Distribution of preproadrenomedullin mRNA in the rat central nervous system and its modulation by physiological stressors

Adrenomedullin in paraventricular nucleus attenuates adipose afferent reflex and sympathoexcitation via receptors mediated nitric oxide-gamma-aminobutyric acid A type receptor pathway in rats with obesity-related hypertension

BACKGROUND

Hypothalamic paraventricular nucleus (PVN) is an important central site for the control of the adipose afferent reflex (AAR) that increases sympathetic outflow and blood pressure in obesity-related hypertension (OH).

METHOD

In this study, we investigated the effects of nitric oxide (NO) and cardiovascular bioactive polypeptide adrenomedullin (ADM) in the PVN on AAR and sympathetic nerve activity (SNA) in OH rats induced by a high-fat diet.

RESULTS

The results showed that ADM, total neuronal NO synthase (nNOS) and phosphorylated-nNOS protein expression levels in the PVN of the OH rats were down-regulated compared to the control rats. The enhanced AAR in OH rats was attenuated by PVN acute application of NO donor sodium nitroprusside (SNP), but was strengthened by the nNOS inhibitor nNOS-I, guanylyl cyclase inhibitor (1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one, ODQ) and gamma-aminobutyric acid A type receptor (GABAA) antagonist Bicuculline. Moreover, PVN ADM microinjection not only decreased basal SNA but also attenuated the enhanced AAR in OH rats, which were effectively inhibited by ADM receptor antagonist ADM22-52, nNOS-I, ODQ or Bicuculline pretreatment. Bilateral PVN acute microinjection of ADM also caused greater increases in NO and cyclic guanosine monophosphate (cGMP) levels, and nNOS phosphorylation. Adeno-associated virus vectors encoding ADM (AAV-ADM) transfection in the PVN of OH rats not only decreased the elevated AAR, basal SNA and blood pressure (BP), but also increased the expression and activation of nNOS. Furthermore, AAV-ADM transfection improved vascular remodeling in OH rats.

CONCLUSION

Taken together, our data highlight the roles of ADM in improving sympathetic overactivation, enhanced AAR and hypertension, and its related mechanisms associated with receptors mediated NO-cGMP-GABAA pathway in OH condition.

Centrally acting adrenomedullin in the long-term potentiation of sympathetic vasoconstrictor activity induced by intermittent hypoxia in rats

NEW FINDINGS

What is the central question of this study? Adrenomedullin in the rostral ventrolateral medulla (RVLM) increases sympathetic activity; given that adrenomedullin is released during hypoxia, what are the effects of its agonism and antagonism in the RVLM after chronic intermitent hypoxia (CIH) exposure? What is the main finding and its importance? CIH exposure sensitizes adrenomedullin-dependent mechanisms in the RVLM, supporting its role as a sympathoexcitatory neuromodulator. A novel mechanism was identified for the generation of sympathetic overdrive and hypertension associated with hypoxia, providing potential guidance on new therapeutic approaches for controlling sympathetic hyperactivity in diseases such as sleep apnoea and neurogenic hypertension.

ABSTRACT

Adrenomedullin in the rostral ventrolateral medulla (RVLM) has been shown to increase sympathetic activity whereas the antagonism of its receptors inhibited this autonomic activity lowering blood pressure in conditions of hypertension. Given that hypoxia is a stimulant for releasing adrenomedullin, we hypothesized that the presence of this peptide in the RVLM associated with chronic intermittent hypoxia (CIH) would cause sympathetic overdrive. Juvenile male rats (50-55 g) submitted to CIH (6% oxygen every 9 min, 8 h day^-1 for 10 days) were studied in an arterially perfused in situ preparation where sympathetic activity was recorded. In control rats (n = 6), exogenously applied adrenomedullin in the RVLM raised baseline sympathetic activity when combined with episodic activation of peripheral chemoreceptors (KCN 0.05%, 5 times every 5 min). This sympathoexcitatory response was markedly amplified in rats previously exposed to CIH (n = 6). The antagonism of adrenomedullin receptors in the RVLM caused a significant reduction in sympathetic activity in the CIH group (n = 7), but not in controls (n = 8). The transient reflex-evoked sympathoexcitatory response to peripheral chemoreceptor stimulation was not affected by either adrenomedullin or adrenomedullin receptor antagonism in the RVLM of control and CIH rats. Our findings indicate that CIH sensitizes the sympathoexcitatory networks within the RVLM to adrenomedullin, supporting its role as an excitatory neuromodulator when intermittent hypoxia is present. These data reveal novel state-dependent mechanistic insights into the generation of sympathetic overdrive and provide potential guidance on possible unique approaches for controlling sympathetic discharge in diseases such as sleep apnoea and neurogenic hypertension.

Effect of Valsartan on Cerebellar Adrenomedullin System Dysregulation During Hypertension

Adrenomedullin (AM) and its receptors components, calcitonin-receptor-like receptor (CRLR), and receptor activity-modifying protein (RAMP1, RAMP2, and RAMP3) are expressed in cerebellum. Cerebellar AM, AM binding sites and receptor components are altered during hypertension, suggesting a role for cerebellar AM in blood pressure regulation. Thus, we assessed the effect of valsartan, on AM and its receptor components expression in the cerebellar vermis of Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Additionally, we evaluated AM action on superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) activity, and thiobarbituric acid reactive substances (TBARS) production in cerebellar vermis. Animals were treated with valsartan or vehicle for 11 days. Rats were sacrificed by decapitation; cerebellar vermis was dissected; and AM, CRLR, RAMP1, RAMP2, and RAMP3 expression was quantified by Western blot analysis. CAT, SOD, and GPx activity was determined spectrophotometrically and blood pressure by non-invasive plethysmography. We demonstrate that AM and RAMP2 expression was lower in cerebellum of SHR rats, while CRLR, RAMP1, and RAMP3 expression was higher than those of WKY rats. AM reduced cerebellar CAT, SOD, GPx activities, and TBARS production in WKY rats, but not in SHR rats. Valsartan reduced blood pressure and reversed the altered expression of AM and its receptors components, as well the loss of AM capacity to reduce antioxidant enzyme activity and TBARS production in SHR rats. These findings demonstrate that valsartan is able to reverse the dysregulation of cerebellar adrenomedullinergic system; and they suggest that altered AM system in the cerebellum could represent the primary abnormality leading to hypertension.

Dysregulation of Cerebellar Adrenomedullin Signaling During Hypertension

Adrenomedullin (AM) is a peptide involved in blood pressure regulation. AM activates three different receptors, the AM type 1 (AM1), type 2 (AM2), and calcitonin gene-related peptide 1 (CGRP1) receptors. AM triggers several signaling pathways such as adenylyl cyclase (AC), guanylyl cyclase (GC), and extracellular signal-regulated kinases (ERK) and modulates reactive oxygen species (ROS) metabolism. Cerebellar AM, AM-binding sites, and its receptor components are altered during hypertension, although it is unknown if these alterations are associated with changes in AM signaling. Thus, we assessed AM signaling pathways in cerebellar vermis of 16-week-old Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). Animals were sacrificed by decapitation, and cerebellar vermis was microdissected under stereomicroscopic control. Tissue was stimulated in vitro with AM. Then the production of cyclic guanosine monophosphate (cGMP), nitric oxide (NO) and cyclic adenosine monophosphate (cAMP) were assessed along with ERK1/2 activation and three antioxidant enzymes' activity: glutathione peroxidase (GPx), catalase (CAT), and superoxide dismutase (SOD). Our findings demonstrate that in the cerebellar vermis of normotensive rats, AM increases cGMP, NO, cAMP production, and ERK1/2 phosphorylation, while decreases basal antioxidant enzyme activity. In addition, AM antagonizes angiotensin II (ANG II)-induced increment of antioxidant enzyme activity. Hypertension blunts AM-induced cGMP and NO production and AM-induced decrease of antioxidant enzyme activity. Meanwhile, AM-induced effects on cAMP production, ERK1/2 activation, and AM-ANG II antagonism were not altered in SHR rats. Our results support a dysregulation of several AM signaling pathways during hypertension in cerebellar vermis.

