KATP) channels and large-conductance Ca2+-activated K+ (BK) channels. The KATP inhibitor glibenclamide and the BK inhibitor paxilline blocked CSE/H2S-dependent dilation of pial arterioles to ET-1. In contrast, the vasoconstrictor response of pial arterioles to 10-8 M ET-1 was not modulated by PPG, BCA, glibenclamide, or paxilline and, therefore, was independent of CSE/H2S influences. Pial arteriolar constriction response to higher levels of ET-1 was independent of CSE/H2S and KATP/BKCa channel activation. These data suggest that H2S is an endothelium-derived factor that mediates the vasodilator effects of ET-1 in the cerebral circulation via a mechanism that involves activation of KATP and BK channels in vascular smooth muscle. NEW & NOTEWORTHY Disorders of the cerebral circulation in newborn infants may lead to lifelong neurological disabilities. We report that vasoactive peptide endothelin-1 exhibits vasodilator properties in the neonatal cerebral circulation by stimulating production of H2S, an endothelium-derived messenger with vasodilator properties. The ability of endothelin-1 to stimulate brain production of H2S may counteract the reduction in cerebral blood flow and prevent the cerebral vascular dysfunction caused by stroke, asphyxia, cerebral hypoxia, ischemia, and vasospasm.

Involvement of TRPA1 in ET-1-induced pain-like behavior in mice

Transient receptor potential ankyrin subfamily member 1 (TRPA1) is a nonselective cation channel known as a noxious cold-activated ion channel. Recent findings implicated its involvement in acute and chronic cold nociception processes. Here, we investigated whether TRPA1 is involved in endothelin-1 (ET-1)-induced spontaneous pain-like behavior in C57BL/6J mice. We found that TRPA1 antagonists, HC-030031 and AP18, significantly reduced the pain-like behavior caused by ET-1. AP18 also significantly reduced the pain caused by cinnamaldehyde, an agonist of TRPA-1. However, AP18 did not alleviate the pain caused by capsaicin. The pain-like behavior caused by ET-1 was inhibited by phospholipase C inhibitor, but not by protein kinase C inhibitor. Low dose of ET-1 could potentiate cinnamaldehyde-induced nociception. Our results suggested that TRPA1 is involved in ET-1-induced spontaneous pain-like behavior in mice.

O-GlcNAcylation Contributes to Augmented Vascular Reactivity Induced by Endothelin 1

O-GlcNAcylation augments vascular contractile responses, and O-GlcNAc-proteins are increased in the vasculature of deoxycorticosterone-acetate salt rats. Because endothelin 1 (ET-1) plays a major role in vascular dysfunction associated with salt-sensitive forms of hypertension, we hypothesized that ET-1–induced changes in vascular contractile responses are mediated by O-GlcNAc modification of proteins. Incubation of rat aortas with ET-1 (0.1 μmol/L) produced a time-dependent increase in O-GlcNAc levels and decreased expression of O -GlcNAc transferase and β-N-acetylglucosaminidase, key enzymes in the O-GlcNAcylation process. Overnight treatment of aortas with ET-1 increased phenylephrine vasoconstriction (maximal effect [in moles]: 19±5 versus 11±2 vehicle). ET-1 effects were not observed when vessels were previously instilled with anti– O -GlcNAc transferase antibody or after incubation with an O -GlcNAc transferase inhibitor (3-[2-adamantanylethyl]-2-[{4-chlorophenyl}azamethylene]-4-oxo-1,3-thiazaperhyd roine-6-carboxylic acid; 100 μmol/L). Aortas from deoxycorticosterone-acetate salt rats, which exhibit increased prepro–ET-1, displayed increased contractions to phenylephrine and augmented levels of O-GlcNAc proteins. Treatment of deoxycorticosterone-acetate salt rats with an endothelin A antagonist abrogated augmented vascular levels of O-GlcNAc and prevented increased phenylephrine vasoconstriction. Aortas from rats chronically infused with low doses of ET-1 (2 pmol/kg per minute) exhibited increased O-GlcNAc proteins and enhanced phenylephrine responses (maximal effect [in moles]: 18±2 versus 10±3 control). These changes are similar to those induced by O-(2-acetamido-2-deoxy- d -glucopyranosylidene) amino-N-phenylcarbamate, an inhibitor of β-N-acetylglucosaminidase. Systolic blood pressure (in millimeters of mercury) was similar between control and ET-1–infused rats (117±3 versus 123±4 mm Hg; respectively). We conclude that ET-1 indeed augments O-GlcNAc levels and that this modification contributes to the vascular changes induced by this peptide. Increased vascular O-GlcNAcylation by ET-1 may represent a mechanism for hypertension-associated vascular dysfunction or other pathological conditions associated with increased levels of ET-1.

