Abstract: A 43-year-old woman was admitted to the Ospedali Riuniti Bergamo for a renal biopsy to evaluate a rising serum creatinine 14 months after receiving a cadaveric renal allograft at the same institution. The patient initially had developed renal failure due to chronic glomerulonephritis (proliferative extracapillary glomerulonephritis) and hypertension, which required chronic hemodialysis beginning 10 years ago. After receiving a kidney transplant 7 years ago, she received immunosuppressive treatment with cyclosporine (Sandimmune), azathioprine, and prednisone. The renal allograft functioned well initially; the serum creatinine concentration fell to 1.2 mg/dL on day 4 but rose to 2.1 mg/dL on day 22. The blood cyclosporine (CsA) level was 323 ng/mL. A clinical diagnosis of acute graft rejection prompted the initiation of methylprednisolone pulse therapy. Her renal function gradually recovered; beginning on the 34th postoperative day, the serum creatinine level stabilized at a baseline of 1.0 mg/dL to 1.2 mg/dL over the next 13 months. A CsA pharmacokinetic profile performed on day 32 documented an area-under-the-blood concentration-time curve (AUC) of 9722 ng/mL/h, a blood CsA trough level of 357 ng/mL, and a peak blood CsA concentration of 1897 ng/mL (one hour after dosing). Along with immunosuppressants given from the immediate post-transplant period, a calcium-channel blocker also was administered to control blood pressure. Two months after transplantation, her blood pressure still was not well controlled, and a beta blocker was added to the antihypertensive therapy. Approximately six months after surgery, the serum creatinine was 1.0 mg/dL, and proteinuria was virtually absent (0.12 g/day). The patient did well until one month before admission; the serum creatinine then rose slowly from 1.2 mg/dL to 2.0 mg/dL. On admission to the hospital, her blood pressure was 110/80 mm Hg; the renal graft was neither swollen nor tender. The CsA level was 169 ng/mL and her serum creatinine concentration was 2.1 mg/dL. Renal function, estimated by the plasma clearance of nonradiolabeled iohexol, was 49 mL/min/1.73 m2; renal plasma flow, measured by the renal clearance of para-aminohippuric acid, was 208 mL/min/1.73 m2. A percutaneous renal biopsy disclosed normal glomeruli and arterioles. Focal isometric vacuolization of proximal tubules was observed. Prominent tubular atrophy and striped interstitial fibrosis were present. Mild focal collection of mononuclear cells in the interstitium also was documented. Intense staining for endothelin-1 (ET-1) mRNA by in situ hybridization was found in tubules but not in glomeruli, which were essentially negative for the ET-1 mRNA signal. High-intensity signal for ET-1 mRNA was mainly observed in the epithelial cells of tubules located in areas of interstitial fibrosis. Staining for MCP-1 mRNA also was selectively localized in tubules. In addition, the tubules stained markedly for RANTES mRNA, which was also detected minimally in glomeruli. Dr. Ariela Benigni (Head, Department of Molecular Medicine, Mario Negri Institute for Pharmacological Research, Bergamo, Italy): In the last 20 years, it has become clear that the endothelium participates directly in regulating vascular tone through the release of a wide variety of vasoactive substances. The discovery of prostacyclin in 19761Moncada S. Gryglewski R. Bunting S. Vane J.R. An enzyme isolated from arteries transforms prostaglandin endoperoxides to an unstable substance that inhibits platelet aggregation.Nature. 1976; 263: 663-665Crossref PubMed Scopus (2840) Google Scholar was followed in 1980 by evidence that the endothelium regulates vascular smooth muscle tone by elaborating potent endothelium-dependent vasodilators2Furchgott R.F. Zawadzki J.V. The obligatory role of endothelial cells in the relaxation of arterial smooth muscle by acetylcholine.Nature. 