The pharmacological properties of the peptide, endothelin

Tight Junction Proteins and Signaling Pathways in Cancer and Inflammation: A Functional Crosstalk

The ability of epithelial cells to organize through cell–cell adhesion into a functioning epithelium serves the purpose of a tight epithelial protective barrier. Contacts between adjacent cells are made up of tight junctions (TJ), adherens junctions (AJ), and desmosomes with unique cellular functions and a complex molecular composition. These proteins mediate firm mechanical stability, serves as a gatekeeper for the paracellular pathway, and helps in preserving tissue homeostasis. TJ proteins are involved in maintaining cell polarity, in establishing organ-specific apical domains and also in recruiting signaling proteins involved in the regulation of various important cellular functions including proliferation, differentiation, and migration. As a vital component of the epithelial barrier, TJs are under a constant threat from proinflammatory mediators, pathogenic viruses and bacteria, aiding inflammation and the development of disease. Inflammatory bowel disease (IBD) patients reveal loss of TJ barrier function, increased levels of proinflammatory cytokines, and immune dysregulation; yet, the relationship between these events is partly understood. Although TJ barrier defects are inadequate to cause experimental IBD, mucosal immune activation is changed in response to augmented epithelial permeability. Thus, the current studies suggest that altered barrier function may predispose or increase disease progression and therapies targeted to specifically restore the barrier function may provide a substitute or supplement to immunologic-based therapies. This review provides a brief introduction about the TJs, AJs, structure and function of TJ proteins. The link between TJ proteins and key signaling pathways in cell proliferation, transformation, and metastasis is discussed thoroughly. We also discuss the compromised intestinal TJ integrity under inflammatory conditions, and the signaling mechanisms involved that bridge inflammation and cancer.

Concentration-related effects of nitric oxide and endothelin-1 on human trabecular meshwork cell contractility

The contractility status of trabecular meshwork (TM) cells influences aqueous humor outflow resistance and intraocular pressure. Using human TM cells as a model, the goal of the present study was to examine concentration-response relationships of two prototypical molecules, nitric oxide (NO) and endothelin-1 (ET-1), known to differentially influence vascular smooth muscle contractility. Efficacy of ET-1, two NO donors (DETA-NO and SNP) and a cGMP analog (8-Br-cGMP) were assessed using two complementary methods: functionally in a gel contraction assay and biochemically using a myosin light chain phosphorylation assay. The NO donors DETA-NO and SNP dose dependently relaxed cultured human TM cells (EC50 for DETA-NO = 6.0 ± 2.4 μM, SNP = 12.6 ± 8.8 μM), with maximum effects at 100 μM. Interestingly, at concentrations of NO donors above 100 μM, the relaxing effect was lost. Relaxation caused by DETA-NO (100 μM) was dose dependently blocked by the soluble guanylate cyclase specific inhibitor ODQ (IC50 = 460 ± 190 nM). In contrast to the NO donors, treatment of cells with the cGMP analog, 8-Br-cGMP produced the largest relaxation (109.4%) that persisted at high concentrations (EC50 = 110 ± 40 μM). ET-1 caused a dose-dependent contraction of human TM cells (EC50 = 1.5 ± 0.5 pM), with maximum effect at 100 pM (56.1%) and this contraction was reversed by DETA-NO (100 μM). Consistent with functional data, phosphorylation status of myosin light chain was dose dependently reduced with DETA-NO, and increased with ET-1. Together, data show that TM cells rapidly change their contractility status over a wide dynamic range, well suited for the regulation of outflow resistance and intraocular pressure.

Inhibitory effect of co-administration of atorvastatin and endothelin-1 receptor antagonist on the progression of atherosclerosis in rabbit

Atorvastatin, a hydroxymethylglutaryl-CoA reductase inhibitor, and endothelin-1 (ET-1) receptor antagonist have been separately indicated to ameliorate disease progression in atherosclerosis. However, no study has evaluated the effect of their combination on atherosclerosis. The objective of the current study was to evaluate the direct in vivo effects of a combination regimen of atorvastatin and ET-1 receptor antagonist on male New Zealand white rabbit models of atherosclerosis (injury-induced). Thirty-two atherosclerotic rabbits were divided into four experimental groups: (a) injury group - fed high-fat diet; (b) ET-1 receptor antagonist preventive group - fed high-fat diet, but with intragastric administration of the ET-1 receptor antagonist, darusentan; (c) combined preventive group - fed high-fat diet, but with intragastric administration of both darusentan and atorvastatin; and (d) treatment group - fed high-fat diet for the first 8 weeks, followed by normal diet and intragastric administration of both darusentan and atorvastatin up to 16 weeks. A further eight non-atherosclerotic rabbits were fed normal diet and classified as the control group. At the end of 8 and 16 weeks, compared with the injury group, the combined preventive group had significant reduction in both the concentration of serum lipids and inflammatory factors and atherosclerosis formation, indicative of a multifaceted anti-atherosclerotic impact. The relative area of atherosclerotic lesions in the injury group (30.84%) was significantly higher than the control group (4.62%; p < 0.05). The combined preventive group showed a significantly robust effect on lowering serum lipid, inflammatory cytokines, and maintained homeostatic balance of free radicals, and important downstream effectors like ET-1 and matrixmetalloproteinase-9. Our data show that atorvastatin and ET-1 receptor antagonist co-administration may decrease lipid levels, stabilize plaques and relieve vascular inflammation. By reducing the plaque burden, this regimen may minimize the risk of atherosclerotic plaque rupture or arterial occlusion.

Human choroidal melanocyte signal transduction responses to various pharmacological agents: focus on endothelin receptors

PURPOSE

The receptor-coupled signal transduction systems present in isolated human choroidal melanocytes (HCOMs) were investigated.

METHODS

[(3)H]-inositol phosphates ([(3)H]-IPs) generated in the cells were measured by ion-exchange chromatography. cAMP generated in the cells was quantified using an enzyme immunoassay.

RESULTS

Initially, HCOM cells were challenged with a relatively high concentration (e.g., 1 µM-1 mM) of a variety of pharmacological agents in order to determine which functional receptors were present in these cells. Full concentration-response pharmacological studies were subsequently conducted on endothelin receptors. While a number of prostaglandins (PGs) (e.g., PGD(2), PGE(2), PGF(2α), cloprostenol, latanoprost acid, U-46619), histamine, carbachol, bombesin, and arginine-vasopressin were essentially inactive at stimulating the phosphoinositide (PI) hydrolysis response, endothelin-1 (ET-1) potently and efficaciously generated [(3)H]-IPs. Concentration-response studies yielded the following potency (EC(50)) and efficacy (E(max) relative to ET-1) data: ET-1 EC(50) = 3.4 ± 1.4 nM, E(max) = 100%, n = 3; BQ-3020 (ET(B) receptor-selective agonist) EC(50) = 13 ± 4 nM, E(max) = 73 ± 2%, n = 3). The effects of ET-1 on [(3)H]-IPs production were blocked by the ET(B) receptor-selective antagonist, BQ-788 (IC(50) = 10 ± 5 nM, n = 3), while the ET(A) receptor-selective antagonist (BQ-610) was essentially inactive. In the adenylyl cyclase (AC) assay, while isoproterenol (10 µM), ET-1 (1 µM) and PGE(2) (10 µM) stimulated cAMP production, numerous other PGs (e.g., PGD(2), PGF(2α), PGI(2), latanoprost, latanoprost acid, U-46619 and BW245C [all at > 10 µM]) were inactive.

