A novel potent vasoconstrictor peptide produced by vascular endothelial cells

Plasma endothelin levels in patients with uraemia

Plasma immunoreactive endothelin concentrations were measured in patients with uraemia and in non-uraemic controls. Concentrations were beneath the detection limit of the assay in most patients without uraemia but were readily detectable in those undergoing haemodialysis. Plasma endothelin concentrations in patients with uraemia who were not undergoing haemodialysis were lower than in those on maintenance dialysis.

Specific binding of endothelin on human vascular smooth muscle cells in culture

Endothelin is a newly discovered, potent vasoconstrictor peptide secreted by endothelial cells. The binding of endothelin was studied on cultured human vascular smooth muscle cells obtained from umbilical veins. A single specific binding site for 125I-endothelin was identified, with an apparent Kd of 126 pM and a maximal binding capacity of approximately 10,000 sites per smooth muscle cell. At room temperature the binding was saturable, reached equilibrium at 2 h (using 20 pM endothelin), and was slowly and only partially reversed by unlabeled endothelin. The calcium antagonists nifedipine, nicardipine, and diltiazem did not compete for the same binding site. Conditioned medium from cultured human umbilical vein endothelial cells inhibited the binding of 125I-endothelin dose dependently. This effect was antagonized by anti-endothelin antiserum. We conclude that human umbilical vein smooth muscle cells possess specific binding sites for endothelin, and that human endothelial cells secrete an endothelinlike material.

Endothelin activates the dihydropyridine-sensitive, voltage-dependent Ca2+ channel in vascular smooth muscle

Endothelin is a potent endothelium-derived vasoconstrictor peptide recently characterized from porcine and human vascular endothelial cells. Here we provide evidence that endothelin activates the dihydropyridine-sensitive, voltage-dependent Ca2+ channel in porcine coronary artery smooth muscle. The vasoconstrictor action of endothelin is efficiently antagonized by low doses of the dihydropyridine Ca2+-channel blocker nicardipine. Endothelin augments the Ca2+-induced contraction in a high-K+ depolarizing solution, markedly enhances high-threshold Ca2+-channel current on the whole-cell patch clamp recording, and causes a sustained increase in the intracellular Ca2+ that is largely dependent on extracellular Ca2+. These findings suggest that endothelin exerts its vasoconstrictor effect by either directly or indirectly activating the voltage-dependent Ca2+ channel.

Balloon catheter injury to rabbit carotid artery. II. Selective increase in reactivity to some vasoconstrictor drugs

The present study examined the changes in reactivity to a variety of vasoconstrictor drugs of the rabbit carotid artery during development of an intimal thickening induced by injury with an inflated balloon catheter. The injured and the unoperated contralateral carotid arteries were studied at 2 and 6 weeks after the operation. To differentiate areas of the injured artery lined by modified smooth muscle cells from areas lined by regenerated endothelial cells, each rabbit was injected with Evans blue dye before sacrifice. Ring segments (3 mm length) from the control and injured arteries were mounted in organ baths to record the circumferential isometric force with a technique that ensured that all rings were set to equivalent initial resting conditions of passive transmural stretch. Compared with the controls, the experimental arteries had a significantly decreased maximum contraction (Emax) in response to KCl at both 2 and 6 weeks. The experimental arteries were also significantly less sensitive to the alpha 1-adrenoceptor agonist, methoxamine, at both 2 weeks (approximately sevenfold) and 6 weeks (fourfold), with a marked decrease in Emax at 2 weeks, which returned to control values at 6 weeks. There was no change in Emax to either serotonin or the thromboxane A2-mimetic, U46619, in the experimental arteries at either time. There was, however, a small but significant increase in the sensitivity to both drugs. There was no difference in response to any of the constrictor agents between the white and blue regions of the experimental vessels.(ABSTRACT TRUNCATED AT 250 WORDS)

Update on systemic necrotizing vasculitis

The systemic necrotizing vasculitides are classified into vasculitic syndromes on the basis of the pattern of clinical and pathologic involvement. The vasculitides have certain common clinical and laboratory abnormalities. Systemic necrotizing vasculitis is diagnosed on the basis of clinical features, and the vascular nature of the disease is determined by biopsy of involved tissue or angiography. The outcome is dependent on the extent of visceral involvement. Vascular inflammation influences the physiologic features of the vessel and may trigger vasoconstriction. Although glucocorticoids combat the inflammation, they may augment vasoconstriction and platelet aggregation. These effects must be considered in designing a management approach and in evaluating the cause and management of ischemic complications.