Cerebellar Adrenomedullinergic System. Role in Cardiovascular Regulation

Adrenomedullin (AM) is a multifunctional peptide which exerts numerous biological activities through the activation of AM1 (CRLR + RAMP2) and AM2 (CRLR + RAMP3) receptors. AM immunoreactivity, AM binding sites and CRLR, RAMP1, RAMP2 and RAMP3 are expressed in rat cerebellar vermis. AM binding sites are discretely and differentially distributed in the rat cerebellar cortex with higher levels detected in SHR when compared with WKY rats. In addition, there is an up-regulation of cerebellar CGRP1 (CRLR + RAMP1) and AM2 (CRLR + RAMP3) receptors and a down-regulation of AM1 (CRLR + RAMP2) receptor during hypertension associated with a decreased AM expression. These changes may constitute a mechanism which contributes to the development of hypertension, and supports the notion that cerebellar AM is involved in the regulation of blood pressure. Cerebellar AM activates ERK, increases cAMP, cGMP and nitric oxide, and decreases antioxidant enzyme activity. These effects are mediated through AM₁ receptor since they are blunted by AM(22-52). AM-stimulated cAMP production is mediated through AM2 and CGRP receptors. In vivo administration of AM into the cerebellar vermis caused a profound, specific and dose-dependent hypotensive effect in SHR, but not in normotensive WKY rats. This effect was mediated through AM1 receptor since it was abolished by AM(22-52). In addition, AM injected into the cerebellar vermis reduced vasopressor response to footshock stress. These findings demonstrate dysregulation of cerebellar AM system during hypertension, and suggest that cerebellar AM plays an important role in the regulation of blood pressure. Likewise, they constitute a novel mechanism of blood pressure control which has not been described so far.

Role of cerebellar adrenomedullin in blood pressure regulation

Adrenomedullin (AM) and their receptor components, calcitonin-receptor-like receptor (CRLR) and receptor activity-modifying protein (RAMP1, RMP2 and RAMP3) are widely expressed in the central nervous system, including cerebellum. We have shown that AM binding sites are altered in cerebellum during hypertension, suggesting a role for cerebellar adrenomedullinergic system in blood pressure regulation. To further evaluate the role of AM in cerebellum, we assessed the expression of AM, RAMP1, RAMP2, RAMP3 and CRLR in the cerebellar vermis of 8 and 16week old spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats. In addition, the effect of microinjection of AM into rat cerebellar vermis on arterial blood pressure (BP) was determined. Animals were sacrificed by decapitation and cerebellar vermis was dissected for quantification of AM, CRLR, RAMP1, RAMP2 and RAMP3 expression using western blot analysis. Another group of male, 16week old SHR and WKY rats was anesthetized, and a cannula was implanted in the cerebellar vermis. Following recovery AM (0.02 to 200pmol/5μL) or vehicle was injected into cerebellar vermis. BP was determined, before and after treatments, by non-invasive plethysmography. In addition, to establish the receptor subtype involved in AM action in vivo, animals received microinjections of AM22-52 (200pmol/5μL), an AM1 receptor antagonist, or the CGRP1 receptor antagonist, CGRP8-37 (200pmol/5μL) into the cerebellar vermis, administered simultaneously with AM or vehicle microinjection. Cannulation was verified post mortem with the in situ injection of a dye solution. Our findings demonstrated that the expression of CRLR, RAMP1 and RAMP3 was higher in cerebellum of SHR rats, while AM and RAMP2 expression was lower than those of WKY rats, both in 8 and 16week old rats. In vivo microinjection of AM into the cerebellar vermis caused a profound, dose dependent, hypotensive effect in SHR but not in normotensive WKY rats. Coinjections of a putative AM receptor antagonist, AM22-52 abolished the decreases in mean arterial pressure (MAP) evoked by AM, showing that AM acts through its AM1 receptor in the vermis to reduce MAP. These findings demonstrate a dysregulation of cerebellar AM-system during hypertension, and suggest that cerebellar AM plays an important role in the regulation of BP. Likewise; they constitute a novel mechanism of BP control which has not been described so far.

Upregulation of pronociceptive mediators and downregulation of opioid peptide by adrenomedullin following chronic exposure to morphine in rats

Adrenomedullin (AM) belongs to a calcitonin gene-related peptide (CGRP) family and has been demonstrated to recruit CGRP following chronic use of morphine and neuronal nitric oxide synthase (nNOS) in inflammation. The present study investigated the possibility that AM initiates the changes of other molecules contributing to the development of morphine tolerance in its chronic use. Intrathecal (i.t.) co-administration of the AM receptor antagonist AM22-52 (35.8 μg) inhibited tolerance to morphine-induced analgesia while a daily injection of the AM receptor agonist AM1-50 (8 μg, i.t., bolus) for 9 days induced a decrease in the potency of morphine analgesia and thermal hyperalgesia. Persistent exposure of cultured dorsal root ganglion (DRG) explants to morphine (3.3 μM) for 4 days resulted in an increase in AM and CGRP mRNA levels. However, morphine failed to produce these effects in the presence of AM22-52 (2 μM). The i.t. administration of morphine for 6 days increased the expression of nNOS in the spinal dorsal horn and DRG neurons but decreased expression of the endogenous opioid peptide bovine adrenal medulla 22 (BAM22) in small- and medium-sized neurons in DRG. Particularly, the co-administration of AM22-52 (35.8 μg) inhibited the morphine-induced alterations in nNOS and BAM22. These results indicated that the increase in nNOS and CGRP expressions and the decrease in BAM22 were attributed to the increased AM receptor signaling induced by chronic morphine. The present study supports the hypothesis that the enhancement of AM bioactivity triggered upregulation of pronociceptive mediators and downregulation of pain-inhibiting molecule in a cascade contributing to the development of morphine tolerance.

Intrathecal adrenomedullin modulates acute inflammatory pain in the rat formalin test

Adrenomedullin (AM), a member of the calcitonin gene-related peptide (CGRP) family, has been demonstrated to be a pronociceptive mediator. This study was undertaken to investigate the role of AM in acute inflammatory pain induced by formalin injection in rats. Interestingly Cerebrospinal fluid (CSF) levels of AM increased 45 min after formalin injection and a selective AM receptor antagonist, AM22-52, administered intrathecally (i.t.) decreased phase 2 flinching in a dose-dependent manner but not phase 1 flinching during the formalin test. This anti-hyperalgesic effect of i.t. AM22-52 lasted for 4 h or more. AM in the CSF contributes to the modulation of acute inflammatory pain in the formalin test, and blocking downstream signaling effects of the AM receptor has the potential to relieve pain associated with acute inflammation.

Brainstem neuropeptides and vagal protection of the gastric mucosal against injury: role of prostaglandins, nitric oxide and calcitonin-gene related peptide in capsaicin afferents

Earlier experimental studies indicated that the integrity of vagal pathway was required to confer gastric protection against damaging agents. Several peptides located in the brainstem initially identified to influence vagal outflow to the stomach, as assessed by electrophysiological approach or by vagal dependent alterations of gastric secretory and motor function, were investigated for their influence in the vagal regulation of the resistance of the gastric mucosa to injury. Thyrotropin releasing hormone (TRH), or its stable TRH analog, RX-77368, injected at low doses into the cisterna magna or the dorsal motor nucleus (DMN) was the first peptide reported to protect the gastric mucosa against ethanol injury through stimulation of vagal cholinergic pathways, inducing the release of gastric prostaglandins/nitric oxide (NO) and the recruitment of efferent function of capsaicin sensitive afferent fibers containing calcitonin-gene related peptide (CGRP). Activation of endogenous TRH-TRH1 receptor signaling located in the brainstem plays a role in adaptive gastric protection against damaging agents. Since then, an expanding number of peptides, namely peptide YY, CGRP, adrenomedullin, amylin, glugacon-like peptide, opioid peptides acting on µ, δ1 or δ2 receptors, nocicpetin, nocistatin, ghrelin, leptin and TLQP-21, a peptide derived from VGF prohormone, have been reported to act in the brainstem to afford gastric protection against ethanol injury largely through similar peripheral effectors mechanisms than TRH. Therefore gastric prostaglandins and CGRP/NO pathways represent a common final mechanism through which brain peptides confer vagally mediated gastroprotection against injury. A better understanding of brain circuitries through which these peptides are released will provide new strategies to recruit integrated and multifaceted gastroprotective mechanisms.