Enhanced cell death in hippocampus and emergence of cognitive impairments following a localized mini‐stroke in hippocampus if preceded by a previous episode of acute stress

This series of experiments represents a test of a theory concerning the etiology of age-related cognitive decline, including Alzheimer's disease (AD). The theory suggests that multiple combinations of cofactors produce variants of these disorders. Two factors that have been linked to the etiology of AD, that are of interest to our laboratories, are stress and vascular strokes. The current experiments tested the cofactors theory by evaluating the neuronal and functional effects of localized subthreshold strokes in the hippocampus of different groups of rats. One group experienced episodes of stress prior to stroke induction while the other did not. The results showed that a low dose of endothelin-1 (ET-1) injected into the hippocampus of groups of rats that had previously experienced stressful episodes showed enhanced hippocampal cell death and neurodegeneration that did not occur in the rats that did not experience stress prior to stroke induction. The results also showed that the stressed rats given subthreshold ET-1 injections into the hippocampus showed hippocampal-based learning and memory deficits that were not present in the non-stressed group given the same injections. This pattern of results suggests that individuals that are under stress are more vulnerable to insults to the hippocampus that have little effect on an individual that is not stressed. This vulnerability might be due to the actions of stress hormones, like the glucocorticoids, that have been previously shown to endanger hippocampal neurons.

The role of endothelin-1 in vascular remodeling in vivo

See article by Dao et al. [4] (pages 61–68) in this issue. Vascular smooth muscle cells (VSMCs) are a major component of the arterial wall and play a critical role in the development of occlusive vascular lesions. In normal vessels, VSMCs are quiescent, differentiated, and contractile and function to maintain vascular tone and blood pressure. In pathological processes such as the response to vascular injury, VSMCs undergo a phenotypic transition whereby they proliferate, migrate from the medial to the intimal layer, and lead to neointimal formation and subsequent vascular remodeling. These resultant vascular changes contribute to the pathological basis of atherosclerosis and restenosis that occur after revascularization procedures such as angioplasty, stenting, and bypass grafting. Endothelin-1 (ET-1) is a potent 21-amino acid vasoconstrictor peptide. ET-1 is mainly generated from the endothelium of blood vessels and functions in a paracrine or autocrine manner on ETA and ETB receptors. These receptors present on VSMCs have been shown to induce contraction and stimulate cell hypertrophy and/or hyperplasia, while endothelial ETB receptors stimulate the production of nitric oxide and prostacyclin and accordingly elicit vasorelaxation. Accumulating evidence indicates that endogenous ET-1 is involved in the vascular remodeling in cardiovascular diseases. For example, local ET-1 production has been shown to be increased in vascular lesions, in neointimal formation after vascular injury, and in atherosclerosis, hypercholesterolemia, and hypertension. Indeed, the administration of ET receptor antagonists reduced the neointimal formation after vascular injury and prevented vascular remodeling in deoxycorticosterone acetate (DOCA)-salt hypertensive rats; this suggested the possibility that ET-1 induces VSMC hyperplasia in this process in vivo. However, several studies using cultured VSMCs showed that ET-1 stimulates VSMC hypertrophy but not hyperplasia in vitro [1–3]. Therefore, it is necessary to develop an understanding of the effect of ET-1 on VSMC hypertrophy and/or hyperplasia in vivo. In the current issue of Cardiovascular Research, Dao et al. [4] have examined the mitogenic or trophic effect of ET-1 in rat small mesenteric arteries in vivo and demonstrated that administration of low doses of ET-1 stimulated protein synthesis (hypertrophy) in the arteries, whereas high doses stimulated both protein and DNA synthesis (hyperplasia).

Endothelin-1-induced airway and parenchymal mechanical responses in guinea-pigs: the roles of ETA and ETB receptors.