Role of the coronary endothelium in the regulation of sympathetic transmitter release in isolated rabbit hearts

The roles of endothelium-derived relaxing factor (EDRF) and endothelin in the regulation of vascular tone are intensely studied at present. Since factors which directly affect vascular tone also frequently modulate sympathetic transmitter release, we found it of interest to study whether EDRF or endothelin displays such modulatory activity as well. Isolated rabbit hearts were perfused according to Langendorff, and the release of transmitter induced by sympathetic nerve stimulation was estimated by analysis of the effluent content of noradrenaline (NA) with liquid chromatography. The activity of EDRF spontaneously formed in the heart was counteracted by addition of haemoglobin (Hb, 2.4-15 g l-1) or facilitated by addition of superoxide dismutase (SOD, 14-140 U ml-1), to the perfusion solution. In other experiments authentic endothelin (0.1-10 nm) was given to the heart. Nerve stimulation (5 Hz for 30 s) elicited a release of NA into the cardiac effluent amounting to 319 +/- 28 pmol (n = 53). Hb lowered the coronary flow to 68 +/- 9% (P less than 0.01) and impaired the outflow of NA to 62 +/- 9% of control (P less than 0.01). SOD facilitated coronary flow by 11 +/- 4% (P less than 0.005), and augmented the outflow of NA by 15 +/- 6% (P less than 0.05). Endothelin dose-dependently inhibited the coronary flow, with an IC50 of about 1 nM, and in parallel decreased the efflux of NA. Mechanical obstruction of the coronary flow induced an attenuation of the efflux of NA that was quantitatively similar to the flow reduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Glomerular actions of endothelin in vivo

In Munich-Wistar rats, a micropipette was inserted into a first-order branch of the left main renal artery and continuously infused with human/porcine endothelin (0.4 ng/min). Micropuncture measurements revealed substantial differences within the cortical microcirculation of the same left kidney: SNGFR was some 35% lower in glomeruli exposed to endothelin compared with non-endothelin-perfused glomeruli (P less than 0.005). Similarly, glomerular plasma flow rate was some 38% lower in the endothelin-exposed glomeruli (P less than 0.001). The hypoperfusion and hypofiltration in the endothelin-exposed glomeruli reflected an increase in resistances in the afferent and efferent arterioles. There was no difference in the value of the glomerular capillary ultrafiltration coefficient between the two populations of glomeruli. We also studied kidneys that underwent 25 min of renal artery clamping 48 h before study. Antiendothelin antibody infused into one of the branches of the main renal artery ameliorated the vasoconstriction characteristic of postischemic nephrons: within the cortical microcirculation, the SNGFR in glomeruli exposed to antiendothelin antibody was 27.0 +/- 3.1 nl/min as compared with 17.4 +/- 1.7 measured in glomeruli not perfused with the antibody (P less than 0.001). Similarly, glomerular plasma flow rate was higher in the glomeruli exposed to antiendothelin antibody (128.7 +/- 14.4 nl/min vs. 66.6 +/- 5.6, P less than 0.005). Resistances in both the afferent and efferent arterioles were substantially lower in the antibody-exposed glomeruli. It is, therefore, suggested that endothelin, presumably released from damaged endothelium, may play an important intermediary role in the hypoperfusion and hypofiltration observed in postischemic kidneys.

The effect of atherosclerosis on endothelium-dependent relaxation in the aorta and intracranial arteries of rabbits

The effect of hypercholesterolemia on vascular responsiveness was studied in isolated rabbit arteries. The arteries of animals maintained on a cholesterol-rich (1%) diet for 6 months had more pronounced intimal lesion than those receiving the diet for 3 months. The aortas were more severely damaged than the carotid or basilar arteries. Segments of the arteries were mounted in organ chambers for isometric tension recording or for measurement of the endothelium-derived relaxing factor. Endothelium-independent relaxation induced by glyceryl trinitrate was not affected even in the most severely damaged arteries; endothelium-dependent relaxation in response to acetylcholine (ACh) and A23187 was progressively inhibited as the degree of fatty streak formation increased. In the carotid arteries, mean (+/- standard deviation) relaxation induced by 10(-5) M of ACh (expressed as a percentage of the maximum relaxation induced by 10(-4) M of papaverine) decreased from 87.33% +/- 6.30% in control tissues to 60.90% +/- 4.64% in vessels from animals subjected to 6 months of hypercholesterolemia (p less than 0.01); in the aortas, mean relaxation due to 10(-5) M of ACh was 85.08% +/- 8.03% in control tissues and 41.35% +/- 13.68% in hypercholesterolemic tissues (p less than 0.01). In the carotid arteries, mean relaxation induced by 10(-7) M of A23187 decreased from 95.81% +/- 3.58% in control tissues to 55.95% +/- 2.81% in hypercholesterolemic tissues (p less than 0.01); in the aortas, relaxation in response to 10(-7) M of A23187 was 73.73% +/- 4.35% in control tissues and 29.35% +/- 6.77% in hypercholesterolemic tissues (p less than 0.01). Intimal lesions were not produced in the basilar arteries even in rabbits with 12 months of hypercholesterolemia, and endothelium-dependent relaxation was preserved.