1980; 288: 373-376Crossref PubMed Scopus (9605) Google Scholar. Rubanyi and Vanhoutte reported in 1985 that hypoxia induces release of a diffusible vasoconstrictor substance from endothelial cells independent of prostaglandin synthesis3Rubanyi G.M. Vanhoutte P.M. Hypoxia releases a vasoconstrictor substance from the canine vascular endothelium.J Physiol. 1985; 364: 45-56Crossref PubMed Scopus (359) Google Scholar. But it was not until 1988 that Yanagisawa and coworkers isolated from porcine aortic endothelial cells an extremely potent vasoconstrictor that they identified as endothelin-1 (ET-1)4Yanagisawa M. Kurihara H. Kimura S. Tomobe Y. Kobayashi M. Mitsui Y. Yazaki Y. Goto K. Masaki T. A novel potent vasoconstrictor peptide produced by vascular endothelial cells.Nature. 1988; 322: 411-415Crossref Scopus (9964) Google Scholar. Endothelin-1 belongs to a family of peptides comprising two other isopeptides: endothelin-2 and endothelin-3. Each isopeptide contains 21 amino acids, two intrachain disulfide bonds constraining the overall structure, and a conserved C-terminal sequence necessary for biologic activity5Inoue A. Yanagisawa M. Kimura S. Kasuya Y. Miyauchi T. Goto K. Masaki T. The human endothelin family: Three structurally and pharmacologically distinct isopeptides predicted by three separate genes.Proc Natl Acad Sci USA. 1989; 86: 2863-2867Crossref PubMed Scopus (2508) Google Scholar. Screening of a genomic DNA library allowed cloning of three distinct human endothelin-related genes located in different chromosomes in human as well as in porcine and rat genomes, each encoding a specific precursor for one of the three mature isoforms. The 5′ gene-flanking region of the human ET-1 precursor contains consensus motifs for the binding sites of the fos/jun complex, activating protein 1, and nuclear factor 1, the latter two possibly mediating angiotensin II and transforming growth factor-β (TGF-β) induction of ET-1. Sequences for the acute-phase reactant regulatory elements probably involved in ET-1 induction under acute physical stress in vivo are also expressed. The 3′ region contains a sequence that regulates selective destabilization of the ET-1 precursor mRNA, possibly accounting for its short half-life5Inoue A. Yanagisawa M. Kimura S. Kasuya Y. Miyauchi T. Goto K. Masaki T. The human endothelin family: Three structurally and pharmacologically distinct isopeptides predicted by three separate genes.Proc Natl Acad Sci USA. 1989; 86: 2863-2867Crossref PubMed Scopus (2508) Google Scholar. These sites potentially regulate ET-1 synthesis at the transcriptional level. The product of the ET-1 gene transcription is preproendothelin-1, consisting of 212 amino acid residues. It is cleaved at two sites by a neutral endopeptidase forming the biologically inactive precursor big endothelin, which ultimately is converted to the mature peptide by a phosphoramidon-sensitive membrane-bound metalloprotease called endothelin-converting enzyme (ECE). Three different ECE-1 isoforms differing in their N-terminal regions derive from a single gene through the use of alternative promoters6Schweizer A. Valdenaire O. Nelbock P. Deuschle U. Dumas Milne Edwards J.-B. Stumpf J.G. Loffler B.-M. Human endothelin-converting enzyme (ECE-1): Three isoforms with distinct subcellular localizations.Biochem J. 1997; 328: 871-877Crossref PubMed Scopus (188) Google Scholar. Immunofluorescence microscopy showed distinct subcellular localizations: ECE-1a and ECE-1c are localized at the cell surface, whereas ECE-1b resides intracellularly, possibly in the trans-Golgi network6Schweizer A. Valdenaire O. Nelbock P. Deuschle U. Dumas Milne Edwards J.