Endothelin-1 (ET-1) has been shown to have a constrictor effect on the airways and parenchyma; however, the roles of the ETA and ETB receptors in the ET-1-induced changes in the airway and tissue compartments have not been fully explored. Low-frequency pulmonary impedance (ZL) was measured in anaesthetized, paralysed, open-chest guinea-pigs. ZL spectra were fitted by a model to estimate airway resistance (Raw) and inertance (Iaw), and coefficients of tissue damping (G) and elastance (H), and hysteresivity (eta = G/H). Two successive doses of ET-1 (0.05 and 0.2 nmol x kg(-1)) each evoked significant dose-related increases in Raw, G, H and eta. Pretreatment with 20 nmol x kg(-1) BQ-610 (a highly selective ETA receptor antagonist) resulted in a significantly decreased elevation only in H after the lower dose of ET-1. However, all parameters changed significantly less on the administration of ET-1 after pretreatment with 80 nmol-kg(-1) BQ-610, with 20 nmol x kg(-1) ETR-P1/fl (a novel ETA receptor antagonist) or with 20 nmol x kg(-1) IRL 1038 (an ETB receptor antagonist). The results of the separate assessments of the airway and tissue mechanics demonstrate that endothelin-1 induces airway and parenchymal constriction via stimulation of both receptor types in both compartments.

Hypoxia augments conversion of big-endothelin-1 and endothelin ET B receptor-mediated actions in rat lungs

We have examined the effect of endothelin-1, sarafotoxin-6C, big-endothelin-1 and other agents on perfused lungs from chronically hypoxic rats. Increases in pulmonary perfusion pressure induced by big-endothelin-1, endothelin-1, phenylephrine and potassium chloride were enhanced in hypoxic lungs, while the constrictor action of sarafotoxin-6C was not increased. When basal pulmonary perfusion pressure was raised, low doses of endothelin-1 and sarafotoxin-6C produced decreases in pulmonary perfusion pressure which were significantly greater in chronically hypoxic lungs, whereas responses to sodium nitroprusside were unchanged. Endothelin ET B receptor-mediated bronchoconstrictor responses were also potentiated in hypoxic lungs, whereas responses to carbachol were not. In hypoxic lungs, conversion of big-endothelin-1 to endothelin-1 was significantly increased. These data provide evidence for a generalised increase in vasomotor activity in chronically hypoxic lungs, and a more selective increase in endothelin ET B receptor-mediated vasodilator and bronchoconstrictor responses. Hypoxia also augments the conversion of big-endothelin-1 to endothelin-1.

Role of Endothelin Receptor Subtypes in the Behavioral Effects of the Intracerebroventricular Administration of Endothelin-1 in Conscious Rats

The role of endothelin receptor subtypes, i.e., ET A and ET B receptors, in the behavioral effects of the intracerebroventricular (ICV) administration of endothelin-1 were examined in conscious rats. ICV administration of endothelin-1 (1–9 pmol/rat) dose dependently produced barrel rolling and other convulsive behaviors including bodily twitching, rigidity, back crawling, fore/hindlimb dystonia, fore/hindlimb clonus, tail extension, and facial clonus. Moreover, a marked increase in spontaneous locomotor activity was observed in animals that were treated with a low dose of endothelin-1 (1 pmol/rat, ICV). Endothelin-1 (9 pmol/rat, ICV)-induced barrel rolling and other convulsive behaviors were completely suppressed by the coadministration of BQ-123 (15 nmol, ICV), a specific endothelin ET A receptor antagonist, but not of BQ-788 (15 nmol/rat, ICV), a specific endothelin ET B receptor antagonist. In contrast, increased locomotor activity produced by treatment with a low dose of endothelin-1 (1 pmol/rat, ICV) was antagonized by coadministration of BQ-788, but not of BQ-123. These results indicate that endothelin-1, which has affinity for both endothelin ET A and ET B receptors, most likely acts on central ET A receptors to evoke barrel rolling and other convulsive behaviors. In addition, activation of central ET B receptors may be involved in the increase in spontaneous locomotor activity. These results suggest that brain endothelin receptor subtypes may be involved in the regulation of various physiological functions.

Effect of endothelin-1 on cardiovascular parameters of lewis and wistar rats in immobilization stress

Effect of low doses of endothelin-1 on the dynamics of blood pressure and heart rate is studied in Lewis and Wistar rats during 1-h immobilization stress. It is shown that endothelin-1 significantly lowers blood pressure in stress-sensitive Lewis rats during stress and has no effect on hemodynamic parameters in immobilized stress-resistant Wistar rats in comparison with the control.

