Urotensin II is an inverse predictor of incident cardiovascular events in end-stage renal disease

Identifying Circulating Urotensin II and Urotensin II-Related Peptide-Generating Enzymes in the Human Plasma Fraction Cohn IV-4

Urotensin II (UII) and UII-related peptide (URP) are vasoactive peptide hormones causing strong vasoconstriction or vasodilation, depending on the type of blood vessel. In humans, the active forms are resulting from proteolytic cleavage of their inactive precursor protein. In blood plasma, a defined protease converting the inactive UII and URP precursors into their active forms has not been identified yet. Using mass spectrometry-based enzyme screening for detecting UII- and URP-converting enzymes, the human plasma fraction Cohn IV-4 was chromatographed, and the resulting fractions were screened for UII- or URP-generating activity. Plasma kallikrein (PK) as a UII- and URP-generating protease was identified. URP generation was also found for the serine protease factor XIa, plasmin, thrombin, and, to a smaller extent, factor XIIa. It was demonstrated that in the Cohn IV-4 fraction, PK accounts for a significant amount of UII- and URP-generating activity.

Plasma Urotensin II levels in children and adolescents with chronic kidney disease: a single-centre study

Background

Increased plasma Urotensin II (UII) levels have been found in adults with renal diseases. Studies in children are scarce. The objective of the study is to estimate plasma UII levels in subjects with chronic kidney disease (CKD) stages 3 to 5 and renal transplant recipients (RTR). In addition, the correlation of UII with anthropometric features and biochemical parameters was assessed.

Methods

Fifty-four subjects, aged 3 to 20 years old, 23 with CKD, 13 with end-stage kidney disease (ESKD) undergoing hemodialysis (HD) and 18 RTR were enrolled. A detailed clinical evaluation was performed. Biochemical parameters of renal and liver function were measured. Plasma UII levels were measured in all patients and in 117 healthy controls, using a high sensitive enzyme immunoassay (EIA) kit. All data were analyzed using STATA™ (Version 10.1).

Results

Median UII and mean log-transformed UII levels were significantly higher in CKD and RTR patients compared to healthy subjects (p < 0.001). HD patients had higher but not statistically significant UII and log-UII levels than controls. UII levels increased significantly at the end of the HD session and were higher than controls and in line to those of other patients. The geometric scores of UII in HD (before dialysis), CKD and RTR patients increased respectively by 42, 136 and 164% in comparison with controls. Metabolic acidosis was associated with statistical significant change in log-UII levels (p = 0.001). Patients with metabolic acidosis had an increase in UII concentration by 76% compared to those without acidosis.

Conclusions

Children and adolescents with CKD, particularly those who are not on HD and RTR, have significantly higher levels of UII than healthy subjects. UII levels increase significantly at the end of the HD session. The presence of metabolic acidosis affects significantly plasma UII levels.

The urotensin system is up-regulated in the pre-hypertensive spontaneously hypertensive rat

Urotensin II (UII) concentrations are raised both in humans with hypertension and in spontaneously hypertensive rats (SHR). Since the urotensin system acts to regulate glomerular filtration in the kidney it may play a greater role in the pre-hypertensive SHR in which renal dysfunction is known to precede the onset of severe hypertension. This study aimed to determine the renal actions and expression of the urotensin system in the young SHR. Intravenous rat UII (6 pmol. min^-1. 100 g body weight^-1) had no significant effect on GFR; however urotensin-related peptide (URP) reduced GFR (P<0.05) in 4-5 week old SHR. Administration of the UT antagonist SB-706375 evoked marked increases in GFR (baseline 0.38 ± 0.07 vs antagonist 0.76 ± 0.05 ml. min^-1. 100 g body weight^-1, P<0.05), urine flow and sodium excretion (baseline 2.5 ± 0.4 vs antagonist 9.1 ± 2.1 µmol. min^-1. 100 g body weight^-1, P<0.05) in the SHR. Normotensive Wistar-Kyoto rats showed little response to UT antagonism. Quantitative RT-PCR showed that neither UII nor UT mRNA expression differed between the kidneys of young SHR and WKY rats; however expression of URP was 4-fold higher in the SHR kidney. Renal transcriptional up-regulation indicates that URP is the major UT ligand in young SHR and WKY rats. Enhanced tonic UT activation may contribute to known renal dysfunction in pre-hypertensive SHR.