Blockade of adrenomedullin receptors reverses morphine tolerance and its neurochemical mechanisms

Adrenomedullin (AM) has been demonstrated to be involved in the development of opioid tolerance. The present study further investigated the role of AM in the maintenance of morphine tolerance, morphine-associated hyperalgesia and its cellular mechanisms. Intrathecal (i.t.) injection of morphine for 6 days induced a decline of its analgesic effect and hyperalgesia. Acute administration of the AM receptor antagonist AM(22-52) resumed the potency of morphine in a dose-dependent manner (12, 35.8 and 71.5 μg, i.t.). The AM(22-52) treatment also suppressed morphine tolerance-associated hyperalgesia. Furthermore, i.t. administration of AM(22-52) at a dose of 35.8 μg reversed the morphine induced-enhancement of nNOS (neuronal nitric oxide synthase) and CGRP immunoreactivity in the spinal dorsal horn and/or dorsal root ganglia (DRG). Interestingly, chronic administration of morphine reduced the expression of the endogenous opioid peptide bovine adrenal medulla 22 (BAM22) in small- and medium-sized neurons in DRG and this reduction was partially reversed by the administration of AM(22-52) (35.8 μg). These results suggest that the activation of AM receptors was involved in the maintenance of morphine tolerance mediating by not only upregulation of the pronociceptive mediators, nNOS and CGRP but also the down-regulation of pain-inhibiting molecule BAM22. Our data support the hypothesis that the level of both pronociceptive mediators and endogenous pain-inhibiting molecules has an impact on the potency of morphine analgesia. Targeting AM receptors is a promising approach to maintain the potency of morphine analgesia during chronic use of this drug.

A role for protein kinase C-dependent upregulation of adrenomedullin in the development of morphine tolerance in male rats

Adrenomedullin (AM) belongs to calcitonin gene-related peptide (CGRP) family and is a pronociceptive mediator. This study investigated whether AM plays a role in the development of tolerance to morphine-induced analgesia. Repetitive intrathecal injection of morphine increased the expression of AM-like immunoreactivity (AM-IR) in the spinal dorsal horn and dorsal root ganglion (DRG) neurons. Ganglion explant culture study showed that this upregulation of AM-IR was μ-opioid receptor dependent through the use of another agonist, fentanyl, and a selective antagonist, CTAP (D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2)). The coadministration of the selective AM receptor antagonist AM(22-52) markedly attenuated the development of morphine tolerance, associated thermal hyperalgesia, and increase in AM-IR. A likely autocrine mechanism is supported by the finding that AM-IR is colocalized with AM receptor components in DRG neurons. Furthermore, opiate-induced increase in AM content was blocked by protein kinase C (PKC) inhibitors, whereas a PKC activator increased AM synthesis and release. A treatment with AM(22-52) also inhibited increases in the expression of CGRP-IR in the spinal cord and DRGs as well as in culture ganglion explants, whereas exposure to CGRP failed to alter AM content. Together, these results reveal that a sustained opiate treatment induces an upregulation of AM through the activation of μ-opioid receptors and the PKC signaling pathway. This phenomenon contributes to the development of tolerance to the antinociceptive effects of opiates at least partially via the upregulation of CGRP. Targeting AM and its receptors should be considered as a novel approach to preserve the analgesic potency of opiates during their chronic use.

Circulating hormone adrenomedullin and its binding protein protect neural cells from hypoxia-induced apoptosis

BACKGROUND

Brain ischemia is the underlying cause of neuron death during stroke and brain trauma. Neural cells exposed to ischemia can undergo apoptosis. Adrenomedullin (AM) in combination with its enhancing binding protein, AMBP-1, has been shown to reduce tissue damage in inflammation.

METHODS

To evaluate a beneficial effect of AM/AMBP-1 administration in brain ischemia, we employed an in vitro model of neuronal hypoxia using differentiated human neuroblastoma SH-SY5Y cells.

RESULTS

After exposure to 1% O(2) for 20 h, neural cells were injured with decreased ATP levels and increased LDH release. Pre-administration of AM/AMBP-1 significantly reduced hypoxia-induced cell injury. Moreover, AM/AMBP-1 treatment reduced the number of TUNEL-positive cells and activation of caspase-3, compared to cells exposed to hypoxia alone. AM/AMBP-1 prevented a reduction of cAMP levels and protein kinase A (PKA) activity in neural cells after hypoxia exposure. Correspondingly, an elevation of cAMP levels by forskolin protected neural cells from hypoxia-induced injury. Inhibition of PKA by KT5720 abolished the protective effect of AM/AMBP-1 on hypoxia-induced apoptosis.

CONCLUSIONS

AM/AMBP-1 elevates cAMP levels, followed by activating PKA, to protect neural cells from the injury caused by hypoxia.

GENERAL SIGNIFICANCE

AM/AMBP-1 may be used as therapeutic agents to prevent neuron damage from brain ischemia.

Lack of adrenomedullin in the mouse brain results in behavioral changes, anxiety, and lower survival under stress conditions

The adrenomedullin (AM) gene, adm, is widely expressed in the central nervous system (CNS) and several functions have been suggested for brain AM. Until now, a formal confirmation of these actions using genetic models has been elusive since the systemic adm knockout results in embryo lethality. We have built a conditional knockout mouse model using the Cre/loxP approach. When crossed with transgenic mice expressing the Cre recombinase under the tubulin Talpha-1 promoter, we obtained animals with no AM expression in the CNS but normal levels in other organs. These animals lead normal lives and do not present any gross morphological defect. Specific areas of the brain of animals lacking CNS AM contain hyperpolymerized tubulin, a consequence of AM downregulation. Behavioral analysis shows that mice with no AM in their brain have impaired motor coordination and are hyperactive and overanxious when compared to their wild-type littermates. Treatment with methylphenidate, haloperidol, and diazepam did not show differences between genotypes. Circulating levels of adrenocorticotropic hormone and corticosterone were similar in knockout and wild-type mice. Animals with no brain AM were less resistant to hypobaric hypoxia than wild-type mice, demonstrating the neuroprotective function of AM in the CNS. In conclusion, AM exerts a beneficial action in the brain by maintaining homeostasis both under normal and stress conditions.

Adrenomedullin enhances baroreceptor reflex response via cAMP/PKA signaling in nucleus tractus solitarii of rats

Adrenomedullin (ADM), a 52-amino acid peptide, elicits differential cardiovascular responses when it is administered systemically or directly to the brain. We evaluated in the present study the hypothesis that ADM may modulate baroreceptor reflex (BRR) response through an ADM receptor-mediated cAMP/ protein kinase A (PKA)-dependent mechanism in the nucleus tractus solitarii (NTS), the terminal site for primary baroreceptor afferents, using Sprague-Dawley rats. Our immunoblot and immunohistochemical results showed that the two component proteins of the ADM(1) receptor complex, calcitonin receptor-like receptor (CRLR) and receptor activity modifying protein (RAMP)-2, were uniformly distributed and highly co-localized in the NTS. Site-specific microinjection of ADM (0.02-0.2pmol) unilaterally into the NTS significantly increased BRR response and sensitivity in a time- and dose-related manner, without affecting arterial pressure and heart rate. The BRR enhancing effect of ADM was also temporally correlated with an up-regulation of PKA(beta), the active form of PKA and an increase in PKA activity. In addition, the ADM-evoked BRR enhancement or PKA activation was abolished by co-microinjection with a selective ADM(1) receptor antagonist, ADM(22-52), an adenylyl cyclase inhibitor, SQ22536, or a PKA inhibitor, Rp-8-bromo-cAMP. These results suggest that ADM enhances BRR via activation of a cAMP/PKA-dependent mechanism by acting site-specifically on ADM(1) receptors in NTS.

