Urotensin II acts centrally to increase epinephrine and ACTH release and cause potent inotropic and chronotropic actions

Urotensin-related gene transcripts mark developmental emergence of the male forebrain vocal control system in songbirds

Songbirds communicate through learned vocalizations, using a forebrain circuit with convergent similarity to vocal-control circuitry in humans. This circuit is incomplete in female zebra finches, hence only males sing. We show that the UTS2B gene, encoding Urotensin-Related Peptide (URP), is uniquely expressed in a key pre-motor vocal nucleus (HVC), and specifically marks the neurons that form a male-specific projection that encodes timing features of learned song. UTS2B-expressing cells appear early in males, prior to projection formation, but are not observed in the female nucleus. We find no expression evidence for canonical receptors within the vocal circuit, suggesting either signalling to other brain regions via diffusion or transduction through other receptor systems. Urotensins have not previously been implicated in vocal control, but we find an annotation in Allen Human Brain Atlas of increased UTS2B expression within portions of human inferior frontal cortex implicated in human speech and singing. Thus UTS2B (URP) is a novel neural marker that may have conserved functions for vocal communication.

Acute Effect of Central Administration of Urotensin II on Baroreflex and Blood Pressure in Conscious Normotensive Rabbits

In the present study, we examined the effects of central administration of Urotensin II on blood pressure, heart rate, and baroreceptor heart rate reflexes in conscious normotensive rabbits. Preliminary operations were undertaken to implant a balloon cuff on the inferior vena cava for baroreflex assessments and to implant cannula into the lateral and fourth ventricle. After 2 weeks of recovery cumulative dose response curves to Urotensin II (10, 100 ng, 1, 10, and 100 μg) given into the ventricles, or Ringer's solution as a vehicle were performed on separate days. Injections were given each hour and baroreflex assessments were made 30 min after each administration. Analysis of the dose response curves to Urotensin II compared to vehicle administered into the lateral or fourth ventricle, indicated little change to blood pressure or heart rate. Analysis of the time course to the highest dose over a 30 min period revealed a small (−5 mmHg) depressor response maximal at 10 min when injected into the fourth ventricle but no effect when injected into the lateral ventricle. Baroreflex assessments made at each dose showed that there was no change in baroreflex sensitivity but that an increase in the upper plateau was observed when Urotensin was injected into the lateral ventricle and a tendency for a reduced lower heart rate plateau was observed after fourth ventricle administration. Clonidine administration in the fourth ventricle decreased blood pressure and heart rate, thus confirming catheter patency. In conclusion, our findings suggest that Urotensin II in the forebrain and brainstem may play a role in modulating cardiac sympathetic and vagal baroreflexes but only during large acute changes in blood pressure.

Central and Peripheral Effects of Urotensin II and Urotensin II-Related Peptides on Cardiac Baroreflex Sensitivity in Trout

The baroreflex response is an essential component of the cardiovascular regulation that buffers abrupt changes in blood pressure to maintain homeostasis. Urotensin II (UII) and its receptor UT are present in the brain and in peripheral cardiovascular tissues of fish and mammals. Intracerebroventricular (ICV) injection of UII in these vertebrates provokes hypertension and tachycardia, suggesting that the cardio-inhibitory baroreflex response is impaired. Since nothing is known about the effect of UII on the cardiac baroreflex sensitivity (BRS), we decided to clarify the changes in spontaneous BRS using a cross spectral analysis technique of systolic blood pressure (SBP) and R-R interval variabilities after ICV and intra-arterial (IA) injections of trout UII in the unanesthetized trout. We contrasted the effects of UII with those observed for the UII-related peptides (URP), URP1 and URP2. Compared with vehicle-injected trout, ICV injection of UII (5-500 pmol) produced a gradual increase in SBP, a decrease in the R-R interval (reflecting a tachycardia) associated with a dose-dependent reduction of the BRS. The threshold dose for a significant effect on these parameters was 50 pmol (BRS; -55%; 1450 ± 165 ms/kPa vs. 3240 ± 300 ms/kPa; P < 0.05). Only the 500-pmol dose of URP2 caused a significant increase in SBP without changing significantly the R-R interval but reduced the BRS. IA injection of UII (5-500 pmol) caused a dose-dependent elevation of SBP. Contrasting with the ICV effects of UII, the R-R interval increased (reflecting a bradycardia) up to the 50-pmol dose while the BRS remained unchanged (50 pmol; 2530 ± 270 ms/kPa vs. 2600 ± 180 ms/kPa; P < 0.05). Nonetheless, the highest dose of UII reduced the BRS as did the highest dose of URP1. In conclusion, the contrasting effect of low picomolar doses of UII after central and peripheral injection on the BRS suggests that only the central urotensinergic system is involved in the attenuation of the BRS. The limited and quite divergent effects of URP1 and URP2 on the BRS, indicate that the action of UII is specific for this peptide. Further studies are required to elucidate the site(s) and mechanisms of action of UII on the baroreflex pathways. Whether such effects of central UII on the BRS exist in mammals including humans warrants further investigations.

International Union of Basic and Clinical Pharmacology. XCII. Urotensin II, urotensin II-related peptide, and their receptor: from structure to function

Urotensin II (UII) is a cyclic neuropeptide that was first isolated from the urophysis of teleost fish on the basis of its ability to contract the hindgut. Subsequently, UII was characterized in tetrapods including humans. Phylogenetic studies and synteny analysis indicate that UII and its paralogous peptide urotensin II-related peptide (URP) belong to the somatostatin/cortistatin superfamily. In mammals, the UII and URP genes are primarily expressed in cholinergic neurons of the brainstem and spinal cord. UII and URP mRNAs are also present in various organs notably in the cardiovascular, renal, and endocrine systems. UII and URP activate a common G protein-coupled receptor, called UT, that exhibits relatively high sequence identity with somatostatin, opioid, and galanin receptors. The UT gene is widely expressed in the central nervous system (CNS) and in peripheral tissues including the retina, heart, vascular bed, lung, kidney, adrenal medulla, and skeletal muscle. Structure-activity relationship studies and NMR conformational analysis have led to the rational design of a number of peptidic and nonpeptidic UT agonists and antagonists. Consistent with the wide distribution of UT, UII has now been shown to exert a large array of biologic activities, in particular in the CNS, the cardiovascular system, and the kidney. Here, we review the current knowledge concerning the pleiotropic actions of UII and discusses the possible use of antagonists for future therapeutic applications.

