Urocortin has cell-proliferative effects on cardiac non-myocytes

Stress hormones mediate developmental plasticity in vertebrates with complex life cycles

The environment experienced by developing organisms can shape the timing and character of developmental processes, generating different phenotypes from the same genotype, each with different probabilities of survival and performance as adults. Chordates have two basic modes of development, indirect and direct. Species with indirect development, which includes most fishes and amphibians, have a complex life cycle with a free-swimming larva that is typically a growth stage, followed by a metamorphosis into the adult form. Species with direct development, which is an evolutionarily derived developmental mode, develop directly from embryo to the juvenile without an intervening larval stage. Among the best studied species with complex life cycles are the amphibians, especially the anurans (frogs and toads). Amphibian tadpoles are exposed to diverse biotic and abiotic factors in their developmental habitat. They have extensive capacity for developmental plasticity, which can lead to the expression of different, adaptive morphologies as tadpoles (polyphenism), variation in the timing of and size at metamorphosis, and carry-over effects on the phenotype of the juvenile/adult. The neuroendocrine stress axis plays a pivotal role in mediating environmental effects on amphibian development. Before initiating metamorphosis, if tadpoles are exposed to predators they upregulate production of the stress hormone corticosterone (CORT), which acts directly on the tail to cause it to grow, thereby increasing escape performance. When tadpoles reach a minimum body size to initiate metamorphosis they can vary the timing of transformation in relation to growth opportunity or mortality risk in the larval habitat. They do this by modulating the production of thyroid hormone (TH), the primary inducer of metamorphosis, and CORT, which synergizes with TH to promote tissue transformation. Hypophysiotropic neurons that release the stress neurohormone corticotropin-releasing factor (CRF) are activated in response to environmental stress (e.g., pond drying, food restriction, etc.), and CRF accelerates metamorphosis by directly inducing secretion of pituitary thyrotropin and corticotropin, thereby increasing secretion of TH and CORT. Although activation of the neuroendocrine stress axis promotes immediate survival in a deteriorating larval habitat, costs may be incurred such as reduced tadpole growth and size at metamorphosis. Small size at transformation can impair performance of the adult, reducing probability of survival in the terrestrial habitat, or fecundity. Furthermore, elevations in CORT in the tadpole caused by environmental stressors cause long term, stable changes in neuroendocrine function, behavior and physiology of the adult, which can affect fitness. Comparative studies show that the roles of stress hormones in developmental plasticity are conserved across vertebrate taxa including humans.

Corticotropin-releasing factor (CRF) system localization in human fetal heart

OBJECTIVE

The corticotropin-releasing factor (CRF) family consists of the neuropeptides CRF, Ucn I, II and III and the binding sites CRFR1, CRFR2 and CRF-BP. It regulates stress response and the homeostasis of an organism. In this study, we examined the presence of the CRF system in the human hearts of normal and pathological fetuses.

DESIGN

Heart tissues from 40 archival human fetuses were divided into Group A (without pathology, 'normal'), Group B (with chromosomal abnormalities) and Group C (with congenital disorders). Immunohistochemistry was used to localize the CRF system. Results correlated to gestational trimester and pathology.

RESULTS

Immunoreactivity for all antigens was found in cardiac myocytes of all groups, in almost all samples, except Ucn III which was present in almost half of the fetuses of Groups B and C and was not detected at all in Group A. Ucn III was more often present during the earlier stage of development (<21 weeks) and in fetuses with congenital disorders. In a fetus diagnosed with heart pathology, all but Ucn III antigens were also present.

CONCLUSIONS

We localized a complete CRF system in the human fetal heart and correlated the presence of Ucn III to development and pathology. More studies are needed to verify and clarify the exact role of the CRF system in the human fetal heart.