Potential pathophysiologic role of endothelin-1 in canine pericardial fluid.

Recently, extremely high levels of endothelin-1 (ET-1) were detected in the pericardial fluid of patients undergoing cardiac surgery. This study was designed to assess the pathophysiologic importance of this finding by infusing ET-1 into the closed pericardial sac of anesthetized dogs. Systemic arterial blood pressure, heart rate, and standard ECG were recorded. Intrapericardial infusion of ET-1 (11 and 33 pmol/kg/min; n = 4/4) for 40 min induced ventricular arrhythmias in all instances. The lower dose of ET-1 induced a substantial number of ventricular extrasystoles, couplets, and triplets. In one instance, ventricular extrasystoles accelerated into nonsustained ventricular tachycardia (VT). In animals receiving the higher dose, nonsustained VTs occurred regularly, whereas sustained VTs were detected in two of four animals. Before the onset of arrhythmias, QT time was significantly prolonged [ET-1 (11 pmol/kg/min) 180 +/- 12 to 198 +/- 10 ms, p < 0.05; ET-1 (33 pmol/kg/min) 192 +/- 15 to 233 +/- 13 ms, p < 0.01]. Hemodynamic variables did not change significantly before the onset of ventricular arrhythmias. Our results show that administration of exogenous ET-1 into the pericardial space induces ventricular arrhythmias associated with prolongation of QT time.

ETAReceptor Blockade Potentiates the Bronchoconstrictor Response to ET-1 in the Guinea Pig Airway

The effect of ETAreceptor blockade on the bronchopulmonary response to endothelin-1 was determined in the airway of the anesthetized, spontaneously breathing guinea pig. Endothelin-1 administered as an aerosol increased lung resistance and decreased dynamic lung compliance. Delivery of the ETAreceptor antagonist, FR139317, 5 min prior to giving endothelin-1 greatly potentiated these changes. A lower dose of endothelin-1 that had no effect on resistance or compliance produced large and significant changes when pretreated with FR139317. In contrast, aerosolized FR139317 had no effect on the bronchopulmonary response to intravenously administered endothelin-1. These data suggest a non-contractile function of ETAreceptors accessible from the airways that serve to buffer the constrictor effects of non-ETAreceptors.

Cardiovascular Effects of Centrally Administered Endothelin-1 in Rats

The effect of centrally administered endothelin-1 (ET-1) or IRL 1620 (5, 15, and 45 ng) on systemic hemodynamics was studied in anesthetized rats using a radioactive microsphere technique. Administration of saline (5 microliters, i.c.v.) did not product any significant cardiovascular effects. The lower doses of ET-1 (5 and 15 ng) did not produce any significant effect on blood pressure (BP), heart rate (HR), cardiac output (CO), stroke volume (SV), and total peripheral resistance (TPR). However, the highest dose (45 ng) produced a transient rise followed by a sustained fall in BP. The CO and SV decreased significantly, whereas HR and TPR were not affected. Pretreatment with BQ-123 (10 micrograms, i.c.v.) 15 min before administration of ET-1, completely antagonized the systemic hemodynamic effects of ET-1. Centrally administered IRL 1620, a specific ETB receptor agonist, did not produce any effect on BP, HR, CO, SV, and TPR in rats. It is concluded that ETA but not ETB receptors are involved in the central cardiovascular actions of ET.

Cerebral vasodilatory effect of high-dose, intravascular endothelin-1: inhibition by [formula omitted

The effects of intracarotid administration of endothelin-1 on the cerebral microvessels were examined in anesthetized cats. The local cerebral blood volume in the cortex, which reflects the cumulative dimensions of the cerebral microvessels, was measured by our photoelectric method. A low dose of endothelin-1 (0.1 nmol) elicited mild but significant declines in cerebral blood volume. Following a high dose of endothelin-1 (3 nmol), the cerebral blood volume was initially reduced, probably due to the marked fall in arterial blood pressure, but was subsequently increased significantly. The increase in cerebral blood volume was not secondary to the rise in blood pressure, since it was unaffected by inhibition of the blood pressure changes with BQ-123 (1 mg/kg), an endothelin antagonist. However, the cerebral blood volume increase was prevented by continuous administration of N G - monomethyl- l- arginine (0.35 mg/kg per min), an inhibitor of nitric oxide synthesis, plus BQ-123. BQ-123 itself had no significant effects on cerebral blood volume or blood pressure. We conclude that while a low dose of intravascular endothelin-1 steadily constricts the cerebral microvessels, a high dose dilates the cerebral microvessels through the induction of nitric oxide synthesis, probably in the endothelium.