Urotensin II promotes vagal-mediated bradycardia by activating cardiac-projecting parasympathetic neurons of nucleus ambiguus

Urotensin II (U-II) is a cyclic undecapeptide that regulates cardiovascular function at central and peripheral sites. The functional role of U-II nucleus ambiguus, a key site controlling cardiac tone, has not been established, despite the identification of U-II and its receptor at this level. We report here that U-II produces an increase in cytosolic Ca(2+) concentration in retrogradely labeled cardiac vagal neurons of nucleus ambiguus via two pathways: (i) Ca(2+) release from the endoplasmic reticulum via inositol 1,4,5-trisphosphate receptor; and (ii) Ca(2+) influx through P/Q-type Ca(2+) channels. In addition, U-II depolarizes cultured cardiac parasympathetic neurons. Microinjection of increasing concentrations of U-II into nucleus ambiguus elicits dose-dependent bradycardia in conscious rats, indicating the in vivo activation of the cholinergic pathway controlling the heart rate. Both the in vitro and in vivo effects were abolished by the urotensin receptor antagonist, urantide. Our findings suggest that, in addition, to the previously reported increase in sympathetic outflow, U-II activates cardiac vagal neurons of nucleus ambiguus, which may contribute to cardioprotection.

Discovery of new antagonists aimed at discriminating UII and URP-mediated biological activities: insight into UII and URP receptor activation

BACKGROUND AND PURPOSE

Recent evidence suggested that urotensin II (UII) and its paralog peptide UII-related peptide (URP) might exert common but also divergent physiological actions. Unfortunately, none of the existing antagonists were designed to discriminate specific UII- or URP-associated actions, and our understanding, on how these two endogenous peptides can trigger different, but also common responses, is limited.

EXPERIMENTAL APPROACH

Ex vivo rat and monkey aortic ring contraction as well as dissociation kinetics studies using transfected CHO cells expressing the human urotensin (UT) receptors were used in this study.

KEY RESULTS

Ex vivo rat and monkey aortic ring contraction studies revealed the propensity of [Pep(4)]URP to decrease the maximal response of human UII (hUII) without any significant change in potency, whereas no effect was noticeable on the URP-induced vasoconstriction. Dissociation experiments demonstrated the ability of [Pep(4)]URP to increase the dissociation rate of hUII, but not URP. Surprisingly, URP, an equipotent UII paralog, was also able to accelerate the dissociation rate of membrane-bound (125)I-hUII, whereas hUII had no noticeable effect on URP dissociation kinetics. Further experiments suggested that an interaction between the glutamic residue at position 1 of hUII and the UT receptor seems to be critical to induce conformational changes associated with agonistic activation. Finally, we demonstrated that the N-terminal domain of the rat UII isoform was able to act as a specific antagonist of the URP-associated actions.

CONCLUSION

Such compounds, that is [Pep(4)]URP and rUII(1-7), should prove to be useful as new pharmacological tools to decipher the specific role of UII and URP in vitro but also in vivo.

Urotensin II receptor antagonism confers vasoprotective effects in diabetes associated atherosclerosis: studies in humans and in a mouse model of diabetes

AIMS/HYPOTHESIS

The small, highly conserved vasoactive peptide urotensin II (UII) is upregulated in atherosclerosis. However, its effects in diabetes-associated atherosclerosis have not been assessed.

METHODS

Endothelial cells were grown in normal- and high-glucose (5 and 25 mmol/l) media with and without UII (10⁻⁸ mol/l) and/or the UII receptor antagonist, SB-657510 (10⁻⁸ mol/l). Apoe knockout (KO) mice with or without streptozotocin-induced diabetes were treated with or without SB-657510 (30 mg kg⁻¹ day⁻¹; n = 20 per group) and followed for 20 weeks. Carotid endarterectomy specimens from diabetic and non-diabetic humans were also evaluated.

RESULTS

In high (but not normal) glucose medium, UII significantly increased CCL2 (encodes macrophage chemoattractant protein 1 [MCP-1]) gene expression (human aortic endothelial cells) and increased monocyte adhesion (HUVECs). UII receptor antagonism in diabetic Apoe KO mice significantly attenuated diabetes-associated atherosclerosis and aortic staining for MCP-1, F4/80 (macrophage marker), cyclooxygenase-2, nitrotyrosine and UII. UII staining was significantly increased in carotid endarterectomies from diabetic compared with non-diabetic individuals, as was staining for MCP-1.

CONCLUSIONS/INTERPRETATION

This is the first report to demonstrate that UII is increased in diabetes-associated atherosclerosis in humans and rodents. Diabetes-associated plaque development was attenuated by UII receptor antagonism in the experimental setting. Thus UII may represent a novel therapeutic target in the treatment of diabetes-associated atherosclerosis.

Role of urotensin-Ⅱ in the pathogenesis of liver cirrhosis and portal hypertension and collateral circulation

Urotensin-Ⅱ (U-Ⅱ) is a somatostatin-like cyclic peptide which has a potent vasoactive effect and can promote vascular reconstruction and hyperplasia. Research shows that UⅡ plays an important role in the development of liver cirrhosis and portal hypertension. UⅡ influences intrahepatic resistance and splanchnic hemodynamics through a variety of pathways, causing portal hypertension and participating in the formation of esophageal and gastric varices. UⅡ receptor antagonists can reduce portal pressure in cirrhotic rats, but this finding need to be confirmed clinically.

Genetic and pharmacological manipulation of urotensin II ameliorate the metabolic and atherosclerosis sequalae in mice

OBJECTIVE

Urotensin II (UII) is a potent vasoactive peptide that binds to the urotensin receptor-coupled receptor-14 (known as UT) and exerts a wide range of actions in humans and experimental animals. We tested the hypothesis that UII gene deletion or UT blockade ameliorate experimental atherosclerosis.