CONCLUSIONS

It is concluded that HCOMs express functionally active ET(B) receptors that mediate the production of [(3)H]-IPs. Additionally, HCOMs generate cAMP in response to ET-1, PGE(2), and isoproterenol. These data may have relevance to the melanogenic activity of HCOM cells.

Intracellular signaling in human iridial fibroblasts and iridial melanocytes in response to prostaglandins, endothelin, isoproterenol, and other pharmacological agents

PURPOSE

The receptor-coupled signal transduction systems present in isolated human iridial fibroblasts (HIF) and in human iridial melanocytes (HIM) were investigated. Cell responsiveness to numerous prostaglandins (PGs), and other compounds of interest, was profiled in order to better understand their involvement in the iridial hyper-pigmentation process observed during treatment of elevated intraocular pressure with FP-receptor against PG analogs.

METHODS

[(3)H]-inositol phosphates ([(3)H]-IPs) generated in the cells were measured by ion-exchange chromatography followed by liquid scintillation spectroscopy. cAMP generated in the cells was quantified using an enzyme immunoassay.

RESULTS

HIF cells exhibited a robust phosphoinositide (PI) hydrolysis response to FP-class PG analogs, such as cloprostenol (potency, EC(50) = 2.4 ± 0.5 nM, n = 5), fluprostenol (EC(50) = 5.3 ± 0.6 nM, n = 3), PGF(2α) (EC(50) = 54 ± 18 nM, n = 5), and latanoprost acid (EC(50) = 121 ± 17 nM, n = 4). Other PGs exhibited the following potencies (EC(50)) for stimulating [(3)H]-IPs accumulation in HIF cells: PGD(2) EC(50) = 327 ± 195 nM, n =3; PGE(2) EC(50) = 550 ± 50 nM, n = 3; and two TP-receptor agonists (I-BOP, EC(50) = 23 ± 8 nM, n = 3; U-46619 EC(50) = 1.1 ± 0.4 µM, n = 3). Endothelin-1 (ET-1) and histamine increased [(3)H]-IPs production in HIF and HIM cells. HIM cells exhibited minimal PI turnover response to cloprostenol, latanoprost acid, latanoprost, PGF(2α), PGE(2), and histamine, but there were robust responses to ET-1 (EC(50) = 4.6 nM, n = 2) and an ET(B)-receptor agonist (BQ-3020, EC(50) = 5 nM, n = 2) that were blocked by an ET(B)-antagonist (BQ-788, IC(50) = 21 ± 6 nM, n = 3). In the adenylyl cyclase activation assay, numerous PGs (1 and 10 µM) stimulated cAMP production in HIF cells yielding the following rank order of efficacy: PGI(2) > PGE(2) > misoprostil > isoproterenol = BW245C > PGD(2) = PGF(2α) = fluprostenol. In HIM cells, PGE(2) (EC(50) = 1.3 ± 0.3 nM) and isoproterenol (β-agonist; EC(50) = 89 ± 13 nM) potently and efficaciously stimulated cAMP production and ICI-118851 (β(2)-antagonist) attenuated the effects of isoproterenol. However, latanoprost acid, latanoprost, ET-1, and BW245C (DP-receptor agonist) were relatively less efficacious than isoproterenol and PGE(2) in HIM cells at stimulating cAMP production.

CONCLUSIONS

These studies have shown that while HIF cells express FP prostaglandin and histamine receptors coupled to phospholipase C to produce [(3)H]-IPs, the HIM cells lack such functionally active FP-receptors. In contrast, HIF and HIM cells express functional ET-1 receptors coupled to [(3)H]-IPs production and both cell-types respond to PGE(2), BW245C, and isoproterenol by generating cAMP. It is concluded that human iridial fibroblasts and melanocytes respond differently to PGs and histamine, but in the same manner to ET-1, isoproterenol and BW245C. This may have relevance to the intercellular communication within the iris relative to the melanogenic processes.

Characterization of the in vitro responses of equine cecal longitudinal smooth muscle to endothelin-1

OBJECTIVE

To characterize the in vitro response of equine cecal longitudinal smooth muscle (CLSM) to endothelin (ET)-1 and assess the role of ETA and ETB receptors in those ET-1-induced responses.

ANIMALS

36 horses without gastrointestinal tract disease.

PROCEDURE

To determine cumulative concentration-response relationships, CLSM strips were suspended in tissue baths containing graded concentrations of ET-1 (10(-9) to 10(-6)M) with or without BQ-123 (ETA receptor antagonist); with or without IRL-1038 (ETB receptor antagonist); or with both antagonists at concentrations of 10(-9), 10(-7), and 10(-5)M. To determine the percentage change in baseline tension of CLSM, the areas under the curve during the 3-minute periods before and after addition of each dose were compared. Also, the effects of ET-1 and a combination of selective ETA and ETB receptor antagonists on electrically evoked contractions were studied.

RESULTS

ET-1 caused sustained increases in CLSM tension in a concentration-dependent manner. Contractile responses to ET-1 were not significantly inhibited by either BQ-123 or IRL-1038 alone at any concentration; however, responses were significantly inhibited by exposure to the antagonists together at a concentration of 10(-5)M. Electrical field stimulation did not change the spontaneous contractile activity of CLSM and did not significantly alter the tissue response to ET-1, BQ-123, or IRL-1038.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that ET-1 has a contractile effect on equine CLSM that is mediated via ETA and ETB receptors. In vitro spontaneous contractions of equine CLSM apparently originate in the smooth muscle and not the enteric nervous system.

Endothelin causes contraction of human esophageal muscularis mucosae through interaction with both ETA and ETB receptors

Endothelin (ET) causes contraction of the muscularis mucosae in the guinea pig esophagus, but its role in the human esophagus remains unknown. To investigate effects of ET in the human esophagus, we measured contraction of isolated human esophageal muscularis mucosae strips caused by ET related peptides and binding of 125I-ET-1 to cell membranes prepared from the human esophageal muscularis mucosae. Autoradiography demonstrated specific binding of 125I-ET-1 to the muscularis mucosae and muscularis propria (muscularis externa) of the human esophagus. ET-1 caused tetrodotoxin and atropine-insensitive contraction of muscularis mucosae strips. In terms of the maximal tension of contraction, ET-1 and ET-2 were equal in efficacy. The relative potencies for ET related peptides to cause contraction were ET-1=ET-2>ET-3>sarafotoxin S6c (SX6c), an ETB receptor agonist. ET-1 caused contraction was mildly inhibited by BQ-123, an ETA receptor antagonist, and not by BQ-788, an ETB receptor antagonist. It was moderately inhibited by the combination of both antagonists, indicating synergistic inhibition. Furthermore, desensitization to SX6c with SX6c pretreatment failed to abolish the contractile response to ET-1, which was completely inhibited by BQ-123. These indicate the involvement of both ETA and ETB receptors in the contraction. Binding of 125I-ET-1 to cell membranes of the muscularis mucosae was saturable and specific. Analysis of dose-inhibition curves demonstrated the presence of ETA and ETB receptors. This study demonstrates that, the muscularis mucosae of the human esophagus, similar to that of the guinea pig esophagus, possesses both ETA and ETB receptors mediating muscle contraction.

