The direct observation of arteriolar constriction induced by endothelin in vivo

Cell-free synthesis of isotopically labelled peptide ligands for the functional characterization of G protein-coupled receptors

Cell‐free systems exploit the transcription and translation machinery of cells from different origins to produce proteins in a defined chemical environment. Due to its open nature, cell‐free protein production is a versatile tool to introduce specific labels such as heavy isotopes, non‐natural amino acids and tags into the protein while avoiding cell toxicity. In particular, radiolabelled peptides and proteins are valuable tools for the functional characterization of protein–protein interactions and for studying binding kinetics. In this study we evaluated cell‐free protein production for the generation of radiolabelled ligands for G protein‐coupled receptors (GPCRs). These receptors are seven‐transmembrane‐domain receptors activated by a plethora of extracellular stimuli including peptide ligands. Many GPCR peptide ligands contain disulphide bonds and are thus inherently difficult to produce in bacterial expression hosts or in Escherichia coli‐based cell‐free systems. Here, we established an adapted E. coli‐based cell‐free translation system for the production of disulphide bond‐containing GPCR peptide ligands and specifically introduce tritium labels for detection. The bacterial oxidoreductase DsbA is used as a chaperone to favour the formation of disulphide bonds and to enhance the yield of correctly folded proteins and peptides. We demonstrate the correct folding and formation of disulphide bonds and show high‐affinity ligand binding of the produced radio peptide ligands to the respective receptors. Thus, our system allows the fast, cost‐effective and reliable synthesis of custom GPCR peptide ligands for functional and structural studies.

Aβ degradation or cerebral perfusion? Divergent effects of multifunctional enzymes

There is increasing evidence that deficient clearance of β-amyloid (Aβ) contributes to its accumulation in late-onset Alzheimer disease (AD). Several Aβ-degrading enzymes, including neprilysin (NEP), endothelin-converting enzyme (ECE), and angiotensin-converting enzyme (ACE) reduce Aβ levels and protect against cognitive impairment in mouse models of AD. In post-mortem human brain tissue we have found that the activity of these Aβ-degrading enzymes rise with age and increases still further in AD, perhaps as a physiological response that helps to minimize the build-up of Aβ. ECE-1/-2 and ACE are also rate-limiting enzymes in the production of endothelin-1 (ET-1) and angiotensin II (Ang II), two potent vasoconstrictors, increases in the levels of which are likely to contribute to reduced blood flow in AD. This review considers the possible interdependence between Aβ-degrading enzymes, ischemia and Aβ in AD: ischemia has been shown to increase Aβ production both in vitro and in vivo, whereas increased Aβ probably enhances ischemia by vasoconstriction, mediated at least in part by increased ECE and ACE activity. In contrast, NEP activity may help to maintain cerebral perfusion, by reducing the accumulation of Aβ in cerebral blood vessels and lessening its toxicity to vascular smooth muscle cells. In assessing the role of Aβ-degrading proteases in the pathogenesis of AD and, particularly, their potential as therapeutic agents, it is important to bear in mind the multifunctional nature of these enzymes and to consider their effects on other substrates and pathways.

Local antinociception induced by endothelin-1 in the hairy skin of the rat's back

Subcutaneous injection of endothelin-1 (ET-1) into the glabrous skin of the rat's hind paw is known to produce impulses in nociceptors and acute nocifensive behavioral responses, such as hind paw flinching, and to sensitize the skin to mechanical and thermal stimulation. In this report, we show that in contrast to the responses in glabrous skin, ET-1 injected subcutaneously into rat hairy skin causes transient antinociception. Concentrations of 1 to 50 microM ET-1 (in 0.05 mL) depress the local nocifensive response to noxious tactile probing at the injection site with von Frey filaments for 30 to 180 minutes; distant injections have no effect at this site, showing that the response is local. Selective inhibition of ET(A) but not of ET(B) receptors inhibits this antinociception, as does coinjection with nimodipine (40 muM), a blocker of L-type Ca(2+) channels. Local subcutaneous injection of epinephrine (45 microM) also causes antinociception through alpha-1 adrenoreceptors, but such receptors are not involved in the ET-1-induced effect. Both epinephrine and ET-1, at antinociceptive concentrations, reduce blood flow in the skin; the effect from ET-1 is largely prevented by subcutaneous nimodipine. These data suggest that ET-1-induced antinociception in the hairy skin of the rat involves cutaneous vasoconstriction, presumably through neural ischemia, resulting in conduction block.

