Specific receptors for adrenomedullin in cultured rat vascular smooth muscle cells

Sympathetic and Sensory-Motor Nerves in Peripheral Small Arteries

Small arteries, which play important roles in controlling blood flow, blood pressure, and capillary pressure, are under nervous influence. Their innervation is predominantly sympathetic and sensory motor in nature, and while some arteries are densely innervated, others are only sparsely so. Innervation of small arteries is a key mechanism in regulating vascular resistance. In the second half of the previous century, the physiology and pharmacology of this innervation were very actively investigated. In the past 10-20 yr, the activity in this field was more limited. With this review we highlight what has been learned during recent years with respect to development of small arteries and their innervation, some aspects of excitation-release coupling, interaction between sympathetic and sensory-motor nerves, cross talk between endothelium and vascular nerves, and some aspects of their role in vascular inflammation and hypertension. We also highlight what remains to be investigated to further increase our understanding of this fundamental aspect of vascular physiology.

Adrenomedullin - Current perspective on a peptide hormone with significant therapeutic potential

The peptide hormone adrenomedullin (ADM) consists of 52 amino acids and plays a pivotal role in the regulation of many physiological processes, particularly those of the cardiovascular and lymphatic system. Like calcitonin (CT), calcitonin gene-related peptide (CGRP), intermedin (IMD) and amylin (AMY), it belongs to the CT/CGRP family of peptide hormones, which despite their low little sequence identity share certain characteristic structural features as well as a complex multicomponent receptor system. ADM, IMD and CGRP exert their biological effects by activation of the calcitonin receptor-like receptor (CLR) as a complex with one of three receptor activity-modifying proteins (RAMP), which alter the ligand affinity. Selectivity within the receptor system is largely mediated by the amidated C-terminus of the peptide hormones, which bind to the extracellular domains of the receptors. This enables their N-terminus consisting of a disulfide-bonded ring structure and a helical segment to bind within the transmembrane region and to induce an active receptor confirmation. ADM is expressed in a variety of tissues in the human body and is fundamentally involved in multitude biological processes. Thus, it is of interest as a diagnostic marker and a promising candidate for therapeutic interventions. In order to fully exploit the potential of ADM, it is necessary to improve its pharmacological profile by increasing the metabolic stability and, ideally, creating receptor subtype-selective analogs. While several successful attempts to prolong the half-life of ADM were recently reported, improving or even retaining receptor selectivity remains challenging.

Adrenomedullin as a Protein with Multifunctional Behavior and Effects in Various Organs and Tissues

In literature, it has been reported that adrenomedullin, which is generally thought to have vasodilator, natriuretic and diuretic effects, is synthesized in almost all body, especially CNS, vascular muscles and endothelium, heart, liver, lung, kidney, gastric mocosa, intestinal endothelium and various blood cells. It has been found that the possible effects of adrenomedullin can be demonstrated directly or indirectly by means of active mediators, neuropeptides, enzymes and hormones. It is also suggested that it regulates the endocrine system by affecting the hypothalamic-pituitary axis. It increases in heart failure, acute coronary syndromes, hypertensive conditions, cerebrovascular accessory, chronic renal failure and periodontitis and decreases in peptic ulcer and intestinal diseases. However, it is still not clear whether increase/decrease in adrenomedullin level is a cause of a disease or is a result of damage due to an illness. This peptide, which could be thought to multifunctional, should be considered as a molecule with genetic coding that may have different effects on different tissues and conditions. For all these reasons, we aimed to review the multifonctional behavior of adrenomedullin in the light of the current literature to pioneer new hypotheses and discuss possible mechanisms.

Adrenomedullin, a Novel Target for Neurodegenerative Diseases

Neurodegenerative diseases represent a heterogeneous group of disorders whose common characteristic is the progressive degeneration of neuronal structure and function. Although much knowledge has been accumulated on the pathophysiology of neurodegenerative diseases over the years, more efforts are needed to understand the processes that underlie these diseases and hence to propose new treatments. Adrenomedullin (AM) is a multifunctional peptide involved in vasodilation, hormone secretion, antimicrobial defense, cellular growth, and angiogenesis. In neurons, AM and related peptides are associated with some structural and functional cytoskeletal proteins that interfere with microtubule dynamics. Furthermore, AM may intervene in neuronal dysfunction through other mechanisms such as immune and inflammatory response, apoptosis, or calcium dyshomeostasis. Alterations in AM expression have been described in neurodegenerative processes such as Alzheimer's disease or vascular dementia. This review addresses the current state of knowledge on AM and its possible implication in neurodegenerative diseases.

Adrenomedullin and Adrenomedullin-Targeted Therapy As Treatment Strategies Relevant for Sepsis

Sepsis remains a major medical challenge, for which, apart from improvements in supportive care, treatment has not relevantly changed over the last few decades. Vasodilation and vascular leakage play a pivotal role in the development of septic shock, with vascular leakage being caused by disrupted endothelial integrity. Adrenomedullin (ADM), a free circulating peptide involved in regulation of endothelial barrier function and vascular tone, is implicated in the pathophysiology of sepsis. ADM levels are increased during sepsis, and correlate with extent of vasodilation, as well as with disease severity and mortality. In vitro and preclinical in vivo data show that administration of ADM exerts anti-inflammatory, antimicrobial, and protective effects on endothelial barrier function during sepsis, but other work suggests that it may also decrease blood pressure, which could be detrimental for patients with septic shock. Work has been carried out to negate ADMs putative negative effects, while preserving or even potentiating its beneficial actions. Preclinical studies have demonstrated that the use of antibodies that bind to the N-terminus of ADM results in an overall increase of circulating ADM levels and improves sepsis outcome. Similar beneficial effects were obtained using coadministration of ADM and ADM-binding protein-1. It is hypothesized that the mechanism behind the beneficial effects of ADM binding involves prolongation of its half-life and a shift of ADM from the interstitium to the circulation. This in turn results in increased ADM activity in the blood compartment, where it exerts beneficial endothelial barrier-stabilizing effects, whereas its detrimental vasodilatory effects in the interstitium are reduced. Up till now, in vivo data on ADM-targeted treatments in humans are lacking; however, the first study in septic patients with an N-terminus antibody (Adrecizumab) is currently being conducted.

Extracellular elevation of adrenomedullin, a gene associated with schizophrenia, suppresses heat shock protein 1A/1B mRNA

Several recent gene expression studies on schizophrenia, including one using monozygotic twins discordant for the disease, have reported the upregulation of adrenomedullin (ADM), which was initially identified as a vasodilator hormone. It has been hypothesized that upregulation of ADM may be a susceptibility factor for schizophrenia, although the exact role of ADM in the central nervous system remains unclear. In this study, we used a microarray analysis to investigate the changes in global gene expression induced by the administration of exogenous ADM in SK-N-SH cells, which allowed us to evaluate the effects of elevated ADM on the central nervous system. A quantitative reverse-transcription PCR study showed that the levels of HSPA1A/1B mRNA, another gene that has been associated with schizophrenia, were significantly suppressed after exogenous ADM treatment. These results indicate that elevated ADM may be involved in the etiology of schizophrenia through the regulation of heat shock protein signaling.

