Adrenomedullin binds with high affinity, elevates cyclic AMP, and stimulates c-fos mRNA in C6 glioma cells

Calcitonin gene-related peptide induces the histone H3 lysine 9 acetylation in astrocytes associated with neuroinflammation in rats with neuropathic pain

Aims

Calcitonin gene‐related peptide (CGRP) as a regulator of astrocyte activation may facilitate spinal nociceptive processing. Histone H3 lysine 9 acetylation (H3K9ac) is considered an important regulator of cytokine and chemokine gene expression after peripheral nerve injury. In this study, we explored the relationship between CGRP and H3K9ac in the activation of astrocytes, and elucidated the underlying mechanisms in the pathogenesis of chronic neuropathic pain.

Methods

Astroglial cells (C6) were treated with CGRP and differentially enrichments of H3K9ac on gene promoters were examined using ChIP‐seq. A chronic constriction injury (CCI) rat model was used to evaluate the role of CGRP on astrocyte activation and H3K9ac signaling in CCI‐induced neuropathic pain. Specific inhibitors were employed to delineate the involved signaling.

Results

Intrathecal injection of CGRP and CCI increased the number of astrocytes displaying H3K9ac in the spinal dorsal horn of rats. Treatment of CGRP was able to up‐regulate H3K9ac and glial fibrillary acidic protein (GFAP) expression in astroglial cells. ChIP‐seq data indicated that CGRP significantly altered H3K9ac enrichments on gene promoters in astroglial cells following CGRP treatment, including 151 gaining H3K9ac and 111 losing this mark, which mostly enriched in proliferation, autophagy, and macrophage chemotaxis processes. qRT‐PCR verified expressions of representative candidate genes (ATG12, ATG4C, CX3CR1, MMP28, MTMR14, HMOX1, RET) and RTCA verified astrocyte proliferation. Additionally, CGRP treatment increased the expression of H3K9ac, CX3CR1, and IL‐1β in the spinal dorsal horn. CGRP antagonist and HAT inhibitor attenuated mechanical and thermal hyperalgesia in CCI rats. Such analgesic effects were concurrently associated with the reduced levels of H3K9ac, CX3CR1, and IL‐1β in the spinal dorsal horn of CCI rats.

Conclusion

Our findings highly indicate that CGRP is associated with the development of neuropathic pain through astrocytes‐mediated neuroinflammatory responses via H3K9ac in spinal dorsa horn following nerve injury.

This study found that CGRP act on their astrocytic receptors and lead to H3K9 acetylation (H3K9ac), which are mainly associated with proliferation‐, autophagy‐, and inflammation‐related gene expression. The number of astrocytes with H3K9ac expression is increased after nerve injury. Inhibition of CGRP attenuates the development of neuropathic pain, which was accompanied by the suppression of H3K9ac, CX3CR1, and IL‐1β expression in CCI rats.

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.

Cyclic AMP-dependent down regulation of ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) in rat C6 glioma

In this communication, we demonstrate that an increase in intracellular cAMP by 1) addition of dibutyrylic cAMP (dbcAMP), a membrane-permeable cAMP-analogue, or 2) activation of the β-adrenoceptor with (-)-isoproterenol, down regulates the levels of ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) mRNA, NPP1 protein and ecto-NPPase activity in rat C6 glioma cells. DbcAMP and (-)-isoproterenol inhibit NPP1 expression in a time and dose-dependent manner. After 48h of stimulation, 1mM dbcAMP or 5μM (-)-isoproterenol decreases the amount of NPP1 protein by 75±3% and 81±1% respectively. Contrary to down regulation of NPP1, we observe an up regulation of glial fibrillary acidic protein (GFAP), a differentiation marker for astrocytic cells. Using specific inhibitors and activators, we have shown that Ca(2+), PKA, PI 3-K/PKB/GSK-3, Epac/Rap1/PP2A and MAP kinase modules are not involved in the inhibition of NPP1 gene expression. The transcription factor c-jun is significantly reduced while c-fos becomes up regulated after cAMP elevation. However an electrophoretic mobility shift assay with the activator protein-1 motif present in the promoter of the rat NPP1 gene indicates that this motif is not involved in the cAMP-dependent inhibition of NPP1 expression. In conclusion, these results indicate that intracellular cAMP levels regulate the expression of NPP1 in rat C6 glioma cells by a signalling pathway that is different from the GFAP signal transduction pathway.