Adrenomedullin in the rostral ventrolateral medulla inhibits baroreflex control of heart rate: a role for protein kinase A

1 The rostral ventrolateral medulla (RVLM) is an essential vasomotor center in the brainstem which participates in maintaining resting levels of arterial pressure and for regulating baroreflex activity. We have demonstrated that microinjections of adrenomedullin (ADM), a vasoactive neuropeptide, into the RVLM cause increased resting mean arterial pressure (MAP) and heart rate (HR). However, the effect of ADM on baroreflex function remains unclear. 2 The purposes of the present study were to investigate the effect of ADM in the RVLM on the regulation of baroreflex activity and to identify the underlying mechanisms. Baroreflex curves were generated with intravenous injections of multiple doses of phenylephrine and nitroprusside. The upper and lower plateaus, reflex range, MAP at the midpoint of HR range (MAP(50)), and gain were evaluated before and after various microinjections were made into the RVLM of urethane-anesthetized rats. 3 Microinjections of ADM decreased the upper plateau, reflex range, and gain, and increased MAP(50), indicating that ADM in the RVLM impairs baroreflex function. 4 ADM(22-52), a putative ADM receptor antagonist, significantly increased the baroreflex gain and upper plateau, demonstrating that endogenous ADM tonically inhibits the baroreflex. Coinjections of ADM(22-52) with ADM blocked the ADM-induced baroreflex responses. 5 ADM's effect was abolished with H-89, a protein kinase A (PKA) inhibitor. 6 Our results show that ADM in the RVLM exerts an inhibitory effect on baroreflex activity via an ADM receptor-mediated mechanism, and that activation of PKA is involved in this event.

Increased levels of nitric oxide, cortisol and adrenomedullin in patients with chronic schizophrenia

OBJECTIVE

To investigate the levels of serum cortisol, dehydroepiandrosterone sulfate (DHEA-S), nitric oxide (NO) and adrenomedullin (AM) in schizophrenic patients.

SUBJECTS AND METHODS

Sixty-six male patients with chronic schizophrenia and 28 normal male subjects participated in this study. The duration of disease was 145 +/- 120 (mean +/- SD) months. Serum levels of cortisol and DHEA-S were measured by electrochemiluminescence; plasma nitrite levels as an index of NO were measured with the Griess reaction, while plasma AM concentration was measured by using high-performance liquid chromatography.

RESULTS

Patients (12.48 +/- 3.2 microg/dl), as compared to controls (10.31 +/- 3.1 microg/dl), had higher levels of baseline cortisol (p < 0.05). DHEA-S levels were lower in patients though this did not reach statistical significance (302 +/- 156 microg/dl compared to control, 322 +/- 96 microg/dl, p > 0.05). The mean levels of plasma AM and NO in the schizophrenic group (44.33 +/- 5.07 pmol/l and 36.27 +/- 17.6 micromol/l) were significantly higher than the levels in the control group (14.56 +/- 4.03 pmol/l and 32.54 +/- 7.14 micromol/l; p < 0.001, p < 0.03, respectively). There was a positive association between duration of disease and cortisol/DHEA-S ratio and cortisol level.

CONCLUSION

The data show that schizophrenia is associated with abnormal levels of cortisol, DHEA-S, NO and AM.

Immunohistochemical mapping of adrenomedullin in the human medulla oblongata

We studied by immunocytochemistry the expression of adrenomedullin (AM) in the human medulla oblongata, sampled from 13 adult subjects (mean age: 38 years), whose medical history was negative for neurological and neurovascular pathologies. Immunoreactive neurons were found in the medulla oblongata with statistically significant differences among the various nuclei (one-way ANOVA, P < 0.001). The hypoglossal nucleus showed higher AM expression than that of the spinal tract of the trigeminal nerve (P < 0.05), solitary tract nucleus (P < 0.05), nucleus intercalatus (P < 0.05), and area postrema (P < 0.05). The arcuate nucleus and inferior olivary nuclear complex showed lower AM expression than the hypoglossal nucleus (P < 0.001), vestibular nuclei (P < 0.01), cuneate and gracile nuclei (P < 0.05), lateral column of the reticular formation (P < 0.05), and nucleus ambiguous (P < 0.05). Furthermore the nuclei were grouped with reference to their function, into somatic sensitive nuclei, somatic motor nuclei, visceral nuclei, reticular formation, and nuclei involved in cerebellar functions. The ANOVA revealed statistically significant differences (P < 0.001) in mean AM scores among the different groups. Nuclei involved in cerebellar function showed the lowest mean AM score (P < 0.05). The difference in AM score between somatic motor nuclei and visceral nuclei was also statistically significant (P < 0.05). Widespread AM immunoreactivity in the nuclei of the medulla oblongata may account for the role of the peptide in neuronal function and regulation of regional blood flow. Differences in the expression of AM in the nuclei studied indicate the different involvement of AM in neurotransmission and neuromodulation.

Characterization and effects on cAMP accumulation of adrenomedullin and calcitonin gene-related peptide (CGRP) receptors in dissociated rat spinal cord cell culture

Adrenomedullin (AM) and calcitonin gene-related peptide (CGRP) have structural similarities, interact with each others receptors (calcitonin receptor-like receptor (CLR)/receptor-activity-modifying proteins (RAMPs)) and show overlapping biological activities. AM and CGRP receptors are chiefly coupled to cAMP production. In this study, a method of primary dissociated cell culture was used to investigate the presence of AM and CGRP receptors and their effects on cAMP production in embryonic spinal cord cells. Both neuronal and non-neuronal CLR immunopositive cells were present in our model. High affinity, specific [(125)I]-AM binding sites (K(d) 79 +/- 9 pM and B(max) 571 +/- 34 fmol mg(-1) protein) were more abundant than specific [(125)I]-CGRP binding sites (K(d) 12 +/- 0.7 pM and B(max) 32 +/- 2 fmol mg(-1) protein) in embryonic spinal cord cells. Specific [(125)I]-AM binding was competed by related molecules with a ligand selectivity profile of rAM > hAM(22-52) > rCGRPalpha > CGRP(8-37) >> [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). Specific [(125)I]-CGRP binding was competed by rCGRPalpha > rAM > or = CGRP(8-37) > or = BIBN4096BS > hAM(22-52). Cellular levels of cAMP were increased by AM (pEC(50) 10.2 +/- 0.2) and less potently by rCGRPalpha (pEC(50) 8.9 +/- 0.4). rCGRPalpha-induced cAMP accumulation was effectively inhibited by CGRP(8-37) (pA(2) 7.63 +/- 0.44) and hAM(22-52) (pA(2) 6.18 +/- 0.21) while AM-stimulation of cAMP levels was inhibited by CGRP(8-37) (pA(2) 7.41+/- 0.15) and AM(22-52) (pA(2) 7.26 +/- 0.18). BIBN4096BS only antagonized the effects of CGRP (pA(2) 8.40 +/- 0.30) on cAMP accumulation. These pharmacological profiles suggest that effects of CGRP are mediated by the CGRP(1) (CLR/RAMP1) receptor in our model while those of AM are related to the activation of the AM(1) (CLR/RAMP2) receptor subtype.

Pathophysiologic and therapeutic implications of adrenomedullin in cardiovascular disorders

Adrenomedullin (AM) is a vasodilator peptide that originally isolated from pheochromocytoma tissue. However, the mRNA is expressed in the normal adrenal gland, heart, kidney and blood vessels. The human AM gene is located in the short arm of chromosome 11 and is composed of 4 exons. There are 2 single nucleotide polymorphisms in introns 1 and 3, and the 3'-end of the AM gene is flanked by a microsatellite marker of cytosine-adenine repeats that is associated with an increased risk of developing hypertension and diabetic nephropathy. AM gene expression is promoted by various stimuli, including inflammation, hypoxia, oxidative stress, mechanical stress and activation of the renin-angiotensin and sympathetic nervous systems. The AM gene promoter region possessed binding site for several transcription factors, including nuclear factor for interleukin-6 expression (NF-IL6) and activator protein 2 (AP-2). Further, plasma AM levels are increased in patients with various cardiovascular diseases, including hypertension, heart failure and renal failure. These findings suggest that AM plays a role in the development of or response to cardiovascular disease. Indeed, experimental and clinical studies have demonstrated that systemic infusion of AM may have a therapeutic effect on myocardial infarction, heart failure and renal failure. Further, vasopeptidase inhibitors which augment the bioactivity of endogenous AM may benefit patients with hypertension and arteriosclerosis. Finally, the angiogenic and cytoprotective properties of AM may have utility in revascularization and infarcted myocardium and ischemic limbs. Because of the potential clinical benefits of AM, indications for use and optimal dosing strategies should be established.