Adrenomedullin and angiotensin II signaling pathways involved in the effects on cerebellar antioxidant enzymes activity

Human adrenomedullin (AM) is a 52-amino acid peptide involved in cardiovascular control. AM has two specific receptors formed by the calcitonin-receptor-like receptor (CRLR) and receptor activity-modifying protein (RAMP) 2 or 3, known as AM1 and AM2 receptors, respectively. In addition, AM has appreciable affinity for the calcitonin gene-1 related peptide receptor (CGRP1), composed of CRLR/RAMP1. In brain, AM and their receptors are expressed in several localized areas, including the cerebellum. AM has been reported as an antioxidant. Little is known about the role of AM in the regulation of cerebellar reactive oxygen species (ROS) metabolism. We assessed the effect of AM on three antioxidant enzymes activity: catalase (CAT), glutathione peroxidase (GPx) and superoxide dismutase (SOD) and on thiobarbituric acid reactive substances (TBARS) production in rat cerebellar vermis, as well the receptor subtypes involved in AM actions. Additionally, we evaluated the role of angiotensin II (ANG II), protein kinase A (PKA) activity, and protein kinase C/nicotinamide adenine dinucleotide phosphate oxidase (PKC/NAD(P)H) (oxidase) pathway. Sprague-Dawley rats were sacrificed by decapitation and cerebellar vermis was microdissected under stereomicroscopic control. CAT, GPx, SOD activity and TBARS production was determined spectrophotometrically. Our findings demonstrated that in cerebellar vermis, AM decreased and ANG II increased CAT, GPx and SOD activity and TBARS production. Likewise, AM antagonized ANG II-induced increase antioxidant enzyme activity. AM(22-50) and CGRP(8-37) blunted AM-induced decrease of antioxidant enzymes activity and TBARS production indicating that these actions are mediated through AM and CGRP₁ receptors. Further, PKA inhibitor (PKAi) blunted AM action and apocynin and chelerythrine reverted ANG II action, suggesting that AM antioxidant action is mediated through stimulation of PKA activity, while ANG II-induced stimulation through PKC/NAD(P)H oxidase pathway. Our results support the role of AM in the regulation of cerebellar antioxidant enzymes activity and suggest a physiological role for AM in cerebellum.

The Role of Adrenomedullin in Cardiovascular Response to Exercise - A Review

Adrenomedullin (ADM), the product of the vascular endothelial and smooth muscle cells, and cardiomyocytes, is considered to be a local factor controlling vascular tone, cardiac contractility and renal sodium excretion. The aim of this article was to review the existing data on the effect of different types of exercise on plasma ADM concentration in healthy men. The results of studies on the effect of dynamic exercise on the plasma ADM are contradictory. Some authors reported an increase in plasma ADM, while others showed a slight decrease or did not observe any changes. The inverse relationship between plasma ADM and mean blood pressure observed during maximal exercise support the concept that ADM might blunt the exercise-induced systemic blood pressure increase. Positive relationships between increases in plasma ADM and those in noradrenaline, atrial natriuretic peptide (ANP) or interleukin-6 observed during prolonged exercise suggest that the sympathetic nervous system and cytokine induction may be involved in ADM release. Increased secretion of ADM and ANP during this type of exercise may be a compensatory mechanism attenuating elevation of blood pressure and preventing deterioration of cardiac function. Studies performed during static exercise have showed an increase in plasma ADM only in older healthy men. Positive correlations between increases in plasma ADM and those in noradrenaline and endothelin-1 may indicate the interaction of these hormones in shaping the cardiovascular response to static exercise. Inverse relationships between exercise-induced changes in plasma ADM and those in cardiovascular indices may be at least partly associated with inotropic action of ADM on the heart. Interactions of ADM with vasoactive peptides, catecholamines and hemodynamic factors demonstrate the potential involvement of this peptide in the regulation of blood pressure and myocardial contractility during exercise.

Pregnancy Increases Relaxation in Human Omental Arteries to the CGRP Family of Peptides

Calcitonin gene-related peptide (CALCB) and its family members adrenomedullin (ADM) and intermedin (ADM2) play important roles in maintaining vascular adaptations during pregnancy in animal models. The present study was designed to evaluate the responses of omental arteries to CALCB, ADM, and ADM2 in pregnant and nonpregnant women, and to determine the mechanisms involved. By using resistance omental arteries collected from nonpregnant women (n = 15) during laparotomy and from term pregnant women (n = 15) at cesarean delivery, this study shows that the receptor components--calcitonin receptor-like receptor (CALCRL) and receptor activity-modifying proteins (RAMPs) 1, 2 and 3--are localized to endothelial and smooth muscle cells in omental arteries, with increased expressions of both mRNA and protein in pregnant compared with nonpregnant women. The myography study demonstrated that CALCB, ADM, and ADM2 (0.1-100 nM) dose dependently relax U46619 (1 muM) precontracted omental artery segments, and the maximum possible effects to CALCB and ADM2, but not to ADM, are significantly enhanced in pregnant compared with nonpregnant women. Further, the vasodilatory responses to CALCB, ADM, and ADM2 are reduced by inhibitors of nitric oxide (NO) synthase (L-NAME), adenylyl cyclase (SQ22536), voltage-activated potassium channels (4-aminopyrodin and tetrabutylammonium), Ca(2+)-activated potassium channel (charybdotoxin), and cyclooxygenase (indomethacin). In conclusion, the CALCB family of peptides, CALCB and ADM2, increase human omental artery relaxation during pregnancy through diverse mechanisms, including NO, endothelium-derived hyperpolarizing factors (EDHFs) and prostaglandins, and thus could contribute to the vascular adaptations during pregnancy in the human.

Pharmacological characterisation of the mechanisms underlying the relaxant effect of adrenomedullin in the rat carotid artery

OBJECTIVES

We investigated the mechanisms underlying the relaxant effect of adrenomedullin (AM) in the rat carotid artery and verified the expression of AM system components in this tissue.

METHODS

The carotid artery was isolated from male Wistar rats and immunohistochemical, Western immunoblotting, real-time polymerase chain reaction and functional assays were conducted.

KEY FINDINGS

Protein and mRNA expression of AM, calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMP)1, 2, 3 were detected in carotid segments from male Wistar rats. Immunohistochemical assays showed that AM and CRLR receptors are expressed in the endothelium and smooth muscle cells. Functional assays showed that AM concentration dependently relaxed carotid rings with intact endothelium. Endothelial removal reduced, but not abolished, the relaxation induced by AM. AM22-52 (selective antagonist for AM receptors) and calcitonin gene-related peptide (CGRP)8-37 (selective CGRP receptor antagonist) reduced AM-induced relaxation in endothelium-intact rings. Pre-incubation of endothelium-intact rings with N-nitro-L-arginine methyl ester, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one or Rp-8-Bromo-?-phenyl-1,N2-ethenoguanosine 3',5'cyclic monophosphorothioate reduced AM-induced relaxation. Inhibition of cyclooxygenase-1 and protein kinase A (PKA) reduced AM-induced relaxation. The relaxation induced by AM was attenuated by the K(+) channel blockers apamin and glibenclamide. AM increased nitrate levels and 6-keto-prostaglandin F1α (stable product of prostacyclin) in the rat carotid. In endothelium-denuded rings, AM22-52 , glibenclamide and PKA inhibition by H89 reduced AM-induced relaxation.

CONCLUSIONS

The novelty of this work is that it first demonstrated functionally that AM-induced relaxation is mediated by AM and CGRP receptors located on the endothelium and AM receptors located on smooth muscle of rat carotid arteries. AM-induced relaxation involves the nitric oxide-cGMP pathway, a vasodilator prostanoid, the opening of K(+) channels and the activation of PKA.

Adrenomedullin and diabetes

Adrenomedullin (ADM) is a peptide hormone widely expressed in different tissues, especially in the vasculature. Apart from its vasodilatatory and hypotensive effect, it plays multiple roles in the regulation of hormonal secretion, glucose metabolism and inflammatory response. ADM regulates insulin balance and may participate in the development of diabetes. The plasma level of ADM is increased in people with diabetes, while in healthy individuals the plasma ADM concentration remains low. Plasma ADM levels are further increased in patients with diabetic complications. In type 1 diabetes, plasma ADM level is correlated with renal failure and retinopathy, while in type 2 diabetes its level is linked with a wider range of complications. The elevation of ADM level in diabetes may be due to hyperinsulinemia, oxidative stress and endothelial injury. At the same time, a rise in plasma ADM level can trigger the onset of diabetes. Strategies to reduce ADM level should be explored so as to reduce diabetic complications.

