Investigation of CGRP receptors and peptide pharmacology in human coronary arteries. Characterization with a nonpeptide antagonist

Differential expression of components of the CGRP-receptor family in human coronary and human middle meningeal arteries: functional implications

BACKGROUND

Different responses in human coronary arteries (HCA) and human middle meningeal arteries (HMMA) were observed for some of the novel CGRP receptor antagonists, the gepants, for inhibiting CGRP-induced relaxation. These differences could be explained by the presence of different receptor populations in the two vascular beds. Here, we aim to elucidate which receptors are involved in the relaxation to calcitonin gene-related peptide (CGRP), adrenomedullin (AM) and adrenomedullin 2 (AM2) in HCA and HMMA.

METHODS

RNA was isolated from homogenized human arteries (23 HCAs; 12 F, 11 M, age 50 ± 3 years and 26 HMMAs; 14 F, 12 M, age 51 ± 3 years) and qPCR was performed for different receptor subunits. Additionally, relaxation responses to CGRP, AM or AM2 of the human arteries were quantified using a Mulvany myograph system, in the presence or absence of the adrenomedullin 1 receptor antagonist AM22-52 and/or olcegepant.

RESULTS

Calcitonin-like receptor (CLR) mRNA was expressed equally in both vascular beds, while calcitonin receptor (CTR) and receptor activity-modifying protein 3 (RAMP3) expression was low and could not be detected in all samples. RAMP1 expression was similar in HCA and HMMA, while RAMP2 expression was higher in HMMA. Moreover, receptor component protein (RCP) expression was higher in HMMA than in HCA. Functional experiments showed that olcegepant inhibits relaxation to all three agonists in both vascular beds. In HCA, antagonist AM22-52 did not inhibit relaxation to any of the agonists, while a trend for blocking relaxation to AM and AM2 could be observed in HMMA.

CONCLUSION

Based on the combined results from receptor subunit mRNA expression and the functional responses in both vascular tissues, relaxation of HCA is mainly mediated via the canonical CGRP receptor (CLR-RAMP1), while relaxation of HMMA can be mediated via both the canonical CGRP receptor and the adrenomedullin 1 receptor (CLR-RAMP2). Future research should investigate whether RAMP2 predominance over RAMP1 in the meningeal vasculature results in altered migraine susceptibility or in a different response to anti-migraine medication in these patients. Moreover, the exact role of RCP in CGRP receptor signalling should be elucidated in future research.

The Neuropeptide α-Calcitonin Gene-Related Peptide as the Mediator of Beneficial Effects of Exercise in the Cardiovascular System

Regular physical activity exerts cardiovascular protective effects in healthy individuals and those with chronic cardiovascular diseases. Exercise is accompanied by an increased plasma concentration of α-calcitonin gene-related peptide (αCGRP), a 37-amino acid peptide with vasodilatory effects and causative roles in migraine. Moreover, mouse models revealed that loss of αCGRP disrupts physiological adaptation of the cardiovascular system to exercise in normotension and aggravates cardiovascular impairment in primary chronic hypertension, both can be reversed by αCGRP administration. This suggests that αCGRP agonists could be a therapeutic option to mediate the cardiovascular protective effects of exercise in clinical setting where exercise is not possible or contraindicated. Of note, FDA has recently approved αCGRP antagonists for migraine prophylaxis therapy, however, the cardiovascular safety of long-term anti-CGRP therapy in individuals with cardiovascular diseases has yet to be established. Current evidence from preclinical models suggests that chronic αCGRP antagonism may abolish the cardiovascular protective effects of exercise in both normotension and chronic hypertension.

The effect of pramlintide, an antidiabetic amylin analogue, on angiogenesis-related markers in vitro

Background and purpose:

Irregularities of angiogenesis may participate in the pathogenesis of diabetes complications. Pramlintide is an amylin analogue administered for the treatment of type 1 and type 2 diabetes. The present investigation aimed at surveying the effect of pramlintide on angiogenesis-related markers in human umbilical vein endothelial cells (HUVECs).