-B. Stumpf J.G. Loffler B.-M. Human endothelin-converting enzyme (ECE-1): Three isoforms with distinct subcellular localizations.Biochem J. 1997; 328: 871-877Crossref PubMed Scopus (188) Google Scholar. Transfer experiments of ECE-1 cDNA to Chinese hamster ovary cells that normally secrete only big ET-1 revealed that the extracellular form of ECE-1 cleaves the big ET-1 supplied from outside the cell, whereas the intracellular form of ECE-1 converts endogenously produced ET-17Xu D. Emoto N. Giaid A. Slaughter C. Kaw S. deWit D. Yanagisawa M. ECE-1: A membrane-bound metalloprotease that catalyzes the proteolytic activation of big endothelin-1.Cell. 1994; 78: 473-485Abstract Full Text PDF PubMed Scopus (845) Google Scholar. This arrangement possibly explains why ET-1 is generally thought to be a paracrine and autocrine, rather than a circulating, hormone. Two distinct secretory pathways for the transport and release of ET-1 have been proposed on the basis of immunoelectron microscopic localization of the peptide in human umbilical vein endothelial cells8Russell F.D. Skepper J.N. Davenport A.P. Human endothelial cell storage granules: A novel intracellular site for isoforms of the endothelin-converting enzyme.Circ Res. 1998; 83: 314-321Crossref PubMed Scopus (102) Google Scholar as well as in human coronary artery cells9Russell F.D. Skepper J.N. Davenport A.P. Evidence using immunoelectron microscopy for regulated and constitutive pathways in the transport and release of endothelin.J Cardiovasc Pharmacol. 1998; 31: 424-430Crossref PubMed Scopus (63) Google Scholar. Endothelin-1 is continuously transported in and released from secretory vesicles by the constitutive pathway through a cAMP-independent mechanism. Endothelin-1 is also stored in Weiber-Palade bodies with other vasoactive compounds and is released at the cell surface after an appropriate stimulus. Endothelin-1 is synthesized not only in the endothelial and smooth muscle cells of blood vessels but also in the kidney (mesangial, endothelial, and epithelial cells), heart, brain, lung, pancreas, and spleen5Inoue A. Yanagisawa M. Kimura S. Kasuya Y. Miyauchi T. Goto K. Masaki T. The human endothelin family: Three structurally and pharmacologically distinct isopeptides predicted by three separate genes.Proc Natl Acad Sci USA. 1989; 86: 2863-2867Crossref PubMed Scopus (2508) Google Scholar. Secretion of the peptide by endothelial and epithelial cells is predominantly toward the basolateral side10Wagner O.F. Christ G. Wojta J. Vierhapper J. Parzer S. Nowotney P.J. Schneider B. Waldhausl W. Binder B. Polar secretion of endothelin-1 by cultured endothelial cells.J Biol Chem. 1992; 267: 16066-16068Abstract Full Text PDF PubMed Google Scholar,11Zoja C. Morigi M. Figliuzzi M. Bruzzi I. Oldroyd S. Benigni A. Ronco P.M. Remuzzi G. Proximal tubular cell synthesis and secretion of endothelin-1 on challenge with albumin and other proteins.Am J Kidney Dis. 1995; 26: 934-941Abstract Full Text PDF PubMed Scopus (218) Google Scholar. Angiotensin II, TGF-β, interleukin-1, adrenalin, insulin, and physicochemical factors such as hypoxia stimulate ET-1 synthesis; nitric oxide, natriuretic peptides, vasodilatory prostanoids, and increased shear stress inhibit ET-1 generation12Noris M. Morigi M. Donadelli R. Aiello S. Foppolo M. Todeschini M. Orisio S. Remuzzi G. Remuzzi A. Nitric oxide synthesis by cultured endothelial cells is modulated by flow conditions.Circ Res. 1995; 76: 536-543Crossref PubMed Scopus (447) Google Scholar. Because endothelin is hydrophilic and therefore unable to cross the plasma membrane, it must bind to specific cell surface receptors, the expression of which governs cell response to the peptide. Distinct endothelin isoforms with diverse functions predicted the existence of distinct receptors: indeed, two have been identified as seven transmembrane domain G protein-coupled receptors13Arai H. Hori S. Aramori I. Ohkubo H. Nakanishi S. Cloning and expression of a cDNA encoding an endothelin receptor.Nature. 