Radioimmunoassay for endothelin and immunoreactive endothelin in culture medium of bovine endothelial cells

Using a synthetic 21-residue endothelin as antigen, we have produced an antiserum for endothelin and developed a specific and sensitive radioimmunoassay (RIA) for endothelin. The minimum detection limit of the RIA was 1 pg/tube. Immunoreactive (ir-) endothelin was extracted from the culture medium by Bondelute C8 column. The ir-endothelin in the culture medium of endothelial cells (EC) from bovine pulmonary artery and carotid artery was 1.48 ng/ml and 3.31 ng/ml, respectively. Reverse-phase high performance liquid chromatography coupled with the RIA revealed that ir-endothelin in the culture medium comprised one major component corresponding to synthetic endothelin. In addition, the cultured EC of bovine pulmonary artery were specifically stained by immunohistochemical technique. These results suggest that endothelin could be produced in the EC of the pulmonary and carotid arteries besides the aorta. The RIA presented in this study could be an useful tool to investigate the pathophysiologic significance of endothelin.

Inhibition by nicardipine of endothelin-mediated inositol phosphate formation and Ca2+ mobilization in smooth muscle cell

We have investigated the effects of endothelin on phosphoinositide metabolism and Ca2+ mobilization in cultured A10 cells. Endothelin stimulated a significant increase in inositol phosphate formation in a time- and dose-dependent manner. IP3 was significantly elevated by 30 sec and reached a 2.0-fold above control at 1 min. The EC50 for endothelin was 0.5 nM. The initiation of inositol phosphate formation was independent of extracellular Ca2+, and the Ca2+ ionophore, A23187, did not stimulate IP3 formation. However, the sustained elevation of inositol phosphates was partially inhibited by incubating cells in buffer lacking Ca2+ or in buffer containing nicardipine. Endothelin mobilized both intracellular and extracellular Ca2+ reaching a peak intracellular concentration of 350 +/- 11 nM by 1 min when cells were bathed with Ca2+-complete buffer. Intracellular Ca2+ remained 2-fold above baseline for at least 15 min. In contrast, when cells were exposed to endothelin in Ca2+-free buffer, the peak value of [Ca2+]i was 195 +/- 20 nM and returned to baseline by 2 min. Nicardipine completely blocked the influx of extracellular Ca2+ but did not interfere with the mobilization of intracellular stores. We conclude that endothelin produces a rapid and sustained elevation in inositol phosphate formation. The rapid production of IP3 is consistent with the time course for mobilization of intracellular Ca2+. Elevated cytosolic Ca2+ levels are maintained by the influx of extracellular Ca2+ through a nicardipine-sensitive Ca2+ channel and are involved in the sustained formation of inositol phosphates. These data provide an explanation for the sustained, nicardipine-inhibitable contraction of coronary artery strips induced by endothelin.

Endothelin-induced mobilization of Ca2+ and the possible involvement of platelet activating factor and thromboxane A2

Endothelin (ET) caused transient and sustained elevations of cytosolic free Ca2+ concentrations ([Ca2+]i) in cultured rat and rabbit vascular smooth muscle cells (VSMC). Specific platelet activating factor (PAF) antagonists (CV-6209 and WEB-2086) and arachidonic acid (AA) cascade blockers (chlorpromazine, indomethacin, CV-4151 and AA-2414) potently inhibited the ET-induced increase in [Ca2+]i. Additionally, these compounds inhibited the PAF-induced increase in [Ca2+]i. These results suggest that PAF and thromboxane A2 (TXA2) may be involved in the mechanism of ET-induced mobilization of Ca2+ in cultured rat and rabbit VSMC.

Endothelin stimulates the release of prostacyclin from rat mesenteric arteries

The effect of endothelin on the release of prostacyclin was examined in perfused rat mesenteric arteries with or without their pretreatment with indomethacin. Porcine endothelin at 10 pmol (a subpressor dose) and 40 pmol stimulated the release of 6-keto-PGF1 alpha, a stable metabolite of prostacyclin. Rat endothelin also stimulated its release, but less than porcine endothelin. Pretreatment with indomethacin completely inhibited this 6-keto-PGF1 alpha release. These results indicate that endothelin stimulates the release of prostacyclin from mesenteric arteries. This release may modulate the action of endothelin locally.

Phorbol ester dissociates endothelin-stimulated phosphoinositide hydrolysis and arachidonic acid release in vascular smooth muscle cells

Endothelin-stimulated [3H]-inositol phosphate formation and [3H]-arachidonic acid release were measured in cultured vascular smooth muscle cells from rabbit renal artery. Both responses were partially inhibited by pretreatment with pertussis toxin, indicating the involvement of pertussis toxin-sensitive guanine nucleotide binding regulatory proteins in the coupling processes. Pretreatment with the phorbol ester PMA inhibited endothelin-stimulated [3H]-inositol phosphate formation, but potentiated endothelin-stimulated [3H]-arachidonic acid release, suggesting that these two coupling processes occur in a parallel and independent manner in vascular smooth muscle cells.

