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 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.

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.

Ontogeny of the renal urotensin II system in the rat.

Urotensin II (UII), a peptide hormone which influences glomerular filtration rate and urine concentration, and its receptor, UT, are expressed in the adult rat kidney. The ability of the kidney to reabsorb sodium and water starts to develop in utero and matures during early postnatal life in the rat, yet little is known about the ontogeny of the renal UII system. This study mapped renal expression of the urotensin system during the fetal and postnatal periods and determined renal activity of UII in the immature rat. Urotensin II peptide and mRNA were present in Sprague-Dawley (SD) rat metanephroi from the earliest stage examined, embyonic day 19 (E19; rat gestation 22 days); levels increased to peak at 4 weeks of age. In contrast, UT protein and mRNA expression declined rapidly between E19 and birth and remained at a similar level postnatally. Infusion of rat UII [6-60 pmol min(-1) (100 g body weight)(-1)] or rat urotensin-related peptide [6 pmol min(-1) (100 g body weight)(-1)] in anaesthetized 4-week-old SD rats had no influence on measured renal parameters; however, infusion of UT antagonist, SB-706375 (0.01 mg kg(-1) min(-1)), provoked a pronounced diuresis [vehicle 23.5 ± 1.9 versus antagonist 75.3 ± 12.5 µl min(-1) (100 g body weight)(-1); P < 0.001] and natriuresis, accompanied by modest increases in effective renal blood flow and glomerular filtration rate [vehicle 0.4 ± 0.1 versus antagonist 1.1 ± 0.2 ml min(-1) (100 g body weight)(-1); P < 0.0001] and a significant increase in fractional sodium excretion. These results indicate that the endogenous rat UII system may influence renal sodium and water excretion before the onset of full urine concentrating capacity in the SD rat.

Urantide alleviates monocrotaline induced pulmonary arterial hypertension in Wistar rats.

Pulmonary arterial hypertension (PAH) is a serious disorder with poor prognosis. Urotensin II (UII) has been confirmed to be powerful vasoconstrictor than endothelin-1, which may play an important role in PAH development. The aim of this study is to observe the effects of urantide, a UII receptor antagonist, on monocrotaline (MCT) induced PAH in rats. 60 male Wistar rats were divided into six groups. For early treatment experiment, rats were divided into normal control group, MCT(4w) model group (MCT + saline × 3 wks from the 8th day of MCT injection) and urantide early treatment group (MCT + urantide 10 µg/kg/d × 3 wks, 1 week after MCT injection once). For late treatment experiment, rats were divided as controls, MCT(6w) model group (MCT + saline × 2 wks, 4 weeks after MCT injection once) and urantide late treatment group (MCT + urantide 10 µg/kg/d × 2 wks, 4 weeks after MCT injection once). At the end of experiments, mean pulmonary arterial pressures (mPAP) and mean blood pressure (MBP) of rats in each group were measured by catheterization. Right ventricular weight ratio was also weighed. Relaxation effects of urantide on intralobar pulmonary arterial rings of normal control and MCT(4w) model rats were investigated. Pulmonary artery remodeling was detected by hematoxylin and eosin (HE) staining and immunohistochemistry analysis. Serum nitric oxide (NO) levels in all six groups were assayed by ELISA kits. Urantide markedly reduced the mPAP levels of MCT induced PAH in both early and late treatment groups. It didn't change the MBP. Urantide dose-dependently relaxed the pulmonary arterial rings of normal control and MCT(4w) model rats. Moreover, N(G)-Nitro-l-arginine Methyl Ester (l-NAME) blocked the dilation response induced by urantide. In addition, urantide inhibited the pulmonary vascular remodeling remarkably. Serum NO level elevated in both early and late treatment rats with urantide infusion. These results suggest that urantide effectively alleviated MCT induced rats PAH may through relaxing pulmonary arteries and inhibiting pulmonary vascular remodeling. NO pathway might be one of the mechanisms in urantide induced pulmonary artery dilation. Thus, it is expected that urantide may be a novel therapy for PAH.

Urantide alleviates the symptoms of atherosclerotic rats in vivo and in vitro models through the JAK2/STAT3 signaling pathway.