Vasoprotective effects of urocortin 1 against atherosclerosis in vitro and in vivo

AIM

Atherosclerosis is the complex lesion that consists of endothelial inflammation, macrophage foam cell formation, vascular smooth muscle cell (VSMC) migration and proliferation, and extracellular matrix production. Human urocortin 1 (Ucn1), a 40-amino acid peptide member of the corticotrophin-releasing factor/urotensin I family, has potent cardiovascular protective effects. This peptide induces potent and long-lasting hypotension and coronary vasodilation. However, the relationship of Ucn1 with atherosclerosis remains unclear. The present study was performed to clarify the effects of Ucn1 on atherosclerosis.

METHODS

We assessed the effects of Ucn1 on the inflammatory response and proliferation of human endothelial cells (ECs), human macrophage foam cell formation, migration and proliferation of human VSMCs, extracellular matrix expression in VSMCs, and the development of atherosclerosis in apolipoprotein E-deficient (Apoe-/-) mice.

RESULTS

Ucn1 significantly suppressed cell proliferation without inducing apoptosis, and lipopolysaccharide-induced up-regulation of monocyte chemoattractant protein-1 and intercellular adhesion molecule-1 in human ECs. Ucn1 significantly reduced oxidized low-density lipoprotein-induced foam cell formation with a significant down-regulation of CD36 and acyl-CoA:cholesterol acyltransferase 1 in human monocyte-derived macrophages. Ucn1 significantly suppressed the migration and proliferation of human VSMCs and increased the activities of matrix metalloproteinase-2 (MMP2) and MMP9 in human VSMCs. Intraperitoneal injection of Ucn1 into Apoe-/- mice for 4 weeks significantly retarded the development of aortic atherosclerotic lesions.

CONCLUSIONS

This study provided the first evidence that Ucn1 prevents the development of atherosclerosis by suppressing EC inflammatory response and proliferation, macrophage foam cell formation, and VSMC migration and proliferation. Thus, Ucn1 could serve as a novel therapeutic target for atherosclerotic cardiovascular diseases.

Distribution of urocortins and corticotropin-releasing factor receptors in the cardiovascular system

Urocortins are human homologues of urotensin I, a fish corticotropin-releasing-factor- (CRF-) like peptide secreted from the urophysis. There are three urocortins: urocortin 1, urocortin 2, and urocortin 3 in mammals. We have shown that urocortin 1 and urocortin 3 are endogenously synthesized in the myocardial cells of human heart and may act on CRF type 2 receptor (CRFR2) expressed in the heart. Expression levels of urocortin 1 in the heart and plasma urocortin 1 levels are elevated in patients with heart failure. Recent studies have shown that urocortins have various biological actions in the cardiovascular system, such as a vasodilator action, a positive inotropic action, a cardioprotective action against ischemia/reperfusion injury, and suppressive actions against the renin angiotensin system and the sympathetic nervous system. Urocortins and CRFR2 may therefore be a potential therapeutic target for cardiovascular diseases, such as congestive heart failure, hypertension, and myocardial infarction.

Clinical perspectives of urocortin and related agents for the treatment of cardiovascular disease

The effects of corticotropin-releasing hormone, also known as corticotropin-releasing factor (CRF), on the cardiovascular system have been intensively researched since its discovery. Moreover, the actions of urocortin (Ucn) I on the cardiovascular system have also been intensively scrutinized following the cloning and identification of its receptor, CRF receptor type 2 (CRFR2), in peripheral tissues including the heart. Given the cardioprotective actions of CRFR2 ligands, the clinical potential of not only Ucn I but also Ucn II and III, which were later identified as more specific ligands for CRFR2, has received considerable attention from researchers. In addition, recent work has indicated that CRF type 1 receptor may be also involved in cardioprotection against ischemic/reperfusion injury. Here we provide a historical overview of research on Ucn I and related agents, their effects on the cardiovascular system, and the clinical potential of the use of such agents to treat cardiovascular diseases.