Experimental approach:

The proliferation of cells was assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT) method. The effect of pramlintide on migration was estimated by Transwell® assay. in vitro evaluation of angiogenesis was performed by tube formation assay. The secretion of vascular endothelial growth factor (VEGF) to the supernatant of HUVECs was measured by an enzyme- linked immunosorbent assay (ELISA) kit. All experiments were performed in triplicate.

Findings / Results:

Pramlintide exhibited no inhibitory effect on HUVECs proliferation. It significantly increased cell migration at the concentration of 1 μg/mL. Pramlintide (1 μg/mL) also enhanced average tubules length, size, and the mean number of junctions. However, there was not any significant change in VEGF release from HUVECs.

Conclusion and implications:

Findings of this research revealed the effect of pramlintide on angiogenesis- related markers via enhancing migration and tubulogenesis in vitro, suggesting a worthwhile proposition for further clinical researches on improving vascular complications and healing of diabetic wounds.

Blood Pressure Normalization-Independent Cardioprotective Effects of Endogenous, Physical Activity-Induced αCGRP (α Calcitonin Gene-Related Peptide) in Chronically Hypertensive Mice

RATIONALE

αCGRP (α calcitonin gene-related peptide), one of the strongest vasodilators, is cardioprotective in hypertension by reducing the elevated blood pressure.

OBJECTIVE

However, we hypothesize that endogenous, physical activity-induced αCGRP has blood pressure-independent cardioprotective effects in chronic hypertension.

METHODS AND RESULTS

Chronically hypertensive (one-kidney-one-clip surgery) wild-type and αCGRP^-/- sedentary or voluntary wheel running mice were treated with vehicle, αCGRP, or the αCGRP receptor antagonist CGRP8-37. Cardiac function and myocardial phenotype were evaluated echocardiographically and by molecular, cellular, and histological analysis, respectively. Blood pressure was similar among all hypertensive experimental groups. Endogenous αCGRP limited pathological remodeling and heart failure in sedentary, chronically hypertensive wild-type mice. In these mice, voluntary wheel running significantly improved myocardial phenotype and function, which was abolished by CGRP8-37 treatment. In αCGRP^-/- mice, αCGRP treatment, in contrast to voluntary wheel running, improved myocardial phenotype and function. Specific inhibition of proliferation and myofibroblast differentiation of primary, murine cardiac fibroblasts by αCGRP suggests involvement of these cells in αCGRP-dependent blunting of pathological cardiac remodeling.

CONCLUSIONS

Endogenous, physical activity-induced αCGRP has blood pressure-independent cardioprotective effects and is crucial for maintaining cardiac function in chronic hypertension. Consequently, inhibiting endogenous αCGRP signaling, as currently approved for migraine prophylaxis, could endanger patients with hypertension.

Neuropeptides Substance P and Calcitonin Gene Related Peptide Accelerate the Development and Fibrogenesis of Endometriosis

Endometriotic lesions are known to be hyperinnervated, especially in lesions of deep endometriosis (DE), which are frequently in close proximity to various nerve plexuses. DE lesions typically have higher fibromuscular content than that of ovarian endometriomas (OE) lesions, but the underlying reason remains elusive. Aside from their traditional role of pain transduction, however, whether or not sensory nerves play any role in the development of endometriosis is unclear. Here, we show that, thorough their respective receptors neurokinin receptor 1 (NK1R), calcitonin receptor like receptor (CRLR), and receptor activity modifying protein 1 (RAMP-1), neuropeptides substance P (SP) and calcitonin gene related peptide (CGRP) induce epithelial-mesenchymal transition (EMT), fibroblast-to-myofibroblast transdifferentiation (FMT) and further turn stromal cells into smooth muscle cells (SMCs) in endometriotic lesions, resulting ultimately in fibrosis. We show that SP and CGRP, or the rat dorsal root ganglia (DRG) supernatant, through the induction of NK1R and CGRP/CRLR/RAMP-1 signaling pathways, promoted EMT, FMT and SMM in endometriosis, resulting in increased migratory and invasive propensity, cell contractility, production of collagen, and eventually to fibrosis. Neutralization of NK1R and/or CGRP/CRLR/RAMP-1 abrogated these processes. Extended exposure of endometriotic stromal cells to SP and/or CGRP or the DRG supernatant induced increased expression of α-SMA, desmin, oxytocin receptor, and smooth muscle myosin heavy-chain. Finally, we show that DE lesions had significantly higher nerve fiber density, increased staining levels of α-SMA, NK1R, CRLR, and RAMP-1, concomitant with higher lesional fibrotic content than that of OE lesions. The extent of lesional fibrosis correlated positively with the staining levels of NK1R, CRLR, and RAMP-1, as well as the nerve fiber density in lesions. Thus, this study provides another piece of evidence that sensory nerves play an important role in promoting the development and fibrogenesis of endometriosis. It explains as why DE frequently have higher fibromuscular content than that of OE, highlights the importance of lesional microenvironment in shaping the lesional fate, gives more credence to the idea that ectopic endometrium is fundamentally wounds that go through repeated tissue injury and repair, and should shed much needed light into the pathophysiology of endometriosis.