PERSPECTIVE

The pain-inducing effects of ET-1 have been well documented in glabrous skin of the rat, a frequently used test site. The opposite behavioral effect, antinociception, occurs from ET-1 in hairy skin and is correlated with a reduction in blood flow. Vasoactive effects are important in assessing mechanisms of peripherally acting agents.

Effects of low doses of endothelin-1 on basal vascular tone and autoregulatory vasodilation in canine coronary microcirculation in vivo

The plasma level of endothelin-1 (ET-1) increases in several cardiovascular disorders. The present study examined whether threshold doses of ET-1 affect vascular tone and autoregulatory vasodilation during a reduction in perfusion pressure in the coronary microcirculation in vivo. In anesthetized open-chest dogs, arterial microvessels in the epimyocardium were observed through a microscope equipped with a floating objective. In 6 dogs, ET-1 (10(-13) to 10(-8)mol/L) was superfused onto the epimyocardium in a cumulative fashion. In another set of dogs (n= 16), the perfusion pressure of the observed vascular bed was reduced to 60 mmHg (mild stenosis) and to 40 mmHg (severe stenosis) by a hydraulic occluder, and the microvascular responses were observed in the presence (n=9) or absence (n=7) of ET-1 (10(-12) or 10(-11) mol/L). ET-1 > or =10(-11) mol/L constricted coronary arterioles (< or =100 microm in diameter) and small arteries (>100 microm in diameter) in a dose-dependent fashion. ET-1 of 10(-12) mol/L affected neither the basal diameters nor the dilation of vessels during the pressure reduction. ET-1 of 10(-11) mol/L decreased the diameters of arterioles and small arteries before and during the mild and severe stenosis. However, ET-1 did not attenuate the percentage dilation of arterioles from the baseline in response to the mild and severe stenosis. The data indicates the following: (1) ET-1 at doses > or =10(-11) mol/L similarly constricts coronary arterioles and small arteries; (2) ET-1 at 10(-11) mol/L, which is slightly higher than the pathophysiological plasma level, increases the basal vascular tone, but does not attenuate the autoregulatory vasodilation of the coronary microcirculation.

Acute infusion of nicotine potentiates norepinephrine-induced vasoconstriction in the hamster cheek pouch

Although cigarette smoking and the components of cigarette smoke appear to alter nitric oxide synthase-dependent dilation of blood vessels, the effect of these substances on constrictor responses of resistance arterioles has not been examined. Thus the goal of this study was to examine the effect of a major component of cigarette smoke-that is, nicotine-on constrictor responses of cheek pouch arterioles. The diameter of cheek pouch arterioles (approximately 50 microm in diameter) was measured by using intravital microscopy. We examined the responses of arterioles to angiotensin II, arginine vasopressin, norepinephrine, and the thromboxane analog U-46619 before and after treatment with vehicle (saline solution), N(G)-monomethyl-L-arginine (L-NMMA; 1.0 micromol/L), or nicotine (2.0 microg/kg/min i.v. for 30 minutes followed by a maintenance dose of 0.35 microg/kg/min for 30 minutes). Topical application of angiotensin II (0.01 and 0.1 nmol/L), arginine vasopressin (1.0 and 10 pmol/L), norepinephrine (1.0 and 10 nmol/L), and U-46619 (0.01 and 0.1 nmol/L) produced marked reproducible constriction of cheek pouch arterioles in hamsters treated with vehicle. Topical application of L-NMMA potentiated constrictor responses of arterioles to the high dose of arginine vasopressin (28%+/-4% versus 36%+/-4%; P<.05) and to both doses of norepinephrine (14%+/-1% and 24%+/-2% versus 19%+/-1% and 31%+/-3%; P<.05). The infusion of nicotine did not alter responses to angiotensin II, arginine vasopressin, or U-46619 but modestly potentiated vasoconstriction in response to norepinephrine (12%+/-2% and 22%+/-2% versus 14%+/-2% and 26%+/-2%; P<.05). These findings suggest that the synthesis/release of nitric oxide may modulate constrictor responses of cheek pouch resistance arterioles to selected agonists. In addition, nicotine, at levels observed in smokers, may potentiate norepinephrine-induced vasoconstriction. We suggest that preservation/potentiation of vasoconstrictor responses may contribute to the pathogenesis of vascular abnormalities associated with cigarette smoking.