1990; 348: 730-732Crossref PubMed Scopus (2472) Google Scholar,14Sakurai T. Yanagisawa M. Inoue A. Ryan U.S. Kimura S. Mitsui Y. Goto K. Masaki T. cDNA cloning, sequence analysis and tissue distribution of rat preproendothelin-1 mRNA.Biochem Biophys Res Commun. 1991; 175: 44-47Crossref PubMed Scopus (233) Google Scholar. Endothelin type-A receptor (ETA) has higher affinity for ET-1 and ET-2 and lower for ET-3; ETB, the type-B receptor, binds the three isopeptides with nearly identical affinity. The ETA receptors reside in vascular smooth muscle cells and mediate vasoconstriction and cell proliferation, whereas the ETB receptors on endothelial cells mediate vasodilation via nitric oxide. A variety of additional functions have been attributed to ETB receptors, however; in certain instances, they even can elicit vessel contraction15Moreland S. McMullen D.M. Delaney C.L. Lee V.G. Hunt J.T. Venous smooth muscle contains vasoconstrictor ETB-like receptors.Biochem Biophys Res Commun. 1992; 184: 100-106Crossref PubMed Scopus (250) Google Scholar. Clearance of ET-1 from the circulation also appears linked to ETB receptors16Fukuroda T. Fujikawa T. Ozaki S. Ishikawa K. Yano M. Nishikibe M. Clearance of circulating endothelin-1 by ETB receptors in rats.Biochem Biophys Res Commun. 1994; 199: 1461-1465Crossref PubMed Scopus (580) Google Scholar. Moreover, the ETB receptor initiates a positive autocrine loop by which ET-1 regulates its own gene expression by increasing preproET-1 transcription and mRNA stability17Saijonmaa O. Nyman T. Fyhrquist F. Endothelin-1 stimulates its own synthesis in human endothelial cells.Biochem Biophys Res Commun. 1992; 188: 286-291Crossref PubMed Scopus (66) Google Scholar,18Iwasaki S. Homma T. Matsuda Y. Kon V. Endothelin receptor subtype B mediates autoinduction of endothelin-1 in rat mesangial cells.J Biol Chem. 1995; 270: 6997-7003Crossref PubMed Scopus (88) Google Scholar. Coupling of activated receptors to diverse effector systems generates second messengers. These second messengers include inositol phosphates, diacylglycerols, and calcium and are ultimately responsible for the biologic effects of the peptide. Endothelin-producing tissues all express specific binding sites. Thus, ET is likely subject to local rather than circulating hormone-type regulation. Plasma concentration of endothelins is consistently in the picomolar order, far below the pharmacologic threshold. Specific binding sites for endothelin have been identified in numerous fetal and adult organs including lung, heart, brain, and kidney19Benigni A. Remuzzi G. Endothelin antagonists.Lancet. 1999; 353: 133-138Abstract Full Text Full Text PDF PubMed Scopus (240) Google Scholar. Rat cardiac atrium contains ETA receptors as a major component, but ETB receptors have been reported as well. In brain, the ETB receptor appears the predominant subtype. The relative abundance of ETA and ETB receptors in the kidney depends on the species19Benigni A. Remuzzi G. Endothelin antagonists.Lancet. 1999; 353: 133-138Abstract Full Text Full Text PDF PubMed Scopus (240) Google Scholar. The ETA/ETB ratio approaches one in rats, but in humans ETB largely prevails in renal tubules19Benigni A. Remuzzi G. Endothelin antagonists.Lancet. 