Activity of the L-Arginine/Nitric Oxide Pathway and Endothelin-1 in Experimental Heart Failure

Neurohumoral changes influencing peripheral vascular resistance play a major role in congestive heart failure (CHF). We studied vascular function in 1-year-old cardiomyopathic syrian hamsters with pulmonary congestion and age-matched control hamsters. Aorta and mesenteric resistance arteries were suspended in organ chambers and myographs, respectively, for isometric tension recording. In aorta and mesenteric resistance arteries, contractile responses to norepinephrine (NE) were comparable in cardiomyopathic hamsters and controls. After inhibition of nitric oxide (NO) formation with nitro-L-arginine methylester (L-NAME), contractions to NE were enhanced in aorta of cardiomyopathic hamsters (p < 0.05); no effect was noted in controls or mesenteric resistance arteries. Low doses of endothelin-1 (ET-1 10(-10)-10(-9) M) caused stronger contractions in aorta of cardiomyopathic hamsters as compared with controls (p < 0.05). The sensitivity and maximal contraction to ET were more pronounced in mesenteric resistance arteries as compared with aorta in both cardiomyopathic and control hamsters (p < 0.05-0.001). In both aorta and mesenteric resistance arteries, acetylcholine (ACh 10(-9)-10(-5) M) induced concentration-dependent relaxation, which was prevented by L-NAME (p < 0.001). Maximal endothelium-dependent relaxation was more pronounced in aorta of cardiomyopathic hamsters (p < 0.05), but not different in mesenteric resistance arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

The paradoxical vascular interactions between endothelin‐1 and calcitonin gene‐related peptide in the rat gastric mucosal microcirculation

1. The interactions between local intra-arterial infusion of endothelin-1 (ET-1) and rat alpha-calcitonin gene-related peptide (alpha-CGRP) on gastric mucosal damage and blood flow have been investigated in the pentobarbitone-anaesthetized rat. 2. Close-arterial infusion of ET-1 (2-200 pmol kg-1 min-1) induced a significant and dose-dependent increase in gastric mucosal haemorrhagic injury. 3. Close-arterial infusion of the higher doses of ET-1 (100 and 200 pmol kg-1 min-1) resulted in a biphasic effect on mucosal blood flow, as determined by laser Doppler flowmetry (LDF). This consisted of an initial transient increase followed by a pronounced and sustained fall in LDF. 4. Local microvascular constriction may thus contribute to the mechanisms underlying the gastric injury induced by these higher doses of ET-1. 5. However, close-arterial infusion of lower doses of ET-1 (2-50 pmol kg-1 min-1), that also provoked substantial mucosal damage, induced only a sustained and significant mucosal hyperaemia, which may be secondary to microvascular injury. 6. Concurrent dose-arterial administration of rat alpha-CGRP (50 pmol kg-1 min-1) significantly inhibited the extent of gastric mucosal injury induced by ET-1 (5 pmol kg-1 min-1). 7. Furthermore, concurrent close-arterial infusion of this dose of alpha-CGRP, which itself increased mucosal LDF, significantly inhibited the hyperaemic response induced by close-arterial infusion of ET-1 (5 pmol kg-1 min-1). 8. These results indicate a damaging action on the gastric mucosa by low doses of ET-1 which is independent of local vasoconstriction, that may involve a direct injury of the microvascular endothelium. The protective action of alpha-CGRP thus seems unlikely to be due to a local vasodilator effect but may reflect protective actions on the microvascular endothelium

Low doses of endothelin-1 inhibit atrial natriuretic peptide secretion.