Endothelin-1 focally constricts pulmonary veins in rats

Serum endothelin levels increase during sepsis, ischemia, reperfusion, pulmonary operations, and systemic hypertension after surgery. Despite extensive study, the site and extent of action of endothelin on the pulmonary microcirculation are not well established. To assess the effect of endothelin on the pulmonary vasculature, especially the veins, the circulation of the lung was cast with methyl methacrylate 10 minutes after endothelin-1 was given intravenously to rats. Endothelin-1, at concentrations of 0.1, 1.0, and 10.0 micrograms/kg of body weight, increased the mean systemic arterial blood pressure 8%, 7%, and 17% (p < 0.01) and mean pulmonary arterial blood pressure 15%, 28%, and 53%, respectively (p < 0.01). The proportional increases in the pulmonary pressures were greater than those of the systemic pressures (p < 0.01). Scanning electron microscopy of cast blood vessels showed more contraction of the veins than the arteries. For doses of 0, 0.1, 1.0, and 10.0 micrograms/kg, the respective focal contraction of small veins was 6.7% (+/- 4.4), 15.4% (+/- 9.1), 23.3% (+/- 10.1), and 14.4% (+/- 9.0) of the vessel diameter (p < 0.01). In addition, the diameter of capillaries increased (p < 0.01) and the capillary interspaces decreased (p < 0.01) after endothelin administration, but not in a linear dose-dependent manner. The dose of endothelin correlated with the change in the mean systemic (r = 0.82, p < 0.01) and the mean pulmonary (r = 0.80, p < 0.01) blood pressures. The mean pulmonary pressure change correlated with the focal venous contraction on the casts (r = 0.35, p < 0.01), capillary diameter (r = 0.64, p < 0.01), and capillary interspace distance (r = -0.34, p < 0.01). The venous contraction was related to the capillary diameter (r = 0.26, p < 0.01). The most notable effect of endothelin-1 in rat pulmonary microcirculation is focal constriction of small veins. Because this effect may lead to pulmonary edema, endothelin antagonists may be of benefit in a variety of clinical situations.

Protective effects of endothelin-1 on acute pancreatitis in rats

Endothelin-1, a 21-residue peptide isolated from vascular endothelial cells, has a broad spectrum of actions. To clarify the involvement of endothelin-1 in acute pancreatitis, we examined the effects of endothelin-1 and its receptor antagonist BQ-123 on cerulein-induced pancreatitis in rats. Rats were infused intravenously with heparin-saline (control), endothelin-1 (100 pmol/kg/hr), cerulein (5 micrograms/kg/hr), or cerulein plus endothelin-1 for 3.5 hr. In another experiment, cerulein or cerulein plus BQ-123 (3 mg/kg/hr) was infused. Infusion of cerulein caused hyperamylasemia and pancreatic edema. Endothelin-1, when infused with cerulein, decreased the extent of pancreatic edema with a significant increase in the pancreatic dry- to wet-weight ratio. Histological changes induced by cerulein were markedly attenuated when endothelin-1 was given with cerulein. In contrast, endothelin-receptor blockade with BQ-123 further augmented pancreatic edema caused by cerulein. The extent of inflammatory cell infiltration was greater than BQ-123 was given with cerulein. Endothelin-1 or BQ-123 had no influence on hyperamylasemia. This study suggests that endothelin-1 has protective effects on experimental acute pancreatitis.

Differential release of endothelin in myocutaneous island flaps in response to gradually insetting venous stasis or arterial ischemia