Role of endothelin ETA and ETB receptors in the guinea-pig urinary bladder contraction

The distribution and function of endothelin receptors in the guinea-pig urinary bladder were examined. Specific [125I]endothelin-1 binding sites with both the endothelin ET(A) and ET(B) receptor subtypes were distributed in the muscle layer. Endothelin-1 elicited a tonic contraction which was inhibited by cyclo(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ123) but not by N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-methoxycarbonyltryptophanyl-D-norleucine (BQ788) and which was inhibited more strongly by a combination of BQ123 and BQ788. Sarafotoxin S6c elicited a contraction which was abolished by BQ788. The concentration of endothelin-1 in the muscle layer was 707.0+/-67.5 pg/g wet weight. Thus, endothelin-1 may regulate muscle tone via both subtypes of endothelin receptors in an autocrine manner in the guinea-pig urinary bladder.

Ionic mechanisms and Ca(2+) regulation in airway smooth muscle contraction: do the data contradict dogma?

In general, excitation-contraction coupling in muscle is dependent on membrane depolarization and hyperpolarization to regulate the opening of voltage-dependent Ca(2+) channels and, thereby, influence intracellular Ca(2+) concentration ([Ca(2+)](i)). Thus Ca(2+) channel blockers and K(+) channel openers are important tools in the arsenals against hypertension, stroke, and myocardial infarction, etc. Airway smooth muscle (ASM) also exhibits robust Ca(2+), K(+), and Cl(-) currents, and there are elaborate signaling pathways that regulate them. It is easy, then, to presume that these also play a central role in contraction/relaxation of ASM. However, several lines of evidence speak to the contrary. Also, too many researchers in the ASM field view the sarcoplasmic reticulum as being centrally located and displacing its contents uniformly throughout the cell, and they have focused almost exclusively on the initial single [Ca(2+)] spike evoked by excitatory agonists. Several recent studies have revealed complex spatial and temporal heterogeneity in [Ca(2+)](i), the significance of which is only just beginning to be appreciated. In this review, we will compare what is known about ion channels in ASM with what is believed to be their roles in ASM physiology. Also, we will examine some novel ionic mechanisms in the context of Ca(2+) handling and excitation-contraction coupling in ASM.

Two classes of endothelin receptors mediating contraction in esophageal muscularis mucosae

Endothelin (ET) causes contraction of the esophageal muscularis mucosae. To characterize the ET receptor subtypes involved in contraction, we measured contraction of isolated muscularis mucosae strips caused by ET-related peptides and binding of (125)I-ET-1 to cell membranes prepared from the guinea pig esophageal muscularis mucosae. Autoradiography demonstrated (125)I-ET-1 binding to the muscularis mucosae and muscularis propria. ET-1 caused tetrodotoxin and atropine-insensitive contraction of esophageal muscularis mucosae strips. The relative potencies for ET isopeptides to cause contraction were ET-1=ET-2>ET-3. FR-139317, an ET(A) receptor antagonist, or BQ-788, an ET(B) receptor antagonist, alone did not alter responses to ET-1. However, the combination of both antagonists almost abolished the ET-1-induced contraction, indicating synergistic inhibition. Desensitization to sarafotoxin S6c, an ET(B) receptor agonist, failed to abolish the response to ET-1, which was completely inhibited by FR-139317. These indicate the involvement of both ET(A) and ET(B) receptors in the contraction. Binding of (125)I-ET-1 to cell membranes of the muscularis mucosae was saturable and specific. Analysis of dose-inhibition curves demonstrated the presence of ET(A) and ET(B) receptors. This study demonstrates that the esophageal muscularis mucosae possesses both ET(A) and ET(B) receptors mediating muscle contraction. There is cooperation between these two subtypes of ET receptors in the esophagus mediating muscle contraction.

Ileal and colonic contractions by endothelin-1 in experimentally induced paralytic ileus in rats

The aim of the present study was to investigate the effect of endothelin-1 on the isolated distal ileum and proximal colon in an experimentally induced ileus in rats. Ileal and colonic contractions by endothelin-1, acetylcholine alone and with endothelin-1 were recorded both in normal and experimentally induced paralytic ileus in rats. In the control group, all the responses to acetylcholine were found to be potentiated significantly when used together with endothelin-1 but in paralytic ileus group, no detectable change was observed in the responses of the amine after administration of acetylcholine together with endothelin-1. This study indicates that endothelin-1 might have an effect on gastrointestinal motility and postoperative paralytic ileus.

Pharmacological characterization of endothelin-induced contraction in the guinea-pig oesophageal muscularis mucosae

1. In the oesophageal muscularis mucosae, we examined the effects of endothelin-1 (ET-1), endothelin-2 (ET-2), endothelin-3 (ET-3) and sarafotoxin S6c (SX6c) as agonists, and FR139317, BQ-123 and RES-701-1 as endothelin receptor antagonists. 2. All of the endothelins produced tonic contractions which were frequently superimposed on rhythmic motility in a concentration-dependent manner. The order of potency (-log EC50) was ET-1 (8.61)=SX6c (8.65)>ET-2 (8.40)>ET-3 (8.18). 3. FR139317 (1-3 microM) and BQ-123 (1 microM) caused parallel rightward shifts of the concentration-response curve to ET-1, but at higher concentrations caused no further shift. RES-701-1 (3 microM) caused a rightward shift of the concentration-response curve to ET-1, while RES-701-1 (10 microM) had no additional effect. RES-701-1 (0.1-1 microM) concentration-dependently caused a rightward shift of the concentration-response curve to SX6c. The contraction to ET-1 (10 nM) in preparations desensitized to the actions of SX6c was greatly inhibited by pretreatment with FR139317 (10 microM). 4. Modulation of the Ca2+ concentration in the Krebs solution caused the concentration-response curve to ET-1 or SX6c to shift to the right and downward as external Ca2+ concentrations decreased. Verapamil (30 microM) abolished rhythmic motility induced by ET-1 or SX6c. Ni2+ (0.1 mM) weakly inhibited ET-1- or SX6c-induced tonic contraction. SK&F 96365 (60 microM) completely inhibited ET-1-induced contractions. 5. We conclude that there are two types of ET-receptors, excitatory ET(A)- and ET(B)-receptors in the oesophageal muscularis mucosae. These receptors mediate tonic contractions predominantly by opening receptor-operated Ca2+ channels (ROCs) and partly by opening T-type Ca2+ channels, and mediate rhythmic motility by opening L-type Ca2+ channels.