Catecholamines, cardiac natriuretic peptides and chromogranin A: evolution and physiopathology of a 'whip-brake' system of the endocrine heart

In the past 50 years, extensive evidence has shown the ability of vertebrate cardiac non-neuronal cells to synthesize and release catecholamines (CA). This formed the mindset behind the search for the intrinsic endocrine heart properties, culminating in 1981 with the discovery of the natriuretic peptides (NP). CA and NP, co-existing in the endocrine secretion granules and acting as major cardiovascular regulators in health and disease, have become of great biomedical relevance for their potent diagnostic and therapeutic use. The concept of the endocrine heart was later enriched by the identification of a growing number of cardiac hormonal substances involved in organ modulation under normal and stress-induced conditions. Recently, chromogranin A (CgA), a major constituent of the secretory granules, and its derived cardio-suppressive and antiadrenergic peptides, vasostatin-1 and catestatin, were shown as new players in this framework, functioning as cardiac counter-regulators in 'zero steady-state error' homeostasis, particularly under intense excitatory stimuli, e.g. CA-induced myocardial stress. Here, we present evidence for the hypothesis that is gaining support, particularly among human cardiologists. The actions of CA, NP and CgA, we argue, may be viewed as a hallmark of the cardiac capacity to organize 'whip-brake' connection-integration processes in spatio-temporal networks. The involvement of the nitric oxide synthase (NOS)/nitric oxide (NO) system in this configuration is discussed. The use of fish and amphibian paradigms will illustrate the ways that incipient endocrine-humoral agents have evolved as components of cardiac molecular loops and important intermediates during evolutionary transitions, or in a distinct phylogenetic lineage, or under stress challenges. This may help to grasp the old evolutionary roots of these intracardiac endocrine/paracrine networks and how they have evolved from relatively less complicated designs. The latter can also be used as an intellectual tool to disentangle the experimental complexity of the mammalian and human endocrine hearts, suggesting future investigational avenues.

Differentiation dependent expression of urocortin's mRNA and peptide in human osteoprogenitor cells: influence of BMP-2, TGF-beta-1 and dexamethasone

Urocortin-1 (UCN) a corticotropin releasing-factor (CRF) related peptide, has been found to be expressed in many different tissues like the central nervous system, the cardiovascular system, adipose tissue, and skeletal muscle. The effects of UCN are mediated via stimulation of CRF-receptors 1 and 2 (CRFR1 and 2, CRFR’s) with a high affinity for CRFR2. It has been shown that the CRF-related peptides and CRFR’s are involved in the regulation of stress-related endocrine, autonomic and behavioural responses. Using immunocytochemistry, immunohistochemistry and RT–PCR, we now can show the differentiation dependent expression of UCN mRNA and peptide in human mesenchymal progenitor cells (MSCs) directed to the osteoblastic phenotype for the first time. UCN expression was down regulated by TGF-beta and BMP-2 in the early proliferation phase of osteoblast development, whereas dexamethasone (dex) minimally induced UCN gene expression during matrix maturation after 24 h stimulation. Stimulation of MSCs for 28 days with ascorbate/beta-glycerophosphate (asc/bGp) induced UCN gene expression at day 14. This effect was prevented when using 1,25-vitamin D3 or dex in addition. There was no obvious correlation to osteocalcin (OCN) gene expression in these experiments. In MSCs from patients with metabolic bone disease (n = 9) UCN gene expression was significantly higher compared to MSCs from normal controls (n = 6). Human MSCs did not express any of the CRFR’s during differentiation to osteoblasts. Our results indicate that UCN is produced during the development of MSCs to osteoblasts and differentially regulated during culture as well as by differentiation factors. The expression is maximal between proliferation and matrix maturation phase. However, UCN does not seem to act on the osteoblast itself as shown by the missing CRFR’s. Our results suggest new perspectives on the role of urocortin in human skeletal tissue in health and disease.