Possible role of adrenomedullin and nitric oxide in major depression

Adrenomedullin (ADM) and nitric oxide (NO) have been implicated in the pathogenesis of certain psychiatric disorders such as schizophrenia and bipolar disorder. ADM induces vasorelaxation by activating adenylate cyclase and stimulating the release of NO. These two molecules are known to influence cerebral activity. In this study, we aimed to examine the serum levels of ADM and NO in patients with major depression (MD). We enrolled 50 patients with MD and 50 healthy control subjects. The diagnosis of MD was established on the basis of a structured clinical interview using the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV). The severity of depressive symptoms was evaluated using Hamilton's 17-item Depression Rating Scale. The mean serum levels of ADM and NO in patients with MD were significantly higher than those in healthy subjects (p=0.001, for both). The severity of psychomotor retardation in patients with MD was significantly correlated with the ADM (r=0.37, p=0.007) and NO levels (r=0.29, p=0.038). The patients with obvious psychomotor retardation had significantly higher levels of ADM and NO than did the patients with no psychomotor retardation (p=0.025, p=0.030). A significantly positive correlation was found between ADM and NO levels in patients with MD (r=0.79, p=0.001). Serum levels of ADM and NO levels were not correlated with the severity or duration of depression or depressive symptoms (except psychomotor retardation). In conclusion, our study indicates that serum levels of ADM and NO are elevated in patients with MD and that increased serum levels of ADM and NO may be associated with psychomotor retardation. The ADM-NO system may serve as a new target in the treatment of patients with MD and psychomotor retardation.

Adrenomedullin receptors on human T cells are glucocorticoid-sensitive

Adrenomedullin (AM) is a novel vasodilatatory peptide which acts primarily through the calcitonin receptor-like receptor (CLR) in combination with either receptor-activity-modifying-protein (RAMP) 2 or 3 (forming receptors, AM(1) and AM(2) respectively). AM plays an important role during inflammation, with its expression increasing following cytokine treatment, promoting macrophage action in situ and high expression by T cells during hypoxic conditions. Examination of T cell AM receptor expression has previously been incomplete, hence we here consider the presentation of AM receptors and their responsiveness to AM and glucocorticoids (GC). AM receptor expression was examined by PCR and flow cytometry in primary human T cells, revealing that RAMP2, 3 and CLR are physiologically expressed in unstimulated T cells, both intracellularly and on the cell surface. PHA stimulation decreased receptor proteins, significantly so for CLR and RAMP3. Incubation with AM elicited limited receptor alterations however, GC treatment (10(-6) M; 24 h) markedly affected cell surface expression, significantly increasing receptor components in unstimulated cells and significantly decreasing the same in stimulated T cells. Our findings indicate that human T cells utilize both AM(1) and AM(2) receptors, which are GC-sensitive in an activation-state dependent manner.

The structure of secretin family GPCR peptide ligands: implications for receptor pharmacology and drug development

The secretin family G protein-coupled receptors, characterized by a large N-terminal extracellular domain and seven transmembrane helices, are drug targets in many diseases, including migraine, cardiovascular disease, diabetes, osteoporosis and inflammatory disorders. Their activating ligands are peptides with an average length of 30 amino acids. In this article we review the available structural data for these peptides and how this explains their activity. We emphasize how this information may be used to accelerate the development of new drugs against these receptors.

Cardiovascular effects of the intracerebroventricular injection of adrenomedullin: roles of the peripheral vasopressin and central cholinergic systems

Our objective was to investigate in conscious Sprague-Dawley (6-8 weeks, 250-300 g) female rats (N = 7 in each group) the effects of intracerebroventricularly (icv) injected adrenomedullin (ADM) on blood pressure and heart rate (HR), and to determine if ADM and calcitonin gene-related peptide (CGRP) receptors, peripheral V₁ receptors or the central cholinergic system play roles in these cardiovascular effects. Blood pressure and HR were observed before and for 30 min following drug injections. The following results were obtained: 1) icv ADM (750 ng/10 µL) caused an increase in both blood pressure and HR (ΔMAP = 11.8 ± 2.3 mmHg and ΔHR = 39.7 ± 4.8 bpm). 2) Pretreatment with a CGRP receptor antagonist (CGRP_8-37) and ADM receptor antagonist (ADM_22-52) blocked the effect of central ADM on blood pressure and HR. 3) The nicotinic receptor antagonist mecamylamine (25 µg/10 µL, icv) and the muscarinic receptor antagonist atropine (5 µg/10 µL, icv) prevented the stimulating effect of ADM on blood pressure. The effect of ADM on HR was blocked only by atropine (5 µg/10 µL, icv). 4) The V₁ receptor antagonist [β-mercapto-β-β-cyclopentamethylenepropionyl¹, O-me-Tyr²,Arg⁸]-vasopressin (V2255; 10 µg/kg), that was applied intravenously, prevented the effect of ADM on blood pressure and HR. This is the first study reporting the role of specific ADM and CGRP receptors, especially the role of nicotinic and muscarinic central cholinergic receptors and the role of peripheral V₁ receptors in the increasing effects of icv ADM on blood pressure and HR.

Characterization of iodinated adrenomedullin derivatives suitable for lung nuclear medicine

INTRODUCTION

We have recently demonstrated the effectiveness of 99m-technetium adrenomedullin (AM) as a new molecular lung imaging agent that could provide significant advantages for the diagnosis and follow-up of disorders affecting the pulmonary circulation such as pulmonary embolism and pulmonary hypertension. Having the possibility to conjugate the targeting molecule with different radionuclides would offer more flexibility and potential advantages depending on clinical situations. Since various iodine isotopes are currently used in nuclear medicine and in pharmacological studies, we have evaluated which iodination method should be privileged in order to produce a good iodinated AM-derived nuclear medicine agent.

METHODS

Synthetic AM was labeled with iodine through chemical and lactoperoxidase oxidation methods. Position of the iodine atom on the peptide was determined by MALDI-TOF mass spectrometry analysis following cyanogen bromide cleavage and carboxypeptidase Y digestion. Binding affinity of iodinated AM analogues was evaluated by competition and saturation binding experiments on dog lung preparations.

RESULTS

In this study, we demonstrated that, upon lactoperoxidase oxidation, iodination occurred at Tyr(1) and that this radioligand retained higher binding affinity and specificity over preparations obtained through chemical oxidation.

CONCLUSIONS

These results emphasize the fact that even a small chemical modification, i.e. iodination, might deeply modify the pharmacological profile of a compound and support observations that the C-terminal tail of human AM plays an important role in the AM receptor binding process. Consequently, incorporation of a radionuclide to produce an AM-based nuclear medicine agent should privilege the N-terminus of the molecule.

Adrenomedullin in rat follicles and corpora lutea: expression, functions and interaction with endothelin-1

BACKGROUND

Adrenomedullin (ADM), a novel vasorelaxant peptide, was found in human/rat ovaries. The present study investigated the interaction of ADM and endothelin-1 (ET-1) in follicles and newly formed corpora lutea (CL) and the actions of ADM on progesterone production in CL during pregnancy.

METHODS

The peptide and gene expression level of adrenomedullin in small antral follicles, large antral follicles and CL was studied by real-time RT-PCR and EIA. The effect of ADM treatment on oestradiol production in 5-day follicular culture and on progesterone production from CL of different pregnant stages was measured by EIA. The interaction of ADM and ET-1 in follicles and CL at their gene expression level was studied by real-time RT-PCR.