Actions of endothelin-1, 2, and 3 in the microvasculature of bone

Endothelins have recently been associated with hypoxia-related vascular smooth-muscle constriction and with the so-called no-reflow phenomenon following reperfusion. Their action is tissue dependent. The role of endothelins on vascular smooth muscle in bone is unknown. An ex vivo perfusion model was used to investigate the effects of the three different endothelins on the vascular resistance in the canine tibia. Endothelin-1 and endothelin-2 had molar potencies similar to that of norepinephrine, whereas endothelin-3 was less potent. Tachyphylaxis to the same dose of endothelin-1 did not occur. The calcium channel blocker, diltiazem, attenuated (45% reduction) the vasoconstrictor responses to norepinephrine (p < 0.005) but had a smaller effect (24% reduction) on the responses to endothelin (p < 0.025). Vascular smooth muscle in bone appears to have endothelin receptors that are similar to those in other organs.

The significant role of endothelin-3 in potentiating electrically stimulated contractions in the rat iris sphincter

1. We determined the endothelin (ET) receptor subtype involved in the facilitation of electrical field stimulation-(EFS) induced contraction using the ETB receptor agonist sarafotoxin S6c (STX S6c) and the ET receptor antagonists TTA-386 and bosentan. 2. ET-3-and ETB-receptor-selective agonist STX S6c enhanced EFS-induced contractions. The increasing effect of ET-3 was partially reduced by the desensitization to STX S6c or the ETA receptor antagonist TTA-386. After simultaneous treatment with TTA and desensitization, ET-3-induced potentiation was completely abolished. The combined ETA/B receptor blocker bosentan (Ro 47-0203) eliminated the ET-3-evoked neuronal effect. Both ETB and ETA receptors are involved in the facilitating effects of ETs on EFS contraction. 3. ET-3 immunoreactivity occurs densely in this tissue and was released from neuronal sites by electrical stimulation. We suggest that endogenous ET-3 has a more predominant role than ET-1.

Endothelin-receptor antagonist FR 139317 reduces infarct size in a rabbit model when given before, but not after, coronary artery occlusion

Endothelins are potent vasoactive peptides that exist as isoforms having different affinities for two main receptor subtypes, ETA and ETB. Based on their potential to produce adverse effects as a result of marked vasoconstrictor actions, these mediators have been widely studied to investigate their role in disease states involving the cardiovascular system. In this study, we examined the effect of a selective ETA-receptor antagonist, FR 139317, on myocardial infarct size by using a rabbit arterial-occlusion model. The main coronary artery of 32 New Zealand white rabbits was occluded for 60 min, followed by 3 h of reperfusion. Sixteen animals received FR 139317 (5.0 mg/kg as a bolus + 30 mg/kg given over a 90-min period), whereas the remaining 16 control rabbits received the drug vehicle. Treatment began at 15 min before coronary artery occlusion and ended at 15 min after the start of tissue reperfusion. Infarct size, expressed as a percentage of the area at risk of infarction, was 64 +/- 4% in the control group and 41 +/- 2% in the treated animals (p < 0.001). In a second set of rabbits, five animals received the same treatment regimen and were compared with five controls; however, unlike the initial protocol, treatment was initiated 45 min after coronary artery occlusion (15 min before reperfusion) and ended after 75 min of reperfusion. In this case, infarct size was 65 +/- 4% in the control group and 56 +/- 10% in the animals that received FR 139317 (NS). The results suggest that endothelin is involved in the extension of myocardial infarction in this rabbit model and that its primary action is manifest during occlusion of the coronary artery.

Endothelin-1: a scientist's curiosity, or a real player in ischemic heart disease?

Endothelin-1, the most potent endothelium-derived vasoconstrictor peptide identified so far, exerts multiple biologic effects that are potentially relevant for the pathogenesis of coronary atherosclerosis and ischemic heart disease. Since the discovery of the peptide, a good deal of experimental and clinical data have been accumulated to support an important role of endothelin-1 in ischemic heart disease. In experimental animals, exogenous endothelin-1 was found to cause coronary vasoconstriction and, at higher doses, ventricular fibrillation and death. Endothelin receptor subtypes have been demonstrated and pharmacologically characterized in the coronary vascular bed. The plasma levels of immunoreactive endothelin-1 were found to be increased in patients with coronary atherosclerosis, acute myocardial infarction, and angina. Given its growth-promoting and mitogenic action, endothelin-1 has also been suspected to participate in the mechanism of restenosis after PTCA. The purpose of this study was to critically review the experimental and clinical data supporting the involvement of endothelin-1 in ischemic heart disease and the results of more recent studies on the effects of endothelin-1 blockade on experimental myocardial necrosis and restenosis after PTCA.

Endothelin induces vasoconstriction in the bone vasculature in vitro: an effect mediated by a single receptor population

The aim of this study was to define the types of endothelin receptors present in the canine tibial vasculature. Endothelin receptor agonists and antagonists were used in two different models: isolated nutrient tibial arteries in organ bath and in vitro-perfused canine tibial bones. In isolated nutrient tibial arteries, endothelin-1 caused concentration-dependent contractions of rings with and without endothelium. BQ-123, a selective endothelin-A antagonist, induced a significant rightward shift of endothelin-1 concentration-response curves. No contractions were observed with sarafotoxin S6c, a selective endothelin-B agonist. The responses of endothelin-1 were not affected by the presence of NG-monomethyl-L-arginine acetate plus indomethacin or by removal of the endothelium. In perfused tibial bones, endothelin-1 was more potent than endothelin-3 in causing concentration-dependent contractions. Neither endothelin-1, endothelin-3, nor sarafotoxin S6c caused relaxations. Neither the inhibition of nitric oxide nor the inhibition of prostaglandins significantly altered contractions to endothelin-1. These concordant data indicate that endothelin is a vasoconstrictor in the bone vasculature, an effect that appears to be mediated only through endothelin-A receptors.

Endothelin-1-induced in vitro cerebral venoconstriction is mediated by endothelin ETA receptors

The in vitro effects of endothelin-1 on cerebral veins were studied using cylindrical segments, 5 mm long, from dog pial veins. Isometric responses to endothelin-1 (10(-12)-10(-7) M) and to the endothelin ET(B) receptor agonist, IRL 1620 (Suc-[Glu9,Ala11,15]endothelin-1-(8-21), 10(-12) -10(-7) M), were recorded in veins under control conditions and pretreated with the endothelin ET(A) receptor antagonist, BQ-123 (cyclo-(D-Asp-Pro-D-Val-Leu-D-Trp), 10(-8) -10(-5) M), and the endothelin ETB receptor antagonist, BQ-788 (N-[N-[N-[(2,6-dimethyl-1-piperidinyl)carbonyl]-4-methyl-L-leucyl]-1-(me thoxycarbonyl)-D-tryptophyl]-D-norleucine monosodium, 10(-6) and 10(-5) M). The response to endothelin-1 was also recorded in veins pretreated with the nitric oxide synthesis inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME, 10(-4) M), or the cyclooxygenase inhibitor, meclofenamate (10(-5) M), and in veins without endothelium or placed in medium without Ca2+ but with EDTA (0.1 mM). In control veins, endothelin-1 produced a concentration-dependent contraction (EC50 = 2.0 x 10(-10) M; maximal contraction = 113 +/- 6 mg) and IRL 1620 induced no effects or a small contraction only with high concentrations (10(-8) - 10(-6) M) (EC50 = 1.5 x 10 (-8) M; maximal contraction = 9 +/- 3 mg). BQ-123 shifted the response to endothelin-1 to the right in a parallel, concentration-dependent way, whereas BQ-788, L-NAME or meclofenamate did not modify the response to endothelin-1. Compared with the control, veins in a medium without Ca2+ had similar EC50 values, but a lower maximal contraction induced by endothelin-1 (57 +/- 10 mg, P < 0.05), and veins without endothelium exhibited similar EC50 values. Thus, endothelin-1 produces marked cerebral venoconstriction that could be mainly mediated by activation of endothelin ETA receptors, may be dependent on extracellular Ca2+, and may be independent of endothelium, nitric oxide and prostanoids.