Stress hormones mediate environment-genotype interactions during amphibian development

Environments experienced by organisms during early development shape the character and timing of developmental processes, leading to different probabilities of survival in the developmental habitat, and often profound effects on phenotypic expression later in life. Amphibian larvae have immense capacity for plasticity in behavior, morphology, growth and development rate. This creates the potential for extreme variation in the timing of, and size at metamorphosis, and subsequent phenotype in the juvenile and adult stage. Hormones of the neuroendocrine stress axis play pivotal roles in mediating environmental effects on animal development. Corticotropin-releasing factor, whose secretion by hypothalamic neurons is induced by environmental stress, influences the timing of amphibian metamorphosis by controlling the activity of the thyroid and interrenal (adrenal; corticosteroids) glands. At target tissues, corticosteroids synergize with thyroid hormone to promote metamorphosis. Thus, environmental stress acts centrally to increase the activity of the two principle endocrine axes controlling metamorphosis, and the effectors of these axes synergize at the level of target tissues to promote morphogenesis. While stress hormones can promote survival in a deteriorating larval habitat, costs may be incurred such as reduced tadpole growth and size at metamorphosis. Furthermore, exposure to elevated corticosteroids early in life can cause permanent changes in the expression of genes of the neuroendocrine stress axis, leading to altered physiology and behavior in the juvenile/adult stage. Persistent effects of stress hormone actions early in life may have important fitness consequences.

Ontogeny of the corticotropin-releasing factor system in zebrafish

The corticotropin-releasing factor (CRF) system in fish functions to maintain homeostasis during stress in part by regulating cortisol production via the hypothalamus-pituitary-interrenal (HPI) axis. Towards understanding the role of the CRF system in vertebrate development, we describe the ontogeny of the CRF system, cortisol, and the stress response in the zebrafish, Danio rerio. Early embryonic expression of mRNA encoding CRF, urotensin I (UI), CRF-binding protein (CRF-BP), and two CRF receptors (CRF-R1 and CRF-R2) suggest a function in the early organization of the developing embryo. The expression patterns of CRF, UI, and CRF-BP in the larval brain are consistent with the adult distribution patterns for these genes and support HPI-axis independent functions. The relative amounts of CRF and UI mRNA in the heads and tails of developing and adult zebrafish suggest that CRF functions primarily in the brain while UI also plays an important role in the caudal neurosecretory system. The amount of cortisol in developing zebrafish is low and relatively constant through the first 6 days of development. The commencement of feeding after 4 dpf, however, significantly increases basal cortisol production. Finally, we show that zebrafish larvae are able to respond to an osmotic stressor as early as 3 dpf. Overall, results from this study establish the zebrafish as a model species for research on stress during ontogeny and offer new insights into an HPI-axis independent function for the CRF system during embryogenesis.

Urocortin: a protective peptide that targets both the myocardium and vasculature

The urocortins are a family of endogenously produced peptide hormones that show great promise as potential drugs for the treatment of heart disease. They can increase contractility and cardiac output without causing changes in mean arterial blood pressure. As expected, the receptor for these peptides is present in cardiomyocytes, and they can bind and protect these cells from simulated ischemia and reperfusion in vitro. The receptor is present, however, in much higher density in the endothelial cells that form a continuous lining of the coronary vasculature. Functionally, the urocortin peptides have been shown to have potent local vasodilatory effects, and may affect other aspects of vascular function. In this review, we will attempt to distinguish the "cardio" from the "vascular" effects of urocortin and its homologues, including the archetypal family member, corticotrophin releasing hormone.

Immediate and sustained blood pressure lowering by urocortin 2: a novel approach to antihypertensive therapy?

Recently, novel corticotropin-releasing factor-related peptides, named urocortin 1, 2, and 3, and a distinct cardiac and peripheral vascular receptor (corticotropin-releasing factor receptor 2) were described being part of a peripheral corticotropin-releasing factor system modulating cardiovascular function in response to stress. Vasorelaxation and blood pressure lowering have been reported after acute administration of these peptides. No data are available on the acute and chronic effects of urocortin 2 on blood pressure in models of arterial hypertension. To test these effects, hypertensive salt-sensitive and normotensive salt-resistant Dahl rats were randomly assigned to twice-daily applications of urocortin 2 or vehicle for 5 weeks. Blood pressure, heart rate, and left ventricular dimension and function were recorded at baseline, after initial application, and, together with cardiac and aortic expression of urocortin 2 and its receptor, after 5 weeks of treatment. Urocortin 2 significantly reduced blood pressure in hypertensive rats without affecting heart rate. Long-term urocortin 2 treatment in hypertensive rats induced sustained blood pressure reduction and diminished the development of hypertension-induced left ventricular hypertrophy and the deterioration of left ventricular contractile function. Corticotropin-releasing factor receptor 2 expression was preserved despite chronic stimulation by urocortin 2. In conclusion, our study shows that, in an animal model of arterial hypertension, urocortin 2 has immediate and sustained blood pressure-lowering effects. Beneficial effects on blood pressure, left ventricular dimension, and function, together with preserved receptor expression, suggest that corticotropin-releasing factor receptor 2 stimulation by urocortin 2 may represent a novel approach to the treatment of arterial hypertension.