RESULTS

In the rat ovary, the gene expression of Adm increased during development from small antral follicles to large antral follicles and CL. In vitro treatment of preantral follicular culture for 5 days with ADM increased oestradiol production but did not affect follicular growth or ovulation rate. The regulation of progesterone production by ADM in CL in culture was pregnancy-stage dependent, inhibitory at early and late pregnancy but stimulatory at mid-pregnancy, which might contribute to the high progesterone production rate of the CL at mid-pregnancy. Moreover, the interaction between ADM and ET-1 at both the production and functional levels indicates that these two vasoactive peptides may form an important local, fine-tuning regulatory system together with LH and prolactin for progesterone production in rat CL.

CONCLUSIONS

As the CL is the major source of progesterone production even after the formation of placenta in rats, ADM may be an important regulator in progesterone production to meet the requirement of pregnancy.

Shared and separate functions of the RAMP-based adrenomedullin receptors

Adrenomedullin (AM) is a novel hypotensive peptide that exerts a variety of strongly protective effects against multiorgan damage. AM-specific receptors were first identified as heterodimers composed of calcitonin-receptor-like receptor (CLR), a G protein coupled receptor, and one of two receptor activity-modifying proteins (RAMP2 or RAMP3), which are accessory proteins containing a single transmembrane domain. RAMPs are required for the surface delivery of CLR and the determination of its phenotype. CLR/RAMP2 (AM₁ receptor) is more highly AM-specific than CLR/RAMP3 (AM₂ receptor). Although there have been no reports showing differences in intracellular signaling via the two AM receptors, in vitro studies have shed light on their distinct trafficking and functionality. In addition, the tissue distributions of RAMP2 and RAMP3 differ, and their gene expression is differentially altered under pathophysiological conditions, which is suggestive of the separate roles played by AM₁ and AM₂ receptors in vivo. Both AM and the AM₁ receptor, but not the AM₂ receptor, are crucial for the development of the fetal cardiovascular system and are able to effectively protect against various vascular diseases. However, AM₂ receptors reportedly play an important role in maintaining a normal body weight in old age and may be involved in immune function. In this review article, we focus on the shared and separate functions of the AM receptor subtypes and also discuss the potential for related drug discovery. In addition, we mention their possible function as receptors for AM2 (or intermedin), an AM-related peptide whose biological functions are similar to those of AM.

Calcitonin gene-related peptide inhibits chemokine production by human dermal microvascular endothelial cells

This study examined whether the sensory neuropeptide calcitonin gene-related peptide (CGRP) inhibits release of chemokines by dermal microvascular endothelial cells. Dermal blood vessels are associated with nerves containing CGRP, suggesting that CGRP-containing nerves may regulate cutaneous inflammation through effects on vessels. We examined CGRP effects on stimulated chemokine production by a human dermal microvascular endothelial cell line (HMEC-1) and primary human dermal microvascular endothelial cells (pHDMECs). HMEC-1 cells and pHDMECs expressed mRNA for components of the CGRP and adrenomedullin receptors and CGRP inhibited LPS-induced production of the chemokines CXCL8, CCL2, and CXCL1 by both HMEC-1 cells and pHDMECs. The receptor activity-modifying protein (RAMP)1/calcitonin receptor-like receptor (CL)-specific antagonists CGRP₈-₃₇ and BIBN4096BS, blocked this effect of CGRP in a dose-dependent manner. CGRP prevented LPS-induced IκBα degradation and NF-κB binding to the promoters of CXCL1, CXCL8 and CCL2 in HMEC-1 cells and Bay 11-7085, an inhibitor of NF-κB activation, suppressed LPS-induced production of CXCL1, CXCL8 and CCL2. Thus, the NF-κB pathway appears to be involved in CGRP-mediated suppression of chemokine production. Accordingly, CGRP treatment of LPS-stimulated HMEC-1 cells inhibited their ability to chemoattract human neutrophils and mononuclear cells. Elucidation of this pathway may suggest new avenues for therapeutic manipulation of cutaneous inflammation.

Coexpression of adrenomedullin and its receptor component proteins in the reproductive system of the rat during gestation

BACKGROUND

Adrenomedullin (ADM), a novel vasorelaxant peptide, was found in human/rat ovaries and uteri. Plasma ADM level increases in pregnant women and pregnant rats.

METHODS

The gene expression levels of Adm and its receptor components - Crlr, Ramp1, Ramp2 and Ramp3, the ADM peptide concentration and localization in the rat female reproductive system during gestation were studied by real-time RT-PCR, EIA and immunohistochemical techniques.

RESULTS

The mRNAs of Adm and its receptor component and ADM were differentially distributed between implantation sites and inter-implantation sites of the pregnant uterus. The day on which vaginal sperm were found was taken to be pregnancy day 1. The Adm mRNA levels in the implantation sites of the uteri in mid- (day 12) and late pregnancy (day 17) were more than 10-fold higher than those in nonpregnancy, pre-implantation (day 3) or early (day 7) pregnancy. ADM was localized in the endometrial stroma with increased immunoreactivity from nonpregnancy to pregnancy. The ADM level and the mRNA levels of Adm, Crlr, Ramp2 and Ramp3 in the corpus luteum all increased in late pregnancy compared with early pregnancy. The gene expression of Adm and it receptor components and intense immunostaining of ADM were also found in the oviduct during pregnancy.

CONCLUSIONS

The gene expressions levels of Adm and its receptor components - Crlr, Ramp1, Ramp2 and Ramp3, and ADM peptide concentration exhibited a spatio-temporal pattern in the rat female reproductive system during gestation and this suggests that ADM may play important roles in gestation.

Human adrenomedullin combined with human adrenomedullin binding protein-1 is protective in gut ischemia and reperfusion injury in the rat

Previous studies have demonstrated that co-administration of rat adrenomedullin (AM) and human AM binding protein-1 (AMBP-1) has various beneficial effects following adverse circulatory conditions. In order to reduce rat proteins to elicit possible immune responses in humans, we determined the effect of human AM combined with human AMBP-1 after intestinal ischemia and reperfusion (I/R). Intestinal ischemia was induced in the rat by occluding the superior mesenteric artery for 90 min. At 60 min after the beginning of reperfusion, human AM/AMBP-1 at 3 different dosages was administered intravenously over 30 min. At 240 min after the treatment, blood and tissue samples were harvested and measured for pro-inflammatory cytokines (i.e., TNF-alpha and IL-6), myeloperoxidase activities in the gut and lungs, and cleaved caspase-3 expression in the lungs, as well as serum levels of hepatic enzymes and lactate. In additional groups of animals, a 10-day survival study was conducted. Results showed that administration of human AM/AMBP-1 reduced pro-inflammatory cytokines, attenuated organ injury, and improved the survival rate in a seemingly dose-response fashion. Co-administration of the highest dose of human AM/AMBP-1 in this study had the optimal therapeutic effect in the rat model of intestinal I/R.

Cyclic AMP-independent CGRP8-37-sensitive receptors mediate adrenomedullin-induced decrease of CaCl2-contraction in pregnant rat mesenteric artery

OBJECTIVES

We tested the hypothesis that adrenomedullin reduces calcium influx independent of potassium channels in depolarized endothelium-denuded mesenteric artery from pregnant rats.