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

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

Pre- and postjunctional actions of endothelin in the rat iris sphincter preparation

Effects of endothelins (ETs) were studied in the rat iris sphincter preparation. Three peptides (ET-1, ET-2 and ET-3) caused contractile responses, and the rank order of agonist potency was: ET-1 = ET-2 > ET-3. The concentration-response curve to ET-1 was shifted to the right by the ETA receptor antagonist cyclo [D-Asp-L-Pro-D-Val-L-Leu-D-Trp] (BQ-123: 10(-7) M), the pA2 value of which was 7.41 +/- 0.09 (n = 4). ET-1 and ET-3, at the concentration of 10(-9) M, potentiated cholinergic contractions evoked by electrical field stimulation (5 and 20 Hz) without affecting the postjunctional sensitivity to carbachol. This potentiating effect was not influenced by BQ-123 (10(-6) M). The ET-evoked percentage increase in the stimulation-induced contraction observed at 5 Hz was significantly greater than that at 20 Hz. A release of immunoreactive ET was detected when the preparation was stimulated at 20 Hz (1.81 +/- 0.36 pg/sphincter n = 6). ET release evoked by 20 Hz stimulation was completely abolished by tetrodotoxin (10(-7) M). In conclusion, ET interacts with two different receptor types, ETA and non-ETA receptors (probably ETB) which exist post- and presynaptically at cholinergic neuroeffector junctions of the rat iris preparation. Stimulation of ETA receptor results in a direct muscle contraction and non-ETA receptor activation facilitates the acetylcholine output from cholinergic nerve endings. It is suggested that ET released from a tetrodotoxin-sensitive site is involved in the modulation of acetylcholine release in the rat iris sphincter preparation.

Contractile actions of endothelins in rat gastric body: evidence for receptor subtypes and involvement of prostaglandin E2

Endothelin-1 produced a phasic contraction in the longitudinal muscle preparation isolated from the rat gastric body, but produced a sustained contraction in the circular muscle preparation. Indomethacin, a cyclo-oxygenase inhibitor, decreased the endothelin-1-induced contraction of the longitudinal preparation, but did not affect the endothelin-1-induced contractions of the circular muscle. In the absence of indomethacin, the maximal contractile tension (Emax) and the concentration producing a half-maximal contraction (EC50) induced by endothelin-3 in the longitudinal muscle preparations were smaller than those for endothelin-1, whereas in the circular muscle preparations there were no significant differences between the values (EC50, Emax) for endothelin-1 and endothelin-3. In the presence of indomethacin, endothelin-3-induced contraction of the longitudinal muscle preparation is more potent than that of endothelin-1. SC-19220, a prostaglandin E2 receptor antagonist, significantly decreased endothelin-1-induced contraction of the longitudinal preparation, prostaglandin E2 produced a concentration-dependent contraction in the longitudinal preparation, but had no effects in the circular muscle preparation. Endothelin-1 (10(-8) M) significantly increased the release of immunoassayable prostaglandin E2 from rat gastric smooth muscle. These results point to the existence of distinct endothelin receptor subtypes in the smooth muscle of rat gastric body, and a potential role of endothelin-1 in regulating gastric motility. Moreover, one of the endothelin receptor subtypes is related to the production of prostaglandin E2.

Medullary hypotensive effect of endothelin1 in anaesthetized animals

In anaesthetized animals, systemic injection of ET1 at doses from 3 to 100 ng.kg-1 provoked only a transient hypotensive effect. At 300 ng.kg-1 we observed the classical biphasic effect, consisting of a transient lowering of the arterial pressure followed by a long-lasting hypertensive effect. Direct injection of the peptide into the vertebral artery of anaesthetized animals only affected arterial pressure (AP) when the blood-brain barrier was permeabilised. Under these conditions, a dose-dependent decrease in AP was observed, which was not associated with a significant effect on the heart rate. Micro-injections of the peptide in the medullary nucleus reticularis lateralis area (NRL), a medullary vasopressive centre, at doses of 30 to 60 ng.kg-1 led to a significant reduction in mean arterial pressure (MAP) (17 +/- 4% and 36.5 +/- 6%) respectively without a significant change in heart rate. These effects lasted less than 2 hours. These results suggest a possible role of ET1 as a neuromodulator involved in the central regulation of vasomotor tone, in the NRL region.

Inhibition of prostaglandin synthesis does not affect contractile responses to noradrenaline, serotonin, angiotensin II nor endothelin-1 in human forearm isolated veins

1. The functional role of endogenous cyclo-oxygenase products was examined in the human forearm isolated vein. 2. Six healthy normal adult males (age > 18 years old) were recruited. Forearm veins were biopsied and ring segments mounted in standard organ baths for recording of isometric force. 3. Noradrenaline (-log molar EC50: 7.75 +/- 0.19; -log molar threshold concentration: 8.80 +/- 0.20), 5-hydroxytryptamine (-log molar EC50: 7.52 +/- 0.17; -log molar threshold concentration: 9.50 +/- 0.64), angiotensin II (-log molar threshold concentration: 9.00 +/- 0.28) and endothelin-1 (-log molar threshold concentration: 9.13 +/- 0.47) were equipotent in this preparation. Indomethacin (10 microM) had no effect on either the threshold concentration or EC50 of noradrenaline, 5-hydroxytryptamine nor the threshold concentration of angiotensin II nor endothelin-1. 4. Sodium nitroprusside (1 nM-10 microM) relaxed noradrenaline-precontracted preparations. Evidence of minimal endothelial influence was confirmed by the lack of relaxant response to acetylcholine (1 nM-10 microM). Histology using silver staining confirmed that endothelial cells were absent over greater than 90% of the lumen surface. 5. We conclude that endogenous prostanoids derived from smooth muscle cells, either released basally or agonist-stimulated, do not play a role in the regulation of vascular tone in the human forearm isolated vein.

Impaired binding properties of endothelin-1 receptors in human endometrial carcinoma tissue

BACKGROUND

Endothelins, potent stimulators of smooth muscle tissue activity, were recently shown to also function as mitogens for numerous cell types. The authors investigated the properties of endothelin-1 (ET-1) receptors in human endometrial tissue compared with human endometrial carcinoma tissue.

METHODS

Tissue samples from 13 patients with endometrial carcinoma and from 12 women undergoing hysterectomy due to uterus myomatous were obtained immediately after surgical removal. Binding properties of the endothelin receptors were studied using 125I-labeled ET-1.