Atherosclerosis is the leading cause of human death, and its occurrence and development are related to the urotensin II (UII) and UII receptor (UT) system and the biological function of vascular smooth muscle cells (VSMCs). During atherosclerosis, impaired biological function VSMCs may promote atherosclerotic plaque formation. The Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) pathway is an important mediator of signal transduction; however, the role of this signaling pathway in atherosclerosis and VSMCs remains unknown. This study aimed to investigate the effects of urantide on the JAK2/STAT3 signaling pathway in atherosclerosis. We examined the effect of urantide on the UII/UT system and the JAK2/STAT3 signaling pathway in a high fat diet induced atherosclerosis rat model and studied the effect and mechanism of urantide on the phenotypic transformation of VSMCs. We found that the UII/UT system and JAK2/STAT3 signaling pathway were highly activated in the thoracic aorta in atherosclerotic rats and in ox-LDL- and UII-induced VSMCs. After urantide treatment, the pathological changes in atherosclerotic rats were effectively improved, and the activities of the UII/UT system and JAK2/STAT3 signaling pathway were inhibited. Moreover, urantide effectively inhibited proliferation and migration and reversed the phenotypic transformation of VSMCs. These results demonstrated that urantide may control the JAK2/STAT3 signaling pathway by antagonizing the UII/UT system, thereby maintaining the biological function of VSMCs and potentially preventing and curing atherosclerosis.

Identification of novel Urotensin-II receptor antagonists with potent inhibition of U-II induced pressor response in mice.

Urotensin II (U-II) has been found to be one of the most potent vasoconstrictor (Ames et al., 1999; Bohm et al., 2002) reported till date. U-II exerts its response via activation of a G-protein coupled receptor, Urotensin II receptor(UT). Binding of U-II to UT leads to an instant increase in the inositol phosphate turnover and intracellular Ca2+. Such an instant Ca2+ release and potent vasoconstriction exerted by U-II is expected to have an important role in the progression of cardiac diseases. We have previously shown that UT antagonist DS37001789 prevents U-II induced blood pressure elevation in mice (Nishi et al., 2019) in a dose dependent manner, with potent efficacy at 30 and 100 mg/kg. Further to this, we have also shown that DS37001789 ameliorates mortality in pressure-overload mice with heart failure (Nishi et al., 2020). We therefore conducted an extensive structure-activity relationship studies to identify molecules with superior efficacy. In the present manuscript, we report the identification of two potent, non-peptide small molecule antagonists of Urotensin II receptor (UT), RCI-0879 and RCI-0298 which blocked the action of U-II, both in vitro and in vivo. These molecules were found to be very potent in in vitro Ca2+ and radioligand binding assays using human and mouse UT over-expressing CHO cells. RCI-0879 and RCI-0298 also exhibited superior efficacy in in vivo mouse pressor response model using C57BL/6 mice, compared to our initial molecules (Nishi et al., 2019) and demonstrated ED50 values of 3.2 mg/kg and 6.8 mg/kg respectively. Our findings reported herewith, further strengthen our concept and belief in UT antagonization as a potential therapeutic approach for the management of chronic heart failure.

Urantide attenuates myocardial damage in atherosclerotic rats by regulating the MAPK signalling pathway.

OBJECTIVE: To explore the effect of urantide on atherosclerotic myocardial injury by antagonizing the urotensin II/urotensin II receptor (UII/UT) system and regulating the mitogen-activated protein kinase (MAPK) signalling pathway. METHODS: Atherosclerosis (AS) was established in rats by administering a high-fat diet and an intraperitoneal injection of vitamin D3. The effect of treatment with urantide (30 µg/kg), a UII receptor antagonist, for 3, 7, or 14 days on AS-induced myocardial damage was evaluated. RESULTS: The heart of rats with AS exhibited pathological changes suggestive of myocardial injury, and the serum levels of creatine kinase (CK) and lactate dehydrogenase (LDH) were significantly increased. Additionally, significant increases in the levels of UII, its receptor (G protein-coupled receptor 14, GPR14), p-P38, p-extracellular signal-regulated kinase (ERK) and p-c-Jun N-terminal kinase (JNK) were observed in the heart. Urantide improved pathological changes in the heart of rats with AS and reduced the serum CK and LDH levels. Additionally, the UII antagonist decreased the increased levels of UII, GPR14, p-P38, p-ERK and p-JNK in the heart. CONCLUSIONS: Urantide alleviates atherosclerotic myocardial injury by inhibiting the UII-GPR14 interaction and regulating the MAPK signalling pathway. We hypothesized that myocardial injury may be associated with the regulation of the MAPK signalling pathway.