Endothelin stimulates aldosterone biosynthesis by dispersed rabbit adreno-capsular cells

The effect of endothelin on aldosterone production by dispersed adreno-capsular cells from rabbits was examined. Porcine endothelin stimulated aldosterone production dose-dependently with an EC50 of 5 x 10(-14) M, but had no effect on corticosterone production. A calcium channel blocker, nicardipine, completely inhibited the stimulatory effect of endothelin on aldosterone production. Endothelin induced prompt and sustained increase in intracellular Ca2+ in fura-2-loaded cells, and nicardipine inhibited this increase in intracellular Ca2+. These results indicate that endothelin stimulates aldosterone biosynthesis in dispersed zona glomerulosa cells of rabbits, and that its effects is related to increase in intracellular calcium through voltage-dependent calcium channels.

Endothelin immunoreactivity in medium from cultured porcine aortic endothelial cells correlates with the biological activity

Using the radioimmunoassay (RIA) of endothelin (ET), we measured immunoreactive ET (IR-ET) in culture medium of porcine aortic endothelial cells. The immunoreactivity in the medium was compared with the biological activity. The amount of IR-ET released into the medium was calculated at 250-350 pg/10(6) cells/hr. The amount of IR-ET released into the culture medium increased progressively with 3-24 hr of incubation and corresponded to the increase in medium-induced vasoconstriction of rat isolated aorta. When the vasoconstrictor activities in the culture medium were plotted against the IR-ET concentration determined by RIA, the concentration-response curve showed similarity to that obtained with synthetic porcine ET. This RIA system will be a useful for investigating mechanisms of ET secretion from endothelial cells.

Endothelin-induced biphasic formation of 1,2-diacylglycerol in cultured rabbit vascular smooth muscle cells--mass analysis with a radioenzymatic assay

Mass analysis of 1,2-diacylglycerol (DG) with a radioenzymatic assay revealed that endothelin induced a biphasic formation of DG with an early transient phase peaking at 30 sec and a late sustained phase peaking at 5 min in cultured rabbit vascular smooth muscle cells (VSMCs). The amounts of DG after the 30-sec and 5-min incubation with endothelin were 0.74 +/- 0.08 (mean +/- SE) nmol and 0.87 +/- 0.10 nmol/100 nmol of lipid phosphorus, representing 2.6- and 3.1-fold increases of the resting level, respectively. The EC50 values of endothelin for the early and late phases of DG formation were about 1 nM and 40 nM, respectively. In the [3H] inositol-labeled VSMCs, endothelin induced a rapid transient formation of inositol tris- and bisphosphates which peaked at 30 sec and a sustained formation of inositol monophosphate which peaked at 5 min. The EC50 values for the formation of these inositol phosphates were the same and about 1 nM. These results suggest that the early transient phase of DG is derived from the hydrolysis of polyphosphoinositides, while a large part of the late sustained phase of DG is from the reaction(s) other than the hydrolysis of phosphoinositides but its sources remain to be clarified.

Inotropic effects of endothelin in ferret ventricular myocardium

The characteristics of the inotropic response to endothelin were studied in isolated ferret papillary muscle preparations. Endothelin (0.1-10 nM) induced concentration-dependent positive inotropic effects. At 10 nM, isometric tension increased by 17%, maximum rate of tension development by 18%, maximum velocity of unloaded shortening by 23% and peak isotonic shortening by 11%. Time to peak isometric tension and half isometric relaxation time were unaltered by endothelin. This pattern of change is similar to that of elevating extracellular calcium concentration.

Autoradiographic localisation of endothelin binding sites in kidney

[125I]Endothelin binding sites occurred in glomeruli of human, monkey, rat and dog kidney but not rabbit glomeruli. The renal medulla had more binding sites in all species, with the greatest densities of all in the rat and monkey renal papillas. Binding in rat kidney was inhibited by [Ala3,11]endothelin with lower potency than endothelin but not by unrelated peptides. These binding sites may represent the endothelin receptors and suggest actions for endothelin on renal function.

Differential activities of two distinct endothelin family peptides on ileum and coronary artery

A synthesized mouse vasoactive intestinal contractor peptide, which belongs to a novel member of the endothelin family, induced a prolonged contraction in mouse ileum as well as porcine coronary artery in vitro. Studies comparing the effects of vasoactive intestinal contractor and endothelin on different tissues revealed that the maximum ileum contraction of vasoactive intestinal contractor was much higher than that of endothelin in both guinea pig and mouse systems, but that the vasoconstriction activity of vasoactive intestinal contractor was weaker than that of endothelin in porcine artery. These results show that vasoactive intestinal contractor might be a novel gastrointestinal hormone.