1999; 353: 133-138Abstract Full Text Full Text PDF PubMed Scopus (240) Google Scholar and appears related to many physiologic functions including sodium excretion. Bolus injections of nanomolar amounts of ET-1, ET-2, and ET-3 initially lower blood pressure. This decrease results from a transient induction of prostacyclin and nitric oxide release from endothelial cells upon endothelial binding of endothelin to specific receptors20De Nucci G. Thomas R. D'orleans-Juste P. Antunes E. Walder C. Warner T.D. Vane J.R. Pressor effects of circulating endothelin are limited by its removal in the pulmonary circulation and by the release of prostacyclin and endothelium-derived relaxing factor.Proc Natl Acad Sci USA. 1988; 85: 9797-9800Crossref PubMed Scopus (1350) Google Scholar. The dose-dependent, remarkable increase in systemic blood pressure that follows4Yanagisawa M. Kurihara H. Kimura S. Tomobe Y. Kobayashi M. Mitsui Y. Yazaki Y. Goto K. Masaki T. A novel potent vasoconstrictor peptide produced by vascular endothelial cells.Nature. 1988; 322: 411-415Crossref Scopus (9964) Google Scholar,5Inoue A. Yanagisawa M. Kimura S. Kasuya Y. Miyauchi T. Goto K. Masaki T. The human endothelin family: Three structurally and pharmacologically distinct isopeptides predicted by three separate genes.Proc Natl Acad Sci USA. 1989; 86: 2863-2867Crossref PubMed Scopus (2508) Google Scholar is prolonged and mostly dependent on renal, mesenteric, and muscular vessel constriction and is sustained by an increased cardiac output. The increase in cardiac output is a direct effect of endothelin, as it is not inhibited by adrenergic receptor blockers or indomethacin. By contrast, the pulmonary circulation is far less sensitive to the pressor effect of endothelins21Lippton H.L. Hauth T.A. Summer W.R. Hyman A.L. Endothelin produces pulmonary vasoconstriction and systemic vasodilation.J Appl Physiol. 1989; 66: 1008-1012PubMed Google Scholar and plays a marginal role in the resultant increase in systemic blood pressure. Endothelin of central nervous system origin also might increase arterial pressure22Siren A.L. Feuerstein G.Z. Haemodynamic effects of endothelin after systemic and central nervous system administration in the conscious rat.Neuropeptides. 1989; 14: 231-236Abstract Full Text PDF PubMed Scopus (33) Google Scholar. Systemic, but not renal, pressor effects of ET-1 were abolished by a selective ETA receptor antagonist in rats23Pollock D.M. Opgenorth T.J. Evidence for endothelin-induced renal vasoconstriction independent of ETA receptor activation.Am J Physiol. 1993; 264: R222-R226PubMed Google Scholar. On the other hand, both systemic and renal vasoconstriction were prevented by a nonselective ETA and ETB receptor antagonist. This difference suggests a role for ETB receptor in the renal response to ET-1. In humans, ET-1 infusion causes profound renal vasoconstriction in healthy volunteers24Rabelink T.J. Kasajager K.A.H. Boer P. Stroes E.G. Braam B. Koomans H.A. Effects of endothelin-1 on renal function in humans: Implications for physiology and pathophysiology.Kidney Int. 1994; 46: 376-381Abstract Full Text PDF PubMed Scopus (130) Google Scholar, whose systemic blood pressure was negligibly affected25Sorensen S.S. Madsen J.K. Pedersen E.B. Systemic and renal effect of intravenous infusion of endothelin-1 in healthy human volunteers.Am J Physiol. 1994; 266: F411-F418PubMed Google Scholar. Available data in humans point strongly to a unique susceptibility of renal vessels to ET-1 vasoconstriction. Endothelin, by its major interaction with volume regulatory hormones, takes part in volume homeostasis by increasing plasma renin activity26Miller W.L. Redfield M.M. Burnett J.C. Integrated cardiac, renal, and endocrine actions of endothelin.J Clin Invest. 