METHODS AND RESULTS

We observed a significant reduction in weight gain, visceral fat, blood pressure, circulating plasma lipids, and proatherogenic cytokines and improvement of glucose tolerance in UII knockout mice compared with wild type (P<0.05). Deletion of UII after an apolipoprotein E knockout resulted in a significant reduction in serum cytokines, adipokines, and aortic atherosclerosis compared with apolipoprotein E knockout mice. Similarly, treatment of apolipoprotein E knockout mice fed on high-fat diet with the UT antagonist SB657510A reduced weight gain, visceral fat, and hyperlipidemia and improved glucose tolerance (P<0.05) and attenuated the initiation and progression of atherosclerosis. The UT antagonist also decreased aortic extracellular signal-regulated kinase 1/2 phosphorylation and oxidant formation and serum level of cytokines (P<0.05).

CONCLUSIONS

These findings demonstrate for the first time the role of UII gene deletion in atherosclerosis and suggest that the use of pharmaceutical agents aimed at blocking the UII pathway may provide a novel approach in the treatment of atherosclerosis and its associated precursors such as obesity, hyperlipidemia, diabetes mellitus, and hypertension.

Intracerebroventricular administration of urotensin II regulates food intake and sympathetic nerve activity in brown adipose tissue

To clarify the functional roles of urotensin II in regulating energy balance, we investigated the effects of a central infusion of urotensin II on food intake, uncoupling protein (UCP) 1 mRNA expression, temperature, and sympathetic nervous system activity in brown adipose tissue (BAT), a site that regulates energy expenditure in rodents. A bolus central infusion of urotensin II at a dose of 1 nmol/rat into the third cerebral ventricle decreased food intake (p<0.05). Additionally, urotensin II induced c-Fos-like-immunoreactivity (c-FLI) in the paraventricular nucleus (PVN) as compared with that in the control (phosphate buffered saline [PBS]-treated) group. Furthermore, urotensin II increased BAT UCP 1 mRNA expression (p<0.05). Finally, central infusion of urotensin II significantly increased BAT sympathetic nerve activity, which was accompanied by a significant elevation in BAT temperature (p<0.05) in rats. Taken together, central infusion of urotensin II regulates food intake and BAT sympathetic nerve activity in rats.

Update on the urotensinergic system: new trends in receptor localization, activation, and drug design

The urotensinergic system plays central roles in the physiological regulation of major mammalian organ systems, including the cardiovascular system. As a matter of fact, this system has been linked to numerous pathophysiological states including atherosclerosis, heart failure, hypertension, diabetes as well as psychological, and neurological disorders. The delineation of the (patho)physiological roles of the urotensinergic system has been hampered by the absence of potent and selective antagonists for the urotensin II-receptor (UT). Thus, a more precise definition of the molecular functioning of the urotensinergic system, in normal conditions as well as in a pathological state is still critically needed. The recent discovery of nuclear UT within cardiomyocytes has highlighted the cellular complexity of this system and suggested that UT-associated biological responses are not only initiated at the cell surface but may result from the integration of extracellular and intracellular signaling pathways. Thus, such nuclear-localized receptors, regulating distinct signaling pathways, may represent new therapeutic targets. With the recent observation that urotensin II (UII) and urotensin II-related peptide (URP) exert different biological effects and the postulate that they could also have distinct pathophysiological roles in hypertension, it appears crucial to reassess the recognition process involving UII and URP with UT, and to push forward the development of new analogs of the UT system aimed at discriminating UII- and URP-mediated biological activities. The recent development of such compounds, i.e. urocontrin A and rUII(1-7), is certainly useful to decipher the specific roles of UII and URP in vitro and in vivo. Altogether, these studies, which provide important information regarding the pharmacology of the urotensinergic system and the conformational requirements for binding and activation, will ultimately lead to the development of potent and selective drugs.

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.

Urotensin II differentially regulates macrophage and hepatic cholesterol homeostasis

Urotensin II (UII) is a vasoactive peptide with pleiotropic activity. Interestingly, UII levels are elevated in hyperlipidemic patients, and UII induces lipase activity in some species. However, the exact role UII plays in cholesterol homeostasis remains to be elucidated. UII knockout (UII KO) mice were generated and a plasma lipoprotein profile, and hepatocytes and macrophages cholesterol uptake, storage and synthesis was determined. UII KO had a decreased LDL cholesterol profile and liver steatosis compared to wildtype mice (WT). UII KO macrophages demonstrated enhanced ACAT activity and LDL uptake in the short term (up to 4h), of which more LDL-delivered exogenously derived cholesterol was incorporated into cholesteryl ester (CE) than the WT macrophages. UII KO macrophages generated more than two times the amount of de novo endogenously synthesized cholesterol, and of this cholesterol more than two times the relative amount was esterified to CE. In comparison, results in hepatocytes demonstrated that far more exogenously derived cholesterol was incorporated into CE in the WT cells, generating almost ten times the amount of CE than UII KO. WT cells synthesize de novo almost ten times the amount of cholesterol than UIIKO, and of that cholesterol, almost two times the amount of CE in WT than UII KO hepatocytes. In addition, more ApoB lipoproteins were secreted from WT than UII KO hepatocytes. These results demonstrate a fundamental difference between macrophages and hepatocytes in terms of cholesterol homeostasis, and suggest an important role for UII in modulating cholesterol regulation.

Urotensin II, from fish to human

The cyclic peptide urotensin II (UII) was originally isolated from the urophysis of teleost fish on the basis of its ability to contract intestinal smooth muscle. The UII peptide has subsequently been isolated from frog brain and, later on, the pre-proUII cDNA has been characterized in mammals, including humans. A UII paralog called urotensin II-related peptide (URP) has been identified in the rat brain. The UII and URP genes originate from the same ancestral gene as the somatostatin and cortistatin genes. In the central nervous system (CNS) of tetrapods, UII is expressed primarily in motoneurons of the brainstem and spinal cord. The biological actions of UII and URP are mediated through a G protein-coupled receptor, termed UT, that exhibits high sequence similarity with the somatostatin receptors. The UT gene is widely expressed in the CNS and in peripheral organs. Consistent with the broad distribution of UT, UII and URP exert a large array of behavioral effects and regulate endocrine, cardiovascular, renal, and immune functions.

The effects of urotensin II and urantide on forearm blood flow and systemic haemodynamics in humans

AIMS

(i) To compare the effects of intra-arterial administration of urotensin II in patients with CVD with healthy volunteers, and (ii) to study the haemodynamic effects of intra-arterial infusion of the urotensin II receptor antagonist, urantide.