To clarify the interaction between endothelin-1 (ET-1) and atrial natriuretic peptide (ANP), the effects of ET-1 on ANP secretion were investigated in isolated perfused rat hearts and in conscious unrestrained rats. Perfusion with 10(-9) M ET-1 stimulated ANP secretion from the isolated perfused rat heart. However, 10(-10) M ET-1 significantly decreased ANP secretion for the initial 15 min of the perfusion period. The perfusion with 10(-11) M ET-1, which is near the plasma level of ET-1 (2 x 10(-12) M), inhibited ANP secretion throughout the perfusion period. The perfusion of 10(-12) M ET-1 slightly decreased ANP secretion. After the ET-1 perfusion period, ANP secretion increased in proportion to ET-1 dose. The inhibitory action of ET-1 on ANP secretion was almost abolished by simultaneous perfusion of indomethacin, a cyclooxygenase inhibitor, but not by methylene blue, an inhibitor of soluble guanylate cyclase. In conscious unrestrained rats the iv infusion of 1 pmol/kg.min ET-1, which doubled the plasma ET-1 level, slightly but significantly decreased the plasma ANP level 5 and 10 min after the initiation of the infusion. The infusion of 10 and 30 pmol/kg.min ET-1 increased the plasma ANP level. These results demonstrate that low doses of ET-1 exert an inhibitory and short-acting action on ANP secretion from the heart, although high doses of ET-1 exert stimulating and long-lasting action, and suggest that prostanoids are involved in this inhibitory action.

Why big endothelin-1 lacks a vasodilator response.

The biphasic arterial blood pressure response to endothelin-1 (ET-1) results from a transient decrease, followed by a longer-lasting increase, in systemic vascular resistance. In contrast to ET-1, big endothelin-1 (bET-1) produces monophasic increases in systemic vascular resistance and arterial blood pressure. This is somewhat surprising, because bET-1 activity is reportedly due to ET-1, bET-1 being converted to ET-1 by a putative converting enzyme. In this study we tested two hypotheses that could explain the singular effect of bET-1 on the arterial vasculature: that bET-1 vasoconstriction, mediated by ETA receptors at the level of the smooth muscle, masks the release of endothelial derived vasodilators, and/or that the endothelium develops tachyphylaxis owing to prolonged activation of endothelial ETB receptors. In anesthetized rats, blockade of the vasoconstrictor activity of bET-1 with BQ-123, an ETA-receptor antagonist, did not reveal a masked bET-1 vasodilator component in the rat hindquarter. Furthermore, in the presence of bET-1 (after 3.0 nmol/kg bET-1 i.v.), low doses of ET-1 (0.03-0.3 nmol/kg) produced dose-dependent hindquarter vasodilation, indicating activation of endothelial ETB and therefore no tachyphylaxis. Collectively, these experiments suggest that i.v. administration of bET-1 results in little or no activation of endothelial ETB receptors and therefore lacks a vasodilator response.

Endothelin-1 enhances vascular permeability in conscious rats: role of thromboxane A 2

The purpose of the present experiments was to study the effects of endothelin-1 (ET-1) on vascular permeability and the involvement of the cyclooxygenase metabolites in the vascular responses to ET-1. Bolus intravenous injection of ET-1 (0.1–1.0 nmol/kg) into conscious rats induced immediate hypotension lasting for 30 s followed by sustained dose-dependent hypertension. A low dose of ET-1 (0.1 nmol/kg) did not modify the hematocrit value but the 1.0-nmol/kg dose increased the hematocrit value from 39.7 to 44.4%. Pretreatment of the animals with BM-13505 (1 mg/kg), a thromboxane A 2 (TxA 2) receptor antagonist, prolonged the duration of the hypotensive response to ET-1 (1.0 nmol/kg) but had no effect on the effect on the pressor response. Pretreatment with OKY-046 (10 mg/kg), a TxA 2 synthesis inhibitor, or indomethacin (10 mg/kg), a cyclooxygenase inhibitor, had no significant effect on ET-1-induced changes in blood pressure. Evans blue dye extravasation, a marker of vascular permeability, increased up to 235% over control levels in specific vascular beds including the upper and lower bronchi, stomach, duodenum and kidney of ET-1 (1.0 nmol/kg)-treated animals. Pretreatment of the animals with BM-13505, OKY-046 or indomethacin reduced by 60–100% the Evans blue extravasation in these tissues. These results suggest that the effect of ET-1 on vascular permeability is partly mediated and/or modulated by the secondary release of TxA 2, whereas its action on arterial blood pressure appears to be independent from prostanoid release in conscious rats.

Effects of endothelin-1 on vascular permeability in the conscious rat: interactions with platelet-activating factor.