Lack of adrenomedullin affects growth and differentiation of adult neural stem/progenitor cells

Adrenomedullin (AM) is a peptide hormone involved in the modulation of cellular growth, migration, apoptosis, and angiogenesis. These characteristics suggest that AM is involved in the control of neural stem/progenitor cell (NSPC) biology. To explore this hypothesis, we have obtained NSPC from the olfactory bulb of adult wild-type animals and brain conditional knockouts for adm, the gene that produces AM. Knockout NSPC contain higher levels of hyperpolymerized tubulin and more abundant filopodia than adm-containing cells, resulting in a different morphology in culture, whereas the size of the knockout neurospheres is smaller than that of the wild-types. Proliferation studies have demonstrated that adm-null NSPC incorporate less 5'-bromodeoxyuridine (BrdU) than their wild-type counterparts. In contrast, BrdU studies in the olfactory bulb of adult animals show more labeled cells in adm-null mice that in wild-types, suggesting that a compensatory mechanism exists that guarantees the sufficient production of neural cells in this organ. In NSPC differentiation tests, lack of adm results in significantly lower proportions of neurons and astrocytes and higher proportions of oligodendrocytes. The oligodendrocytes produced from adm-null neurospheres present an immature phenotype with fewer and shorter processes than adm-containing oligodendrocytes. Thus, AM is an important factor in regulating the proliferation and differentiation of adult NSPC and might be used to modulate stem cell renewal and fate in protocols destined to produce neural cells for regenerative therapies.

Targeting adrenomedullin receptors with systemic delivery of neutralizing antibodies inhibits tumor angiogenesis and suppresses growth of human tumor xenografts in mice

Adrenomedullin (AM) is a multifunctional peptide vasodilator that transduces its effects through calcitonin receptor-like receptor/receptor activity modifying protein-2 and -3 (CLR/RAMP2 and CLR/RAMP3). Previously, we reported on the development of an anti-AM antibody that potently inhibits tumor cell proliferation in vitro and tumor growth in vivo. Here, we report the effect of anti-AM receptor antibodies (alphaAMRs) on angiogenesis and tumor growth. We demonstrate that alphaAMRs decrease in a dose-dependent manner the growth of U87 glioblastoma cells and HT-29 colorectal cancer cells, but not A549 lung cancer cells, in vitro. In vivo, AM in Matrigel plugs induces angiogenesis by promoting recruitment of endothelial cells, pericytes, myeloid precursor cells, and macrophages and by promoting channel formation. Remarkably, systemic administration of alphaAMRs every 3 d markedly reduced neovascularization of Matrigel plugs in a dose-dependent fashion, as demonstrated by reduced numbers of the recruited cells and vessel structures. Several human tumor xenografts in athymic mice were used to examine the effect of alphaAMR treatment on tumor angiogenesis and growth. AlphaAMR treatment significantly suppressed the growth of glioblastoma, lung, and colon tumors. Histological examination of alphaAMR-treated tumors showed evidence of disruption of tumor vascularity with decreased microvessel density, depletion of endothelial and pericyte cells, and increased tumor cell apoptosis. These findings support the conclusion that alphaAMR treatment inhibits tumor growth by suppression of angiogenesis and tumor growth and suggest that AMRs may be useful therapeutic targets.

Adrenomedullin: a new target for the design of small molecule modulators with promising pharmacological activities

Adrenomedullin (AM) is a 52-amino acid peptide with a pluripotential activity. AM is expressed in many tissues throughout the body, and plays a critical role in several diseases such as cancer, diabetes, cardiovascular and renal disorders, among others. While AM is a protective agent against cardiovascular disorders, it behaves as a stimulating factor in other pathologies such as cancer and diabetes. Therefore, AM is a new and promising target for the development of molecules which, through their ability to regulate AM levels, could be used in the treatment of these pathologies.