METHODS

Ten healthy volunteers and 10 patients with CVD received a dose-ramped brachial artery infusion of urotensin II. A further six healthy male volunteers received a prolonged urotensin II infusion and 11 healthy male volunteers received a dose-ramped infusion of urantide. Forearm blood flow (FBF) was measured every 20 min and blood pressure and heart rate were assessed every 20 min.

RESULTS

In healthy volunteers and patients with CVD, intra-arterial infusion of urotensin II had no effect on FBF ratio. A dose-ramped infusion of urantide similarly had no effect on FBF ratio. During dose-ramped infusions of urotensin II and urantide, systolic and mean arterial blood pressure increased significantly. In healthy volunteers, urotensin II and urantide, respectively, increased systolic blood pressure from 133 +/- 6 to 137 +/- 5 mmHg (P < 0.01) and from 113 +/- 4 to 120 +/- 4 mmHg (P < 0.01). In patients with CVD, heart rate also significantly increased during dose-ramped infusion of urotensin II from 59 +/- 3 to 62 +/- 4 bpm (P < 0.05).

CONCLUSIONS

We have shown no in vivo effect of urotensin II or urantide on human forearm resistance vessels. Previous discrepancies do not seem to relate to either the age or CVD status of subjects. Changes in systemic cardiovascular haemodynamics during the dose-ramped infusion studies are unlikely to be caused by urotensin II receptor modulation.

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.

A rat brain atlas of urotensin-II receptor expression and a review of central urotensin-II effects

Urotensin-II (U-II) is an 11-amino acid cyclic peptide which exerts its actions through a G(q) protein-coupled receptor, UT. Much of the research focus of U-II is as a peptide of the periphery, particularly cardiovascular. Despite this, U-II was originally identified as a neuropeptide, and its expression is broad throughout the central nervous system. This brief review article catalogs the known sites of expression of UT within the CNS in the form of a diagrammatic rat brain atlas. Furthermore, the functional consequences of UT activation within specific brain regions are discussed along with the likely actions of synthetic UT ligands. Areas of high, medium, and low expression include the arcuate, paraventricular, and pedunculopontine tegmental nuclei, respectively. In the arcuate and paraventricular nuclei, where expression is high and moderate, U-II produces a pressor/tachycardic response in the former and a weaker response in the latter. Based on the known pharmacology of UT ligands (and assuming density is the primary determinant of efficacy in this case), we predict a weak response in the arcuate nucleus and possible antagonism of endogenous U-II response in the paraventricular nucleus by a low-efficacy partial agonist. These predicted responses lend themselves to relatively simple experimental verification.

Chronic urotensin-II infusion induces diastolic dysfunction and enhances collagen production in rats

The vasoactive peptide urotensin-II (U-II) is likely to play a key causal role in cardiac remodeling that ultimately leads to heart failure. Its contribution, specifically to the development of diastolic dysfunction and the downstream intracellular signaling, however, remains unresolved. This study interrogates the effect of chronic U-II infusion in normal rats on cardiac structure and function. The contribution of Rho kinase (ROCK) signaling to these pathophysiological changes is evaluated in cell culture studies. Chronic high-dose U-II infusion over 4 wk significantly impaired diastolic function in rats on echocardiography-derived Doppler indexes, including E-wave deceleration time (vehicle 56.7 +/- 3.3 ms, U-II 118.0 +/- 21.5 ms; P < 0.01) and mitral valve annulus peak early/late diastolic tissue velocity (vehicle 2.01 +/- 0.19 ms, U-II 1.04 +/- 0.25 ms; P < 0.01). A lower dose of U-II infusion (1 nmol.kg(-1).h(-1)) yielded comparable changes. Diastolic dysfunction was accompanied by molecular [significant increases in procollagen-alpha(1)(I) gene expression on real-time PCR] and morphological (increases in total collagen, P < 0.05, and collagen type-I protein deposition, P < 0.001) evidence of left ventricular (LV) fibrosis following high-dose U-II infusion. The ROCK inhibitor GSK-576371 (10(-7) to 10(-5) M) elicited concentration-dependent inhibition of U-II (10(-7) M)-stimulated cardiac fibroblast collagen synthesis and cardiac myocyte protein synthesis. Chronic U-II infusion causes diastolic dysfunction, caused by fibrosis of the LV. The in vitro data suggest that this may be in part occurring via a ROCK-dependent pathway.

Effect of the urotensin-II receptor antagonist palosuran on secretion of and sensitivity to insulin in patients with Type 2 diabetes mellitus

AIMS

To investigate the effects of palosuran, a nonpeptidic, potent and selective antagonist of the urotensin-II receptor, on insulin and glucose regulation in 20 diet-treated patients with Type 2 diabetes mellitus in a double-blind, placebo-controlled, randomized, crossover, proof-of-concept study.

METHODS

After 4 weeks' oral treatment with 125 mg palosuran or placebo b.i.d.,effects on insulin secretion and sensitivity and blood glucose levels were assessed by means of a hyperglycaemic glucose clamp, meal tolerance test, homeostasis model assessment-insulin resistance score, and daily self-monitoring of blood glucose. Plasma concentrations of palosuran were determined for 12 h on the last day of intake.

RESULTS

Palosuran did not affect second-phase insulin response (primary end-point) during the hyperglycaemic glucose clamp in comparison with placebo [paired difference of -1.8 microU ml(-1), 95% confidence interval (CI) -7.8, 4.2]. Likewise, no effects of palosuran were detected on the first-phase insulin response, or on insulin secretion and blood glucose levels during the meal tolerance test or on homeostasis model assessment-insulin resistance score. No clinically significant effects on daily blood glucose profiles were observed during the study. Geometric mean C(max) and AUC(tau) (95% CI) and median t(max) (range) in this patient population were 180 ng ml(-1) (125, 260), 581 ng.h ml(-1) (422, 800) and 3.0 h (0.67, 4.3), respectively.

CONCLUSIONS

The results of this study indicate that antagonism of the urotensin-II system does not influence insulin secretion or sensitivity or daily blood glucose levels in diet-treated patients with Type 2 diabetes.