Secretory mechanism of immunoreactive endothelin in cultured bovine endothelial cells

To elucidate the cellular mechanism by which endothelin (ET) is secreted, we have studied the effects of a variety of vasoactive agents on the secretion of immunoreactive (IR)-ET from cultured bovine endothelial cells (EC). Confluent bovine EC cultured in serum-free medium secreted IR-ET as a function of time. Not only thrombin, but also vasoconstrictive hormones, such as arginine-vasopressin (AVP) and angiotensin (ANG) II, dose-dependently stimulated IR-ET secretion, and these effects were completely abolished by V1-receptor antagonist and [Sar1,Ala8]-ANG II, respectively. Protein kinase C (PKC)-activating phorbol ester and Ca2+ ionophore ionomycin had stimulatory effects on IR-ET secretion, and the combination of both compounds had a synergistic effect. These data suggest that AVP and ANG II, like thrombin, stimulate ET secretion from EC by a mechanism possibly involving receptor-mediated mobilization of intracellular Ca2+ and activation of PKC.

Receptor binding activity and cytosolic free calcium response by synthetic endothelin analogs in cultured rat vascular smooth muscle cells

Using a variety of synthetic analogs of porcine endothelin (pET), we have studied the effects of these analogs on receptor binding activity and cytosolic free Ca2+ concentrations ([Ca2+]i) in cultured rat vascular smooth muscle cells (VSMC). Removal of C-terminal Trp21 residue, truncated derivatives pET(1-15) and (16-21), substitution of disulfide bond, Cys(3-11) or Cys(1-15), by Cys (Acm), all resulted in a complete loss of receptor binding activity and [Ca2+]i response, while N-terminal elongation of Lys-Arg residues, but not oxidation of Met7 residue, decreased receptor binding activity and [Ca2+]i response. [Cys1-15,Cys3-11]pET was far more potent than [Cys1-11,Cys3-15]pET in receptor binding and [Ca2+]i response. These data indicate that the C-terminal Trp21 as well as the proper double cyclic structure formed by the intramolecular disulfide bonds of the pET molecule are essential for receptor binding and subsequent [Ca2+]i increase in rat VSMC.

Influence of endothelin on systemic arterial pressure and regional blood flow in the cat

Regional vascular responses to endothelin were investigated in the anesthetized cat. I.v. injection of endothelin at 0.1 nmol/kg decreased arterial pressure and renal vascular resistance but increased vascular resistance in the small intestine. At 0.3 nmol/kg i.v. the peptide caused a greater decrease in arterial pressure and increased mesenteric resistance but had no significant effect on renal resistance. In contrast, at 1 nmol/kg i.v. endothelin caused a biphasic change in arterial pressure and marked increases in mesenteric and renal resistance. Injection of the peptide in doses of 0.1-1 nmol/kg i.v. caused only increases in carotid blood flow. These data suggest that responses to endothelin are dependent on dose and vascular bed studied.

Prominent depressor response to endothelin in spontaneously hypertensive rats

Administration of endothelin (0.03-3.0 micrograms/kg i.v.) caused transient depressor responses followed by sustained pressor responses in anesthetized spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). The initial depressor response occurred at lower doses (0.1 versus 0.3 micrograms/kg i.v.) in SHR versus WKY. The secondary pressor response was attenuated in SHR compared to WKY in both the threshold dose (3.0 versus 0.1 microgram/kg i.v.) and maximum effect at high doses (52 versus 91% at 3.0 micrograms/kg i.v.). In conscious SHR and WKY, endothelin elicited comparable initial depressor responses with increases in heart rate; the secondary pressor responses were attenuated compared to those in anesthetized rats. Therefore endothelin elicits a prominent depressor response, which may be associated with afterload reduction, in SHR.

Effect of endothelin on renal function in rats

The effect of synthetic porcine endothelin on glomerular filtration rate, renal plasma flow and electrolyte excretion was studied in rats. Endothelin, 1 nmol/kg body weight given as a bolus, induced a transient decrease in glomerular filtration rate (72%) and in renal plasma flow (76%) as well as in sodium excretion, accompanied by a sustained increase in renal vascular resistance. This dose had no sustained effect on mean arterial pressure. It is concluded that endothelin induces a marked decrease in glomerular filtration rate and renal perfusion. This peptide could play a role in the alterations in renal function observed after renal injury.

Putative precursors of endothelin have less vasoconstrictor activity in vitro but a potent pressor effect in vivo

Endothelin (ET-21) induced a sustained contraction of rat thoracic aortae (EC50 = 2.65 x 10(-10) M) in vitro, and caused a potent pressor effect in vivo after intravenous administration to rats. In contrast, the precursor deduced from porcine cDNA coding ET-21 (pET-39) had 100-fold less contractile activity in vitro (EC50 = 3.26 x 10(-8) M), and so did the precursor from human cDNA (hET-38) (EC50 = 1.48 x 10(-8) M). However, both pET-39 and hET-38 caused almost the same dose-dependent pressor effects as ET-21 in vivo. After intravenous bolus injection at 1 nmol/kg, ET-21 caused an initial transient drop of the arterial pressure, and then induced a gradual pressor effect. On the other hand, hET-38 caused only a gradual rise of the arterial pressure. There may be different mechanism(s) for ET-21 and hET-38 which induce changes in the arterial pressure in vivo.