Cellular physiology of rat cardiac myocytes in cardiac fibrosis: in vitro simulation using the cardiac myocyte/cardiac non-myocyte co-culture system

An understanding of the cellular physiology of cardiac myocytes (MCs) and non-myocytes (NMCs) may help to explain the mechanisms underlying cardiac hypertrophy. Despite numerous studies using MC/NMC co-culture systems, it is difficult to precisely evaluate the influence of each cell type because of the inherent cellular heterogeneity of such a system. Here we developed a co-culture system using Wistar rat neonatal MCs and NMCs isolated by discontinuous Percoll gradient and adhesion separation methods and cultured on either side of insert well membranes. Co-culture of MCs and NMCs resulted in significant increases in [3H]-leucine incorporation by MCs, in the amount of protein synthesized by MCs, and in the secretion of natriuretic peptides, while the addition of MCs to NMC cultures significantly reduced [3H]-thymidine incorporation by NMCs. Interestingly, the percentage of the brain natriuretic peptide (BNP) component of total natriuretic peptide secreted (atrial natriuretic peptide+BNP) increased as the number of NMCs placed in the MC/NMC co-culture system increased. However, MCs did not affect production of angiotensin II (Ang II) by NMCs or secretion of endothelin-1 and transforming growth factor-beta1 into the MC/NMC co-culture system. This finding was supported by the anti-hypertrophic and anti-fibrotic actions of RNH6270, an active form of olmesartan, on MCs in the MC/NMC co-culture system and on NMCs that may synthesize Ang II in the heart. The present data indicate that cardiac fibrosis may not only facilitate MC hypertrophy (possibly through the local angiotensin system) but may also change particular pathophysiological properties of MCs, such as the secretory pattern of natriuretic peptides.

Widespread tissue distribution and diverse functions of corticotropin-releasing factor and related peptides

Peptides of the corticotropin-releasing factor (CRF) family are expressed throughout the central nervous system (CNS) and in peripheral tissues where they play diverse roles in physiology, behavior, and development. Current data supports the existence of four paralogous genes in vertebrates that encode CRF, urocortin/urotensin 1, urocortin 2 or urocortin 3. Corticotropin-releasing factor is the major hypophysiotropin for adrenocorticotropin, and also functions as a thyrotropin-releasing factor in non-mammalian species. In the CNS, CRF peptides function as neurotransmitters/neuromodulators. Recent work shows that CRF peptides are also expressed at diverse sites outside of the CNS in mammals, and we found widespread expression of CRF and urocortins, CRF receptors and CRF binding protein (CRF-BP) genes in the frog Xenopus laevis. The functions of CRF peptides expressed in the periphery in non-mammalian species are largely unexplored. We recently found that CRF acts as a cytoprotective agent in the X. laevis tadpole tail, and that the CRF-BP can block CRF action and hasten tail muscle cell death. The expression of the CRF-BP is strongly upregulated in the tadpole tail at metamorphic climax where it may neutralize CRF bioactivity, thus promoting tail resorption. Corticotropin-releasing factor and urocortins are also known to be cytoprotective in mammalian cells. Thus, CRF peptides may play diverse roles in physiology and development, and these functions likely arose early in vertebrate evolution.