1989; 83: 317-320Crossref PubMed Scopus (484) Google Scholar and stimulating aldosterone secretion26Miller W.L. Redfield M.M. Burnett J.C. Integrated cardiac, renal, and endocrine actions of endothelin.J Clin Invest. 1989; 83: 317-320Crossref PubMed Scopus (484) Google Scholar. Data that endothelin augments atrial natriuretic peptide and inhibits peripheral nerve norepinephrine release highlight the complex interplay of endothelin with volume regulatory hormones27Simonson M.S. Dunn M.J. Renal actions of endothelin peptides.Curr Opin Nephrol Hypertens. 1993; 2: 51-60Crossref PubMed Scopus (23) Google Scholar. To add to the complexity, endothelin affects sodium and water balance, so that its renal effects add to the ones of angiotensin II (Ang II), aldosterone, vasopressin, and atrial natriuretic peptide in regulating volume homeostasis27Simonson M.S. Dunn M.J. Renal actions of endothelin peptides.Curr Opin Nephrol Hypertens. 1993; 2: 51-60Crossref PubMed Scopus (23) Google Scholar. Besides its vasoactive and hormonal properties, ET-1 increases c-fos and c-myc mRNA levels and proliferation of cultured vascular smooth muscle cells28Komuro I. Kurihara H. Sugiyama T. Takaku F. Yazaki Y. Endothelin stimulates c-fos and c-myc expression and proliferation of vascular smooth muscle cells.FEBS Lett. 1988; 238: 249-252Abstract Full Text PDF PubMed Scopus (673) Google Scholar,29Bobik A. Grooms A. Millar J.A. Mitchell A. Grinpukel S. Growth factor activity of endothelin on vascular smooth muscle.Am J Physiol. 1990; 258: C408-C415PubMed Google Scholar and stimulates mitogenesis in human umbilical vein endothelial cells30Takagi N. Fukase M. Takata S. Yoshimi H. Tokunaga O. Fujita T. Autocrine effect of endothelin on DNA synthesis in human vascular endothelial cells.Biochem Biophys Res Commun. 1990; 168: 537-543Crossref PubMed Scopus (58) Google Scholar. Further, ET-1 is a strong mitogen for mesangial cells31Simonson M.S. Wann S. Mené P. Dubyak G.R. Kester M. Nakazato Y. Sedor J.R. Dunn M.J. Endothelin stimulates phospholipase C, Na+/H+ exchange, c-fos expression, and mitogenesis in rat mesangial cells.J Clin Invest. 1989; 83: 708-712Crossref PubMed Scopus (517) Google Scholar and fibroblasts, and by favoring cell proliferation, it also promotes matrix protein gene transcription (abstract, Ishimura et al, J Am Soc Nephrol 2:546, 1991). Endothelin-1 is chemotactic for blood monocytes32Remuzzi G. Ruggenenti P. Benigni A. Understanding the nature of renal disease progression.Kidney Int. 1997; 51: 2-15Abstract Full Text PDF PubMed Scopus (584) Google Scholar, a property which in vivo could contribute to the tubulointerstitial damage that accompanies most progressive renal diseases32Remuzzi G. Ruggenenti P. Benigni A. Understanding the nature of renal disease progression.Kidney Int. 1997; 51: 2-15Abstract Full Text PDF PubMed Scopus (584) Google Scholar. The ability of ET-1 to increase vascular tone and to activate the sympathetic nervous system and renin-angiotensin system makes it a plausible mediator of hypertension. In-vitro mesenteric vascular tissue from spontaneous hypertensive rats (SHR) generates more ET-1 than that from normotensive control Wistar-Kyoto rats. Strain-related difference has been reported, however; immunoreactivity to endothelin in blood vessels from deoxycorticosterone acetate (DOCA)-salt rats is greater than that in blood vessels from SHR rats33Schiffrin E.L. Lariviere R. Li J.S. Sventek P. Touyz R.M. Endothelin-1 gene expression and vascular hypertrophy in DOCA-salt hypertension compared to spontaneously hypertensive rats.Clin Exp Pharmacol Physiol. 1995; 22: S188-S190Crossref Scopus (9) Google Scholar. Plasma concentrations of ET-1 in animal models of hypertension are not raised unless accelerated hypertension is present34Kohno M. Murakawa K.