Magnolol depresses urotensin-II-induced cell proliferation in rat cardiac fibroblasts.

1. Accumulating evidence suggests that oxidative stress plays a key role in the development of cardiac fibrosis. Urotensin-II (U-II) has been reported to play an important role in cardiac remodelling and fibrosis. Recently, we demonstrated the involvement of reactive oxygen species (ROS) production in U-II-induced cardiac fibroblast proliferation. Magnolol is an anti-oxidant compound extracted from the cortices of Magnolia officinalis. Thus, it is feasible that magnolol may attenuate cardiac fibroblast proliferation by inhibiting ROS production. Therefore, the aims of the present study were to determine whether magnolol alters U-II-induced cell proliferation and to identify the putative underlying signalling pathways in rat cardiac fibroblasts. 2. Cultured rat cardiac fibroblasts were pretreated with magnolol (1, 3 and 10 micromol/L) for 30 min, followed by exposure to U-II (30 nmol/L) for 24 h, after which cell proliferation and endothelin-1 (ET-1) protein secretion was examined. The effects of magnolol on U-II-induced ROS formation and extracellular signal-regulated kinase (ERK) phosphorylation were examined to elucidate the intracellular mechanisms by which magnolol affects cell proliferation and ET-1 expression. 3. Urotensin-II (30 nmol/L) stimulated cell proliferation, ET-1 protein secretion and ERK phosphorylation, all of which were inhibited by magnolol (10 micromol/L). Pretreatment of cardiac fibroblasts with N-acetylcysteine (5 mmol/L) for 30 min prior to exposure to U-II resulted in inhibition of U-II increased ROS formation. Similar effects were observed with 10 micromol/L magnolol. 4. In conclusion, the results suggest that magnolol inhibits cardiac fibroblast proliferation by interfering with ROS generation. Thus, the present study provides important new insights into the molecular pathways involved, which may contribute to our understanding of the effects of magnolol on the cardiovascular system.

Urotensin receptor antagonist palosuran attenuates cyclosporine-a-induced nephrotoxicity in rats.

BACKGROUND: Cyclosporine-A (CsA) is widely used for immunosuppressive therapy in renal transplantation. Nephrotoxicity is the main dose-limiting undesirable consequence of CsA. Urotensin II (U-II), a novel peptide with a powerful influence on vascular biology, has been added to the list of potential renal vascular regulators. Upregulation of the urotensin receptors and elevation of plasma U-II levels are thought to possibly play a role in the etiology of renal failure. OBJECTIVES: The present study examines this hypothesis by evaluating renal function and histology with regard to the potential role of U-II and its antagonist, palosuran, in the pathogenesis of CsA-induced nephrotoxicity in rats. MATERIAL AND METHODS: Male Sprague-Dawley rats were treated with CsA (15 mg/kg, for 21 days, intraperitoneally) or CsA + palosuran (300 mg/kg, for 21 days). Renal function was measured and histopathology, U-II immunostaining and protein detection with western blotting of the kidneys were performed. RESULTS: Cyclosporine-A administration caused a marked decline in creatinine clearance (Ccr). Fractional sodium excretion (FENa) tended to increase in the CsA-treated rats. Plasma U-II levels decreased in the CsA-treated rats. Cyclosporine-A treatment resulted in a marked deterioration in renal histology and an increase in the expression of U-II protein in the kidneys. Palosuran's improvement of renal function manifested as a significant decrease in serum creatinine levels and a significant increase in urine creatinine levels, resulting in a marked increase in Ccr. Palosuran produced a significant normalization of kidney histology and prevented an increase in U-II expression. CONCLUSIONS: Cyclosporine-A-induced renal impairment was accompanied by an increase in U-II expression in kidneys and a contrary decrease in systemic U-II levels. Palosuran improved the condition of rats suffering from renal dysfunction by preventing the decrease in renal U-II expression without affecting the systemic levels of U-II. The protective effect of palosuran in CsA nephrotoxicity is possibly independent of its U-II receptor antagonism.