Corticotropin-releasing factor is cytoprotective in Xenopus tadpole tail: coordination of ligand, receptor, and binding protein in tail muscle cell survival

Upon metamorphosis, amphibian tadpoles lose their tails through programmed cell death induced by thyroid hormone (T3). Before transformation, the tail functions as an essential locomotory organ. The binding protein for the stress neuropeptide corticotropin-releasing factor (CRF; CRF-BP) is strongly up-regulated in the tail of Xenopus tadpoles during spontaneous or T3-induced metamorphosis. This finding led us to investigate physiological roles for CRF and CRF-BP in tadpole tail. We found CRF, CRF-BP, and functional CRF1 receptor in tail and CRF and functional CRF1 receptors, but not CRF-BP, in the tail muscle-derived cell line XLT-15. CRF, acting via the CRF1 receptor, slowed spontaneous tail regression in explant culture and caused a reduction in caspase 3/7 activity. CRF increased, but stable CRF-BP overexpression decreased, [3H]thymidine incorporation in XLT-15 cells. Overexpression of CRF-BP in vivo accelerated the loss of tail muscle cells during spontaneous metamorphosis. Lastly, exposure of tail explants to hypoxia increased CRF and urocortin 1 but strongly decreased CRF-BP mRNA expression. We show that CRF is expressed in tadpole tail, is up-regulated by environmental stressors, and is cytoprotective. The inhibitory binding protein for CRF is regulated by hormones or by environmental stressors and can modulate CRF bioactivity.

Effects of urocortin II on neonatal rat cardiac myocytes and non-myocytes

Urocortin (Ucn) II and III, homologous peptides of Ucn that are specific ligands for corticotropin-releasing hormone (CRH) type 2 receptor (CRH-R2), have recently been identified. The present study was designed to elucidate the effects of Ucn II, which is predominantly expressed in rodent heart, on neonatal rat cardiac myocytes (MCs) and cardiac non-myocytes (NMCs). Ucn II increased the incorporation of [3H]-leucine into MCs, as well as the accumulation of cAMP and the secretion of atrial natriuretic peptide. However, no significant changes were demonstrated in NMCs or an MC/NMC co-culture system. The effects of Ucn II were attenuated by astressin2-B, a specific antagonist of CRH-R2, and/or H89, an inhibitor of protein kinase A (PKA). These results indicate that Ucn II may be another endogenous cardiovascular substance that acts via CRH-R2 and the cAMP-dependent PKA pathway.

Effects of urocortin via ion mechanisms or CRF receptors?

Urocortin (UCN), a newly isolated peptide related to hypothalamic corticotrophin releasing factor (CRF) family, had been reported to play biologically diverse roles in several systems such as cardiovascular, reproductive, appetite, stress, and inflammatory responses, etc. It was thought previously to be an endogenous agonist, producing the several actions previously attributed to CRF. But, recently, it was shown to directly reduce L-type calcium currents of acute isolated cardiac myocytes and T-type calcium currents in mouse spermatogenic cells via inhibiting calcium channel instead of binding first to its CRF-R2 receptors. UCN could also reduce the intracellular calcium in vascular smooth muscle cells via inhibiting calcium channel directly. Furthermore, UCN could increase the gene expression of ATP-sensitive potassium channels (K(ATP)) and activate sarcolemmal ATP-sensitive potassium current during normal or hypoxia, which could be inhibited by glibenclamide, a specific K(ATP) blocker. This review will highlight the current novel findings on the ionic mechanisms by which UCN may exert its several actions.

Urocortin reduces the viability of adult rat vascular smooth muscle cells via inhibiting L-type calcium channels