Rationale and design of the Sodium Lowering In Dialysate (SoLID) trial: a randomised controlled trial of low versus standard dialysate sodium concentration during hemodialysis for regression of left ventricular mass

BACKGROUND

The current literature recognises that left ventricular hypertrophy makes a key contribution to the high rate of premature cardiovascular mortality in dialysis patients. Determining how we might intervene to ameliorate left ventricular hypertrophy in dialysis populations has become a research priority. Reducing sodium exposure through lower dialysate sodium may be a promising intervention in this regard. However there is clinical equipoise around this intervention because the benefit has not yet been demonstrated in a robust prospective clinical trial, and several observational studies have suggested sodium lowering interventions may be deleterious in some dialysis patients.

METHODS/DESIGN

The Sodium Lowering in Dialysate (SoLID) study is funded by the Health Research Council of New Zealand. It is a multi-centre, prospective, randomised, single-blind (outcomes assessor), controlled parallel assignment 3-year clinical trial. The SoLID study is designed to study what impact low dialysate sodium has upon cardiovascular risk in dialysis patients. The study intends to enrol 118 home hemodialysis patients from 6 sites in New Zealand over 24 months and follow up each participant over 12 months. Key exclusion criteria are: patients who dialyse more frequently than 3.5 times per week, pre-dialysis serum sodium of <135 mM, and maintenance hemodiafiltration. In addition, some medical conditions, treatments or participation in other dialysis trials, which contraindicate the SoLID study intervention or confound its effects, will be exclusion criteria. The intervention and control groups will be dialysed using dialysate sodium 135 mM and 140 mM respectively, for 12 months. The primary outcome measure is left ventricular mass index, as measured by cardiac magnetic resonance imaging, after 12 months of intervention. Eleven or more secondary outcomes will be studied in an attempt to better understand the physiologic and clinical mechanisms by which lower dialysate sodium alters the primary end point.

DISCUSSION

The SoLID study is designed to clarify the effect of low dialysate sodium upon the cardiovascular outcomes of dialysis patients. The study results will provide much needed information about the efficacy of a cost effective, economically sustainable solution to a condition which is curtailing the lives of so many dialysis patients.

TRIAL REGISTRATION

Australian and New Zealand Clinical Trials Registry number: ACTRN12611000975998.

Urotensin II and the kidney

PURPOSE OF REVIEW

Urotensin II (UTS2), the most potent vasoconstrictor identified thus far, is an undecapeptide hormone with a structure that is highly conserved through mammalian phylogeny. In spite of its broad expression across the invertebrate and vertebrate world, the precise role of UTS2 in physiology and disease is still unknown. The first description of human UTS2 and its receptor brought initial promise of a potential therapeutic target for progressive renal disease, with vasoconstrictive and profibrotic actions within an autocrine and paracrine system and local renal generation that was upregulated with renal pathology.

RECENT FINDINGS

However, the last decade has not brought the successful development of new treatments first hoped for, with one small human clinical trial bearing negative results. What has become apparent is that the spectrum of actions of UTS2 is broad and often paradoxical. This ancient hormone has both vasoconstrictor and vasodilatory actions, has both profibrotic and antiapoptotic activity, as well as actions which are highly contextual on the particular vascular bed studied and on the presence or absence of superimposed disease state.

SUMMARY

With current development of newer UTS2 antagonists attempting to more closely replicate the ligand-receptor kinetics of UTS2 and its receptor, the focus on potential clinical applications of UTS2 inhibition has moved away from the kidney to the treatment of chronic lung and cardiovascular diseases.