-I. Horio T. Yokokawa K. Yasunari K. Fukui T. Takeda T. Plasma immunoreactive endothelin-1 in experimental malignant hypertension.Hypertension. 1991; 18: 93-100Crossref PubMed Scopus (92) Google Scholar. Moreover, hepatic overexpression of human preproET-1 in rats increases plasma ET-1 levels to values found in disease conditions and causes systemic hypertension through activation of the ETA receptor35Niranjan V. Télémaque S. dewit D. Gerard R.D. Yanagisawa M. Systemic hypertension induced by hepatic overexpression of human preproendothelin-1 in rats.J Clin Invest. 1996; 98: 2364-2372Crossref PubMed Scopus (29) Google Scholar. Interpretation of these experimental findings is uncertain. Evidence for normalization of blood pressure in genetic models by ETA or ETA/ETB receptor blockade36Nishikibe M. Tsuchida S. Okada M. Fukuroda T. Shimamoto K. Yano M. Ishikawa K. Ikemoto F. Antihypertensive effects of a newly synthesized endothelin antagonist, BQ123, in a genetic hypertensive model.Life Sci. 1993; 52: 717-724Crossref PubMed Scopus (109) Google Scholar,37Douglas S.A. Gellai M. Ezekial M. Feuerstein G.Z. Elliot J.D. Ohlstein E.H. Antihypertensive actions of the novel nonpeptide endothelin receptor antagonist SB 209670.Hypertension. 1995; 25: 818-822Crossref PubMed Google Scholar suggests that ET-1 participates in the pathophysiology of hypertension. But this evidence stands in contrast to findings that ET-1 knockout mice are actually hypertensive38Kurihara Y. Kurihara H. Suzuki H. Kodama T. Maemura K. Nagal R. Oda H. Kuwaki T. Cao W.-H. Kamada N. Jishage K. Ouchi Y. Azuma S. Toyoda Y. Ishikawa T. Kumada M. Yazaki Y. Elevated blood pressure and craniofacial abnormalities in mice deficient in endothelin-1.Nature. 1994; 368: 703-710Crossref PubMed Scopus (867) Google Scholar. Data in humans also are conflicting. In support of a role for endothelin in hypertension is the case of two patients with malignant hemangioendothelioma, a rare vascular neoplasm of endothelial cell proliferation, who had systemic hypertension and elevated circulating ET-1 levels39Yokokawa K. Tahara H. Kohno M. Murakawa K. Yasunari K. Nakagawa K. Hamada T. Otani S. Yanagisawa M. Takeda T. Hypertension associated with endothelin-secreting malignant hemangioendothelioma.Ann Intern Med. 1991; 114: 213-215Crossref PubMed Scopus (161) Google Scholar. The tumors contained eight times more ET-1 per gram of tissue than did normal skin. In both patients, removal of the tumor lowered systemic blood pressure and normalized circulating ET-1. Recurrence of the tumor in one of the patients was accompanied by high blood pressure and increased circulating ET-1 concentration. However, more common causes of systemic hypertension are not clearly linked to high circulating levels of ET-1. One study found high plasma ET-1 in essential hypertension40Saito Y. Nakao K. Mukoyama M. Imura H. Increased plasma endothelin level in patients with essential hypertension.N Engl J Med. 1990; 322: 205Crossref PubMed Scopus (405) Google Scholar, but other studies have not41Davenport A.P. Ashby M.J. Easton P. Ella S. Bedford J. Dickerson C. Nunez D.J. Capper S.J. Brown M.J. A sensitive radioimmunoassay measuring endothelin-like immunoreactivity in human plasma: Comparison of levels in patients with essential hypertension and normotensive control subjects.Clin Sci. 1990; 78: 261-264Crossref PubMed Scopus (206) Google Scholar. Circulating plasma ET-1 levels, moreover (even when elevated in certain disease states), are lower than those required to elicit most of the biologic actions of ET-1. Note, however, that like other local hormones, ET-1 acts as an autocrine/paracrine substance on the underlying vascular smooth muscle, where its concentration can be several orders of magnitude higher