RESULTS

Adrenomedullin reduced the CaCl(2)-induced contraction, while the receptor antagonist calcitonin gene-related peptide (CGRP)(8-37), but not adrenomedullin(22-52), reversed these effects. Adenylate cyclase inhibition by SQ22536 did not prevent adrenomedullin effects on CaCl(2)-induced contraction. Adrenomedullin did not inhibit depolarization-induced calcium entry to isolated vascular smooth muscle. Inhibition of myosin light-chain (MLC) phosphatase by calyculin A reversed the effects of adrenomedullin on contraction caused by submillimolar concentrations of CaCl(2), while adrenomedullin still inhibited contraction caused by higher concentrations of CaCl(2). However, the ratio of phosphorylated to total myosin phosphatase target 1, the regulatory subunit of MLC phosphatase, did not change with adrenomedullin, indicating a lack of MLC phosphatase activation. Interestingly, sodium fluoride, a nonspecific protein phosphatase inhibitor, completely blocked the effect of adrenomedullin on CaCl(2)-induced contraction. Adrenomedullin inhibited calcium mobilization from intracellular stores induced by thapsigargin.

CONCLUSION

Adrenomedullin inhibits CaCl(2)-induced contraction, without affecting calcium influx, through a CGRP(8-37)-sensitive receptor, but not using the cyclic adenosine monophosphate pathway, probably through activation of protein phosphatases. Inhibition of intracellular calcium release is an additional role played by adrenomedullin in calcium homeostasis in vascular smooth muscle.

Adrenomedullin and adrenomedullin-binding protein-1 downregulate inflammatory cytokines and attenuate tissue injury after gut ischemia-reperfusion

BACKGROUND

Recent studies have shown that adrenomedullin (AM) and AM-binding protein-1 (AMBP-1) possess anti-inflammatory properties in sepsis. We hypothesized that administration of AM/AMBP-1 after gut ischemia-reperfusion (I/R) downregulates inflammatory cytokines and attenuates tissue injury.

METHODS

Male Sprague-Dawley rats (275-325 g) were used. Gut ischemia was induced by placing a microvascular clip across the superior mesenteric artery (SMA) for 90 minutes. Upon release of the SMA clamp, the animals were treated by AM (12 microg per kilogram of body weight) and AMBP-1 (40 microg per kilogram of body weight) in combination, or vehicle (1 mL 0.9% NaCl) over 30 minutes via a femoral vein catheter. The animals undergoing sham operation or ischemia for 90 minutes only, did not receive AM/AMBP-1 treatment. At 60 minutes after the completion of the treatment (ie, 90 minutes after reperfusion), blood samples were collected. Plasma AM and AMBP-1 were measured by radioimmunoassay and Western blot analysis, respectively. Serum levels of TNF-alpha, interleukin (IL)-1beta, IL-6, IL-10, transaminases (ie, alanine aminotransaminase, aspartate aminotransaminase), lactate, and creatinine were determined with the use of enzyme-linked immunosorbent assay and other standard methods. In additional groups of animals, the 10-day survival rate was recorded after gut I/R.

RESULTS

Ischemia alone was sufficient to downregulate both AM and AMBP-1. Unlike AMBP-1 that remained decreased, AM levels increased significantly after reperfusion. I/R but not ischemia alone significantly increased serum levels of inflammatory cytokines. Moreover, I/R-induced tissue injury was evidenced by increased levels of transaminases, lactate, and creatinine. Administration of AM/AMBP-1 after ischemia, however, markedly reduced cytokine levels, attenuated tissue injury, and improved survival.

CONCLUSIONS

AM/AMBP-1 may be a novel treatment to attenuate the reperfusion injury after gut ischemia.

Adrenomedullin Peptide: Gene Expression of Adrenomedullin, its Receptors and Receptor Activity Modifying Proteins, and Receptor Binding in Rat Testis—Actions on Testosterone Secretion1

Adrenomedullin (ADM) has been shown to be present in the human and rat male reproductive systems. This study demonstrates the expression of ADM in the rat testis and its effect on the secretion of testosterone. Whole testicular extracts had 5.43 +/- 0.42 fmol of immunoreactive ADM per milligram of protein and 84 +/- 8 fg of ADM mRNA per picogram of Actb (beta-actin) mRNA. Immunocytochemical studies showed positive ADM immunostaining in the Leydig cells and in the Sertoli cells. Gel filtration chromatography of testicular extracts showed two peaks, with the predominant one eluting at the position of the ADM precursor. Furthermore, the testis was shown to coexpress mRNAs encoding the calcitonin receptor-like receptor and receptor activity modifying protein 1 (Ramp1), Ramp2, and Ramp3. These account for the specific binding of ADM to the testis, which was partially inhibited by human ADM (22-52) and by human calcitonin gene-related peptide (8-37), the ADM and calcitonin gene-related peptide receptor antagonists, respectively. Administration of ADM to testicular blocks in vitro resulted in a dose-dependent inhibition of hCG-stimulated release of testosterone, which was abolished by the administration of ADM (22-52). Our results suggest a paracrine effect of ADM on testicular steroidogenesis.

Endothelium-independent relaxation by adrenomedullin in pregnant rat mesenteric artery: role of cAMP-dependent protein kinase A and calcium-activated potassium channels

The mechanisms of relaxation of adrenomedullin were investigated in isolated mesenteric artery from pregnant rats. Adrenomedullin (1 nM-0.3 microM) produced concentration-dependent relaxation of endothelium-denuded mesenteric artery rings precontracted with norepinephrine at a concentration required to produce 70% of maximal response (ED70). The concentration-response curve of adrenomedullin was shifted to the right by adrenomedullin receptor antagonist adrenomedullin(22-52) (10 microM) or calcitonin gene-related peptide(8-37) (1 microM). Inhibition of adenylate cyclase by 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ22536) (10 microM) or protein kinase A [Rp-cyclic adenosine monophosphorothioate (Rp-cAMP); 10 microM] reduced the adrenomedullin-induced relaxation to the same magnitude. Adrenomedullin increased the intracellular cAMP level from 0.38 +/- 0.07 to 2.00 +/- 0.47 pmol/mg tissues, which was completely inhibited by adrenomedullin(22-52) (100 microM). Extracellular high potassium (80 mM), which inactivates the potassium channels, reduced the adrenomedullin-induced relaxation. Blockade of ATP-sensitive, voltage-gated, or inward rectifier potassium channels did not affect the adrenomedullin-induced relaxation. Blockade of calcium-activated K+ channels (KCa) by tetraethylammonium (1 mM) or iberiotoxin (100 nM) inhibited the adrenomedullin-induced relaxation, whereas there was no additional inhibition by SQ22536 or Rp-cAMP when KCa channels were already inhibited. In conclusion, this study provides evidence that cAMP-dependent protein kinase A and KCa channels seem to mediate as the cellular pathways in the adrenomedullin-induced endothelium-independent relaxation of mesenteric artery from pregnant rats.

Adrenomedullin: molecular mechanisms and its role in cardiac disease

Adrenomedullin (AM) is a potent, long-lasting vasoactive peptide originally isolated from human pheochromocytoma. Since its discovery, serum and tissue AM expression have been shown to be increased in experimental models and in patients with cardiac hypertrophy, myocardial infarction and end-stage heart failure with several beneficial effects. Considerable evidence exists for a wide range of autocrine, paracrine and endocrine mechanisms for AM which include vasodilatory, anti-apoptotic, angiogenic, anti-fibrotic, natriuretic, diuretic and positive inotropic. Thus, through regulation of body fluid or direct cardiac mechanisms, AM has additive and beneficial effects in the context of heart disease. Notable molecular mechanisms of AM include cyclic adenosine monophosphate, guanosine-3',5'-monophosphate, PI3K/Akt and MAPK-ERK-mediated cascades. Given the endogenous and multifunctional nature of AM, we consider this molecule to have great potential in the treatment of cardiovascular diseases. In agreement, early experimental and preliminary clinical studies suggest that AM is a new and promising therapy for cardiovascular diseases.