Is plasma urotensin II concentration an indicator of myocardial damage in patients with acute coronary syndrome?

INTRODUCTION

Urotensin II (UII) is a vasoactive peptide secreted by endothelial cells. Increased plasma UII concentration was observed in patients with heart failure, liver cirrhosis, diabetic nephropathy and renal insufficiency. In patients with myocardial infarction both increased and decreased plasma UII concentrations were demonstrated. The aim of this study was to analyze whether plasma UII concentration reflects the severity of acute coronary syndrome (ACS).

MATERIAL AND METHODS

One hundred and forty-nine consecutive patients with ACS, without age limit, were enrolled in the study. In all patients plasma concentration of creatinine, creatine kinase isoenzyme MB (CK-MB), troponin C, N-terminal prohormone of brain natriuretic peptide (NT-pro BNP), and UII were assessed, and echocardiography was performed in order to assess the degree of left ventricular hypertrophy, ejection fraction (EF) and mass (LVM).

RESULTS

In patients with the highest risk (TIMI 5-7) plasma UII concentration was significantly lower than in those with low risk (TIMI 1-2): 2.61±1.47 ng/ml vs. 3.60±2.20 ng/ml. Significantly lower plasma UII concentration was found in patients with increased concentration of troponin C (2.60±1.52 ng/ml vs. 3.41±2.09 ng/ml). There was a significant negative correlation between plasma UII concentration and TIMI score or concentration of troponin C, but not CK-MB. Borderline correlation between plasma UII and ejection fraction (R = 0.157; p=0.063) or NT-proBNP (R = - 0.156; p=0.058) was found.

CONCLUSIONS

Decreased plasma urotensin II concentration in patients with ACS could be associated with more severe injury of myocardium.

A closer look at the role of urotensin II in the metabolic syndrome

Urotensin II (UII) is a vasoactive peptide that was first discovered in the teleost fish, and later in mammals and humans. UII binds to the G protein coupled receptor GPR14 (now known as UT). UII mediates important physiological and pathological actions by interacting with its receptor. The metabolic syndrome (MetS) is described as cluster of factors such as obesity, dyslipidemia, hypertension, and insulin resistance (IR), further leading to development of type 2 diabetes mellitus and cardiovascular diseases. UII levels are upregulated in patients with the MetS. Evidence directly implicating UII in every risk factor of the MetS has been accumulated. The mechanism that links the different aspects of the MetS relies primarily on IR and inflammation. By directly modulating both of these factors, UII is thought to play a central role in the pathogenesis of the MetS. Moreover, UII also plays an important role in hypertension and hyperlipidemia thereby contributing to cardiovascular complications associated with the MetS.

Potential Clinical Implications of the Urotensin II Receptor Antagonists

Urotensin II (UII) binds to its receptor, UT, playing an important role in the heart, kidneys, pancreas, adrenal gland, and central nervous system. In the vasculature, it acts as a potent endothelium-independent vasoconstrictor and endothelium-dependent vasodilator. In disease states, however, this constriction–dilation equilibrium is disrupted. There is an upregulation of the UII system in heart disease, metabolic syndrome, and kidney failure. The increase in UII release and UT expression suggest that UII system may be implicated in the pathology and pathogenesis of these diseases by causing an increase in acyl-coenzyme A:cholesterol acyltransferase-1 (ACAT-1) activity leading to smooth muscle cell proliferation and foam cell infiltration, insulin resistance (DMII), as well as inflammation, high blood pressure, and plaque formation. Recently, UT antagonists such as SB-611812, palosuran, and most recently a piperazino-isoindolinone based antagonist have been developed in the hope of better understanding the UII system and treating its associated diseases.