Endothelin (ET) provokes strong and sustained contraction in preparations of isolated vascular smooth muscle, and the production of ET is thought to increase secondary to increased wall shear stress and hypoxia. The release of ET and blood flow distribution between arteriovenous shunts and capillaries were studied in autoperfused myocutaneous pig island flaps during graded arterial or venous blood flow reduction (N = 12). A group comprising four flaps was not exposed to blood flow reduction and served as controls. Total flap blood flow (venous outflow [VO]) was reduced in 1-hour periods to 50%, 25%, and 0%. Downregulation of VO caused a lower capillary blood flow (CBF) at 25% (P < .05) and at 50% (P < .05) in flaps exposed to venous stasis as compared with flaps with arterial ischemia. The reduction in blood flow was paralleled by decreasing oxygen consumption, although flaps with venous stasis had lower oxygen consumption than flaps exposed to arterial ischemia (P < .05). ET was found to be released from these island flaps before blood flow was reduced. Gradual arterial clamping caused a statistically significant (P < .05) decrease in the release of ET from 8.7 +/- 1.3 fmol/min before ischemia to 4.1 +/- 1.7 at 50% blood flow and 4.1 +/- 1.0 at 25% blood flow. In contrast, the release of ET with venous stasis remained unchanged at a level of 7.5 +/- 1.6 fmol/min before blood flow reduction, 7.3 +/- 0.7 at 50% blood flow, and 8.5 +/- 1.6 at 25% blood flow. These data suggest a relationship between CBF, intravascular pressure, and ET production.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition by SR 140333 of NK1 tachykinin receptor-evoked, nitric oxide-dependent vasodilatation in the hamster cheek pouch microvasculature in vivo

1. This study investigated tachykinin-evoked vasodilatation in the microvasculature of the hamster cheek pouch in vivo. Arterioles and venules were observed by intravital microscopy with video recording, and vasodilatation and constriction, defined as changes in blood vessel diameter, measured by image analysis. All agents were applied topically by superfusion. None of the agents tested had a significant effect on venule diameter. 2. When arterioles were preconstricted (by ca. 50%) with endothelin-1 present in the superfusing medium, substance P (0.3-30 nM) was a potent vasodilator, being 10 fold more active than both neurokinin A and the NK1 receptor-selective agonist, substance P methyl ester. The NK2 receptor-selective agonist, [beta-Ala8]-NKA(4-10)(0.1-10 microM) was active only at high concentrations, and the NK3 receptor-selective agonist senktide (0.1-10 microM) was virtually inactive (n = 8 hamsters). Dilatation evoked by tachykinins and analogues was rapid in onset (< 0.5 min) and readily reversible. 3. At low concentrations (1-10 nM), the non-peptide tachykinin NK1 receptor antagonist SR140333 ((S)1-(2-[3(3,4-dichlorophenyl)-1-(3-iso-propoxyphenylacetyl)pi peridin-3- yl]ethyl)-4-phenyl-1-azoniabicyclo[2.2.2]octone, chloride) had no effect on the diameter of preconstricted arterioles per se, but potently inhibited dilator responses to substance P methyl ester (apparent pKB 9.9 +/- 0.2; n = 5 hamsters, n = 10 estimates). SR140333 (10 nM) did not inhibit submaximal dilator responses evoked by human alpha calcitonin gene-related peptide (alpha CGRPh; 1.0 nM; P > 0.05; n = 5). 4 The nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 10 microM) caused a51.3 +/- 5.4% arteriolar constriction. In the presence of L-NAME, submaximal vasodilator responses to substance P (10-I00 nM) and carbachol (0.1-1.0 microM) were significantly attenuated (n = 5 hamsters;P<0.05) as compared to responses obtained in preparations that were preconstricted to a similar extent by endothelin-l (48.0 +/- 5.6%). L-NAME (10 M) was without effect on submaximal vasodilator responses to alpha CGRPh (0.1 nM) or sodium nitroprusside (1O nM) (n = 5 hamsters; P> 0.05).5 We conclude that tachykinin-evoked arteriolar vasodilatation in the hamster cheek pouch is mediated via NK, receptor activation and depends, at least in part, on the release of nitric oxide. The NKI receptors mediating vasodilatation can be blocked by topical application of SR140333; which may therefore be useful in the investigation of the role of NK1 receptors in neurogenic inflammation in the microvasculature.

Solution conformation of endothelin and point mutants by nuclear magnetic resonance spectroscopy

Two-dimensional NMR techniques were utilized to determine the secondary structural elements of endothelin-1 (ET-1), a potent vasoconstrictor peptide, and two of its point mutants, Met-7 to Ala-7 (ETM7A), and Asp-8 to Ala-8 (ETD8A) in acetic acid-d3/water solution. Sequence specific NMR assignments were determined for all three peptides, as well as chemical shifts and NOE connectivity patterns. The chemical shifts of ET-1 and ETM7A are identical (+/- 0.05 ppm) except for the site of substitution, whereas marked shift changes were detected between ET-1 and ETD8A. These chemical shift differences imply that the Asp-8 to Ala-8 mutation has induced a conformational change relative to the parent conformation. All three molecules show the same basic nuclear Overhauser effect (NOE) pattern, which suggests that the gross conformation of all three molecules is the same. Small changes in sequential NOE intensities and changes in medium-range NOE patterns indicate that there are subtle conformational differences between ET-1 and ETD8A.