RESULTS

A significant difference was demonstrated between binding properties of ET-1 receptors of these two groups. The mean maximal density (Bmax) value of the normal endometrial samples was 2029 +/- 341 fmol/mg protein, whereas that of the neoplastic samples was 356 +/- 121 fmol/mg protein. No differences were found, however, between the mean dissociation constant (Kd) values of these groups.

CONCLUSIONS

These results might be compatible with the increased blood flow that characterizes malignant endometrial tissue. However, they do not indicate an important mitogenic role for ET-1 in the development of endometrial cancer.

Is endothelin involved in the pathogenesis of hypertension?

Endothelins are a family of potent vasoconstrictor peptides released by endothelial cells. The production of endothelin-1 (ET-1) can be stimulated by aggregating platelets and angiotensin II. It is inhibited by increases in intracellular concentration of cyclic GMP. ET-1 causes biphasic changes in arterial blood pressure and of peripheral resistance in several vascular beds: an initial transient decrease (due to release of nitric oxide, prostacyclin, or both from the endothelium) followed by a sustained increase (mainly due to direct activation of vascular smooth muscle). The vasoconstriction induced by the peptide is inhibited by increases in cyclic GMP. Few studies, except in pregnant women with preeclampsia or eclampsia, indicate that the circulating levels of the peptide are augmented in hypertension. Likewise, the information available on changes in responsiveness to endothelins in blood vessels from hypertensive animals is controversial. Until the effect of selective antagonists on the production or action of the peptide can be determined in hypertensive patients, caution must be exerted when implying a role for endothelin in the pathophysiology of hypertension.

Sarafotoxins and endothelins: evolution, structure and function

The venom of the burrowing asp Atractaspis engaddensis contains several 21 amino acid residue peptides known as sarafotoxins. The sarafotoxins are homologous to the mammalian endothelin family, and they have similar biological activities. This review covers recent advances in the study of the chemical and biological properties of the sarafotoxins and endothelins.

Endothelin-1 receptors in the human myometrium: evidence for different binding properties in post-menopausal as compared to premenopausal and pregnant women

OBJECTIVE

We investigated the binding properties of the endothelin receptors in the human myometrium in clinical situations associated with different ovarian steroid levels.

SUBJECTS AND METHODS

Binding properties of the endothelin receptors were studied in myometrial membranes from post-menopausal women (n = 12), myomatous premenopausal women (n = 14) and pregnant women (n = 14), using 125I-labelled endothelin-1.

RESULTS

The mean (+/- SD) maximal receptor density (Bmax) was significantly higher in samples from premenopausal and pregnant women than from post-menopausal women (983 +/- 196, 1116 +/- 201 and 490 +/- 145 pmol/g protein, respectively). Receptor affinity (Kd) did not differ significantly between these groups. Among the pregnant women, mean Bmax and Kd values were similar in those who electively underwent Caesarean section prior to the onset of labour and those operated on during the second stage of spontaneous labour. Binding properties of myometrial membranes of either pre or post-menopausal women were unaffected by the presence of high levels of beta-oestradiol or progesterone in the medium. Among samples of premenopausal women, no significant difference was found in binding properties between those operated on either during mid-follicular phase or during mid-luteal phase.

CONCLUSIONS

In clinical situations associated with relatively high levels of ovarian steroids, the density of endothelin receptors in the myometrium is higher than in situations associated with low ovarian steroid level. Ovarian steroids may exert their influence via the production of other mediators. Changes in density of the endothelin receptor, induced by change in ovarian steroids activity, might play a role in the regulation of myometrial contractility.

Endothelin contracts human uterine myometrium by a partly dihydropyridine-sensitive mechanism

The effect of endothelin (ET), a recently discovered 21-amino-acid polypeptide with powerful vasoconstrictor properties, was examined on human uterine myometrial strips in vitro. ET dose-dependently (10(-11)-10(-7) M) increased the contractile force (monitored as contraction amplitude) of the myometrium with significant effects at 10(-8) and 10(-7) M. ET (10(-8) M and up) also increased the basal tone of the myometrium. The calcium channel blocking agents nifedipine (10(-7) M) and diltiazem (10(-6) M) both inhibited the spontaneous tonic contractions of the myometrium. When ET was given in the presence of nifedipine, the tonic contractions were further inhibited, whereas the ET-induced increase in basal tone remained. The same result was obtained with diltiazem (10(-6) M). The results indicate that the contractility of human myometrium may be modulated by ET, and that the effects of ET on the human myometrium are only partly mediated by dihydropyridine-sensitive calcium channels.

Role of endothelium in endothelin-evoked contractions in the rat aorta

We designed experiments to determine the role of endothelium-derived contracting factor or factors in the response to endothelin-1 and endothelin-3 in the aorta of normotensive and hypertensive rats. Rings of thoracic aortas, with and without endothelium, from normotensive and spontaneously hypertensive rats were suspended in organ chambers for recording of isometric tension in the presence of nitro-L-arginine, an inhibitor of nitric oxide synthase. The removal of endothelium decreased the contractions evoked by both endothelins in the aorta of spontaneously hypertensive but not of normotensive rats. Indomethacin (inhibitor of cyclooxygenase), dazoxiben (inhibitor of thromboxane synthase), and SQ-29,548 (antagonist of thromboxane A2 receptors) reduced, in aortic rings of spontaneously hypertensive rats, the contractions to endothelins in rings with but not in those without endothelium, whereas their effect was not endothelium-dependent in tissues of normotensive rats. BQ-123, a selective endothelin-A receptor antagonist, shifted the concentration-response curve to endothelin-1 to the right in a concentration-dependent manner and abolished the endothelium-dependent component of the contractions evoked by the peptide. The presence of the endothelium increased the basal and endothelin-stimulated release of thromboxane B2, the stable metabolite of thromboxane A2, in aortas of spontaneously hypertensive rats but not in those of normotensive rats. These data suggest that endothelium-derived thromboxane A2 contributes to contractions evoked by endothelin-1 and endothelin-3 in the aorta of the spontaneously hypertensive rat but not in that of the normotensive rat. Both the receptors on the endothelial cells (mediating the release of thromboxane A2) and those on vascular smooth muscle belong to the endothelin-A subtype.