Endothelin increases single-channel calcium currents in coronary arterial smooth muscle cells

Endothelin (ET), a newly identified vasoconstrictor peptide produced by endothelial cells, depends on extracellular calcium for its action [(1988) Nature 332, 411-415]. It is not yet known whether the increase in calcium influx induced by ET results from a direct effect on the Ca2+ channels or is secondary to a reduction in membrane potential. To address this question, we studied the effects of ET on single-channel calcium currents of freshly dissociated porcine coronary artery smooth muscle cells using the cell-attached mode of the patch-clamp technique. We show that ET increases Ca2+-channel activity with no effect on channel open time or conductance. The ability of bath-applied ET to increase single-channel calcium currents in the cell-attached mode is evidence that the peptide acts via a second messenger system.

Rat aortic endothelium antagonizes nitroprusside-induced relaxation by release of the peptide endothelin

1. The effects of porcine endothelin were examined in rat thoracic aortic rings. 2. Endothelin was a potent contractile agonist (EC50 4.0 +/- 0.6 nmol/L). 3. Endothelin (1 nmol/L) did not affect contractile responses to cumulative concentrations of the thromboxane analogue, U46619. 4. In the presence of U46619, but not phenylephrine, endothelin (1 nmol/L) and endothelium abrogated the vasodilator response to cumulative concentrations of sodium nitroprusside. 5. The inhibitory effect of endothelin on vasodilator responses to nitroprusside in the presence of U46619 was abolished by nifedipine (0.1 mumol/L) but unaffected by indomethacin (3 mumol/L) or haemoglobin (10 mumol/L). 6. These data suggest that endothelin generated by native endothelium exerts a physiological antagonism of sodium nitroprusside in the presence of thromboxane.

Potent contractile activity of endothelin on the human isolated urinary bladder

Endothelin (1 nM-0.3 microM) produced a concentration-related contraction of mucosa-free muscle strips excised from the dome of the human urinary bladder. The response to endothelin was unaffected by either atropine (1 microM) or nifedipine (1 microM) at concentrations that abolished the response to carbachol and KCl, respectively. These findings indicate that mechanisms other than activation of dihydropyridine- and voltage-sensitive calcium channels may be involved in the action of endothelin on smooth muscles.

Endothelin potentiates growth factor-stimulated DNA synthesis in Swiss 3T3 cells

A murine cell line, Swiss 3T3, is commonly used for the study of cellular growth. The present study revealed that this cell line possesses high-affinity receptors for endothelin, a vasoactive peptide derived from vascular endothelial cells. In this cell line, endothelin potentiated DNA synthesis stimulated by platelet-derived growth factor, basic fibroblast growth factor or insulin. The endothelin concentration required for potentiating DNA synthesis in this cell line is almost the same as that reported previously in endothelin-induced vasoconstriction. Since endothelin increased intracellular calcium levels, this ion may participate in the signal transduction pathways by which endothelin induces potentiation of DNA synthesis.

Endothelin is blood vessel selective: studies on a variety of human and dog vessels in vitro and on regional blood flow in the conscious rabbit

1. Endothelin (Et), a vasoconstrictor peptide, was 5-10-fold more potent (lower EC50) on isolated ring segments of large veins than on large arteries removed from dog coronary, mesenteric, femoral, renal and internal mammary vasculature and from the human internal mammary pedicle. 2. In the dog large coronary artery, Et (10-30 nmol/L) caused transient relaxations partway through the generation of a concentration-contraction curve. These relaxations were endothelium dependent. 3. In conscious rabbits treated with mecamylamine, Et (0.025-0.4 nmol/kg) caused a marked rise in renal vascular resistance but hindquarter vasodilation. Under the same conditions angiotensin II constricted both beds. 4. These studies suggest that Et is vascular bed and large vein selective in activity. It did not appear to be selective for large or small coronary arteries in vitro.

The veno-arteriolar reflex in free skin flaps

The veno-arteriolar reflex was measured in 10 subjects in whom an area of denervated skin was present in the lower limb following free flap transfer of skin and subcutaneous tissue 3 weeks to 2 years previously. The vasoconstrictor response to dependency was measured in the skin of the flap, in adjacent innervated skin and after chemical dilatation of cutaneous vessels in the skin of the flap. This veno-arteriolar reflex resulting in a reduction of blood flow of 30-40% was present and equal in both normal and denervated skin. The response was abolished by chemical vasodilatation. The results indicate that sympathetic innervation is not essential for the veno-arteriolar reflex, and suggest that myogenic mechanisms may be more important than previously believed.