Towards Targeting the Urotensinergic System: Overview and Challenges.

The urotensinergic system, comprised of a G protein-coupled receptor (UT) and two endogenous ligands named urotensin II (UII) and urotensin II-related peptide (URP), has garnered significant attention due to its involvement in the initiation and/or the evolution of various diseases. Accordingly, multiple studies using animal models have demonstrated that UT antagonists may have utility as potential therapeutic agents for treating atherosclerosis, pulmonary arterial hypertension, heart failure, and cancer. Unfortunately, clinical investigations of UT antagonist candidates showed limited efficacy in humans. This system, which has yet to be effectively targeted, therefore remains to be therapeutically exploited. Here, we discuss various hypotheses that could explain the in vivo failure of UT antagonists.

Novel insights into the role of urotensin II in cardiovascular disease.

Urotensin II (UII) is a vasoactive peptide that interacts with a specific receptor called the UT receptor. UII has been implicated in cardiovascular regulation, with promising therapeutic applications based on UT receptor antagonism. The endogenous ligands of the UT receptor: UII and urotensin-related peptide (URP), differentially bind and activate this receptor. Also, the receptor localization is not restricted to the plasma membrane, possibly inducing different physiological responses that could support its inconsistent, but potent, vasoactive activity. These properties could explain the disappointing outcomes in clinical studies, in contrast to the positive preclinical results regarding heart failure, pulmonary hypertension, atherosclerosis and diabetes mellitus. These aspects should be considered in future investigations to a better comprehension of the role of UII as a potential therapeutic target.

Cafestol Activates Nuclear Factor Erythroid-2 Related Factor 2 and Inhibits Urotensin II-Induced Cardiomyocyte Hypertrophy.

Through population-based studies, associations have been found between coffee drinking and numerous health benefits, including a reduced risk of cardiovascular disease. Active ingredients in coffee have therefore received considerable attention from researchers. A wide variety of effects have been attributed to cafestol, one of the major compounds in coffee beans. Because cardiac hypertrophy is an independent risk factor for cardiovascular events, this study examined whether cafestol inhibits urotensin II (U-II)-induced cardiomyocyte hypertrophy. Neonatal rat cardiomyocytes were exposed only to U-II (1 nM) or to U-II (1 nM) following 12-h pretreatment with cafestol (1-10 µ M). Cafestol (3-10 µ M) pretreatment significantly inhibited U-II-induced cardiomyocyte hypertrophy with an accompanying decrease in U-II-induced reactive oxygen species (ROS) production. Cafestol also inhibited U-II-induced phosphorylation of redox-sensitive extracellular signal-regulated kinase (ERK) and epidermal growth factor receptor transactivation. In addition, cafestol pretreatment increased Src homology region 2 domains-containing phosphatase-2 (SHP-2) activity, suggesting that cafestol prevents ROS-induced SHP-2 inactivation. Moreover, nuclear factor erythroid-2-related factor 2 (Nrf2) translocation and heme oxygenase-1 (HO-1) expression were enhanced by cafestol. Addition of brusatol (a specific inhibitor of Nrf2) or Nrf2 siRNA significantly attenuated cafestol-mediated inhibitory effects on U-II-stimulated ROS production and cardiomyocyte hypertrophy. In summary, our data indicate that cafestol prevented U-II-induced cardiomycyte hypertrophy through Nrf2/HO-1 activation and inhibition of redox signaling, resulting in cardioprotective effects. These novel findings suggest that cafestol could be applied in pharmacological therapy for cardiac diseases.

Urotensin-II and cardiovascular remodeling.