Responses to endothelins in the rat cutaneous microvasculature: a modulatory role of locally-produced nitric oxide

1. The response of the cutaneous microvasculature to intradermal injection of the endothelins (ET-1, ET-2 and ET-3) and the modulatory effect of endogenously produced nitric oxide (NO) have been determined in the rat. 2. Intradermal injection of endothelins (0.1- 10 pmol/site) induced dose-dependent local reductions in blood flow, measured by 133xenon clearance, with the following potency order; ET-1 = ET-2 greater than ET-3. 3. Laser Doppler blood flowmetry established that ET-1 (10 pmol/site) significantly (P less than 0.05) reduced microvascular blood flow for 3 h after injection. Over a wide dose-range, the response to the endothelins did not include any vasodilatation or visible flare. 4. A possible modulatory role of locally-produced NO was investigated by the intradermal injection of the potent inhibitor of NO generation NG-nitro-L-arginine methyl ester (L-NAME). L-NAME (100 nmol/site) injected alone induced a significant decrease in blood flow. The vasoconstriction induced by L-NAME was partially reversed by L-arginine (P less than 0.05) but not observed with NG-nitro-D-arginine methyl ester (D-NAME). 5. L-NAME significantly (P less than 0.05) enhanced the decrease in blood flow induced by submaximal doses of ET-1, ET-2 and ET-3 and vasopressin, although the results do not suggest that any of the vasoconstrictors stimulate NO release. The response to L-NAME was still observed 3.5 h after inducing a prolonged constriction with ET-1 (10 pmol/site).6. These results indicate that locally produced NO maintains a dilator tone in the cutaneous microvasculature of the rat and acts to modulate the effect of vasoconstrictors such as endothelins. Hence, it is suggested that in conditions where endogenous NO release is reduced, vasoconstrictor agents such as the endothelins could induce a dangerous decrease in blood flow possibly leading to ischaemia and tissue necrosis.

Human mast cell tryptase attenuates the vasodilator activity of calcitonin gene-related peptide

Calcitonin gene-related peptide (CGRP) is localized in and released from sensory nerves. It is a potent and long acting vasodilator which has been suggested to play a role in the control of blood flow. Using HPLC and trichloroacetic acid precipitation techniques, we have examined the ability of human mast cell lysates and a purified preparation of mast cell tryptase to degrade CGRP. We found that CGRP is effectively cleaved by tryptase (Km = 6.8 x 10(-6) mol/L at 37 degrees). Enzymatic activity was inhibited by antipain, leupeptin, N-alpha-p-tosyl-L-lysine chloromethyl ketone, benzamidine or aprotinin, but not by soybean trypsin inhibitor or N-tosyl-L-phenylalanine chloromethyl ketone. The degradation of CGRP by lysates of purified skin mast cells showed a similar pattern of inhibition suggesting that tryptase may be the major enzyme involved. The activity of tryptase was not affected by the presence of heparin. Incubation of CGRP with tryptase resulted in a loss of its vasodilator activity as observed by intravital microscopy of the hamster cheek pouch microvasculature. CGRP preincubated with tryptase failed to relax arterioles when added topically. It is suggested that the catalysis of CGRP by tryptase could represent an important means by which the activity of this neuropeptide is regulated in vivo.

Vasoconstrictor effects of endothelin-1 on myocardium microcirculation studied by the Langendorff perfusion method: differential sensitivities among microvessels