than that in plasma. Thus, major increases at local vascular levels might translate into negligible increases in the periphery. For instance, in atherosclerosis, vascular ET-1 increases remarkably in the presence of only a slight increase in the peripheral blood42Lerman A. Edwards B.S. Hallett J.W. Heublein D.M. Sandberg S.M. Burnett J.C. Circulating and tissue endothelin immunoreactivity in advanced atherosclerosis.N Engl J Med. 1991; 325: 997-1001Crossref PubMed Scopus (920) Google Scholar. Endothelin gene expression and the renal synthesis of ET-1 are upregulated in animal models of progressive renal disease that follows the loss of a critical number of nephrons due to immune or nonimmune damage to the kidney. The remnant kidney model in rats is characterized by a time-dependent increase in renal ET-1 gene expression, as well as an increase in urinary excretion of the peptide Figure 1; both correlate with progressive renal damage43Benigni A. Perico N. Gaspari F. Zoja C. Bellizzi L. Gabanelli M. Remuzzi G. Increased renal endothelin production in rats with reduced renal mass.Am J Physiol. 1991; 260: F331-F339PubMed Google Scholar, 44Orisio S. Benigni A. Bruzzi I. Corna D. Perico N. Zoja C. Benatti L. Remuzzi G. Renal endothelin gene expression is increased in remnant kidney and correlates with disease progression.Kidney Int. 1993; 43: 354-358Abstract Full Text PDF PubMed Scopus (177) Google Scholar, 45Bruzzi I. Corna D. Zoja C. Orisio S. Schiffrin E.L. Cavallotti D. Remuzzi G. Benigni A. Time course and localization of endothelin-1 gene expression in a model of renal disease progression.Am J Pathol. 1997; 151: 1241-1247PubMed Google Scholar. Similar results were obtained in rats with passive Heymann nephritis, an immune model of glomerular disease resembling human membranous nephropathy46Zoja C. Liu X.-H. Abbate M. Corna D. Schiffrin E.L. Remuzzi G. Benigni A. Angiotensin II blockade limits tubular protein overreabsorption and the consequent up-regulation of endothelin-1 gene in experimental membranous nephropathy.Exp Nephrol. 1998; 6: 121-131Crossref PubMed Scopus (48) Google Scholar. Other studies have found an upregulation of renal ET-1 and ETB receptor gene expression in NZB/WF1 mice that have an immunologic disease reminiscent of human lupus47Nakamura T. Ebihara I. Fukui M. Osada S. Tomino Y. Masaki T. Goto K. Furuichi Y. Koide H. Renal expression of mRNAs for endothelin-1, endothelin-3 and endothelin receptors in NZB/W F1 mice.Ren Physiol Biochem. 1993; 16: 233-243PubMed Google Scholar. Glomerular ET-1 and ETB receptor mRNAs were higher than normal within days of puromycin aminonucleoside injection and normalized when rats were no longer nephrotic48Nakamura T. Ebihara I. Fukui M. Osada S. Tomino Y. Masaki T. Goto K. Furuichi Y. Koide H. Modulation of glomerular endothelin and endothelin receptor gene expression in aminonucleoside-induced nephrosis.J Am Soc Nephrol. 1995; 5: 1585-1590PubMed Google Scholar. Also, in experimental diabetes, mRNA for ET-1 is overexpressed in the kidney in the presence of unchanged ETA and ETB receptors49Fukui M. Nakamura T. Ebihara I. Osada S. Tomino Y. Masaki T.M. Goto K. Furuichi Y. Koide H. Gene expression for endothelins and their receptors in glomeruli of diabetic rats.J Lab Clin Med. 1993; 122: 149-156PubMed Google Scholar. More direct evidence for ET-1's role in progressive renal damage derives from studies using transgenic animals. Mice overexpressing the human ET-1 promoter form more ET-1 in their kidneys and develop renal lesions despite exhibiting no increase in systemic blood pressure50Hocher B. Thone-Reineke C. Rohmeiss P. Schmager F. Slowinski T. Burst V. Siegmund F. Quertermous T. Bauer C. Neumayer H.-H. Schleuning W.-D. Theuring F.