Adrenomedullin gene expression and levels in the cardiovascular system after treatment with lipopolysaccharide

To study the effect of septicaemia, the temporal changes in tissue adrenomedullin (AM) and preproAM mRNA levels were studied in the heart and blood vessels after lipopolysaccharide (LPS) injection. Radioimmunoassay and solution hybridization-RNase protection assays were used to follow the changes in AM and its mRNA levels respectively after intraperitoneal injection of 10 mg/kg LPS in rats. The preproAM mRNA levels increased at 1 h in the right atrium after LPS injection, while the AM contents decreased at 1 h in the left atrium. The preproAM mRNA levels increased at 3 and 6 h in the left ventricle, whereas it increased at 6 h in the right ventricles after LPS injection. There was an increase in preproAM mRNA levels at 1 and 3 h in the mesenteric artery, while AM levels were increased at 1, 3 and 6 h. However, there were no such changes in the thoracic aorta. There were also increases in tumour necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta and IL-6 in the heart, and in the mesenteric artery (TNF-alpha and IL-1beta) and in thoracic aorta (IL-1beta and IL-6). The present results suggest that the biosynthesis and secretion of AM may be increased in cardiovascular tissues of rats injected with LPS, and that AM may play multiple roles in inflammation.

Adrenomedullin is both proinflammatory and antiinflammatory: its effects on gene expression and secretion of cytokines and macrophage migration inhibitory factor in NR8383 macrophage cell line

Adrenomedullin (ADM) is a potent vasorelaxant peptide that plays important roles in cardiovascular homeostasis and inflammatory response. ADM derived from macrophages is one of the major sources of ADM that is produced in the inflammatory process. To assess the functions of ADM in inflammation, we studied the temporal changes in ADM production and its effect on secretion of macrophage migration inhibitory factor (MIF) and cytokine response of NR8383 rat macrophages activated by lipopolysaccharide (LPS). NR8383 cells were stimulated by LPS in the absence and presence of exogenous ADM, and the concentrations of ADM, MIF, and proinflammatory cytokines (IL-6, TNF-alpha, and IL-1beta) in the culture media and gene expressions of the cells were measured. We confirmed that the secretion and mRNA expression of ADM in the macrophages were markedly increased by LPS. ADM increased initial secretion of MIF and IL-1beta from both nonstimulated and LPS-stimulated cells, and it also increased basal and LPS-induced IL-6 secretion of the cells by 2- to 15-fold. However, it reduced secretion of TNF-alpha from LPS-stimulated cells by 34-56%. Our results suggest that ADM modulates MIF secretion and cytokine production and plays important roles in both the initiation and propagation of the inflammatory response.

The clinical relevance of adrenomedullin: a promising profile?

Adrenomedullin (AM) is a peptide that possesses potentially beneficial properties. Since the initial discovery of the peptide by Kitamura et al. in 1993, the literature has been awash with reports describing its novel mechanisms of action and huge potential as a therapeutic target. Strong evidence now exists that AM is able to act as an autocrine, paracrine, or endocrine mediator in a number of biologically significant functions, including the endothelial regulation of blood pressure, protection against organ damage in sepsis or hypoxia, and the control of blood volume through the regulation of thirst. Its early promise as a potential mediator/modulator of disease was not, however, entirely as a result of the discovery of physiological functions but due more to the observation of increasing levels measured in plasma in direct correlation with disease progression. In health, AM circulates at low picomolar concentrations in plasma in 2 forms, a mature 52-amino acid peptide and an immature 53-amino acid peptide. Plasma levels of AM have now been shown to be increased in a number of pathological states, including congestive heart failure, sepsis, essential hypertension, acute myocardial infarction, and renal impairment. These earliest associations have been further supplemented with evidence of a role for AM in other pathologies including, most intriguingly, cancer. In this review, we offer a timely review of our current knowledge on AM and give a detailed account of the putative role of AM in those clinical areas in which the best therapeutic opportunities might exist.

Effect of Adrenomedullin on Adrenergic Vasoconstriction in Mesenteric Resistance Arteries of the Rat

Adrenomedullin (AM) is a hypotensive peptide that belongs to a family of peptides structurally related to calcitonin gene-related peptide (CGRP). The present study examined the effect of AM on adrenergic nerve-mediated vasoconstriction in rat perfused mesenteric vascular beds without endothelium. Perfusion of AM at 0.1 nM but not 10 nM increased vasoconstrictor responses to periarterial nerve stimulation (PNS) (1-4 Hz), while AM at 10 nM significantly attenuated vasoconstriction induced by bolus injection of norepinephrine (NE). In preparations treated with capsaicin (a CGRP depletor), pressor responses to both PNS and NE injection were markedly attenuated by AM. Perfusion of CGRP(8-37) (a CGRP-receptor antagonist) significantly potentiated the PNS- but not the NE-induced vasoconstriction. Combined perfusion of CGRP(8-37) and AM had no effect on the PNS-induced response and antagonized the inhibitory effect of AM on the NE-induced response. AM(2-52) (an AM-receptor antagonist) did not influence the effect of AM. These findings suggest that AM facilitates adrenergic vasoconstriction by inhibiting neurotransmission of CGRP-containing nerves, which counteract adrenergic nerve-mediated vasoconstriction.

Comparative study of the inhibitory effects of adrenomedullin on angiotensin II contraction in rat conductance and resistance arteries

Adrenomedullin (ADM), a ubiquitous vasoactive peptide, has been the target of a multitude of studies concerning its effect on the vascular tone. The present work aims at clarifying a series of its interactions with the renin-angiotensin system. The study uses the rat aorta ring as a model of conductance vessels, with or without vascular endothelium, and the second order branch of rat mesenteric arteries as a model of resistance arteries. Interactions between various concentrations of ADM and angiotensin II (Ang II) were studied, in the presence of L-NAME (a nitric oxide [NO] synthase inhibitor) and methylene blue (MB; a soluble guanylate cyclase inhibitor). Results point out differences in the mechanism of the inhibitory action of ADM upon Ang II effects in the two vessel types studied. Inhibition of Ang II contraction by ADM involves guanylate cyclase in both cases. However, NO is involved in ADM-induced inhibition of angiotensinergic vasoconstriction only in the conductance arteries, not in the resistance ones.

Receptor autoradiography as mean to explore the possible functional relevance of neuropeptides: focus on new agonists and antagonists to study natriuretic peptides, neuropeptide Y and calcitonin gene-related peptides

Over the past 20 years, receptor autoradiography has proven most useful to provide clues as to the role of various families of peptides expressed in the brain. Early on, we used this method to investigate the possible roles of various brain peptides. Natriuretic peptide (NP), neuropeptide Y (NPY) and calcitonin (CT) peptide families are widely distributed in the peripheral and central nervous system and induced multiple biological effects by activating plasma membrane receptor proteins. The NP family includes atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). The NPY family is composed of at least three peptides NPY, peptide YY (PYY) and the pancreatic polypeptides (PPs). The CT family includes CT, calcitonin gene-related peptide (CGRP), amylin (AMY), adrenomedullin (AM) and two newly isolated peptides, intermedin and calcitonin receptor-stimulating peptide (CRSP). Using quantitative receptor autoradiography as well as selective agonists and antagonists for each peptide family, in vivo and in vitro assays revealed complex pharmacological responses and radioligand binding profile. The existence of heterogeneous populations of NP, NPY and CT/CGRP receptors has been confirmed by cloning. Three NP receptors have been cloned. One is a single-transmembrane clearance receptor (NPR-C) while the other two known as CG-A (or NPR-A) and CG-B (or NPR-B) are coupled to guanylate cyclase. Five NPY receptors have been cloned designated as Y(1), Y(2), Y(4), Y(5) and y(6). All NPY receptors belong to the seven-transmembrane G-protein coupled receptors family (GPCRs; subfamily type I). CGRP, AMY and AM receptors are complexes which include a GPCR (the CT receptor or CTR and calcitonin receptor-like receptor or CRLR) and a single-transmembrane domain protein known as receptor-activity-modifying-proteins (RAMPs) as well as an intracellular protein named receptor-component-protein (RCP). We review here tools that are currently available in order to target each NP, NPY and CT/CGRP receptor subtype and establish their respective pathophysiological relevance.