Renal impairment, hypertension and plasma urotensin II

BACKGROUND

Human urotensin II (UII) is a potent mammalian vasoconstrictor thought to be produced and cleared by the kidneys. Conflicting data exist regarding the relationship between UII concentrations, kidney function and blood pressure (BP). We measured the associations between kidney function [including end-stage renal disease (ESRD)] and levels of BP with plasma concentrations of UII.

METHODS

Ninety-one subjects were enrolled. Thirty-one subjects had ESRD (undergoing haemodialysis), 30 subjects had chronic kidney disease (CKD) and 30 control subjects had no kidney disease. Plasma UII concentrations were measured by radioimmunoassay.

RESULTS

Mean plasma UII concentrations were highest in controls, lower in subjects with ESRD and lowest in subjects with non-ESRD CKD (P<0.0001). UII concentrations correlated negatively with serum creatinine (P=0.0012) and CKD stage, and positively with creatinine clearance (P=0.013). In ESRD subjects, plasma UII (P=0.008) increased after dialysis, while SBP (P=0.007), DBP (P=0.009), serum creatinine (P<0.0001) and serum urea nitrogen (P<0.0001) decreased. UII concentrations were lower in patients with a history of hypertension (HTN) (P=0.016). Age, race and gender did not appear to be associated with UII concentration. However, the distribution of African American race and male gender appear to be associated with increasing stages of chronic kidney disease.

CONCLUSIONS

These data suggest a potential vasodilatory role of UII in humans with kidney disease or hypertension. The reduction in UII levels in CKD also suggests either reduced production or greater clearance, or both, of UII.

Role of urotensin II in health and disease

Urotensin II (UII) is an 11 amino acid cyclic peptide originally isolated from the goby fish. The amino acid sequence of UII is exceptionally conserved across most vertebrate taxa, sharing structural similarity to somatostatin. UII binds to a class of G protein-coupled receptor known as GPR14 or the urotensin receptor (UT). UII and its receptor, UT, are widely expressed throughout the cardiovascular, pulmonary, central nervous, renal, and metabolic systems. UII is generally agreed to be the most potent endogenous vasoconstrictor discovered to date. Its physiological mechanisms are similar in some ways to other potent mediators, such as endothelin-1. For example, both compounds elicit a strong vascular smooth muscle-dependent vasoconstriction via Ca2+ release. UII also exerts a wide range of actions in other systems, such as proliferation of vascular smooth muscle cells, fibroblasts, and cancer cells. It also 1) enhances foam cell formation, chemotaxis of inflammatory cells, and inotropic and hypertrophic effects on heart muscle; 2) inhibits insulin release, modulates glomerular filtration, and release of catecholamines; and 3) may help regulate food intake and the sleep cycle. Elevated plasma levels of UII and increased levels of UII and UT expression have been demonstrated in numerous diseased conditions, including hypertension, atherosclerosis, heart failure, pulmonary hypertension, diabetes, renal failure, and the metabolic syndrome. Indeed, some of these reports suggest that UII is a marker of disease activity. As such, the UT receptor is emerging as a promising target for therapeutic intervention. Here, a concise review is given on the vast physiologic and pathologic roles of UII.

Urotensin II immunoreactivity in the human circulation: evidence for widespread tissue release

BACKGROUND

The sources of secretion and clearance of plasma urotensin II (UII) in the human circulation remain uncertain and may be relevant to understanding the role of UII in human physiology and cardiovascular disease.

METHODS

In 94 subjects undergoing clinically indicated cardiac catheterization, we collected blood samples from arterial and multiple venous sites to measure transorgan gradients of plasma UII immunoreactivity.

RESULTS

Net UII release occurred (in descending order of proportional transorgan gradient) across the heart, kidney, head and neck, liver, lower limb, and pulmonary circulations (P < 0.01). Although no specific clearance site was localized, the absence of an overall subdiaphragmatic aorto-caval peptide gradient indicated that there were lower body segment sites of UII clearance as well as secretion. The proportional increase in UII immunoreactivity was significantly correlated across all sites of net peptide release within an individual (P < or = 0.05). In univariate analyses, mixed venous UII concentrations were correlated with diagnosis of acute coronary syndrome and femoral artery oxygen tension and inversely with systolic blood pressure and body mass index. Diagnosis of acute coronary syndrome and body mass index were independent predictors of mixed venous UII immunoreactivity in multivariate analysis. No correlates of net cardiac UII release were identified.