Adrenomedullin signals through NF-kappaB in epithelial cells

Adrenomedullin is a peptide found in a variety of cells and tissues and involved in a multitude of biological processes. Recently, adrenomedullin has been identified as a host defense peptide and as such it plays a role in the inflammatory response. The transcription factor NF-kappaB is a major regulator of genes involved in the inflammatory response and the aim of this study was to determine whether NF-kappaB played a role in the inflammatory process triggered by adrenomedullin. Skin epithelial cells (HaCaTs) were used as our model in vitro. Western blot analysis from adrenomedullin-stimulated HaCaT cells revealed a rapid degradation of NF-kappaB inhibitor alpha and beta followed by the translocation of free NF-kappaB to the nucleus, where it was detected by Texas Red immunostaining after incubation with adrenomedullin for 15 min. Electromobility shift assay showed that NF-kappaB present in the nucleus was active, since it bound to a probe containing an NF-kappaB binding site. Supershift assays indicated that p50 and p65, members of the NF-kappaB family, were both part of the NF-kappaB dimmers involved in adrenomedullin cell signaling. HaCaTs secreted interleukin-6 in response to AM, which was significantly attenuated by the NF-kappaB inhibitor SN-50. Taken together, the data lend support for an immunoregulatory role for AM.

Steroids and adrenomedullin growth patterns in human ovarian cancer cells: estrogenic-regulation assay

OBJECTIVE

Adrenomedullin is a multifunctional regulatory peptide with mitogenic and angiogenic capabilities. Objectives in this study were: (1) to describe the effects of adrenomedullin and anti-adrenomedullin antibodies on ovarian carcinoma cell proliferation, and (2) to assess the estradiol regulation of adrenomedullin metabolism.

METHODS

We assessed the effects of estradiol, adrenomedullin, and anti-adrenomedullin antibodies on cell growth in three human ovarian cell lines. RT-PCR was used to assess mRNA expression and Western blots to determine protein levels.

RESULTS

Estradiol stimulates BG-1 and PEO4 cells growth but not PEO14 cells. Adrenomedullin mRNA expression and secretion were not under estrogen control. Adrenomedullin and anti-adrenomedullin antibodies had no growth effects in vitro. Adjunction of anti-adrenomedullin antibodies to estradiol-stimulated cells significantly inhibited their growth.

CONCLUSION

Adrenomedullin metabolism is not under estradiol control. Anti-adrenomedullin antibodies display inhibitory effects on cells having high mitogenic activity. This opens the need for additional search toward in vivo specific immunotherapy.

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.

Expression of adrenomedullin and its receptor by chondrocyte phenotype cells

For clarifying a process of de-differentiation in culturing chondrocytes, the present study was undertaken to investigate the secretion of adrenomedullin (AM) by chondrocyte phenotype cells and whether or not AM effects this proliferation in a cAMP-dependent fashion. Chondrocyte phenotype cells expressed AM and the AM receptor, and secreted high concentration of AM into the culture medium. When added to cultures, AM increased the intracellular cAMP level and decreased the number of these cells in a similar concentration-dependent fashion. Addition of forskolin and dibutyryl-cAMP caused a significant decrease in the number of these cells. Furthermore, the effect of AM was inhibited by a cAMP-dependent protein kinase A inhibitor (H89). The present findings indicate that AM has an autocrine/paracrine type of anti-proliferative effect on these cells mediated via a cAMP-dependent pathway and raise the possibility that AM plays a role in the local modulation of a process of de-differentiation by culturing chondrocyte phenotype cells.