Urotensin-II (U-II), a cyclic undecapeptide, and its receptor, UT, have been linked to vascular and cardiac remodeling. In patients with coronary artery disease (CAD), it has been shown that U-II plasma levels are significantly greater than in normal patients and the severity of the disease is increased proportionally to the U-II plasma levels. We showed that U-II protein and mRNA levels were significantly elevated in the arteries of patients with coronary atherosclerosis in comparison to healthy arteries. We observed U-II expression in endothelial cells, foam cells, and myointimal and medial vSMCs of atherosclerotic human coronary arteries. Recent studies have demonstrated that U-II acts in synergy with mildly oxidized LDL inducing vascular smooth muscle cell (vSMC) proliferation. Additionally, U-II has been shown to induce cardiac fibrosis and cardiomyocyte hypertrophy leading to cardiac remodeling. When using a selective U-II antagonist, SB-611812, we demonstrated a decrease in cardiac dysfunction including a reduction in cardiomyocyte hypertrophy and cardiac fibrosis. These findings suggest that U-II is undoubtedly a potential therapeutic target in treating cardiovascular remodeling.

N-alkyl-5H-pyrido[4,3-b]indol-1-amines and derivatives as novel urotensin-II receptor antagonists.

High throughput screening of our compound collection led to the discovery of a novel series of N-alkyl-5H-pyrido[4,3-b]indol-1-amines as urotensin-II receptor antagonists. Synthesis, initial structure and activity relationships, functional and animal ortholog activities of the series are described.

Potent and selective small-molecule human urotensin-II antagonists with improved pharmacokinetic profiles.

Lead compound 1 was successfully redesigned to provide compounds with improved pharmacokinetic profiles for this series of human urotensin-II antagonists. Replacement of the 2-pyrrolidinylmethyl-3-phenyl-piperidine core of 1 with a substituted N-methyl-2-(1-pyrrolidinyl)ethanamine core as in compound 7 resulted in compounds with improved oral bioavailability in rats. The relationship between stereochemistry and selectivity for hUT over the kappa-opioid receptor was also explored.

Aminomethylpiperazines as selective urotensin antagonists.

Aminomethylpiperazines, reported previously as being kappa-opioid receptor agonists, were identified as lead compounds in the development of selective urotensin receptor antagonists. Optimized substitution of the piperazine moiety has provided high affinity urotensin receptor antagonists with greater than 100-fold selectivity over the kappa-opioid receptor. Select compounds were found to inhibit urotensin-induced vasoconstriction in isolated rat aortic rings consistent with the hypothesis that an urotensin antagonist may be useful for the treatment of hypertension.

[The role of urotensin II in human pathophysiology]. / Rola urotensyny II w patofizjologii czlowieka.

Human urotensin II (U-II) is a cyclic peptide generated by proteolytic cleavage from a precursor prohormone. It was first isolated from the fish spinal cord and has been recognized as a hormone in the neurosecretory system of teleost fish. It is expressed in the human central nervous system as well as other tissues, such as kidney, spleen, small intestine, thymus, prostate, pituitary and adrenal gland and circulates in human plasma. The plasma U-II level is elevated in renal failure, congestive heart failure, diabetes mellitus, systemic hypertension and portal hypertension caused by liver cirrhosis. The effect of U-II on the vascular system is variable, depending on species, vascular bed and caliber of the vessel. The net effect on vascular tone is a balance between endothelium-independent vasoconstriction and endothelium-dependent vasodilatation. Urotensin II is also a neuropeptide and may play a role in tumor development. The development of U-II receptor antagonists may provide a useful research tool as well as a novel treatment not only for cardiovascular diseases.

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.

Phenylpiperidine-benzoxazinones as urotensin-II receptor antagonists: synthesis, SAR, and in vivo assessment.

Various 4-phenylpiperidine-benzoxazin-3-ones were synthesized and biologically evaluated as urotensin-II (U-II) receptor antagonists. Compound 12i was identified from in vitro evaluation as a low nanomolar antagonist against both rat and human U-II receptors. This compound showed in vivo efficacy in reversing the ear-flush response induced by U-II in rats.