An intravital fluorescence microscope system was used to investigate the pharmacological effects of endothelin-1 (ET-1) on the coronary microcirculation in the isolated beating hearts of rats. The heart was perfused by retrograde aortic steady flow with an oxygenated Krebs-Ringer solution containing FITC-dextran. Changes in diameters of coronary microvessels accompanying the cumulative injection of ET-1 in the perfusate were observed and recorded with a video camera system. Coronary perfusion pressure was also measured during each experiment. Bolus injections of ET-1 (1-300 pmole) elicited a dose-dependent increase in perfusion pressure from 54 +/- 6 mm Hg (mean +/- SEM; n = 10, before the ET-1 injection) to 144 +/- 9 mm Hg (n = 8, at the ET-1 dose of 300 pmole). A dose-dependent narrowing of microvessels was also observed. This vasoconstriction was especially prominent in small-sized arterioles; the maximum vasoconstriction of the smaller arterioles was significantly higher than that of the larger arterioles (P less than 0.05). The response induced by ET-1 dose of 3-10 pmole was significantly larger in arterioles than in postcapillary venules in the diameter range between 10 and 40 microns. The vasoconstriction produced by ET-1 was inhomogeneous. Some part of bifurcations of arterioles showed a prominent localized vasoconstriction, and occasionally showed a complete luminal obstruction. Such a segmental vasospasm might be attributed to localized sensitivities of arterioles to ET-1. These findings suggest that ET-1 may have an important role in governing the coronary resistance and regulating the capillary flow in the myocardium.

Vascular activities of the endothelins

The endothelins are a family of novel 21 amino-acid peptides and are the most potent vasoconstrictor substances yet discovered. The endothelins not only produce prolonged pressor responses in intact animals but they also constrict large and small arterial and venous vessels studied as isolated vascular preparations, influence autonomic transmission, exert positive inotropic effects on the heart and have been shown to be capable of releasing EDRF, prostanoids and atrial natriuretic factor. Release of endothelins occurs after de novo synthesis which may be stimulated by various agonists, fluid-flow and possibly hypoxia. The endothelins have been implicated in the pathophysiology of a variety of cardiovascular disorders but their precise role remains to be elucidated.

Cerebrospinal fluid endothelin-1 and endothelin-3 levels in normal and neurosurgical patients: a clinical study and literature review

Endothelins are a family of structurally related, potent, long-lasting vasoconstrictor peptides. There are no established normal human levels of endothelin-1 or endothelin-3 in the cerebrospinal fluid. We measured cerebrospinal fluid endothelin-1 and endothelin-3 levels in five groups of patients: normal controls, patients with subarachnoid hemorrhage and cerebral vasospasm, patients with severe head injuries, patients undergoing temporal lobectomy for intractable epilepsy, and a patient with a gunshot injury to the thoracic spine. Endothelin-3 levels were significantly elevated in patients with subarachnoid hemorrhage and may participate in cerebral vasospasm and subsequent neurologic deterioration.

Activities of endothelin-1 in the vascular network of the rabbit ear: a microangiographic study

1. The effects of endothelin-1 on perfusion pressure and on arterial and venous diameters were examined simultaneously in a rabbit isolated ear preparation perfused with physiological buffer. The effects of hypoxia and inhibition of endothelium-derived relaxant factor (EDRF) activity on vascular responses to endothelin-1 were also investigated. 2. Endothelin-1 was potent at increasing perfusion pressure (ED50 = 46.7 +/- 11.0 pmol; Rmax = 85.3 +/- 5.3 mmHg). The potency and maximum reactivity were not significantly affected by hypoxia, inhibition of EDRF activity with 50 microns N-nitro-L-arginine methyl ester (NAME) or a combination of hypoxia and NAME. 3. Endothelin-1 caused equipotent dose-dependent constrictions of the first four generations of arterial branch vessels (G1-G4) but did not influence the diameter of the central ear artery except at high doses of the peptide when paradoxical dilatation' was observed. The peptide was also equipotent at causing constriction of the smaller venous vessels (V1-V4) but did not affect the large veins (V0). 4. Under conditions of hypoxia the potency of endothelin-1 was reduced in G2 and G3, was unaffected in G4 and the peptide did not significantly constrict either G0 or G1. Hypoxia reduced the potency of endothelin-1 in the smaller venous vessels (V1-V4), but conversely unmasked a marked constriction of the large veins (V0), which was not observed under normoxic conditions. 5. NAME 50 micron abolished the vasodilator effects of acetylcholine in this preparation. Inhibition of EDRF activity with NAME under normoxic conditions did not influence the constrictor activity of endothelin-1 on the arterial or venous branch vessels. However, inhibition of EDRF activity under hypoxic conditions prevented the reduction of potency of endothelin-1 as a constrictor of arterial and venous branch vessels which occurred in hypoxia. In the presence of NAME endothelin-1 constricted VO in both normoxia and hypoxia with equipotency but the maximum effect was greatest in hypoxia. 6. In conclusion, endothelin-1 is a powerful vasoconstrictor which acts with greater potency in veins than arteries in the rabbit isolated ear. Although hypoxia does not influence pressor responses it nevertheless alters the spatial pattern of vasoconstriction. In particular hypoxia unmasks constriction of the large veins by endothelin-1. Constriction of these veins was also observed in the absence of EDRF in normoxia, but to a much lesser degree so that the effect of hypoxia may only be partially due to reduced EDRF activity. Hypoxia may therefore directly or indirectly increase the sensitivity of the main veins to endothelin-1.