Effects of endothelin-1 on signal transduction in UMR-106 osteoblastic cells

Endothelin-1 is now recognized to affect the functions of a number of tissues and to activate calcium/phospholipid second messenger pathways in target cells. In the present study, we characterized its effects on signal transduction in UMR-106 cells. To study calcium transients elicited by endothelin-1, cells were loaded either with fluo-3 (for the measurement of cytosolic free calcium) or chlortetracycline (for the measurement of intracellularly stored calcium) as fluorescent probes. Intracellular production of inositol phosphates and cyclic AMP was also measured. Endothelin-1 elicited dose-dependent cytosolic calcium transients with an ED50 of 20 nM. This effect was also seen in EGTA-containing or calcium-free medium; however, the signals were reduced in magnitude. The dihydropyridine calcium channel antagonist nifedipine did not affect the response. Repeated administration of endothelin-1 resulted in homologous desensitization of the response. A 4 minute pretreatment with phorbol ester reduced the initial response to endothelin-1 in both calcium-containing and calcium-free media. A 24 h pretreatment with indomethacin had no effect on response. Using chlortetracycline as an indicator, a significant reduction in intracellularly stored calcium by endothelin-1 was observed. This was prevented by 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate, a blocker of calcium release from internal stores. Endothelin-1 also stimulated the dose-dependent production of inositol phosphates by UMR-106 cells. Indomethacin was also without effect on this process. The increase in inositol trisphosphates was seen within the same time frame as the increase in cytosolic calcium. Endothelin-1 did not influence cyclic AMP production over 5 minutes in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the contractile effects of endothelin-1 and sarafotoxin S6b in goat isolated cerebral arteries

1. The effects of endothelium-derived endothelin-1 and snake venom-derived sarafotoxin S6b, peptides with striking structural and functional similarities, were examined and compared in isolated middle cerebral arteries of goats. 2. Endothelin-1 and sarafotoxin S6b contracted cerebral arteries in a concentration-dependent manner. The potency of endothelin-1 (EC50 = 4.9 (3.9-6.2) x 10(-10) M) was about ten times higher than that of sarafotoxin S6b (EC50 = 5.5 (4.4-6.9) x 10(-9) M). The tension returned to basal values after repeated washings and contraction with endothelin-1 could be reproduced. Endothelin-1 and sarafotoxin S6b induced further contraction in arteries precontracted with prostaglandin F2 alpha (10(-5) M). 3. Mechanical removal of the endothelium or incubation with indomethacin (10(-5) M) displaced the concentration-response curves to endothelin-1 and, more pronouncedly, to sarafotoxin S6b to the left. The maximum response to sarafotoxin S6b was also increased by either of these two treatments. 4. Incubation in 'nominally' Ca(2+)-free medium attenuated the vasoconstrictor response to endothelin-1 but not to sarafotoxin S6b, which was inhibited after incubation in Ca(2+)-free medium to which EGTA (10(-4) M) had been added. Pretreatment with caffeine (2 x 10(-2) M) in Ca(2+)-free medium abolished responses to endothelin-1 and sarafotoxin S6b. 5. Bay K 8644 (10(-10) M, 10(-8) M) enhanced and nicardipine (10(-10) M, 10(-8) M) inhibited in a concentration-dependent manner vasoconstrictor response to endothelin-1. Response to sarafotoxin S6b was only affected by 10(-8) M Bay K 8644 or nicardipine.6. It is concluded that endothelin-1 and sarafotoxin S6b are potent vasoconstrictors of goat cerebral arteries, having direct effects on smooth muscle which are counteracted by the endothelium through the release of a vasodilatator substance, probably prostacyclin. Both endothelin-l and sarafotoxin S6b depend on extracellular Ca2+ and on intracellular, caffeine-sensitive Ca2+ stores to develop vasoconstriction.However, endothelin-l depends to a larger extent than sarafotoxin S6b on free extracellular Ca2+.

Rat gastric relaxation induced by stimulation of endothelin-1 selective receptors

We have investigated the smooth muscle activity of ET-1 and ET-3 on rat fundus strips in vitro as well as the effects of the peptides on gastric motility in vivo. In the isolated tissue with no precontraction ET-1 and ET-3 were potent spasmogens which produced half maximal contractions at concentrations 4.5 and 8.0 nM, respectively. In contrast, under conditions where the isolated tissue was precontracted to approx. 50% of maximum by prostaglandin E2, ET-1 dose-dependently (5 x 10(-10) - 10(-8) M) and temporarily relaxed the fundus strip, whereas ET-3 further increased the contraction. The relaxing capacity of ET-1 was absent when the tissue was precontracted by potassium yet was resistant to pretreatments with tetrodotoxin, capsaicin, propranolol, indomethacin, NG-methyl-L-arginine or glibenclamide. In addition in vivo ET-1 and ET-3 (less than 1 nmol/kg) showed opposite effects on gastric motility as the former reduced basal tonus and spontaneous activity, whereas the latter increased the motor activity of the gastric ventricle. The results support the notion that ET-1 may induce gastric relaxation by stimulation of selective receptors whereas stimulation of nonselective receptors may promote gastric smooth muscle contraction.

Effect of endothelin on production of cerebrospinal fluid in rabbits

BACKGROUND AND PURPOSE

Endothelin is a potent vasoconstrictor in several tissues, including the choroid plexus. The goal of this study was to determine whether endothelin affects the production of cerebrospinal fluid.

METHODS

Ventriculocisternal perfusion was used to measure the production of cerebrospinal fluid in anesthetized rabbits. Changes in production of cerebrospinal fluid were examined in response to vehicle, intravenous endothelin (alone and in the presence of indomethacin), and intraventricular endothelin.

RESULTS

Under control conditions, the reduction in production of cerebrospinal fluid in response to endothelin administered intravenously was only modestly greater than that during infusion of vehicle. Because endothelin releases cyclooxygenase products that attenuate the direct effects of endothelin in several tissues, effects of endothelin on the production of cerebrospinal fluid were also examined after inhibition of cyclooxygenase. Production of cerebrospinal fluid in response to 1 micrograms/kg i.v. endothelin was reduced more in animals treated with indomethacin than in untreated animals (-34 +/- 7% [mean +/- SEM] versus -14 +/- 6%, p less than 0.05). Thus, effects of endothelin on the production of cerebrospinal fluid are attenuated by cyclooxygenase products. Finally, responses to intraventricular endothelin were examined. Intraventricular endothelin produced a modest, but significant, reduction in the production of cerebrospinal fluid.

CONCLUSIONS

In summary, endothelin may play a role in regulation of the brain fluid balance by affecting the rate of production of cerebrospinal fluid, and this effect is modulated by cyclooxygenase products.

The actions of endothelins-1 and -3 on the vascular and capsular smooth muscle of the isolated blood perfused spleen of the dog

1. Endothelin-1 (ET-1), endothelin-3 (ET-3) and noradrenaline (NA) were administered as intra-arterial bolus injections into the isolated, blood-perfused spleen of the dog to assess agonist properties and relative molar potencies on the vascular and capsular smooth muscle. 2. An initial small vasodilatation was observed occasionally at low doses (1.0-10 pmol) of ET-1. 3. ET-1, ET-3 and NA all caused graded increases in splenic arterial vascular resistance. The molar ED50 for the splenic vasoconstrictor response to ET-1 was significantly less (P less than 0.001) than that to ET-3; both peptides were significantly more potent as vasoconstrictor agents than NA. The maximum increase in splenic arterial vascular resistance was not significantly different for either ET-1, ET-3 or NA. 4. The time course of the splenic vasoconstrictor response to ET-1 was significantly (P less than 0.01) longer than that to equieffective doses of ET-3 or NA. 5. The splenic vasoconstrictor responses to ET-1 and ET-3 were accompanied by reductions in spleen volume. The rank order of molar potency in causing splenic capsular contraction was ET-1 greater than ET-3 greater than NA. The maximum reduction in splenic volume was significantly greater for NA than for either ET-1 or ET-3. The two peptides (ET-1, ET-3) were equiefficacious in contracting splenic capsular smooth muscle. 6. The high molar potency of ET-1 as a splenic arterial vasoconstrictor, over 1,700 times more potent than NA, suggests that it may play an important local role in the control of splenic haemodynamics.