Centrally administered adrenomedullin 2 activates hypothalamic oxytocin-secreting neurons, causing elevated plasma oxytocin level in rats

We examined the effects of intracerebroventricular (i.c.v.) administration of adrenomedullin 2 (AM2) on plasma oxytocin (OXT) and arginine vasopressin (AVP) levels in conscious rats. Plasma OXT levels were markedly increased 5 min after i.c.v. administration of AM2 (1 nmol/rat) compared with vehicle and remained elevated in samples taken at 10, 15, 30, and 60 min. By contrast, plasma AVP levels were not significantly elevated in samples taken between 5 and 180 min after i.c.v. administration of AM2 except at the 30-min time point. Fos-like immunoreactivity (Fos-LI) was observed in various brain areas, including the paraventricular (PVN) and the supraoptic nuclei (SON) after i.c.v. administration of AM2 (2 nmol/rat) in conscious rats (measured at 90 min post-AM2 infusion). Dual immunostaining for OXT/Fos and AVP/Fos showed that OXT-LI neurons predominantly exhibited nuclear Fos-LI compared with AVP-LI neurons in the PVN and the SON. In situ hybridization histochemistry showed that i.c.v. administration of AM2 (0.2, 1, and 2 nmol/rat) caused marked induction of the expression of the c-fos gene in the PVN and the SON. This induction was significantly reduced by pretreatment with both the calcitonin gene-related peptide (CGRP) antagonist CGRP-(8-37) (3 nmol/rat) and the AM receptor antagonist AM-(22-52) (27 nmol/rat). These results suggest that centrally administered AM2 mainly activates OXT-secreting neurons in the PVN and the SON, at least in part through the CGRP and/or AM receptors with marked elevation of plasma OXT levels in conscious rats.

Calcitonin gene-related peptide-containing pathways in the rat forebrain

The present study focuses on the topographical distribution of calcitonin gene-related peptide (CGRP)-containing cell bodies and fibers and their connections and pathways in the rat forebrain. We confirm previously reported CGRP projections from the perifornical area of the hypothalamus to the lateral septum, from the posterior thalamus to the caudate putamen and cerebral cortex, and from the parabrachial nuclei to the central extended amygdala, lateral hypothalamus, and ventromedial thalamus. Despite previous descriptions of CGRP in the central nervous system, important neuroanatomical aspects of the forebrain CGRP system remained obscure, which we addressed by using brain lesion techniques combined with modern immunohistology. We first report CGRP terminal fields in the olfactory-anterior septal region and also CGRP projections from the parabrachial nuclei to the olfactory-anterior septal region, the medial prefrontal cortex, the interstitial nucleus of the anterior commissure, the nucleus of the lateral olfactory tract, the anterior amygdaloid area, the posterolateral cortical amygdaloid nucleus, and the dorsolateral part of the lateral amygdaloid nucleus. In addition, we identified a CGRP cell group in the premamillary nuclei and showed that it projects to the medial CGRP layer of the lateral septum. CGRP fibers usually join other pathways rather than forming bundles. They run along the fornix from the hypothalamus, along the supraoptic decussations or the inferior thalamic peduncle-stria terminalis pathway from the posterior thalamus, and along the superior cerebellar peduncle, thalamic fasciculus, and ansa peduncularis from the parabrachial nuclei. This description of the forebrain CGRP system will facilitate investigation of its role in higher brain functions.

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.

Estrogen modulates endothelial and neuronal nitric oxide synthase expression via an estrogen receptor beta-dependent mechanism in hypothalamic slice cultures

Although it is evident that estrogen has important physiological effects in the brain, the signaling mechanisms mediating these effects remain unclear. We recently showed that estrogen mediates attenuated blood pressure responses to psychological stress in ovariectomized female rats through brain nitric oxide (NO). An area likely to mediate these effects is the hypothalamic paraventricular nucleus (PVN), because here NO exerts inhibitory effects on autonomic output to the periphery. Because little is known about how estrogen acts on the NO system in the PVN, our aim was to study the effects of estrogen on the NO system in the PVN of hypothalamic slices cultures. We show that 17beta-estradiol (E2; 1 nm) increases endothelial NO synthase (eNOS) protein expression and decreases the numbers of neuronal NOS (nNOS)-positive neurons in the PVN after 8 and 24 h, respectively. Using the nonselective estrogen receptor (ER) antagonist, ICI 182,780 (10 nm), we determined that E2-induced changes in NOS expression in the PVN are ER dependent. Using the ERbeta agonist, genistein (0.1 microm), we determined that activation of ERbeta induces increased eNOS expression and a decreased number of nNOS-positive neurons. We used the selective ERalpha agonist, propyl-pyrazole-triol (10 nm), and antagonist, methyl-piperidino-pyrazole (1 microm), to exclude the possibility that ERalpha is involved in the E2-induced increase in eNOS and nNOS in the PVN. These results demonstrate that E2 induces changes in NOS expression in the PVN and that these effects are ERbeta dependent.

Adrenomedullin stimulates nitric oxide release from SK-N-SH human neuroblastoma cells by modulating intracellular calcium mobilization

We used SK-N-SH human neuroblastoma cells to test the hypothesis that adrenomedullin (ADM), a multifunctional neuropeptide, stimulates nitric oxide (NO) release by modulating intracellular free calcium concentration ([Ca2+]i) in neuron-like cells. We used a nitrite assay to demonstrate that ADM (10 pM to 100 nM) stimulated NO release from the cells, with a maximal response observed with 1 nM at 30 min. This response was blocked by 1 nM ADM(22-52), an ADM receptor antagonist or 2 microM vinyl-L-NIO, a neuronal NO synthase inhibitor. In addition, 5 microM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester, an intracellular calcium chelator, eliminated the ADM-induced NO release. Similar results were observed when the cells were incubated in calcium-free medium or when L-type calcium channels were inhibited with 5 microM nifedipine or 10 microM nitrendipine. Depletion of calcium stores in the endoplasmic reticulum (ER) with 1 microM cyclopiazonic acid or 150 nM thapsigargin, or inhibition of ryanodine-sensitive receptors in the ER with 10 microM ryanodine attenuated the ADM-induced NO release. NO responses to ADM were mimicked by 1 mM dibutyryl cAMP, a cAMP analog, and were abrogated by 5 microM H-89, a protein kinase A inhibitor. Furthermore, Fluo-4 fluorescence-activated cell sorter analysis showed that ADM (1 nM) significantly increased [Ca2+]i at 30 min. This response was blocked by nifedipine (5 microM) or H-89 (5 microM) and was reduced by ryanodine (10 microM). These results suggest that ADM stimulates calcium influx through L-type calcium channels and ryanodine-sensitive calcium release from the ER, probably via cAMP-protein kinase A-dependent mechanisms. These elevations in [Ca2+)]i cause activation of neuronal NO synthase and NO release.

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.

Decrease in arterial pressure induced by adrenomedullin in the hypothalamic paraventricular nucleus is mediated by nitric oxide and GABA

We tested the hypothesis that the decrease in arterial pressure induced by adrenomedullin (ADM) in the hypothalamic paraventricular nucleus (PVN) is mediated by nitric oxide (NO) and/or GABA. Unilateral microinjections of ADM into the PVN of anesthetized rats caused a significant decrease in mean arterial pressure (MAP). The ADM-induced decrease in MAP was significantly attenuated by pretreatment with N(psi)-nitro-L-arginine methyl ester (L-NAME, a non-selective NOS inhibitor), 7-nitroindazole sodium salt (7-NiNa, a selective neuronal NOS inhibitor), N5-(1-Iminoethyl)-L-ornithine (L-NIO, a selective endothelial NOS inhibitor) or bicuculline methiodide, but pretreatment with S-methylisothiourea (SMIT, a selective inducible NOS inhibitor) had no effect on this ADM-induced effect. In addition, coronal sections of rat brains were processed for combined NADPH-diaphorase (a marker of neuronal NOS-containing neurons) histochemistry and in situ hybridization for the receptor-activity-modifying protein 2 (a specific ADM receptor component). Double-labeled neurons were found in both parvocellular and magnocellular subdivisions of the PVN, confirming that NO-producing neurons in the PVN are capable of mediating ADM's effects. Thus, our data provide evidence that the ADM-induced decrease in MAP in the PVN is mediated by NO from neuronal and endothelial NOS, and by GABA.