Endothelin receptors in rat adrenal gland visualized by quantitative autoradiography

1. The radioligand [125I]-endothelin was used to map receptors for endothelin in rat adrenal gland using in vitro autoradiography and computerized densitometry. 2. In the adrenal, a high density of binding was found in the adrenal medulla (binding affinity constant 0.18 +/- 0.11 X 10(9)M-1) and zona glomerulosa (binding affinity constant 0.18 +/- 0.07 X 10(9)M-1). Binding was low to undetectable in the zona fasciculata and zona reticularis. Unrelated peptides did not displace endothelin. 3. These results provide evidence of endothelin receptor distribution in adrenal gland and suggest that endothelin might exert multiple actions in the adrenal gland on catecholamine and aldosterone biosynthesis and secretion.

Cardiovascular actions of human endothelin in conscious sheep

1. Synthetic human endothelin was injected intravenously over the range 1.5-50 micrograms to examine its cardiovascular actions in conscious sheep. 2. Mean arterial pressure increased by 9-21 mmHg within 30-120 s over the range 5-50 micrograms endothelin. The increase in blood pressure was associated with increased calculated total peripheral resistance and a fall in cardiac output and heart rate. Stroke volume was increased. 3. Injection of endothelin into ganglion blocked sheep produced vasoconstriction and an increased blood pressure response associated with an attenuation of the effects on cardiac output, heart rate and stroke volume. 4. This study suggests that endothelin produces potent arterial vasoconstriction and reflex mediated effects on the heart in conscious sheep.

The human endothelin family: three structurally and pharmacologically distinct isopeptides predicted by three separate genes

Three distinct human endothelin-related genes were cloned by screening a genomic DNA library under a low hybridization stringency with a synthetic oligonucleotide probe encoding a portion of the endothelin sequence. Genomic Southern blot analysis with the same oligonucleotide probe showed three corresponding chromosomal loci not only in the human genome but also in porcine and rat genomes. The nucleotide sequences of the three human genes were highly conserved within the regions encoding the 21-residue (mature) endothelins, in spite of the fact that the immediately upstream exon sequences, which encode a part of the propeptides, retained little similarity. Moreover, each of the human genes predicted a putative 21-residue peptide, similar to but distinct from each other: (i) the "classical" endothelin (ET-1), (ii) [Trp6,Leu7]endothelin (ET-2), and (iii) [Thr2,Phe4,Thr5,Tyr6, Lys7,Tyr14]endothelin (ET-3). Synthetic ET-1, ET-2, and ET-3 were prepared according to the deduced amino acid sequences, and the biological activities were assayed by contraction of isolated porcine coronary artery strips and by intravenous injection to anesthetized rats. All these synthetic peptides produced strong vasoconstrictor and pressor responses. However, the quantitative profiles of the pharmacological activities were considerably different among the three isopeptides, suggesting the possible existence of endothelin receptor subtypes.

Paradoxical effects of endothelin on cardiovascular noradrenergic neurotransmission

1. Pre- and postjunctional effects of endothelin (1-10 nmol/L) have been studied in the rabbit isolated ear artery and in rat isolated atria. 2. Endothelin produced concentration-dependent increases in arterial perfusion pressure, and had positive chronotropic and inotropic effects in rat atria. 3. Vasoconstrictor responses of the arteries to sympathetic nerve stimulation were reduced by 1 nmol/L endothelin and abolished by 10 nmol/L endothelin. In rat atria, the chronotropic responses to nerve stimulation were markedly reduced by 10 nmol/L endothelin. 4. In rabbit ear artery, vasoconstrictor responses to noradrenaline were enhanced by 1 nmol/L endothelin, but were reduced by 10 nmol/L endothelin. In rat atria, endothelin reduced the chronotropic response to isoprenaline. 5. Endothelin (10 nmol/L) increased the stimulation-induced release of radioactivity in arteries and atria labelled with [3H]-noradrenaline by 91% and 23%, respectively. 6. The pre- and postjunctional effects of endothelin persisted in both arterial and atrial preparations for at least 30 min after its removal.

Endothelin and the production of cerebral vasospasm in dogs

We attempted to determine whether or not endothelin (ET) plays a physiological role in cerebral vasospasm. ET (10(-11) - 3 x 10(-8) M) induced a concentration-dependent contraction in isolated canine basilar arteries. Intracisternal injection of 10 to 1,000 pmol ET into dogs induced a dose-dependent decrease in the basilar artery diameter, as measured angiographically on the 1st day. On the 3rd day after the injection of ET (10 pmol), the diameter of the basilar artery had diminished to 76% of the value seen in the control. There were no effects on blood pressure or heart rate. Thus, ET seems to be a potent constrictor of cerebral arteries in vivo, and these effects are long-lasting.