CONCLUSIONS

UII is secreted from the heart and multiple other tissues into the circulation. Related increments in UII immunoreactivity across multiple tissue sites suggest that peptide release occurs via a shared mechanism. Increased UII immunoreactivity is observed in subjects with acute coronary syndrome.

The renin-angiotensin system, adrenomedullins and urotensin II in the kidney: possible renoprotection via the kidney peptide systems

The incidence of chronic kidney disease, such as diabetic nephropathy, is increasing throughout the world. Many biologically active peptides play important roles in the kidney. The classical example is the renin-angiotensin system (RAS). Angiotensin II plays critical roles in the progression of chronic kidney disease through its vasoconstrictor action, stimulatory action on cell proliferation, and reactive oxygen-generating activity. A renin inhibitor, aliskiren, has recently been shown to be a clinically effective drug to reduce proteinuria in patients with diabetic nephropathy. (Pro)renin receptor, a specific receptor for renin and prorenin, was newly identified as a member of the RAS. When bound to prorenin, (pro)renin receptor activates the angiotensin I-generating activity of prorenin in the absence of cleavage of the prosegment, and directly stimulates the pathway of mitogen-activated protein kinase independently from the RAS. The kidney peptides that antagonize the intrarenal RAS may have renoprotective actions. Adrenomedullins, potent vasodilator peptides, have been shown to have renoprotective actions. On the other hand, urotensin II, a potent vasoconstrictor peptide, may promote the renal dysfunction in chronic kidney disease together with the renal RAS. Thus, in addition to the renin inhibitor and (pro)renin receptor, adrenomedullins and urotensin II may be novel targets to develop therapeutic strategies against chronic kidney disease.

Increased expression of urotensin II-related peptide and its receptor in kidney with hypertension or renal failure

Urotensin II-related peptide (URP) is a novel vasoactive peptide that shares urotensin II receptor (UT) with urotensin II. In order to clarify possible changes of URP expression in hypertension and chronic renal failure (CRF), the expressions of URP and UT were studied by quantitative RT-PCR and immunohistochemistry in kidneys obtained from spontaneous hypertensive rats (SHR), Wistar-Kyoto rats (WKY), and WKY with CRF due to 5/6 nephrectomy. Expression levels of URP mRNA and UT mRNA were significantly higher in the kidneys obtained from SHR compared with age-matched WKY (at 5-16 and 16 weeks old, respectively). A dissection study of the kidney into three portions (inner medulla, outer medulla and cortex) showed that the expression levels of URP mRNA and UT mRNA were highest in the inner medulla and the outer medulla, respectively, in both SHR and WKY. The expression levels of URP and UT mRNAs were greatly elevated in the remnant kidneys of CRF rats at day 56 after nephrectomy, compared with sham-operated rats (about 6.5- and 11.9-fold, respectively). Immunohistochemistry showed that URP immunostaining was found mainly in the renal tubules, vascular smooth muscle cells and vascular endothelial cells. UT immunoreactivity was localized in the renal tubules and vascular endothelial cells. These findings suggest that the expressions of URP and UT mRNAs in the kidney are enhanced in hypertension and CRF, and that URP and its receptor have important pathophysiological roles in these diseases.