Endothelin reduces microvascular blood flow by acting on arterioles and venules of the hamster cheek pouch

Superfusion of the cheek pouch with 0.1-10 nM endothelin (E) produced a concentration-related reduction in the clearance of 22Na+ used as an indicator of microvascular plasma flow. The median effective concentration was about 2 nM. The time course of E action was also concentration related. Superfusion with 10 nM E for 10 min caused a greater than 80% reduction in 22Na+ clearance; the rate at which the action of E started was significantly faster than the rate at which its action ended. Recovery did not exceed 70% even though the tissue was superfused with drug-free buffer for 90 min. The E-induced reduction in 22Na+ clearance was associated with vasoconstriction, as determined by intravital microscopy. Arterioles of 4th branching order were more sensitive to E action than arterioles of 1st or 2nd order; however, the constriction lasted considerably longer in the latter vessels. E-induced venular constriction followed a pattern analogous to that of arterioles of the same category, with the exception that the finer venules responded the least. Pretreatment of the cheek pouch with 300 nM nifedipine diminished but did not abolish the 1 nM E-induced reduction in 22Na+ clearance, and the recovery of clearance upon E washout was not accelerated by nifedipine.

Endothelin: a new cardiovascular regulatory peptide

Endothelin, a recently discovered peptide produced by endothelial cells, contracts vascular strips in vitro with greater potency than any previously known vasoconstrictor. Infusions of pharmacologic doses of endothelin in vivo result in a prolonged pressor response and a preferential impairment of renal hemodynamic and excretory functions. Endothelin also directly stimulates the release of aldosterone from the adrenal gland and inhibits renin release in vitro. A highly sensitive and specific radioimmunoassay has confirmed that endothelin circulates in human plasma, and increased plasma endothelin levels have been associated with various cardiovascular disease states. This review summarizes the current knowledge about the molecular biologic features and physiologic actions of endothelin and also explores the role of endothelin, through its local and systemic function, as a regulator of vascular tone in normal and pathophysiologic states.

Uptake and metabolism of endothelin in the isolated perfused rat lung

The uptake and metabolism of endothelin was studied in the isolated perfused rat lung. 125I-Labeled endothelin (4 x 10(-12) M) was rapidly removed from the lung perfusate. More than 90% of the label was removed by 5 min, and only 4-5% remained in the perfusate after 30 min. In the presence of 10(-9) or 5 x 10(-9) M unlabeled endothelin added 6 min before 125I-labeled endothelin, the radiolabel was more slowly removed, so that after 30 min 19 or 73% of the label, respectively, remained in the perfusate. Although a high level of unlabeled endothelin in the perfusate reduced the uptake of 125I-labeled endothelin, it did not displace radiolabel previously taken up by the lung. Analysis of radiolabel composition showed that endothelin metabolism was less than 15% in both the lung and the perfusate after 30 min of lung perfusion. Autoradiography of the lung indicated that the radiolabel was located primarily within the alveolar wall. These results suggest that circulating endothelin is readily but finitely taken up in the pulmonary microvasculature where it is avidly bound but slowly metabolized.

Chronic hypertension produced by infusion of endothelin in rats

Endothelin, a potent vasoconstrictor peptide synthesized by the vascular smooth muscle endothelium, was chronically infused into male Sprague-Dawley rats to determine whether a long-term increase in circulating endothelin levels would cause a sustained elevation in mean arterial pressure. Rats were catheterized, housed in metabolic cages, and maintained on a fixed 6 meq/day sodium intake throughout the experiment with daily measurements including mean arterial pressure, heart rate, water intake, urine output, urinary sodium excretion, urinary potassium excretion, cardiac output, total peripheral resistance, and stroke volume. Infusion of endothelin-1 (ET-1) at rates of 3, 5, or 7.5 pmol/kg/min for 7 days was associated with significant, sustained, and dose-dependent increases in mean arterial pressure and smaller less consistent elevations in total peripheral resistance. Other parameters were unaffected. Similar results were observed in rats receiving endothelin-3 (ET-3), except that a higher dose of ET-3 was required. These results indicate that elevated blood levels of endothelin could produce a maintained hypertension without sodium or water retention and that the hemodynamic basis for the increased mean arterial pressure is similar to that seen in most other forms of experimental and clinical hypertension.