Endothelin enhances adrenergic vasoconstriction in perfused rat mesenteric arteries

The interaction of endothelin with alpha-adrenergic receptors was examined in isolated perfused rat mesenteric arteries. Infusion of porcine or rat endothelin increased the baseline perfusion pressure dose-dependently. Subpressor doses of both porcine (10(-11) and 10(-10)M) and rat (10(-10) and 10(-9)M) endothelin enhanced the pressor responses to norepinephrine. Nicardipine (10(-7)M), a calcium channel blocker, attenuated this potentiation. These results suggest that endothelin enhances the responsiveness of alpha-adrenergic receptors to catecholamines probably through the increase in calcium influx. Thus endothelin may interact with sympathetic nerve activity in addition to having a direct vasoconstrictor action in peripheral vascular tissue.

Transforming growth factor-beta stimulates the expression of endothelin mRNA by vascular endothelial cells

Endothelin is a potent vasoconstrictor peptide produced by vascular endothelial cells. Incubation of the serum-deprived confluent porcine aortic endothelial cells with 10-300 pM TGF-beta 1, resulted in a several fold increase in endothelin mRNA levels with a peak time of 2 h. An enzyme-linked immunosorbent assay revealed that the levels of endothelin in endothelial cell conditioned media was also increased by TGF-beta 1. These results suggest that TGF-beta 1, secreted by activated platelets, is involved not only in wound healing, but in the regulation of local vascular tone by stimulating endothelin production in the endothelial cells.

Stimulation of phospholipase C-mediated hydrolysis of phosphoinositides by endothelin in cultured rabbit aortic smooth muscle cells

Incubation of the [3H] inositol-labeled cultured rabbit vascular smooth muscle cells (VSMCs) with either endothelin or angiotensin II caused a rapid formation of inositol mono-, bis- and trisphosphates (IP1, IP2 and IP3, respectively). Time courses of the endothelin- and angiotensin II-induced formation of these inositol phosphates were similar. The maximal levels of IP1, IP2 and IP3 formation induced by endothelin were about 50%, 25% and 40%, respectively, of those induced by angiotensin II. The doses of endothelin necessary for the half maximal and maximal extents of the formation of IP1 were about 1 nM and 100 nM, respectively. Protein kinase C-activating 12-Q-tetradecanoylphorbol-13-acetate (TPA) inhibited the endothelin-induced formation of IP1 with the half maximal extent of inhibition seen at 3 nM. The inhibitory action of TPA was mimicked by another protein kinase C-activating phorbol ester, phorbol-12,13-dibutyrate, but not by 4 alpha-phorbol-12,13-didecanoate, known to be inactive for this enzyme. These results indicate that endothelin causes the phospholipase C-mediated hydrolysis of phosphoinositides, though to a lesser extent than angiotensin II, in cultured VSMCs and suggest that protein kinase C modulates the signaling mechanism of endothelin to the phospholipase C.

A sensitive sandwich-enzyme immunoassay for human endothelin

A sensitive enzyme immunoassay (EIA) for human endothelin(1-21) has been established. The assay is based on a sandwich method that uses two differing capture and detection anti-endothelin antibodies. A monoclonal anti-endothelin antibody AwETN40, which did not react with an endothelin C-terminal heptapeptide, was used as an immobilized antibody. The Fab' fragment of rabbit antibodies against the endothelin C-terminal heptapeptide was used as an enzyme-labeled detector antibody after being coupled with horseradish peroxidase (HRP). The assay is sensitive enough to detect as little as 0.2 pg/well (80 amol/well) of endothelin. Preliminary investigations indicated that the basal level of immunoreactive endothelin in male plasma (n = 24) extracted with Seppak C-18 cartridges was 1.59 +/- 0.32 pg/ml.

Vasoconstrictor response of large cerebral arteries of cats to endothelin, an endothelium-derived vasoactive peptide

Endothelin, a 21-amino acid peptide produced by vascular endothelial cells, caused a sustained constriction of isolated large cerebral arteries of cats in a dose-dependent manner. The increased tone of the tissue did not return to the resting level after repeated washings. No vasodilator response was evoked by endothelin in the presence of an active tone. The contractile response of cerebral arteries was not inhibited by rubbing of the endothelium, cold storage denervation or indomethacin. In contrast, nicardipine or diltiazem antagonized the endothelin-induced contraction non-competitively. No contraction was evoked by endothelin in a Ca2+-free solution while the addition of Ca2+ ions in the presence of endothelin in a Ca2+-free solution caused a sustained contraction. Ca2+-induced contraction in the Ca2+-free solution containing endothelin was also inhibited by nicardipine. Therefore, endothelin causes a direct contraction of the smooth muscles of cat cerebral arteries, probably by activating the influx of Ca2+ ions through L-type Ca2+ channels of smooth muscles.