Pharmacokinetics and pharmacodynamics of the urotensin-II receptor antagonist palosuran in healthy male subjects

Palosuran is a new potent and specific antagonist of the human urotensin II (U-II) receptor (UT receptor). This entry-into-humans study evaluated the tolerability and safety, pharmacokinetics, and pharmacodynamics of palosuran in a double-blind, placebo-controlled, single ascending-dose design. Oral doses of 5 to 2000 mg were given to 9 sequential groups of 8 healthy young men (6 on active drug, 2 on placebo) each. At regular intervals, tolerability and safety parameters and plasma levels of palosuran and U-II were determined. Urine was collected to determine excretion of sodium, potassium, creatinine, and palosuran. In this study, palosuran was well tolerated. No serious adverse events or dose-related adverse events were reported. No treatment-related pattern was detected for vital signs, clinical laboratory parameters, or electrocardiography parameters. After rapid absorption, palosuran displayed a plasma concentration-time profile characterized by 2 peaks at approximately 1 and 4 hours after drug administration. The apparent terminal elimination half-life was approximately 20 hours. AUC and C(max) values increased proportionally with doses up to 500 mg. Excretion of unchanged palosuran in urine was limited. No consistent effect was found on any of the pharmacodynamic variables measured. The results of this entry-into-humans study warrant further investigation of the therapeutic potential of palosuran.

Elevated expression of urotensin II and its receptor in skeletal muscle of diabetic mouse

Urotensin II (UII) is a somatostatin-like peptide recently identified to be involved in metabolic regulation and to play a significant role in diabetes and its complications. In the present study, we investigated the expression of UII and its receptor UT in the soleus muscle of male diabetic KK/upj-AY/J mice (2DM group) and the effects of UII on glucose uptake by the skeletal muscle to explore the role of skeletal muscle-derived UII in the pathogenesis of insulin resistance and diabetes. Radioimmunoassay, RT-PCR, immunohistochemistry and radio-ligand binding assay were used in this study. Compared with C57BL/6J mice (control group), 2DM mice showed increased UII content, by 34.0% in plasma, 15.4% in skeletal muscle tissue and 30.6% in medium containing UII from muscle (all P<0.05 or P<0.01). UII protein and UT mRNA expression were significantly enhanced in the skeletal muscle of 2DM mice. On [(125)I]UII binding to muscle sarcolemma, UT binding exhibited a saturable single-component characteristic in a specific and time-dependent manner. Scatchard plot analysis showed higher maximal number of specific binding sites (Bmax) in skeletal muscle, by 42.9% (P<0.01), and a lower dissociation constant (Kd), by 26.4% (P<0.01), in the 2DM group than in controls. On in vitro tissue pre-incubation with UII (10(-9), 10(-8) and 10(-7) mol/L), the insulin-stimulated [(3)H]-2-DG uptake by split soleus muscle was lower, by 9.5%, 33.4% and 39.7% (all P<0.01), respectively, than without UII incubation. UII/UT upregulated in skeletal muscle of 2DM mice suggests that UII derived from skeletal muscle might induce the pathogenesis of skeletal muscle insulin resistance as an autocrine factor.

Increased plasma urotensin-II levels are associated with diabetic retinopathy and carotid atherosclerosis in Type 2 diabetes

Human U-II (urotensin-II), the most potent vasoconstrictor peptide identified to date, is associated with cardiovascular disease. A single nucleotide polymorphism (S89N) in the gene encoding U-II (UTS2) is associated with the onset of Type 2 diabetes and insulin resistance in the Japanese population. In the present study, we have demonstrated a relationship between plasma U-II levels and the progression of diabetic retinopathy and vascular complications in patients with Type 2 diabetes. Eye fundus, IMT (intima-media thickness) and plaque score in the carotid artery, BP (blood pressure), FPG (fasting plasma glucose), HbA(1c) (glycated haemoglobin), U-II, angiogenesis-stimulating factors, such as VEGF (vascular endothelial growth factor) and heregulin-beta(1), and lipid profiles were determined in 64 patients with Type 2 diabetes and 24 non-diabetic controls. FPG, HbA(1c) and VEGF levels were significantly higher in patients with Type 2 diabetes than in non-diabetic controls. Diabetes duration, insufficient glycaemic and BP control, plasma U-II levels, IMT, plaque score and nephropathy grade increased significantly across the subjects as follows: non-diabetic controls, patients with Type 2 diabetes without retinopathy (group N), patients with Type 2 diabetes with simple (background) retinopathy (group A) and patients with Type 2 diabetes with pre-proliferative and proliferative retinopathy (group B). The prevalence of obesity and smoking, age, low-density lipoprotein, triacylglycerols (triglycerides) and heregulin-beta(1) were not significantly different among the four groups. In all subjects, U-II levels were significantly positively correlated with IMT, FPG, and systolic and diastolic BP. Multiple logistic regression analysis revealed that, of the above parameters, U-II levels alone had a significantly independent association with diabetic retinopathy. In conclusion, the results of the present study provide the first evidence that increased plasma U-II levels may be associated with the progression of diabetic retinopathy and carotid atherosclerosis in patients with Type 2 diabetes.

Urotensin II is an autocrine/paracrine growth factor for aortic adventitia of rat

Urotensin II (UII) is a potent vasoconstrictive peptide; however, its significance in vascular adventitia has not been clearly elucidated. In this study, rat aortic adventitia showed mRNA expression and immunoreactivity of UII and its receptor (UT). Moreover, radioligand-binding assay showed that maximum binding capacity (Bmax) of [(125)I]-UII was higher in adventitia than in media (28.60+/-1.94 vs. 20.21+/-1.11 fmol/mg, P<0.01), with no difference in binding affinity (dissociation constant [Kd] 4.27+/-0.49 vs. 4.60+/-0.40 nM, P>0.05). Furthermore, in cultured adventitial fibroblasts, UII stimulated DNA synthesis, collagen synthesis and secretion in a concentration-dependent manner. These effects were inhibited by the UII receptor antagonist urantide (10(-6) mol/l), Ca(2+) channel blocker nicardipine (10(-5) mol/l), protein kinase C inhibitor H7 (10(-6) mol/l), and mitogen-activated protein kinase inhibitor PD98059 (10(-6) mol/l) but not the phosphatidyl inositol-3 kinase inhibitor wortmannin (10(-7) mol/l). UII may act as an autocrine/paracrine factor through its receptor and the Ca(2+) channel, protein kinase C, and mitogen-activated protein kinase signal transduction pathways, in the pathogenesis of vascular remodeling by activating vascular adventitia.