Endothelium-derived contractile factors

1. Vascular endothelium releases different substances (endothelium-derived contractile factors, EDCFs), which mediate vasoconstrictor responses induced by several agents. 2. Clear differences have been reported in endothelium-dependent contractions, which suggest at least three distinct EDCFs, named EDCF1, EDCF2 and EDCF3, respectively. 3. EDCF1 is a cyclooxygenase metabolite(s) of arachidonic acid. EDCF2 is a polypeptide released from cultured endothelial cells. It has been isolated and identified as a 21-amino acid peptide called endothelin, which is described as the most potent vasoconstrictor agent known to date. EDCF3 is an unidentified contractile factor(s), which is neither EDCF1 nor EDCF2. 4. The physiological role of these endothelial contractile factors is not yet clear. However, they have been implicated in the local mechanisms involved in blood flow regulation, as well as in some pathological conditions, such as hypertension or cerebral vasospasm.

Endothelin-1 induces potent constriction of lymphatic vessels in situ

The response of lymph vessels, arterioles and venules in the exteriorized rat mesentery to endothelin-1, vasopressin and norepinephrine was examined with the aid of high-resolution television microscopy. On a molar basis, endothelin-1 was more potent than vasopressin to contract the three types of vessels. Norepinephrine, which could constrict blood microvessels, did not act on lymph vessels. Acetylcholine, sodium-nitroprusside and isoproterenol were ineffective to block the constrictive responses of lymph vessels to endothelin-1 and vasopressin. At the same concentrations, however, acetylcholine and sodium-nitroprusside antagonized the responses of arterioles and venules to endothelin-1 and norepinephrine, whereas the responses of blood microvessels to vasopressin remained unaffected. Isoproterenol, at doses capable of blocking the response of the arterioles and venules to norepinephrine, did not interfere with the constriction induced by endothelin-1 and vasopressin on these vessels. It is suggested that endothelin-1 might play a role in the regulation of lymphatic contractility apart from its vasoconstrictor activity on blood vessels.

Molecular biology and biochemistry of the endothelins

Endothelin-1 (ET-1), the first member of the newly discovered mammalian endothelin family of biologically active peptides, was originally identified as a 21 residue potent vasoconstrictor peptide in vascular endothelial cells. However, it has since been demonstrated to possess a wide variety of pharmacological activities in tissues both within and outside the cardiovascular system, and peptides with a striking similarity to ET-1 have been found to be the major toxic component of a snake venom. Moreover, recent studies have suggested that mammals including humans produce three distinct members of this peptide family, ET-1, ET-2 and ET-3, which may have different profiles of biological activity, and may act on distinct subtypes of endothelin receptor. Masashi Yanagisawa and Tomoh Masaki review the current status of the biochemistry and molecular biology of endothelin.

Endothelin--a new family of endothelium-derived peptides with widespread biological properties

Endothelin (ET) is a novel family of three isopeptides (ET-1, ET-2, ET-3) each containing twenty-one amino acids and two disulfide bonds. Initially isolated from the supernatant of cultured porcine aortic endothelial cells, ET is stored as a preproform and released through an unusual proteolytic cleavage. In general, ET-1, ET-2, ET-3 differ quantitatively but not qualitatively in their biologic activity. ET have potent contractile activity in a variety of isolated tissues including arteries veins, trachea, duodenum urinary bladder and uterus. In vivo, ET possesses potent vasodilator and vasoconstrictor properties. Although the mechanisms mediating the hemodynamic effects of ET are not entirely clarified, recent evidence indicates a role for endothelium-derived relaxant factor (EDRF), protein kinase C and extracellular calcium. Moreover, ET appears to produce inflammation and bronchoconstriction through the formation of arachidonic acid metabolites via the cyclooxygenase pathway. The presence of ET binding sites in blood vessels and in several organ systems suggests ET may have important regulatory functions, which remain to be determined.