Urotensin II in cardiovascular regulation

Cardiovascular function is modulated by neuronal transmitters, circulating hormones, and factors that are released locally from tissues. Urotensin II (UII) is an 11 amino acid peptide that stimulates its' obligatory G protein coupled urotensin II receptors (UT) to modulate cardiovascular function in humans and in other animal species, and has been implicated in both vasculoprotective and vasculopathic effects. For example, tissue and circulating concentrations of UII have been reported to increase in some studies involving patients with atherosclerosis, heart failure, hypertension, preeclampsia, diabetes, renal disease and liver disease, raising the possibility that the UT receptor system is involved in the development and/or progression of these conditions. Consistent with this hypothesis, administration of UT receptor antagonists to animal models of cardiovascular disease have revealed improvements in cardiovascular remodelling and hemodynamics. However, recent studies have questioned this contributory role of UII in disease, and have instead postulated a protective effect on the cardiovascular system. For example, high concentrations of circulating UII correlated with improved clinical outcomes in patients with renal disease or myocardial infarction. The purpose of this review is to consider the regulation of the cardiovascular system by UII, giving consideration to methodologies for measurement of plasma concentrations, sites of synthesis and triggers for release.

Urotensin II and urotensin II-related peptide (URP) in cardiac ischemia-reperfusion injury

Circulating urotensin II (UII) concentrations and the tissue expression of its cognate receptor (UT) are elevated in patients with cardiovascular disease (CVD). The functional significance of elevated plasma UII levels in CVD is unclear. Urotensin-related peptide (URP) is a paralog of UII in that it contains the six amino acid ring structures found in UII. Although both peptides are implicated as bioactive factors capable of modulating cardiovascular status, the role of both UII and URP in ischemic injury is unknown. Accordingly, we provide here the first report describing the direct cardiac effects of UII and URP in ischemia-reperfusion injury. Isolated perfused rat hearts were subjected to no-flow global ischemia for 45 min after 30min preconditioning with either 1nM rUII or 10nM URP. Both rUII- and URP-induced significant vasodilation of coronary arteries before (both P<0.05) and after ischemia (both P<0.05). Rat UII alone lowered contractility prior to ischemia (P=0.053). Specific assay of perfusate revealed rUII and URP both significantly inhibited reperfusion myocardial creatine kinase (CK) release (P=0.012 and 0.036, respectively) and atrial natriuretic peptide (ANP) secretion (P=0.025). Antagonism of the UT receptor with 1muM palosuran caused a significant increase in perfusion pressure (PP) prior to and post-ischemia. Furthermore, palosuran significantly inhibited reductions in both PP and myocardial damage marker release induced by both rUII and URP. In conclusion, our data suggests rUII and URP reduce cardiac ischemia-reperfusion injury by increasing flow through the coronary circulation, reducing contractility and therefore myocardial energy demand, and inhibiting reperfusion myocardial damage. Thus, UII and URP present as novel peptides with potential cardioprotective actions.

Cardiorenovascular effects of urotensin II and the relevance of the UT receptor

Urotensin II (U-II) is a vasoactive peptide with many potent effects in the cardiorenovascular system. U-II activates a G-protein-coupled receptor termed UT. UT and U-II are highly expressed in the cardiovascular and renal system. Patients with various cardiovascular diseases show high U-II plasma levels. It was demonstrated that elevated U-II plasma levels and increased UT expression seem to play a role in heart failure, end-stage renal disease and atherosclerosis. U-II induces potent changes in vascular tone regulation. In addition, U-II stimulates vascular smooth muscle cell proliferation and cardiomyocyte hypertrophy. Currently several pharmaceutical companies are developing compounds to control the U-II/UT system. There are preclinical and some clinical studies showing potential benefits of inhibiting U-II function in renal disease, heart failure, and diabetes. This article will review both pre- and clinical data concerning cardiorenovascular effects of U-II.