Calcitonin gene-related peptide partly protects cultured smooth muscle cells from apoptosis induced by an oxidative stress via activation of ERK1/2 MAPK

Oxidative stress induced by a glucose/glucose oxidase (G/GO) generator system dose-dependently decreased the viability of cultured vascular smooth muscle cells (VSMC) as estimated by MTT assay. Cell death was induced in 40% of cells exposed to 0.2 IU/ml of the free radical generating mixture. Annexin-V labeling, Hoechst staining together with DNA laddering demonstrated that apoptosis was responsible for this cell loss. Pretreatment of the cells with 10(-8) M calcitonin gene-related peptide (CGRP) significantly attenuated the damaging effect of the oxidative stress. Indeed, cell viability was estimated to be 80% in CGRP-treated group, instead of 60% in absence of CGRP treatment. This protective effect of CGRP was antagonized by 8-37 CGRP, an antagonist of CGRP-1 receptors, whereas it was not reproduced by amylin, a CGRP analogue. As indicated by the reduction in Hoechst staining and in DNA laddering, CGRP prevented the onset of apoptosis. We also demonstrated that the peptide significantly up-regulated the activation of ERK1/2 and P38 kinases. Inhibitors of the kinases prevented the protective effect of CGRP. We conclude that CGRP antagonizes oxidative stress-induced apoptosis by up-regulating MAP kinase activation and that activation of these kinases was necessary to protection.

The inhibitory effect of adrenomedullin in the rat ileum: cross-talk with beta3-adrenoceptor in the serotonin-induced muscle contraction

In contrast to vascular muscles, the contribution of a hypotensive peptide adrenomedullin (AM) to the regulation of visceral smooth muscles is obscure. The content, synthesis, and effects of AM on the muscular tone in rat ileum were explored. It was found that there was immunoreactive AM (301 pg/mg of protein) and AM mRNA expression (162 fg/pg actin mRNA) in the ileum and that AM evoked relaxation in ileal strips (Ki = 0.85 nM) precontracted with serotonin. Antagonists of both AM (AM(22-52)) and calcitonin gene-related peptide (CGRP(8-37)) receptors did not affect this AM-induced relaxation, whereas it was suppressed by a selective blocker of beta3-adrenoreceptor (SR 59230A). The AM-induced relaxation was accompanied by a production of cAMP. Antagonists of protein kinases A (KT 5720 and H-7) and an inhibitor of the ATP-dependent K(+)-channels (glibenclamide) attenuated the effect of AM. We suggest that AM is a local regulator of the ileal tone, with an inhibitory action on muscle contraction. AM may activate the beta3-adrenoceptors, resulting in protein kinase A activation, which in turn opens the ATP-dependent K(+)-channels.

Novel Approach to Respiratory Pharmacology—Pharmacological Basis of Cough, Sputum and Airway Clearance

Disturbance of the normal mucociliary clearance due to hyperproduction of mucus and modification of its physicochemical characteristics is a common finding in airway diseases. Drugs that affect airway secretion have been developed and used to cleanse the respiratory tract for many centuries and in many countries. On the basis of the mechanism of their actions, the mucoactive drugs are classified into several groups. Some mucoactive drugs have direct effects on the production or composition of airway secretions, resulting in increased effectiveness of mucociliary clearance. Other mucoactive drugs do not have a specific action on mucus, but have beneficial effects on airway structure and function, which lead to correction of the pathophysiologic mechanisms that result in abnormal secretions. However, since many drugs have overlapping effects, it is difficult to classify these drugs into groups based on their major actions. Taken together with previous findings on mucoactive drugs, it appears that an antioxidant effect is a common property of mucoactive drugs and that it is a crucial action to exert their effects against airway diseases. In light of this idea, we must use specific experimental models to simulate pharmacologic events in airway inflammation. The development of new techniques has made it possible to identify and measure the mucus components, measure the rheologic parameters more accurately, and evaluate mucociliary clearance precisely in animals and humans. Therefore, with modifications of methods, we have investigated airway-cleansing drugs from various points of view to reflect actions in inflammatory states for more than two decades. Here, I introduce the methods we have used to study many of the parameters involved in airway clearance, including cough reflex, and describe some of the mucoactive-antitussive drugs that we have studied recently. There is an increasing usage of traditional Chinese herbal medicines in clinics and hospitals, because they tend to have moderate side effects and sometimes remarkable efficacy. To renormalize overall defects in airway disorders, Chinese medicines may be adequate, because they are composed of various herbs with weak but ubiquitous pharmacologic activities. We have been investigating Bakumondo-to. Bakumondo-to has been used for the treatment of bronchitis and pharyngitis accompanying severe dry cough. We found that unlike codeine Bakumondo-to had a notable antitussive activity against the cough associated with bronchitis and the cough increased by angiotensin-converting enzyme inhibitors. Recently, we have found that, in alveolar type II cells, Bakumondo-to attenuated phosphatidylcholine secretion increased by oxygen radicals from activated PMNLS. In addition, we found that Bakumondo-to itself stimulated phosphatidylcholine secretion and increased beta-adrenoceptor gene expression in rat alveolar type II cells. We studied the mechanism of action and clarified that Bakumondo-to increased glucocorticoid-sensitive promotor activity. The effect may contribute to its ubiquitous effectiveness in the treatment of airway diseases. Various parameters (chemical properties, physical properties, mucus production, surfactant phospholipid production, and mucociliary clearance) are considered to be important for the dynamics and mobilization of airway secretions. Pharmacologic investigation, with appropriate techniques, of the ability of an agent to modify these parameters can provide useful information about its mechanism of action. However, since these parameters are interconnected, it is very complicated to elucidate the precise mechanisms of action of mucoactive drugs. This means that the goal of treatment cannot always be achieved by the modification of a single parameter, but should, more realistically, be aimed at a renormalization of several parameters. On the basis of this idea, glucocorticoids are ideal mucoactive drugs because they exert various pharmacologic effects in the lung. From a polypharmacologic point of view, a traditional Chinese medicine can be classified as a glucocorticoid-like drug because Chinese medicines consist of many types of active components that have various pharmacologic effects. As one future course of research, we believe that efforts to seek compatible actions between glucocorticoids and Oriental medicines may lead to new opportunities for development of ideal airway-cleansing drugs with specific actions, i.e., suppression of gene expression.