Adrenomedullin in the rostral ventrolateral medulla increases arterial pressure and heart rate: roles of glutamate and nitric oxide

This study was done to investigate the effects of microinjections of adrenomedullin (ADM), a vasoactive neuropeptide, in the rostral ventrolateral medulla (RVLM) on mean arterial pressure (MAP) and heart rate (HR) in urethane-anesthetized rats, and to assess the potential roles of glutamate and nitric oxide (NO) in these effects. Unilateral injections of ADM (0.01 or 0.1 pmol) into the RVLM significantly increased MAP and HR in a dose-dependent manner, whereas ADM at 0.001 pmol was ineffective. Microinjections of ADM (0.01 pmol) outside the RVLM had no effects on MAP or HR. Coinjections of a putative ADM receptor antagonist, ADM(22-52) (0.01 pmol), abolished the increases in MAP and HR evoked by ADM (0.01 pmol). The vasopressor effects of ADM (0.01 pmol) in the RVLM were abolished by coinjections of either dizocilpine hydrogen maleate (a selective NMDA glutamate receptor antagonist, 500 pmol) or 6-cyano-7-nitroquinoxaline-2,3-dione (a selective non-NMDA glutamate receptor antagonist, 50 pmol). The ADM-induced vasopressor effects were also abolished by coadministration of either 7-nitroindazole sodium salt (a selective neuronal NO synthase inhibitor, 0.05 pmol) or methylene blue (a soluble guanylyl cyclase inhibitor, 100 pmol). These results suggest that ADM in the RVLM stimulates increases in MAP and HR through ADM receptor-mediated mechanisms. These effects are mediated by glutamate via both NMDA and non-NMDA receptors. NO, derived from neuronal NO synthase, also contributes to the ADM-induced vasopressor effects via a soluble guanylyl cyclase-associated signaling pathway.

Expression of spinal cord Fos protein in response to intrathecal adrenomedullin and CGRP in conscious rats

Adrenomedullin (AM) immunoreactivity and mRNA, in addition to a large number of specific AM-binding sites, exist in the rat spinal cord. However, no phenotype has been reported for AM in the spinal cord. Here, expression of c-fos in response to intrathecal (i.t.) administration of AM, proadrenomedullin N-terminal 20 peptide (PAMP) and calcitonin gene-related peptide (CGRP) was examined in the thoracic, lumbar and sacral regions of spinal cord in conscious rats. Two hours after i.t. administration of either CGRP (2.5 and 10 microg) or AM (10 microg), the number of c-Fos immunoreactive nuclei was increased in all the spinal regions examined in this study, with the highest increase observed in the superficial dorsal horn. Few cells with c-fos immunoreactivity were found in the spinal cord of rats 2 h after i.t. injection of either saline or PAMP. Effects of AM (10 microg) and CGRP (2.5 microg) on c-fos expression were blocked when rats were pretreated with 40 microg of intrathecal CGRP8-37 (CGRP1 receptor antagonist). Fos-like immunoreactivity induced by i.t. CGRP and/or AM were also significantly abolished by i.t. administration of the nitric oxide (NO) inhibitor, l-NAME, indicating that endogenous NO is a necessary intermediary in CGRP and AM induced c-fos expression in the rat spinal cord. In conclusion, AM induces c-fos expression in rat spinal cord when administered intrathecally, with the pattern being similar to those produced by i.t. CGRP. Effects of the two peptides are sensitive to CGRP8-37 and l-NAME.

Disassociated increases of adrenomedullin in the rat cerebrospinal fluid and plasma after salt loading and systemic administration of lipopolysaccharide

To determine the role of adrenomedullin (AM) in the fluid electrolyte homeostasis and endotoxin shock, cerebral spinal fluid (CSF) and plasma were sampled from rats after respective challenges. The AM levels were measured by a highly sensitive immunoassay. The AM levels in the CSF of the rats anesthetized with ether (10.7 +/- 0.60 fmol/ml) were significantly higher than those with isoflurane 5.17 +/- 0.70 fmol/ml, P < 0.01), while the plasma level did not differ significantly. The CSF levels of the rats received 2% saline drinking increased to 3 and 4 folds at day 5 and day 7, respectively, while the plasma levels did not differ from controls at both time points. The AM levels in CSF or plasma increased to 1.5 and 3 folds at 1.5 h after intraperitoneal (i.p.) administration of lipopolysaccharide (LPS, 5 mg/kg), reached 6.5 and 30 folds at 6 h, respectively, while no change was observed in the controls. The present findings suggest that AM in the CSF is regulated independently from that in the plasma, the centrally synthesized AM plays and important role in the regulation of the fluid electrolyte homeostasis. Furthermore, the circulatory AM plays an important role in the endotoxin shock.

Identification of a novel adrenomedullin gene family in teleost fish

Adrenomedullin (AM) is a multifunctional peptide known to form a hormone family with calcitonin gene-related peptide (CGRP) and amylin. We have cloned five distinct AM cDNAs from the pufferfish, Takifugu rubripes, and named them TrAM-1, -2, -3, -4, and -5. Judging from the deduced precursor sequences and processing pattern of the C-terminal mature peptides, TrAMs may be divided into at least two groups; AM-2 and -3, and AM-1, -4, and possibly -5. Phylogenetic analysis of the mature peptides, exon-intron structure of their genes, and tissue distribution of their mRNA also support this classification. TrAM-1 and -4 were ubiquitously expressed in various tissues including the kidney and interrenal (adrenal homolog) as in the case of mammalian AM, while TrAM-2 and -3 were expressed most abundantly in the brain followed by the vascular tissues. Synteny of the genes around AM gene showed that TrAM-1 is the ortholog of mammalian AM. The presence of a PAMP-like sequence in the prosegment of TrAM-1 also supports this notion. Multiple AMs were also detected in another pufferfish, Tetraodon nigroviridis, and in zebrafish, Danio rerio. The present study shows for the first time the presence of a novel AM family in teleost fish that is independent from CGRP and amylin, which further suggests the possible existence of multiple AMs in mammals.

The effect of adrenomedullin (ADM) on tyrosine hydroxylase (TH) enzyme activity and blood pressure in cold exposed rats

It is known that, under stress conditions the hypothalamo-pituitary-adrenal (HPA) axis is stimulated and catecholamine production is increased. Adrenomedullin (ADM) is a novel peptide that elicits a long-vasorelaxation, and participates in blood pressure regulation via different mechanisms. In the present study, we investigated the administration of ADM on tyrosine hydroxylase (TH) enzyme activity in cold exposed rats. Four groups of Sprague-Dawley rats were studied for their TH enzyme activity in the adrenal medulla and hypothalamus. In addition to measuring blood pressure in these rats, TH enzyme activity in both the adrenal medulla and hypothalamus were examined in four groups of Sprague-Dawley rats: animals exposed to room temperature and cold stress (8 masculine C, 48 h), and rats injected with ADM (1.0 nmol/kg, i.v.) alone and/or together with cold stress. TH activity was shown to be increased in cold treated groups and decreased in ADM and ADM + cold stress group. Our findings appear to suggest that external ADM application caused an opposite effect on the same system in rats, decreasing the activity of tyrosine hydroxylase (TH) enzyme activity. Furthermore, externally applied ADM was shown to produce its expected hypotensive effect in cold-stressed rats. Our results suggest that a possible explanation for the effects of ADM is that, the uptake of ADM under cold stress may effect TH activity in studied tissues.