Endothelins and sarafotoxins: effects on motility, binding properties and phosphoinositide hydrolysis during the estrous cycle of the rat uterus

The effects of four peptides of the endothelin/sarafotoxin (ET/SRTX) family on the motility of the rat uterus were examined during the different stages of the estrous cycle. ET-1, ET-3, SRTX-b and SRTX-c showed similar effects on the contraction of the uterus: a slight increase in the maximum tension of the spontaneous rhythmic contractions, a suppression of the relaxation phase of these contractions and an increase in their rate. All three effects were concentration dependent. Of the four peptides, ET-1 and SRTX-b showed the highest potency and efficacy, suggesting that among the various peptides of this family so far studied, ET-1 and SRTX-b are the two full agonists. The rank order of susceptibility of the different stages was, in most cases: proestrus greater than estrus greater than metestrus. Freshly excised diestrus uteri showed no spontaneous contractions and did not respond to any of the peptides. The binding potency of ET-1 and SRTX-b to uterine membranes was similar at the various estrous stages, but their maximal binding decreased gradually from proestrus to diestrus. All four peptides induced phosphoinositide (PI) hydrolysis in uterine slices at all four different stages, with ET-1 and SRTX-b again being more potent than ET-3 or SRTX-c. The maximal PI hydrolysis correlated with the increased rate of the rhythmic contractions. It is suggested that the reaction of the rat uterus to the ET/SRTX peptides depends on its hormonal status and that ET may act in concert with steroid hormones in the modulation of the estrous cycle.

Endothelins. Myocardial actions of a new class of cytokines

There is growing evidence to support the existence of a dynamic interaction in vivo between cardiac myocytes and adjacent microvascular endothelial cells in the regulation of both cardiac myocyte and possibly endothelial cell phenotype and function. Endothelins may be only one of several endogenous cytokines or autocoids that are released by the cardiac microvascular and/or endocardial endothelium and transported vectorially to adjacent myocytes that could modify cardiac contractile state, perhaps in response to changes in microvascular blood flow. Similarly, cardiac myocytes themselves could release cytokines that could directly affect endothelial cell proliferation or angiogenesis and indirectly elicit or modify the release of endothelium-derived cytokines and autocoids. Thus, in addition to modifying function, endothelial cell-cardiac myocyte interactions may also be of importance in the dynamic events that lead to myocardial wall remodeling and angiogenesis during hypertrophic growth and in the response to cardiac injury.

Response of rabbit ear artery to endothelin-1 during cooling

1. The effects of cooling on the response of rabbit central ear artery to endothelin-1 and the role of the endothelium in these effects were studied in 2 mm long cylindrical arterial segments. 2. Concentration-response curves for endothelin-1 (10(-10)-3 x 10(-7) M) were recorded isometrically in arteries with and without endothelium at 37 degrees C and during cooling (24 degrees C). To analyze further the endothelial mechanisms of the response to endothelin-1 during cooling, the effects of this peptide in the presence of NG-nitro-L-arginine methyl ester (L-NAME) (10(-4) M) or meclofenamate (10(-5) M) were also determined. 3. In every condition tested, endothelin-1 produced a marked, concentration-dependent arterial contraction. Sensitivity of intact arteries to this peptide was consistently lower at 24 degrees C than at 37 degrees C. At 37 degrees C there were comparable responses of arteries with and without endothelium, but at 24 degrees C arteries without endothelium showed a higher sensitivity than intact arteries to endothelin-1. 4. L-NAME (10(-4) M) increased the maximal contraction at 37 degrees C, and both the sensitivity and maximal contraction at 24 degrees C of intact arteries to endothelin-1. Meclofenamate (10(-5) M) did not affect the arterial response to endothelin-1. 5. Sensitivity of arteries with and without endothelium to nitroprusside (10(-9)-10(-3) M) was significantly decreased during cooling, and endothelium removal did not affect the relaxation to this nitrovasodilator. 6. These results suggest that cooling decreases sensitivity of cutaneous arteries (ear artery) to endothelin-1 probably by increasing the availability of endothelial nitric oxide.

Involvement of the microtubular system in the endothelin-1 secretion from porcine aortic endothelial cells

The effects of certain microtubule-disrupting agents on endothelin-1 (ET-1) secretion from porcine aortic endothelial cells were studied. When endothelial cells were treated with thrombin (1 unit/mL), a significant increase in ET-1 secretion was detected in the incubation medium, while ET-1 secretion in the medium was diminished when the cells were treated simultaneously with either colchicine or vinblastine (10(-8)-10(-6) M). In such cases, however, the ET-1 content detected in the cells increased dose-dependently in accordance with the concentrations of the microtubule-disrupting agents. The intracellular accumulation of ET-1 was observed both in mitochondrial and microsomal fractions. On the other hand, thrombin produced a significant increase in polymerized tubulin content without affecting the total tubulin content. A thrombin-induced increase in the intracellular Ca2+ concentration of endothelial cells was inhibited by treatment with either colchicine or vinblastine. These results seem to indicate that the microtubular system may play an important role in ET-1 secretion from endothelial cells.

Pharmacological modulation of endothelin-induced contraction of guinea-pig isolated airways and thromboxane release

1. The aim of the present experiments was to study the possible involvement of known bronchoconstrictor substances in mediating the myotropic action of endothelin-1 (ET-1, human-porcine endothelin) in guinea-pig isolated airways. 2. ET-1 (1-100 nM) caused a dose-dependent contraction of guinea-pig trachea, upper bronchus and parenchyma. The contractions developed slowly, reaching maximal values 4-6 min after addition of the peptide. 3. The contractile action of ET-1 was significantly attenuated by indomethacin (10 microM), a cyclo-oxygenase blocker. BM 13505 (5 microM), a thromboxane receptor antagonist, FPL 55712 (19 microM) and YM 16638 (1 microM), antagonists of the sulphidopeptide leukotrienes, BN 52021 (10 microM) and WEB 2086 (1 microM), platelet-activating factor receptor antagonists in all three tissue preparations studied. 4. Pretreatment of the airway tissues with compound U 75302 (3 microM), a selective leukotriene B4 receptor antagonist, or with a mixture of antagonists containing methysergide (0.75 microM), phentolamine (0.4 microM), propranolol (13 microM), atropine (0.4 microM) and diphenhydramine (0.45 microM) did not modify the myotropic action of ET-1. 5. ET-1, 10 and 100 nM induced three, and nine fold increases in thromboxane A2 release from lung parenchymal strips. 6. ET-1-induced thromboxane A2 release was completely abolished by indomethacin, and was significantly attenuated by BN 52021, WEB 2086 and FPL 55712. Neither BM 13505 nor YM 16638 exerted a significant effect on thromboxane release. 7. The present findings show that contraction of guinea-pig airway smooth muscle by ET-1 is mediated, in part, by the release of thromboxane A2, sulphidopeptide leukotrienes and platelet-activating factor, and suggest that the increased thromboxane A2 release following ET-1 is partly a consequence of enhanced synthesis of sulphidopeptide leukotrienes and platelet-activating factor.