1. The objectives of the present experiments were to assess the effects of endothelin-1 on the macrovascular permeability in selected vascular beds, to study the involvement of platelet-activating factor (PAF) in vascular responses to endothelin-1 and to examine the vascular effects of combined administration of endothelin-1 and PAF in conscious rats. 2. Intravenous bolus injection of endothelin-1 (0.1-2 nmol kg-1) resulted in a dose-dependent biphasic change in mean arterial blood pressure (MABP) with initial transient hypotension followed by a prolonged pressor action. These changes were accompanied by a dose-dependent increase in haematocrit values. 3. Endothelin-1 (0.1 and 1 nmol kg-1) increased dose-dependently the vascular permeability of the trachea, upper and lower bronchi, stomach, duodenum, spleen and kidney (up to 240%) as measured by the extravasation of Evans blue dye. The permeability of pulmonary parenchyma, liver and pancreas was not affected significantly by endothelin-1 treatment. 4. Pretreatment of animals with the specific PAF receptor antagonist, WEB 2086 (1 mg kg-1, i.v.) or BN 52021 (10 mg kg-1, i.v.) reduced the endothelin-1 (1 nmol kg-1)-induced rise in haematocrit by about 50 and 30%, respectively. Both antagonists were highly effective at inhibiting protein extravasation in the stomach, duodenum and kidney. On the other hand, BN 52021, but not WEB 2086, significantly attenuated the effect of endothelin-1 on permeability in the lower bronchi and spleen. Neither WEB 2086 nor BN 52021 modified the changes in MABP evoked by endothelin-1.5. When low doses of endothelin-1 (0.1 nmolkg-')and PAF (0.19nmolkg-')were administered simultaneously, enhanced protein extravasation was detected in the upper and lower bronchi, whereas neither endothelin-1 nor PAF by themselves affected vascular permeability in these tissues. These changes occurred in the absence of significant changes in MABP.6. Combined administration of higher doses of endothelin-1 (1nmolkg-') and PAF (1.9nmolkg-') resulted in marked increases (up to 530%) in protein extravasation in the airways, pancreas, stomach and duodenum. The effect of endothelin-1 on permeability was not affected by PAF in the spleen, whereas it was completely inhibited by PAF in the kidney. Combined injection of endothelin-1 and PAF resulted in a slight, but significant increase in MABP.7. The present findings show that endothelin-1 is capable of increasing vascular permeability in selected vascular beds including the airways, gastrointestinal tract and kidney, and suggest that PAF may mediate, in part, its action on permeability, but not its hypotensive action. The present data also suggest that endothelin-1 and PAF can act in concert to increase vascular permeability in rat airways and gastrointestinal tract.

Endothelin-1 Has a Dilator Effect on Neonatal Pig Pulmonary Vasculature

Endothelin-1 (ET-1), a 21-residue potent vasoconstrictor peptide produced by endothelial cells, was reported to cause vasodilation in the systemic and pulmonary vascular beds. Therefore, in isolated perfused lungs from 7-day-old piglets, we studied the effects and the mechanisms responsible for the dilator effect of ET-1. ET-1 produced a mild transient decrease in perfusion pressure at low doses (less than 10(-7) M/g dry lung); at higher doses, a potent long-lasting vasoconstriction was noted. Indeed, the constrictor effect of ET-1 was at least equal to or greater than that of U-44069 and prostaglandin D2 (PGD2). When the vascular tone of the preparation was increased with U-46619, another stable endoperoxide analogue, the dilator response to low doses of ET-1 was increased, while the constrictor response remained unchanged. Indomethacin (2.8 x 10(-6) M) and glybenclamide (an ATP-sensitive potassium channel inhibitor) (10(-5) M) did not alter the responses to ET-1. The endothelium-derived relaxing factor (EDRF) inhibitor Nw-nitro-L-arginine (2 x 10(-4) M) not only inhibited the dilator response to ET-1 almost completely, but also potentiated the constrictor response. Finally, Nw-nitro-L-arginine alone had a mild vasoconstrictor effect in newborn pig lung. The results of these studies indicate that ET-1 has both vasodilator and vasoconstrictor activity in neonatal pig pulmonary vascular bed. This vasodilator activity may be mediated by EDRF.(ABSTRACT TRUNCATED AT 250 WORDS)