Adrenomedullin stimulates proliferation and inhibits apoptosis of immature rat thymocytes cultured in vitro

Adrenomedullin (AM) is a hypotensive peptide, which derives from the proteolytic cleavage of pro(p)AM, and acts through two subtypes of receptors, named L1-receptor (L1-R) and calcitonin receptor-like receptor (CRLR). CRLR functions as either a calcitonin gene-related peptide (CGRP) receptor or a selective AM receptor depending on which member of a family of receptor-activity-modifying proteins (RAMPs) is expressed: RAMP1 generates CGRP receptors, while RAMP2 and RAMP3 produce AM receptors. Reverse transcription (RT)-polymerase chain reaction (PCR) consistently allowed the detection of pAM and peptidyl-glycine alpha-amidating monooxygenase (the enzyme converting immature AM to the mature peptide) mRNAs in the thymus cortex of immature (10-day-old) rats. Accordingly, radioimmune assay (RIA) measured low but sizeable AM concentrations in this tissue. RT-PCR also demonstrated the presence of the specific mRNAs of L1-R, CRLR and RAMPs. AM (from 10(-9) to 10(-7)M) increased proliferation index and lowered apoptotic index of cultured immature rat thymocytes, and the effects were annulled by the AM receptor antagonist AM(22-52). In conclusion, our study demonstrated that (1) immature rat thymus cortex expresses AM and the AM receptors L1-R and CRLR/RAMP; and (2) AM, acting via AM(22-52)-sensitive receptors, exerts a potent growth promoting effect on immature rat thymus, by enhancing proliferation and lowering apoptotic death of thymocytes. Taken together, these findings could suggest that AM may play a role in the development of immunity.

Adrenomedullin stimulates the growth of cultured normal human osteoblasts as an autocrine/paracine regulator

Adrenomedullin (AM) is a 52 amino acid peptide that is synthesized in a variety of tissues, including the vessels and bones. This study showed that normal human osteoblast (NHOst) secreted immunoreactive AM and that AM stimulated intracellular cAMP production in these cells. An anti-AM monoclonal antibody, which inhibited endogenous AM, caused the number of NHOst to decrease. The effect of a low concentration AM was inhibited by addition of a cAMP-dependent protein kinase A inhibitor (H89). These data suggest that AM is an autocrine or paracrine regulator that promotes the proliferation of NHOst via the cAMP pathway.

Adrenomedullin functions as an important tumor survival factor in human carcinogenesis

Adrenomedullin (AM) is a pluripotent regulatory peptide initially isolated from a human pheochromocytoma (adrenal tumor) and subsequently shown to play a critical role in cancer cell division, tumor neovascularization, and circumvention of programmed cell death, thus it is an important tumor cell survival factor underlying human carcinogenesis. A variety of neural and epithelial cancers have been shown to produce abundant amounts of AM. Recent findings have implicated elevation of serum AM with the onset of malignant expression. In addition, patients with tumors producing high levels of this peptide have a poor prognostic clinical outcome. Given that most human epithelial cancers display a microenvironment of reduced oxygen tension, it is interesting to note that AM and several of its receptors are upregulated during hypoxic insult. The existence of such a regulatory pathway has been implicated as the basis for the overexpression of AM/AM-R in human malignancies, thereby generating a subsequent autocrine/paracrine growth advantage for the tumor cell. Furthermore, AM has been implicated as a potential immune suppressor substance, inhibiting macrophage function and acting as a newly identified negative regulator of the complement cascade, protective properties which may help cancer cells to circumvent immune surveillance. Hence, AM's traditional participation in normal physiology (cited elsewhere in this issue) can be extended to a primary player in human carcinogenesis and may have clinical relevance as a biological target for the intervention of tumor progression.

Neutralization of adrenomedullin inhibits the growth of human glioblastoma cell lines in vitro and suppresses tumor xenograft growth in vivo