The newly isolated peptide, urocortin (UCN), is a member of the corticotropin-releasing factor (CRF)-related peptides that has been found to have potent cardiovascular protective effects. In order to investigate the effect of UCN on the viability of adult rat vascular smooth muscle cells (VSMC) and the relevant mechanisms, we exposed the VSMC to UCN to observe the change in cell viability using MTT assay and intracellular calcium concentration using confocal laser scanning microscope methods. Our results showed that UCN (10(-7)M) inhibited the viability of VSMC by about 26% (P<0.05, compared to control). The effect was concentration-dependent, but it was not dependent on the affecting time. Glybenclamide (Gly, 10(-5)M), the ATP-sensitive potassium channel (K(ATP) channel) blocker, and astressin (10(-6)M), a competitive antagonist of CRF receptors, had no influence on this inhibition. Bay K8644 (10(-6)M), a special L-type calcium channel activator, increased the viability of VSMC. Pre-treatment of the cells with UCN diminished the effect of Bay K8644 (n=6, P<0.05). UCN was also observed to reduce the intracellular Ca2+ increase induced by KCl and Bay K8644. There was no significant difference in nitrite accumulation between UCN groups and the control. In conclusion, UCN reduced the viability of VSMC through L-type calcium channels. These interesting results might suggest that UCN may be a new vasoactive agent involved in hindering vascular remodeling in combination with previous reports about UCN's hypotensive effects.

Urocortin: a cardiac protective peptide?

Urocortin (UCN), a member of the corticotropin-releasing hormone (CRH)-related peptides, has been reported to play biologically diverse roles in several systems such as cardiovascular, reproductive, appetite, stress, inflammatory responses, etc. In heart, it was reported to have protective effects. On the other hand, it was also reported to have cardiac inotropic and hypertrophic effects and hence to cause cardiac remodeling. This paper will review the effects of UCN in cardiac system.

Urocortin 1, urocortin 3/stresscopin, and corticotropin-releasing factor receptors in human adrenal and its disorders

CONTEXT

Urocortin 1 (Ucn1) and urocortin 3 (Ucn3)/stresscopin are new members of the corticotropin-releasing factor (CRF) neuropeptide family. Ucn1 binds to both CRF type 1 (CRF1) and type 2 receptors (CRF2), whereas Ucn3 is a specific agonist for CRF2. Recently, direct involvement of the locally synthesized CRF family in adrenocortical function has been proposed.

OBJECTIVE, DESIGN, AND SETTING

We examined in situ expression of Ucn and CRF receptors in nonpathological human adrenal gland and its disorders using immunohistochemistry and mRNA in situ hybridization.

RESULTS

Ucn immunoreactivity was localized in the cortex and medulla of nonpathological adrenal glands. Ucn1 immunoreactivity was marked in the medulla, whereas Ucn3 was immunostained mostly in the cortex. Both CRF type 1 and CRF2 were expressed in the cortex, particularly in the zonae fasciculata and reticularis but very weakly or undetectably in the medulla. Immunohistochemistry in serial tissue sections with mirror images revealed that both Ucn3 and CRF2 were colocalized in more than 85% of the adrenocortical cells. mRNA in situ hybridization confirmed these findings above. In fetal adrenals, Ucn and CRF receptors were expressed in both fetal and definitive zones of the cortex. Ucn and CRF receptors were all expressed in the tumor cells of pheochromocytomas, adrenocortical adenomas, and carcinomas, but its positivity was less than that in nonpathological adrenal glands, suggesting that Ucn1, Ucn3, and CRF receptors were down-regulated in these adrenal neoplasms.

CONCLUSIONS

Ucn1, Ucn3, and CRF receptors are all expressed in human adrenal cortex and medulla and may play important roles in physiological adrenal functions.

Cardiovascular effects of long-term central and peripheral administration of urocortin, corticotropin-releasing factor, and adrenocorticotropin in sheep

The neuroendocrine hormones ACTH and corticotropin- releasing factor (CRF), which are involved in the stress response, have acute effects on arterial pressure. New evidence indicates that urocortin (UCN), the putative agonist for the CRF type 2 receptor, has selective cardiovascular actions. The responses to long-term infusions of these hormones, both peripherally and centrally, in conscious animals have not been studied. Knowledge of the long-term effects is important because they may differ considerably from their acute actions, and stress is frequently a chronic stimulus. The present experiments investigated the cardiovascular effects of CRF, UCN, and ACTH in conscious sheep. Infusions were made either into the lateral cerebral ventricles (i.c.v.) or i.v. over 4 d at 5 microg/h. UCN infused i.c.v. or i.v. caused a prolonged increase in heart rate (HR) (P < 0.01) and a small increase in mean arterial pressure (MAP) (P < 0.05). CRF infused i.c.v. or i.v. progressively increased MAP (P < 0.05) but had no effect on HR. Central administration of ACTH had no effect, whereas systemic infusion increased MAP and HR (P < 0.001). In conclusion, long-term administration of these three peptides associated with the stress response had prolonged, selective cardiovascular actions. The striking finding was the large and sustained increase in HR with i.c.v. and i.v. infusions of UCN. These responses are probably mediated by CRF type 2 receptors because they were not reproduced by infusions of CRF.