The role of urotensin II in the metabolic syndrome

Urotensin II is a potent vasoconstrictive peptide that mediates both endothelium-independent vasoconstriction and endothelium-dependent vasodilatation. Its plasma level correlates positively with body weight and is raised in diabetes, renal failure, hypertension, and other cardiovascular diseases including congestive heart failure and carotid atherosclerosis. It can inhibit glucose-induced insulin secretion, and genetic variants in urotensin II gene are associated with insulin resistance and type 2 diabetes. Urotensin II also affects lipid metabolism in fish and food intake in mice. Recent studies have also demonstrated a role of urotensin II in inflammation and endothelial dysfunction. These findings suggest a close relationship between urotensin II and at least some components of the metabolic syndrome, including hypertension, insulin resistance, hyperglycemia, and inflammation.

Role of urotensin II and its receptor in health and disease

Urotensin II (U-II) is currently the most potent vasoconstrictor identified. This action is brought about via activation of a G(q/11)-protein coupled receptor (UT receptor). U-II activation of the UT receptor increases inositol phosphate turnover and intracellular Ca(2+). In addition to producing vasoconstriction, dilation and ionotropic effects have also been described. There is considerable variation in the responsiveness of particular vascular beds from the same and different species, including humans. Receptors for U-II are located peripherally on vascular smooth muscle (contractile responses) and endothelial cells (dilatory responses via nitric oxide). In humans, plasma U-II is elevated in heart failure, renal failure, liver disease, and diabetes. Iontophoresis of U-II in healthy volunteers produces vasodilation (of the forearm) while in patients with heart failure or hypertension a constriction is observed. To date there is only one clinical study using a UT receptor antagonist (palosuran) in diabetic patients with macroalbuminuria. This antagonist reduced albumin excretion, probably by increasing renal blood flow. Studies in other disease conditions are eagerly awaited. In summary, the U-II / UT receptor system has clinical potential, and for the anesthesiologist, this novel peptide-receptor system may be of use in the intensive care unit.

Urotensin-II and cardiovascular diseases

Urotensin-II (U-II) is a vasoactive factor with pleiotropic effects. U-II exerts its activity by binding to a G-protein-coupled receptor termed UT. U-II and its receptor are highly expressed in the cardiovascular system. Increased U-II plasma levels have been reported in patients with cardiovascular disease of varying etiologies. We and others have shown that U-II and UT expression is elevated in both clinical and experimental heart failure and atherosclerosis. U-II induces cardiac fibrosis by increasing fibroblast collagen synthesis. In addition, U-II induces cardiomyocyte hypertrophy and increased vascular smooth muscle cell proliferation. We have shown that U-II antagonism using a selective U-II blocker, SB-611812 reduces neointimal thickening and increases lumen diameter in a rat restenosis model of carotid artery angioplasty. These findings suggest an important role for U-II in cardiovascular dysfunction and remodeling.

Renal and vascular actions of urotensin II

The peptide hormone urotensin II (UII) has been highly conserved through the vertebrates from fish to humans. As it was shown to be the endogenous ligand for the mammalian orphan G-protein-coupled receptor GPR14, now renamed the UT receptor, interest in UII physiology has grown. Initial observations of a potent vasoconstrictor effect have been tempered with the subsequent revelation of an endothelium-dependent vasodilator action. These complex and contrasting vascular actions are both species- and vascular bed-specific. UII also plays a role in body fluid regulation in lower vertebrates, and it now appears that this extends to mammals. The kidney is a major source of both circulating and urinary UII. UII is found in both the proximal tubules and collecting ducts; the UT receptor is localized primarily to the renal medulla, with greatest expression in the inner medullary collecting ducts. Infusion in rats produced conflicting results: exogenous UII has been shown to increase glomerular filtration rate (GFR) and excretion of water and sodium, but also to reduce the same variables. Inhibition of UT receptor activity with the antagonist urantide resulted in an increase in GFR, diuresis, and natriuresis, suggesting that endogenous UII exerts a tonic influence on basal renal function. UII may also play a role in renal disease, being elevated in the circulation or urine of patients with renal failure and in experimental models of cardiovascular disease such as the spontaneously hypertensive rat. It remains to be established whether these changes represent an underlying primary cause or a compensatory response.