Receptor activity modifying protein 2 distribution in the rat central nervous system and regulation by changes in blood pressure

The neuropeptide, adrenomedullin, acts in the central nervous system (CNS) to regulate blood pressure, at least partly through an adrenomedullin receptor which is composed of receptor activity modifying protein 2 (RAMP-2) and calcitonin receptor-like receptor (CRLR). We used in situ hybridization to localize RAMP-2 mRNA throughout the brain, and we performed reverse transcription-polymerase chain reaction to detect CRLR mRNA in the brain. We found that RAMP-2 mRNA is expressed in numerous areas, including autonomic nuclei such as the paraventricular, supraoptic, arcuate and ventromedial nuclei, as well as the nucleus of the solitary tract (NTS), area postrema and dorsal motor nucleus of the vagus. Many regions expressing RAMP-2 mRNA also express low levels of CRLR mRNA. We examined changes in the mRNA expression of RAMP-2 and preproadrenomedullin in the brain in response to blood pressure manipulations. Rats received intravenous infusions of nitroprusside or phenylephrine to decrease or increase blood pressure, respectively. Decreased blood pressure elicited an increase in RAMP-2 mRNA expression in the NTS and a decrease in preproadrenomedullin mRNA expression in the paraventricular nucleus (PVN). Increased blood pressure elicited a decrease in RAMP-2 mRNA expression in the PVN and NTS. The CNS distribution and modulation of adrenomedullin signalling components by changes in blood pressure provide anatomical and physiological evidence for a homeostatic role for adrenomedullin in the brain.

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.

Involvement of the central adrenomedullin peptides in the baroreflex

The peptides derived from post-translational processing of preproadrenomedullin are produced in and act on areas of the autonomic nervous system important for blood pressure regulation. We examined the role of endogenous, brain-derived adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) in the central nervous system arm of the baroreflex by using passive immunoneutralization to block the actions of the endogenous peptides. Our results indicate that the preproadrenomedullin-derived peptides do not play a role in sensing changes in blood pressure (baroreflex sensitivity), but the adrenomedullin peptides do regulate the speed with which an animal returns to a normal, stable blood pressure. These findings suggest that endogenous, brain-derived AM and PAMP participate in the regulation of autonomic activity in response to baroreceptor activation and inactivation.

Adrenomedullin influences dissociated rat area postrema neurons

The area postrema (AP) is one of a specialized group of central nervous system (CNS) structures devoid of a significant blood-brain barrier (BBB), collectively known as the circumventricular organs (CVO). While peptides are normally excluded from access to most regions of the CNS, the AP contains neurons with a high density of receptors for many circulating peptides, very likely including those for adrenomedullin (AM). In this study, whole-cell patch-clamp recordings were obtained from 114 dissociated rat AP neurons. The mean resting membrane potential (RMP) of these neurons (n=79) was -54.3+/-0.8 mV, the mean input resistance (IR) was 3.1+/-0.2 GOmega and the spike amplitude of neurons included in this study was always greater than 90 mV. Current-clamp studies showed that bath application of AM depolarized 39.2% (31 of 79) and hyperpolarized 45.6% (36 of 79) of neurons tested. Both effects were found to be concentration dependent from 10(-12) to 10(-7) M. These data support the idea that specific populations of CNS neurons within the AP are directly influenced by AM and support the concept that AM may act at AP to influence central autonomic control. We also examined the roles of specific ion channels in regulating the AM-induced excitability of AP neurons through voltage-clamp studies. These experiments suggest potential actions of AM in modulating voltage gated calcium channels, effects which have the additional consequence of inhibiting calcium activated potassium conductances (I(K(Ca))). These data demonstrate direct effects of AM on dissociated AP neurons and identify ion channels, the modulation of which, may underlie these effects.

Regulation of production and secretion of adrenomedullin in the cardiovascular system

Adrenomedullin (AM) has multi-functional properties, of which the vasodilatory hypotensive effect is the most characteristic. AM and its gene are ubiquitous in a variety of tissues and organs, in the cardiovascular system, as well as the adrenal medulla. AM secretion, especially in cardiovascular tissues, is regulated mainly by mechanical stressors such as shear stress, inflammatory cytokines such as interleukin (IL)-1, tumor necrosis factor (TNF), and lipopolysaccharide (LPS), hormones such as angiotensin (Ang) II and endothelin (ET)-1, and metabolic factors such as hypoxia, ischemia, or hyperglycemia. Elevation of plasma AM due to overproduction in response to one or more of these stimuli in pathological conditions may explain the raised plasma AM levels present in cardiovascular and renal diseases such as congestive heart failure, myocardial infarction, hypertension, chronic renal failure, stroke, diabetes mellitus, and septic shock. In addition to shear stress, stretching of cardiomyocytes may be another mechanical stimulus for AM synthesis and secretion. Our recent studies have shown the importance of aldosterone and additional hormonal factor on AM secretion in vascular wall.

Autonomic and neuroendocrine actions of adrenomedullin in the brain: mechanisms for homeostasis

In addition to its role as a potent vasodilator, adrenomedullin (ADM) affects an animal's physiological status through its effects in the brain. We have shown that circulating ADM activates neurons, including nitric oxide (NO)-producing neurons, in autonomic centers of the brain such as the hypothalamic paraventricular nucleus (PVN). Systemic ADM gains access to the brain through the area postrema (AP), a brainstem circumventricular organ, and the PVN is a major target of these ADM-sensitive AP neurons. Neurons expressing the preproADM (ppADM) gene are distributed throughout the brain, with high levels in autonomic centers. Lipopolysaccharide (LPS, immune stress), restraint (psychological stress), and 24 h dehydration all down-regulate ppADM gene expression in different subsets of autonomic centers. Receptor-activity-modifying protein (RAMP) 2 and RAMP3, ADM receptor subunits, are expressed in autonomic centers including the PVN and supraoptic nucleus. Intracerebroventricular injections of ADM increase arterial pressure, heart rate, tyrosine hydroxylase mRNA levels in the locus coeruleus, plasma levels of ACTH, and NO production in the hypothalamus. ADM excites putative GABAergic and cholinergic neurons in dissociated cells from a basal forebrain integrative center, the diagonal band of Broca. These results demonstrate that the signalling components necessary for ADM to influence physiological systems are present in the brain and that ADM is an important transmitter of brain autonomic pathways which are involved in regulating homeostatic balance.

Pathophysiological role of nitric oxide and adrenomedullin in autism

Several studies indicate that nitric oxide (NO) is involved in the aetiopathogenesis of many neuropsychiatric disorders such as schizophrenia, bipolar disorder, depression, Alzheimer's disease, Hungtington disease and stroke. Although it has not been investigated yet, several recent studies proposed that NO may have a pathophysiological role in autism. Adrenomedullin (AM), a recently discovered 52-amino acid peptide hormone, induces vasorelaxation by activating adenylate cyclase and also by stimulating NO release. AM immune reactivity is present in the brain consistent with a role as a neurotransmitter. It has been stated that NO and AM do function in the regulation of many neurodevelopmental processes. We hypothesized that NO and AM activities have been affected in autistic patients and aimed to examine these molecules. Twenty-six autistic patients and 22 healthy control subjects were included in this study. AM and total nitrite (a metabolite of NO) levels have been measured in plasma. The mean values of plasma total nitrite and AM levels in the autistic group were significantly higher than control values, respectively (p < 0.001, p = 0.028). There is no correlation between total nitrite and AM levels (r = 0.11, p = 0.31). Certainly, this subject needs much further research investigating autistic patients in earlier periods of life and with subtypes of the disorder.

The possible pathophysiological role of plasma nitric oxide and adrenomedullin in schizophrenia

Evidence is accumulating for a possible role of nitric oxide (NO) in schizophrenia. Adrenomedullin (AM) induces vasorelaxation by activating adenylate cyclase and also by stimulating the release of NO. AM immune reactivity is present in the brain consistent with a role as neurotransmitter. We aimed to examine plasma levels of nitrite (a metabolite of NO) and AM in schizophrenic patients. Eighty-two patients with schizophrenia and 21 healthy control subjects were included in this study. DSM-IV diagnosis of chronic schizophrenia was established on the basis of independent structured clinical interviews and review of records by two qualified psychiatrists which included the Brief Psychiatric Rating Scale (BPRS), The Scale for the Assessment of Negative Symptoms (SANS) and The Scale for the Assessment of Positive Symptoms (SAPS). Total nitrite and AM have been studied in plasma. The mean values of plasma nitrite and AM levels in schizophrenic group were significantly higher than control values, respectively (P=0.03, P<0.0001). AM levels of schizophrenic patients were three fold higher than controls. In correlation analyses, there were statistically significant positive correlations between AM level and SAPS-delusion subscale (r=0.27, P=0.04); SAPS-bizarre behavior subscale (r=0.28, P=0.03) and SAPS-total (r=0.36, P=0.005). There is no correlation between total nitrite and AM levels (r=0.11, P=0.31). Both NO and AM may have a pathophysiological role in schizophrenia, and clinically symptomatology and prognosis of schizophrenia. This subject needs further study including treatment response and subtypes of schizophrenia.