Possible pathogenic link between migraine and urotensin-II

Our aim was to determine the levels of human urotensin-II (hU-II) in the plasma of migraine patients and controls, to ascertain if there were a difference in the pathogenesis of migraine. A total of 27 patients who suffer from migraines and 27 controls were included in the study. Venous blood samples were drawn twice both from migraine patients and controls to measure hU-II plasma levels. The average levels of hU-II during migraine episode, between episodes, and controls were found to be 0.483, 0.493, and 0.737 pg/mL, respectively. The levels of hU-II in the controls were higher significantly. When comparisons were made according to sex, age groups, and types and durations of migraine, there was no significant difference in the levels of hU-II in the patients. The low levels of hU-II in the plasma of migraine patients compared with controls may be an indicator of its role in the pathogenesis.

Characterization of urotensin II, distribution of urotensin II, urotensin II-related peptide and UT receptor mRNAs in mouse: evidence of urotensin II at the neuromuscular junction

Urotensin II (UII) and UII-related peptide (URP) are paralog neuropeptides whose existence and distribution in mouse have not yet been investigated. In this study, we showed by HPLC/RIA analysis that the UII-immunoreactive molecule in the mouse brain corresponds to a new UII(17) isoform. Moreover, calcium mobilization assays indicated that UII(17) and URP were equally potent in stimulating UII receptor (UT receptor). Quantitative RT-PCR and in situ hybridization analysis revealed that in the CNS UII and URP mRNAs were predominantly expressed in brainstem and spinal motoneurons. Besides, they were differentially expressed in the medial vestibular nucleus, locus coeruleus and the ventral medulla. In periphery, both mRNAs were expressed in skeletal muscle, testis, vagina, stomach, and gall bladder, whereas only URP mRNA could be detected in the seminal vesicle, heart, colon, and thymus. By contrast, the UT receptor mRNA was widely expressed, and notably, very high amounts of transcript occurred in skeletal muscle and prostate. In the biceps femoris muscle, UII-like immunoreactivity was shown to coexist with synaptophysin in muscle motor end plate regions. Altogether these results suggest that (i) UII and URP may have many redundant biological effects, especially at the neuromuscular junction; (ii) URP may more specifically participate to autonomic, cardiovascular and reproductive functions.

Urotensin II: a new pharmacologic target in the treatment of cardiovascular disease

Urotensin II was first identified over 30 years ago as a potent vasoconstrictor, and the identification of its receptor in the heart, lungs, blood vessels, and brain have made it a potential target for human pharmacotherapy. Current research would suggest that urotensin II plays a major role in the pathophysiology of various cardiovascular disease entities. This article discusses the biologic effects of urotensin under normal and pathophysiologic conditions, and reviews the research experiences with synthetic urotensin blockers in the treatment of various cardiovascular illnesses.

Structure-activity relationships of urotensin II and URP

Urotensin II (U-II) and urotensin II-related peptide (URP) are the endogenous ligands for the orphan G-protein-coupled receptor GPR14 now renamed UT. At the periphery, U-II and/or URP exert a wide range of biological effects on cardiovascular tissues, airway smooth muscles, kidney and endocrine glands, while central administration of U-II elicits various behavioral and cardiovascular responses. There is also evidence that U-II and/or URP may be involved in a number of pathological conditions including heart failure, atherosclerosis, renal dysfunction and diabetes. Because of the potential involvement of the urotensinergic system in various physiopathological processes, there is need for the rational design of potent and selective ligands for the UT receptor. Structure-activity relationship studies have shown that the minimal sequence required to retain full biological activity is the conserved U-II(4-11) domain, in particular the Cys5 and Cys10 residues involved in the disulfide bridge, and the Phe6, Lys8 and Tyr9 residues. Free alpha-amino group and C-terminal COOH group are not necessary for the biological activity, and modifications of these radicals may even increase the stability of the analogs. Punctual substitution of native amino acids, notably Phe6 and Trp7, by particular residues generates analogs with antagonistic properties. These studies, which provide crucial information regarding the structural and conformational requirements for ligand-receptor interactions, will be of considerable importance for the design of novel UT ligands with increased selectivity, potency and stability, that may eventually lead to the development of innovative drugs.

Immunolocalization of urotensin II and its receptor in human adrenal tumors and attached non-neoplastic adrenal tissues

Urotensin II (UII), first identified from goby urophysis, is a potent vasoactive peptide hormone and an endogenous ligand for an orphan G protein-coupled receptor GPR14, now named urotensin II receptor (UT-R). In addition to its vascular actions, UII has been shown to have mitogenic effects on tumor growth and some regulatory effects on adrenal steroidogenesis. In the present study, we examined expression of UII and UT-R in human adrenal tumors and attached non-neoplastic adrenal tissues by immunohistochemistry. Both UII and UT-R were immunolocalized in tumor cells of all adrenal tumors examined: 8 cases of cortisol-producing adenomas, 8 cases of aldosterone-producing adenomas, 2 cases of non-functioning adenomas, 17 cases of adrenocortical carcinomas, and 8 cases of pheochromocytomas. In attached adrenals, immunoreactivity for UII was detected in medulla, but much weaker in the cortex than in cortical tumors, suggesting that expression of UII was up-regulated in neoplastic adrenocortical tissues. No significant differences were found in the degree of immunoreactivity for UT-R between the tumors and the attached adrenal tissues. The present study showed that both UII and UT-R were expressed in the adrenal tumors and attached non-neoplastic adrenal tissues, and suggests possible roles of UII and UT-R in tumor growth and/or secretory activities of these tumors.

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.

Effect of GABA A receptor activation on UT-coupled signaling pathways in rat cortical astrocytes

Cultured rat cortical astrocytes express two types of urotensin II (UII) binding sites: a high affinity site corresponding to the UT (GPR14) receptor and a low affinity site that has not been fully characterized. Activation of the high affinity site in astroglial cells stimulates polyphosphoinositide (PIP) turnover and provokes an increase in intracellular calcium concentration. We have hypothesized that the existence of distinct affinity sites for UII in rat cortical astrocytes could be accounted for by a possible cross-talk between UT and the ligand-gated ion channel GABA(A) receptor (GABA A R). Exposure of cultured astrocytes to UII provoked a bell-shaped increase in cAMP production, with an EC50 stimulating value of 0.83+/-0.04 pM, that was totally blocked in the presence of the adenylyl cyclase inhibitor SQ 22,536. In contrast, UII was found to inhibit forskolin-induced cAMP formation. In the presence of the specific PKA inhibitor H89, UII provoked a sustained stimulation of cAMP formation. Inhibition of PKA by H89 strongly reduced the stimulatory effect of UII on PIP metabolism. GABA and the GABA A R agonist isoguvacine provoked a marked inhibition of UII-induced cAMP synthesis and a significant reduction of UII-evoked PIP turnover. These data suggest that functional interaction between UT and GABA(A)R negatively regulates coupling of UT to the classical PLC/IP(3) signaling cascade as well as to the adenylyl cyclase/PKA pathway.