Presently, there is no effective treatment for glioblastoma, the most malignant and common brain tumor. Growth factors are potential targets for therapeutic strategies because they are essential for tumor growth and progression. Peptidylglycine alpha-amidating monooxygenase is the enzyme producing alpha-amidated bioactive peptides from their inactive glycine-extended precursors. The high expression of peptidylglycine alpha-amidating monooxygenase mRNA in glioblastoma and glioma cell lines points to the involvement of alpha-amidated peptides in tumorigenic growth processes in the brain. After screening of amidated peptides, it was found that human glioblastoma cell lines express high levels of adrenomedullin (AM) mRNA, and that immunoreactive AM is released into the culture medium. AM is a multifunctional regulatory peptide with mitogenic and angiogenic capabilities among others. Real-time quantitative reverse transcriptase-polymerase chain reaction analysis showed that AM mRNA was correlated to the tumor type and grade, with high expression in all glioblastomas analyzed, whereas a low expression was found in anaplastic astrocytomas and barely detectable levels in low-grade astrocytomas and oligodendrogliomas. In the present study we also demonstrate the presence of mRNA encoding the putative AM receptors, calcitonin receptor-like receptor/receptor activity-modifying protein-2 and -3 (CRLR/RAMP2; CRLR/RAMP3) in both glioma tissues and glioblastoma cell lines and further show that exogenously added AM can stimulate the growth of these glioblastoma cells in vitro. These findings suggest that AM may function as an autocrine growth factor for glioblastoma cells. One way to test the autocrine hypothesis is to interrupt the function of the endogenously produced AM. Herein, we demonstrate that a polyclonal antibody specific to AM, blocks the binding of the hormone to its cellular receptors and decreases by 33% (P < 0.001) the growth of U87 glioblastoma cells in vitro. Intratumoral administration of the anti-AM antibody resulted in a 70% (P < 0.001) reduction in subcutaneous U87 xenograft weight 21 days after treatment. Furthermore, the density of vessels was decreased in the antibody-treated tumors. These findings support that AM may function as a potent autocrine/paracrine growth factor for human glioblastomas and demonstrate that inhibition of the action of AM (produced by tumor cells) may suppress tumor growth in vivo.

Cancer and diabetes: two pathological conditions in which adrenomedullin may be involved

Adrenomedullin (AM) is a regulatory peptide involved in several physiological processes. Among them, AM has been implicated in the regulation of growth, both with mitogenic and antiproliferative activities on normal cells. AM is widely expressed during embryogenesis and may have a significant role in the proliferation and differentiation processes associated with development. AM is also expressed by cancer cell lines and tumors and has been implicated in the growth of malignant cells. Some additional activities associated with AM (antiapoptotic capabilities, angiogenic potential, and upregulation in hypoxic conditions), together with its wide distribution in cancer, suggest that AM may be an important factor in carcinogenesis. Besides its implication in growth, embryogenesis and tumor biology, AM is also involved in pancreatic regulation and diabetes. AM regulates insulin secretion and is overexpressed in the plasma of diabetic patients. Several findings indicate that AM may participate in the pathogenesis and/or clinical complications of this disease.

Gene expression of adrenomedullin, leptin, their receptors and neuropeptide Y in hormone-secreting and non-functioning pituitary adenomas, meningiomas and malignant intracranial tumours in humans

The aim of this study was to assess human intracranial tumours for their gene expression pattern of the vasoactive peptide adrenomedullin (AM), its receptor (AM-R) and leptin, which exerts multiple biological effects including proliferation and angiogenesis via the leptin receptor (OB-Rb). Gene activity of neuropeptide Y (NPY) was monitored additionally. We investigated whether there was a characteristic gene expression pattern of AM and leptin in different intracranial tumours, depending on their proliferation activity and biological behaviour. We investigated 35 non-functioning pituitary adenomas (including eight null cell, four silent plurihormonal, 23 silent gonadotroph adenomas), seven somatotropinomas, seven prolactinomas, eight meningiomas, five astrocytomas, two glioblastoma multiformes and unaffected temporal lobe (n = 8). Quantitative reverse transcriptase-polymerase chain reaction (TaqMan RT-PCR) was performed. AM mRNA was detectable in all tumour specimens. AM/GAPDH (glyceraldehyde-3-phosphate dehydrogenase) ratio was significantly higher in somatotropinomas, as was AM/CD31 ratio in prolactinomas, compared with inactive adenomas (P < 0.05). AM-R mRNA was found in all tumour subgroups in small quantities but, in general, higher in tumours than in temporal lobe tissue, respectively. AM-R/CD31 ratio was significantly higher in prolactinomas than in inactive adenomas (P < 0.05). Leptin was detectable in very low quantities in each subgroup. OB-Rb gene expression was found in all tumour subgroups, OB-Rb/GAPDH ratio was highest for meningiomas (P < 0.0001, compared with temporal lobe). NPY mRNA was detectable in temporal lobe in higher quantities than in tumours (P < 0.0001), and almost undetectable in prolactinomas and astrocytomas. Our data demonstrate that AM and AM-R, NPY, as well as leptin and OB-Rb, are expressed in various intracranial tumours in humans but their particular function has to be elucidated further. At present, there is no evidence for a cross-talk on transcriptional level between the peptidergic vasodilative system AM and the putative angiogenic and proliferation affecting factor leptin.