Possible role of nitric oxide and adrenomedullin in bipolar affective disorder

Nitric oxide (NO) has been implicated to play a role in the pathogenesis of depressive disorders. Adrenomedullin (AM) induces vasorelaxation by activating adenylate cyclase and also by stimulating the release of NO. AM immune reactivity is present in the brain, consistent with a role as neurotransmitter. Therefore, it is suggested that these two molecules may play a role together in the brain. We aimed to examine AM and NO in bipolar affective disorder (BPAD). Forty-four patients with BPAD and 21 healthy control subjects were included in this study. DSM-IV diagnosis of bipolar affective disorder (type I, manic episodes) was independently established by two psychiatrists and the Turkish version of the Bech-Rafaelson Mania Scale was administered. Also, a semistructured form was used to ascertain several sociodemographic and clinical variables of the patients. AM and NO were studied in plasma. The mean value of plasma NO levels in the BPAD group of 46.58 +/- 13.97 micromol/l was significantly higher than that of controls (31.81 +/- 8.14 micromol/l) (z = -4.15, p = 0.000). Mean plasma AM levels were found to be increased in patients with BPAD (35.13 +/- 5.26 pmol/l) compared to controls (16.22 +/- 3.02 pmol/l) (z = -6.16, p = 0.000). AM levels of BPAD patients were approximately 2-fold higher than controls. AM levels were positively correlated with the duration of hospitalization for the current episode and negatively correlated with the total duration of illness. Both NO and AM may have a pathophysiological role in BPAD (type I, manic episodes) and the clinical symptomatology and prognosis of BPAD.

Adrenomedullin and the integrative physiology of fluid and electrolyte balance

Adrenomedullin (AM) is hypothesized to be a physiologically relevant regulator in fluid and electrolyte homeostasis. AM acts within the central nervous system to inhibit both water and salt intake. The peptide has direct actions in the hypothalamus to decrease vasopressin secretion and in the pituitary gland to inhibit ACTH release. AM decreases production and release of aldosterone from the adrenal glands and acts directly in the kidneys to increase renal blood flow and cause diuresis and natriuresis. Whether or not these complementary actions in brain, pituitary, adrenal gland, and kidney reflect coordinated regulatory mechanisms is currently unknown. Development of molecular tools to determine the physiologic role of endogenous AM will greatly enhance our understanding of AM and its regulation of fluid and electrolyte homeostasis.

Intracerebroventricular adrenomedullin stimulates the hypothalamic-pituitary-adrenal axis, the sympathetic nervous system and production of hypothalamic nitric oxide

We tested the hypothesis that central adrenomedullin stimulates activity of the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic output from the brain, and we assessed the effects of central adrenomedullin on the nitric oxide (NO) system in the brain. In conscious rats, intracerebroventricular (i.c.v.) injections of adrenomedullin (2 nmol/kg) increased arterial pressure and heart rate, with return to baseline values within 20 min and 65 min of injections, respectively. Adrenomedullin injections augmented expression of tyrosine hydroxylase mRNA in the locus coeruleus after 4 h. Plasma concentrations of adrenocorticotropic hormone, measured with radioimmunoassay, were also increased by adrenomedullin. i.c.v. Adrenomedullin stimulated Fos expression in neurones within autonomic centres including the paraventricular nucleus (PVN) of the hypothalamus, arcuate nucleus, locus coeruleus, nucleus of the tractus solitarius and area postrema. In the PVN, large proportions of corticotropin releasing factor- and NO-producing neurones were activated (Fos positive). NO production, measured with nitrate/nitrite assays, was elevated in the hypothalamus, but not brainstem, of adrenomedullin-treated rats compared to controls. We conclude that centrally administered adrenomedullin stimulates activity of the HPA axis, the sympathetic nervous system, and the hypothalamic NO system.

Adrenomedullin and central cardiovascular regulation

Adrenomedullin gene products have been localized to neurons in brain that innervate sites known to be important in the regulation of cardiovascular function. Those sites also have been demonstrated to possess receptors for the peptide and central administrations of adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) elevate blood pressure and heart rate in both conscious and anesthetized animals. The accumulated evidence points to a role of the sympathetic nervous system in these cardiovascular effects. These sympathostimulatory actions of AM and PAMP have been hypothesized to be cardioprotective in nature and to reflect the central nervous system (CNS) equivalent of the direct cardiostimulatory effects of the peptides in the periphery. This review summarizes the most recent data on the CNS actions of the adrenomedullin gene-derived peptides and suggests future strategies for the elucidation of the physiologic relevance of the already demonstrated, pharmacologic actions of these peptides.

Neurotoxicant-induced elevation of adrenomedullin expression in hippocampus and glia cultures

Adrenomedullin (AM), a vasoactive peptide first isolated from pheochromocytoma, has been reported to be present in neurons in the central nervous system and in tumors of neural and glial origin. In this study, we investigated AM expression both in the hippocampus and in glial cell cultures using a chemical-induced model of injury. An acute intraperitoneal injection of the organometal trimethyltin (TMT) results in neurodegeneration of the hippocampal CA3-4 pyramidal cell layer. Within 4 days of injection, sparse, punctate staining for AM and lectin was evident in the CA3-4 region; by 10 days, a minimal level of CA3-4 neuronal degeneration was evident, with an increase in glial fibrillary acidic protein (GFAP)-positive astrocytes throughout the hippocampus. Degeneration progressed in severity until 30 days post-TMT, with distinct positive immunoreactivity for AM in the CA4 region. mRNA levels for tumor necrosis factor (TNF)-alpha, interleukin (IL)-1alpha, GFAP, and AM in the hippocampus were increased over control levels within 4 days following TMT. In cultured glial cells, a 6 hr exposure to TMT (10 microM) produced a morphological response of the cells and increased immunoreactivity for vimentin, GFAP, and AM. mRNA levels for TNFalpha, IL-1alpha, GFAP, vimentin, and AM were elevated within 3-6 hr of exposure. In culture, neutralizing antibodies to IL-1alpha and TNFalpha were effective in inhibiting the TMT-induced elevation of AM mRNA. These data suggest an interaction between the proinflammatory cytokines and glia response in the regulation of AM in response to injury.

Expression of receptor-activity modifying protein (RAMP) mRNAs in the mouse brain

Receptor activity modifying proteins (RAMPs) comprise a family of accessory proteins for G protein-coupled receptors (GPCRs). They function as receptor modulators that determine the ligand specificity of receptors for calcitonin gene-related peptide (CGRP), amylin and adrenomedullin (ADM). Here we demonstrate for the first time the characteristic distributions of the RAMP family mRNAs in the brain. Northern blot analysis revealed that mRAMP 1 and 3 mRNAs were intensely expressed in the brain, but mRAMP2 mRNA less abundantly. In situ hybridization studies showed the heterogenous and unique distributions of mRAMP mRNAs; RAMP1 mRNA was widely expressed throughout the brain including the cerebral cortex, caudate putamen, amygdaloid complex, hippocampus, cerebellum and ependyma, mRAMP2 was most abundant in the hippocampus, cerebellum, pia mater and blood vessels, while mRAMP3 was specifically distributed in a variety of thalamic nuclei and the cerebellum. In addition, RAMP1 and -3 genes were also detected in the subfornical organ and area postrema, which are members of circumventricular organs lacking blood-brain barrier. The present results help in understanding the diversification and regulation of receptor functions for calcitonin family peptides, and potentially other GPCRs in the brain.