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.

Elevated expression of urotensin II and its receptor in diabetic cardiomyopathy

OBJECTIVE

Urotensin II (UII) is a somatostatin-like peptide recently identified to have several cardiovascular effects, including potent vasoactive, cardiac inotropic and chronotropic properties. Our aim was to determine the degree of expression of UII and UII receptor (UT) in the myocardium of rats with streptozotocin (STZ)-induced diabetes.

METHODS

Real-time polymerase chain reaction, Western blot, and immunohistochemistry were used to determine the degree of expression and location of UII and UT in the myocardium of STZ-induced diabetic rats.

RESULTS

UII and UT expression were significantly enhanced in the myocardium of rats with diabetes compared with healthy controls on both messenger RNA and protein levels. Both UII and UT protein expression were mainly concentrated in the cardiomyocytes, endothelial cells, cardiac fibroblasts, and smooth muscle cells of diabetic cardiomyopathy (DCM).

CONCLUSIONS

Our results suggest a possible role for the UII/UT system in the pathophysiology of DCM.

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.

Investigation of the mechanisms by which chronic infusion of an acutely subpressor dose of angiotensin II induces hypertension

The mechanisms by which chronic infusion of an initially subpressor low dose of angiotensin II (ANG II) causes a progressive and sustained hypertension remain unclear. In conscious sheep ( n = 6), intravenous infusion of ANG II (2 μg/h) gradually increased mean arterial pressure (MAP) from 82 ± 3 to 96 ± 5 mmHg over 7 days ( P < 0.001). This was accompanied by peripheral vasoconstriction; total peripheral conductance decreased from 44.6 ± 6.4 to 38.2 ± 6.7 ml·min−1·mmHg−1 ( P < 0.001). Cardiac output and heart rate were unchanged. In the regional circulation, mesenteric, renal, and iliac conductances decreased but blood flows were unchanged. There was no coronary vasoconstriction, and coronary blood flow increased. Ganglion blockade (125 mg/h hexamethonium for 4 h) reduced MAP by 13 ± 1 mmHg in the control period and by 7 ± 2 mmHg on day 8 of ANG II treatment. Inhibition of central AT1 receptors by intracerebroventricular infusion of losartan (1 mg/h for 3 h) had no effect on MAP in the control period or after 7 days of ANG II infusion. Pressor responsiveness to incremental doses of intravenous ANG II (5, 10, 20 μg/h, each for 15 min) was unchanged after 7 days of ANG II infusion. ANG II caused no sodium or water retention. In summary, hypertension due to infusion of a low dose of ANG II was accompanied by generalized peripheral vasoconstriction. Indirect evidence suggested that the hypertension was not neurogenic, but measurement of sympathetic nerve activity is required to confirm this conclusion. There was no evidence for a role for central angiotensinergic mechanisms, increased pressor responsiveness to ANG II, or sodium and fluid retention.

Structure-activity relationships of a novel series of urotensin II analogues: identification of a urotensin II antagonist

Urotensin II (U-II) is a potent vasoconstrictor peptide which has been identified as the endogenous ligand for the orphan G protein-coupled receptor GPR14 now renamed UT receptor. As the C-terminal cyclic hexapeptide of U-II (U-II(4-11), H-Asp-Cys-Phe-Trp-Lys-Tyr-Cys-Val-OH) possesses full biological activity, we have synthesized a series of U-II(4-11) analogues and measured their binding affinity on hGPR14-transfected CHO cells and their contractile activity on de-endothelialized rat aortic rings. The data indicate that a free amino group and a functionalized side-chain at the N-terminal extremity of the peptide are not required for biological activity. In addition, the minimal chemical requirement at position 9 of U-II(4-11) is the presence of an aromatic moiety. Most importantly, replacement of the Phe6 residue by cyclohexyl-Ala (Cha) led to an analogue, [Cha6]U-II(4-11), that was devoid of agonistic activity but was able to dose-dependently suppress the vasoconstrictor effect of U-II on rat aortic rings. These new pharmacological data, by providing further information regarding the structure-activity relationships of U-II analogues, should prove useful for the rational design of potent and nonpeptidic UT receptor agonists and antagonists.

Does cigarette smoking increase plasma urotensin II concentrations?

OBJECTIVE

Human urotensin II (UII) acts on the urotensin (UT) receptor and is the most potent mammalian vasoconstrictor identified to date. The role of UII in human cardiovascular regulation remains unclear, and the results of plasma measurements have been conflicting, perhaps because different measurement techniques have been used. The effects of cigarette smoking on plasma UII concentrations are unknown. The primary aim of our study was to demonstrate whether cigarette smoking had any effect on plasma UII concentrations in otherwise healthy volunteers. Our secondary aim was to compare the results obtained from assaying simultaneously using both radioimmunoassay (RIA) and immunoluminometric assay (ILMA).

METHODS

Blood was taken from 20 healthy male non-smokers and 20 healthy male cigarette smokers. Plasma was separated and stored at -70 degrees C. Samples were batch analysed simultaneously for UII using RIA and ILMA.

RESULTS

Median (range) plasma UII concentrations were lower in non-smokers [1.67 (1.0-2.27) pg ml(-1)] compared to smokers [2.62 (1.87-3.46) pg ml(-1)] (P = 0.03) measured using RIA. Those who had smoked a cigarette in the 10 min before sampling had greater concentrations of UII [3.10 (1.87-4.60) pg ml(-1)] compared to controls (P = 0.01). Plasma UII concentrations determined by ILMA were consistently low with no differences between groups.

CONCLUSION

The data obtained by RIA show that smoking may increase plasma concentrations of UII with a more pronounced increase when a cigarette has been smoked recently. There was a complete lack of correlation between RIA and ILMA for the whole data set, which suggests that some of the variability in plasma UII reported in the literature may result from differences between assays.