Localization and physiological roles of urocortin

Urocortin, a 40 amino acid peptide, is a corticotropin-releasing factor (CRF) related peptide, and can bind to all three types of CRF receptors (CRF type 1, type 2a and type 2b receptors) with higher affinities for these receptors than CRF. Immunoreactivity of urocortin is widely distributed in central nervous, digestive, cardiovascular, reproductive, immune and endocrine systems. Urocortin plays important roles in appetite-suppression, immunomodulation, steroidogenesis in the ovary, maintenance of the placental function, labor, and cardioprotection via CRF receptors. Although urocortin has potent adrenocorticotropin (ACTH) releasing activity in vitro, endogenous urocortin does not act on pituitary ACTH secretion in vivo.

Urocortins as cardiovascular peptides

Urocortins (Ucn) 1, 2 and 3, human homologues of fish urotensin I, form the corticotropin-releasing factor (CRF) family, together with CRF, urotensin I and sauvagine. Ucn 3 is a novel member of this family and is a specific ligand for CRF type 2 receptor. CRF type 2 receptor is thought to mediate the stress-coping responses, such as anxiolysis, anorexia, vasodilatation, a positive inotropic action on myocardium and dearousal. Endogenous ligands for the CRF type 2 receptor expressed in the cardiovascular tissues, such as the myocardium, have long been unknown. We have shown expression of Ucn 3 as well as Ucn 1 in the human heart. Ucn 3 is also expressed in the kidney, particularly distal tubules. Studies in various rat tissues showed that high concentrations of immunoreactive Ucn 3 were found in the pituitary gland, adrenal gland, gastrointestinal tract, ovary and spleen in addition to the brain, heart and kidney. These observations suggest that Ucn 3 is expressed in various tissues including heart and kidney, and may regulate the circulation in certain aspects of stress and diseases, such as inflammation. Ucn 1 and 3 appear to have important pathophysiological roles in some cardiovascular diseases.

Cardiac expression of urocortin (Ucn) in diseased heart; preliminary results on possible involvement of Ucn in pathophysiology of cardiac diseases

Recently, several studies reported that urocortin (Ucn) had beneficial effects on cardiovascular system and was expressed both in the normal heart and in the heart of dilated cardiomyopathy (DCM), yet the relationship between high expression of Ucn and pathophysiology of Ucn in diseased heart has been discussed. Thus, the present study was designed to elucidate the expression of Ucn in the diseased heart by immunohistochemical approach using endomyocardial biopsy specimens. The involvement of immunoreactive Ucn in pathophysiology of cardiac disease was evaluated using endomyocardial biopsy specimens obtained from the patients with some heart diseases, including DCM and hypertrophic cardiomyopathy (HCM). Ucn was detected in all endomyocardial biopsy specimens of ventricular tissue obtained from the patients with such cardiac diseases, a specimens of atrial tissue, and normal heart specimens obtained from autopsy cases. In DCM patients, left ventricular end-diastolic pressure significantly elevated in severely stained group. On the contrary, in HCM patients, left ventricular ejection fraction was higher in the severely stained group. Ucn was expressed more abundantly in the diseased heart, especially in HCM and DCM, than in the normal heart. In conclusion, such close relationship between Ucn expression in the heart and cardiac function indicated that clinical features of Ucn resembled those of norepinephrine and Ucn could play a certain pathophysiological roles in the cardiac diseases.