Adrenomedullin, a multifunctional regulatory peptide

Since the discovery of adrenomedullin in 1993 several hundred papers have been published regarding the regulation of its secretion and the multiplicity of its actions. It has been shown to be an almost ubiquitous peptide, with the number of tissues and cell types synthesizing adrenomedullin far exceeding those that do not. In Section II of this paper we give a comprehensive review both of tissues and cell lines secreting adrenomedullin and of the mechanisms regulating gene expression. The data on circulating adrenomedullin, obtained with the various assays available, are also reviewed, and the disease states in which plasma adrenomedullin is elevated are listed. In Section III the pharmacology and biochemistry of adrenomedullin binding sites, both specific sites and calcitonin gene-related peptide (CGRP) receptors, are discussed. In particular, the putative adrenomedullin receptor clones and signal transduction pathways are described. In Section IV the various actions of adrenomedullin are discussed: its actions on cellular growth, the cardiovascular system, the central nervous system, and the endocrine system are all considered. Finally, in Section V, we consider some unresolved issues and propose future areas for research.

Proadrenomedullin NH(2)-terminal 20 peptide (PAMP) and adrenomedullin bind to teratocarcinoma cells

Proadrenomedullin NH(2-)terminal 20 peptide (PAMP) and adrenomedullin (ADM) bind to teratocarcinoma cells. The effects of PAMP and ADM on teratocarcinoma cells were investigated. (125)I-PAMP bound to PA1 cells with moderate affinity (K(d) = 110 nM) to a single class of sites (B(max) = 110 000/cell). Specific (125)I-PAMP binding was inhibited by PAMP (IC(50) of 100 nM) but not ADM, calcitonin gene-related peptide (CGRP), or amylin. Specific (125)I-ADM binding was inhibited with high affinity by ADM, CGRP, and CGRP(8-37) (IC(50) values of 10, 10, and 15 nM respectively) but not PAMP or amylin. ADM elevated cAMP (ED(50) value of 100 nM), whereas PAMP had no effect on basal cAMP but inhibited the increase in cAMP caused by 10 nM ADM. Also, the increase in cAMP caused by ADM was inhibited CGRP(8-37), suggesting that ADM is binding to CGRP receptors. ADM (100 nM) stimulated transiently c-fos mRNA, whereas PAMP (1000 nM) had little effect; however, PAMP inhibited the increase in c-fos mRNA caused by ADM. ADM stimulated [(3)H]thymidine uptake into PA1 cells, whereas PAMP inhibited the increase in thymidine uptake caused by ADM. These results indicate that ADM and PAMP are both biologically active in teratocarcinoma cells.

Adrenomedullin and the control of fluid and electrolyte homeostasis

Two potent hypotensive peptides, adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP), are encoded by the adrenomedullin gene. AM stimulates nitric oxide production by endothelial cells, whereas PAMP acts presynaptically to inhibit adrenergic nerves that innervate blood vessels. Complementary, but mechanistically unique, actions also occur in the anterior pituitary gland where both peptides inhibit adrenocorticotropin release. In the adrenal gland both AM and PAMP inhibit potassium and angiotensin II-stimulated aldosterone secretion. Natriuretic and diuretic actions of AM reflect unique actions of the peptide on renal blood flow and tubular function. In the brain AM inhibits water intake and, in a physiologically relevant manner, salt appetite. Both AM and PAMP act in the brain to elevate sympathetic tone, effects that mirror the positive inotropic action of AM in the heart. Cardioprotective actions in the brain and heart may be important counter-regulatory actions that buffer the extreme hypotensive actions of the peptides when released in sepsis. Thus the biologic actions of the proadrenomedullin-derived peptides seem well coordinated to contribute to the physiologic regulation of volume and electrolyte homeostasis.