Adrenomedullin receptor binding sites in rat brain and peripheral tissues

The existence of specific adrenomedullin receptor binding sites was investigated using the agonist peptide fragment [125I]human adrenomedullin-(13-52) in rat brain, lung and vas deferens homogenates. Saturation-binding experiments suggest that [125I]human adrenomedullin-(13-52) binds to an apparent single population of sites with similar affinities (K(D) of 0.3 to 0.6 nM) but with different maximal binding capacity in the rat brain, lung and vas deferens homogenates (B(max) of 73, 1760 and 144 fmol/mg protein, respectively). Competition-binding experiments using various analogues and fragments of calcitonin gene-related peptide (CGRP) and adrenomedullin were also performed using this radioligand. Competition-binding profiles suggest the possible existence of heterogeneous populations of adrenomedullin receptor binding sites. For example, in rat brain, human adrenomedullin-(1-52) and human adrenomedullin-(13-52) competed against specific [125I]human adrenomedullin-(13-52) sites with competition curves best fitted to a two-site model. Additionally, human calcitonin gene-related peptide alpha (hCGRPalpha), [Cys(Et)(2,7)]hCGRPalpha and [[R-(R,(R*,S*)]-N-[2-[[5-amino-1-[[4-(4-pyridinyl)-1-piperazinyl]carbonyl]pentyl]amino]-1-[(3,5-dibromo-4-hydroxyphenyl)methyl]-2-oxoethyl]-4-(1,4-dihydro-2-oxo-3(2H)-quinazolinyl)-,1-Piperidinecarboxamide] (BIBN4096BS) competed against specific [125I]human adrenomedullin-(13-52) binding with profiles that were also best fitted to a two-site model. Furthermore, binding assays performed in the presence of GTPgammaS (100 microM) revealed that this compound inhibited 20% of specific [125I]human adrenomedullin-(13-52) sites in rat brain homogenates and competition curves of human adrenomedullin-(1-52) and [Cys(Et)(2,7)]hCGRPalpha against specific [125I]human adrenomedullin-(13-52) sites remained best fitted to a two-site model. Moreover, the existence of specific [125I]human adrenomedullin-(13-52) binding sites that are resistant to human adrenomedullin-(22-52) and human CGRP-(8-37) is suggested in the rat brain and vas deferens. Taken together, these data provide evidence for the possible existence of heterogeneous populations of adrenomedullin binding sites in rat brain and peripheral tissues.

Adrenomedullin induces direct (endothelium-independent) vasorelaxations and cyclic adenosine monophosphate elevations that are synergistically enhanced by brain natriuretic peptide in isolated rings of rat thoracic aorta

Our laboratory previously demonstrated that nitric oxide and natriuretic peptides can synergistically enhance cAMP elevations and vasorelaxations in rat aortic rings induced by calcitonin gene-related peptide, likely involving cyclic guanosine monophosphate (cGMP)-mediated inhibition of type-3 phosphodiesterase (PDE3). It was predicted that this cellular mechanism may also serve as a point of synergism between adrenomedullin (ADM) and brain natriuretic peptide (BNP) in aortic smooth muscle cells. The current study shows that ADM (100 nM)-induced vasorelaxations in isolated aortic rings of Sprague-Dawley rats are dependent on endothelium (34.1 +/- 4.2% relaxation with endothelium versus 3.0 +/- 0.6% relaxation without endothelium; P < 0.001). To determine interactions between ADM and BNP in smooth muscle cells without interference from endothelium-derived factors, further studies used aortic rings denuded of endothelium. Pretreatment with BNP (1 nM), which elevated cGMP levels 1.6 fold, uncovered direct vasorelaxant effects of ADM in endothelium-denuded rings, showing 5.6 +/- 1.8%, 20.9 +/- 6.1%, and 55 +/- 9.4% relaxations with ADM at 1, 10, and 100 nM, respectively (n = 6). ADM (100 nM) significantly (P < 0.05) increased cyclic adenosine monophosphate (cAMP) levels in denuded aortic rings pretreated with BNP (1 nM), but not in denuded rings without BNP. Quazinone (20 microM), a PDE3 inhibitor, caused similar enhancement of direct cAMP elevations to ADM (100 nM). The data indicate vasodilatory synergism between ADM and BNP in aorta, likely mediated by enhanced accumulation of cAMP in smooth muscle cells resulting from BNP/cGMP-induced inhibition of PDE3. This synergistic mechanism may be especially important in subjects with dysfunctional endothelium, in which BNP may uncover direct vasorelaxant effects of ADM in arteries that normally require healthy (nitric oxide-releasing) endothelium for ADM-induced vasorelaxations to occur.

Cell and molecular biology of the multifunctional peptide, adrenomedullin

Adrenomedullin (AM) is a recently discovered regulatory peptide involved in many functions including vasodilatation, electrolyte balance, neurotransmission, growth, and hormone secretion regulation, among others. This 52-amino acid peptide is expressed by specific cell types in many organs throughout the body. A complex receptor system has been described for AM; it requires at least the presence of a seven-transmembrane-domain G-protein-coupled receptor, a single-transmembrane-domain receptor activity modifying protein, and a receptor component protein needed to establish the connection with the downstream signal transduction pathway, which usually involves cyclicAMP. In addition, a serum-binding protein regulates the biological actions of AM, frequently by increasing AM functional attributes. Changes in levels of circulating AM correlate with several critical diseases, including cardiovascular and renal disorders, sepsis, cancer, and diabetes. Whether AM is a causal agent, a protective reaction, or just a marker for these diseases is currently under investigation. New technologies seeking to elevate and/or reduce AM levels are being investigated as potential therapeutic avenues.

Adrenomedullin gene delivery inhibits neointima formation in rat artery after balloon angioplasty

Adrenomedullin (AM) is a potent vasodilator expressed in tissues relevant to cardiovascular function. AM peptide has been shown to inhibit the proliferation and migration of vascular smooth muscle cells in vitro. However, the effect of AM on blood vessels after vascular injury in vivo has not been elucidated. In order to explore the potential roles of AM in vascular biology, we evaluated the effect of AM by local gene delivery on neointima formation in balloon-injured rat artery. Adenovirus carrying the human AM cDNA under the control of cytomegalovirus promoter/enhancer (Ad.CMV-hAM) was generated by homologous recombination. After delivery of Ad.CMV-hAM into rat left carotid artery, we identified the expression of human AM mRNA in the left carotid artery, but not in the right carotid artery, heart or kidney by reverse transcription-polymerase chain reaction (RT-PCR) followed by Southern blot analysis. Following local AM gene delivery, we observed a 51% reduction in intima/media ratio at the injured site as compared with that of control rats injected with the luciferase gene (n=7, P<0.01). AM gene transfer resulted in regeneration of endothelium as compared to the control. AM gene delivery significantly increased cGMP levels in balloon-injured arteries. These results indicate that AM contributes to reduction of neointima formation by promotion of re-endothelialization and inhibition of vascular smooth muscle cell proliferation via cGMP-dependent signaling pathway.

Adrenomedullin is an autocrine/paracrine growth factor for rat vascular smooth muscle cells

Adrenomedullin is a potent vasodilator peptide secreted by vascular endothelial and smooth muscle cells. Adrenomedullin stimulates the proliferation of quiescent rat vascular smooth muscle cells (VSMCs) via p42/p44 ERK/MAP kinase activation. Recently, receptor-activity-modifying proteins (RAMPs) have been shown to transport calcitonin-receptor-like-receptor (CRLR) to the cell surface to present either as CGRP receptor or adrenomedullin receptor. We investigated whether adrenomedullin acts as an autocrine/paracrine growth factor for cultured rat VSMCs and whether coexpressions of RAMP isoform and CRLR may mediate p42/p44 ERK/MAP kinase activation by adrenomedullin. Adrenomedullin dose-dependently stimulated the proliferation of quiescent rat VSMCs, and this effect was inhibited by an adrenomedullin receptor antagonist, a MAP kinase kinase inhibitor and phosphatidylinositol 3-kinase inhibitors. Addition of either CGRP(8-37) or anti-adrenomedullin antibody to exponentially growing rat VSMCs inhibited the serum-induced cell proliferation, suggesting its role as an autocrine/paracrine growth factor. Cotransfection of RAMP2 or RAMP3 with CRLR into rat VSMCs potentiated activation of cAMP activity, but not of p42/p44 ERK/MAP kinase activity in response to adrenomedullin. Our results suggest that adrenomedullin is an autocrine/paracrine growth factor for rat VSMCs via p42/p44 ERK/MAP kinase and phosphatidylinositol 3-kinase pathways and that it is not mediated by human RAMP-CRLR receptors.