Urotensin-II induces ear flushing in rats

BACKGROUND AND PURPOSE

While investigating the effects of systemic urotensin II (U-II), a potent vasoactive peptide acting at the UT receptor, we observed ear pinna flushing after systemic administration to conscious rats. In the present study, U-II-induced ear flushing was quantified in terms of ear pinna temperature change and potential mechanisms were explored.

EXPERIMENTAL APPROACH

U-II-induced ear flushing was quantified by measuring lateral ear pinna temperature changes and compared to that of calcitonin gene-related peptide (CGRP), a known cutaneous vasodilator. Further, the effects of a variety of pharmacological agents on U-II-induced ear flushing were explored.

KEY RESULTS

Subcutaneous injection of U-II (9 microg kg(-1))produced localized ear pinna flushing with an onset of approximately 15 min, a duration of approximately 30 min and a maximal temperature change of 9 degrees C. In contrast, CGRP caused cutaneous flushing within multiple cutaneous beds including the ear pinna with a shorter onset and greater duration than U-II. A potent UT receptor antagonist, urantide, blocked U-II-induced ear flushing but did not affect CGRP-induced ear flushing. Pretreatment with indomethacin or L-Nomega-nitroarginine methylester (L-NAME) abolished U-II-induced ear flushing. Mecamylamine or propranolol did not affect this response to U-II. Direct intracerebroventricular injection studies suggested that the ear flushing response to U-II was not mediated directly by the CNS.

CONCLUSION AND IMPLICATIONS

Our results suggest that U-II-induced ear flushing and temperature increase is mediated by peripheral activation of the UT receptor and involves prostaglandin- and nitric oxide-mediated vasodilation of small capillary beds in the rat ear pinna.

Cardiovascular effects of native and non-native urotensin II and urotensin II-related peptide on rat and salmon hearts

Urotensin II (UII) was first discovered in the urophyses of goby fish and later identified in mammals, while urotensin II-related peptide (URP) was recently isolated from rat brain. We studied the effects of UII on isolated heart preparations of Chinook salmon and Sprague-Dawley rats. Native rat UII caused potent and sustained, dose-dependent dilation of the coronary arteries in the rat, whereas non-native UII (human and trout UII) showed attenuated vasodilation. Rat URP dilated rat coronary arteries, with 10-fold less potency compared with rUII. In salmon, native trout UII caused sustained dilation of the coronary arteries, while rat UII and URP caused significant constriction. Nomega-nitro-(l)-arginine methyl (l-NAME) and indomethacin significantly attenuated the URP and rat UII-induced vasodilation in the rat heart. We conclude that UII is a coronary vasodilator, an action that is species form specific. We also provide the first evidence for cardiac actions of URP, possibly via mechanisms common with UII.

Human urotensin II as a link between hypertension and coronary artery disease

Hypertension is a well-known risk factor for atherosclerosis, but the molecular mechanisms that link elevated blood pressure to the progression of atherosclerosis remain unclear. Human urotensin II (U-II), the most potent endogenous vasoconstrictor peptide identified to date, and its receptor (UT receptor) are involved in the etiology of essential hypertension. In patients with essential hypertension, U-II infused into the forearm brachial artery has been shown to induce vasoconstriction. Recent studies have demonstrated elevated plasma U-II concentrations in patients with essential hypertension, diabetes mellitus, atherosclerosis, and coronary artery disease. U-II is expressed in endothelial cells, macrophages, macrophage-derived foam cells, and myointimal and medial vascular smooth muscle cells (VSMCs) of atherosclerotic human coronary arteries. UT receptors are present in VSMCs of human coronary arteries, the thoracic aorta and cardiac myocytes. Lymphocytes are the most active producers of U-II, whereas monocytes and macrophages are the major cell types expressing UT receptors, with relatively little receptor expression in foam cells, lymphocytes, and platelets. U-II accelerates foam cell formation by up-regulation of acyl-coenzyme A:cholesterol acyltransferase-1 in human monocyte-derived macrophages. In human endothelial cells, U-II promotes cell proliferation and up-regulates type 1 collagen expression. U-II also activates nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and plasminogen activator inhibitor-1 in human VSMCs, and stimulates VSMC proliferation with synergistic effects observed when combined with oxidized low-density lipoprotein, lysophosphatidylcholine, reactive oxygen species or serotonin. These findings suggest that U-II plays key roles in accelerating the development of atherosclerosis, thereby leading to coronary artery disease.

Regional heterogeneity in the haemodynamic responses to urotensin II infusion in relation to UT receptor localisation

The aim of the study was to measure regional haemodynamic responses to 6 h infusions of human urotensin II (hUII), to identify possible mediators of the effects observed, and to relate the findings to the distribution of urotensin II receptors (UT receptors). Male, Sprague-Dawley rats had pulsed Doppler flow probes and intravascular catheters implanted for measurement of regional haemodynamics in the conscious, freely moving state. Infusions of saline (0.4 ml h(-1)) or hUII (30, 300 and 3,000 pmol kg(-1) h(-1)) were given i.v. for 6 h, and the effects of pretreatment with indomethacin (5 mg kg(-1) h(-1)), N(G)-nitro-L-arginine methyl ester (L-NAME, 3 mg kg(-1) h(-1)) or propranolol (1 mg kg(-1); 0.5 mg kg(-1) h(-1)) on responses to hUII (300 pmol kg(-1) h(-1) for 6 h) were assessed. Cellular localisation of UT receptor-like immunoreactivity was determined in relevant tissues. hUII caused dose-dependent tachycardia and hindquarters vasodilatation, accompanied by a slowly developing rise in blood pressure. Haemodynamic effects of hUII were attenuated by propranolol or L-NAME and abolished by indomethacin. UT receptor-like immunoreactivity was detected in skeletal and vascular smooth muscle. The findings indicate that in conscious rats, infusions of hUII cause vasodilatation, which, of the vascular beds monitored, is selective for the hindquarters and dependent on cyclooxygenase products and nitric oxide. The pressor effect of hUII under these conditions is likely to be due to an increase in cardiac output, possibly due to a positive inotropic effect. UT receptor-like immunoreactivity present in skeletal muscle is consistent with the haemodynamic pattern.