Comparison between brain natriuretic peptide and calcitonin gene-related peptide in children with dilated cardiomyopathy and controls

Background

Dilated cardiomyopathy (DCM) is revealed with the left ventricular dilatation and systolic dysfunction.

Objective

This study was performed to determine the level of calcitonin gene-related peptide (CGRP) and brain natriuretic peptide (BNP) in children with DCM and controls and comparison of these two biomarkers in patients.

Materials and Methods

This study was performed from April 2014 to March 2015 on patients with DCM. The levels of BNP and CGRP were measured by ELISA, and final amounts of biomarkers were compared with the echocardiographic finding.

Results

In this study, the mean age was 10.567 ± 5.50 and 12.135 ± 4.626 years for controls and cases, respectively (P = 0.321). The majority of echocardiographic indices in the left and right heart had different means in cases and controls (P < 0.05). Means of BNP were 213.814 ± 309.601 and 2.76 ± 1.013 for case and control, respectively (P < 0.001). Means of CGRP were 2.278 ± 1.586 and 1.488 ± 0.501 for cases and controls, respectively, (P = 0.001). In the patients group, however, no significant relationship was observed between CGRP level and Ross classification but observed a direct relationship of Ross classification with BNP (χ² = 15.845, P < 0.05).

Conclusions

The present research was performed on DCM patients and showed that most echocardiographic parameters, mean of CGRP and mean of BNP increased in patients compared to healthy children. The severity of illness based on the Ross classification showed significant and positive correlation with BNP level but not with CGRP. Probably, it could be concluded that BNP would be a better biomarker in DCM patients.

Blockade of CGRP Receptors in the Intracranial Vasculature: A New Target in the Treatment of Headache

In primary headaches, there is a clear association between the headache and the release of calcitonin gene-related peptide (CGRP) but not with any of the other neuronal messengers. The purpose of this review is to describe the role of CGRP in the intracranial circulation and to elucidate a possible role for a specific CGRP receptor antagonist in the treatment of primary headaches. Acute treatment with a 5-HT1B/1D agonist (triptan) results in alleviation of the headache and normalization of the cranial venous CGRP levels, in part due to a presynaptic inhibitory effect on sensory nerves. The central role of CGRP in migraine and cluster headache pathophysiology has led to the search for small molecule CGRP antagonists with few cardiovascular side-effects. The initial pharmacological profile of such a group of compounds has recently been disclosed. One of these compounds has been found to be efficacious in the relief of acute attacks of migraine.

Calcitonin gene-related peptide: physiology and pathophysiology

Calcitonin gene-related peptide (CGRP) is a 37-amino acid neuropeptide. Discovered 30 years ago, it is produced as a consequence of alternative RNA processing of the calcitonin gene. CGRP has two major forms (α and β). It belongs to a group of peptides that all act on an unusual receptor family. These receptors consist of calcitonin receptor-like receptor (CLR) linked to an essential receptor activity modifying protein (RAMP) that is necessary for full functionality. CGRP is a highly potent vasodilator and, partly as a consequence, possesses protective mechanisms that are important for physiological and pathological conditions involving the cardiovascular system and wound healing. CGRP is primarily released from sensory nerves and thus is implicated in pain pathways. The proven ability of CGRP antagonists to alleviate migraine has been of most interest in terms of drug development, and knowledge to date concerning this potential therapeutic area is discussed. Other areas covered, where there is less information known on CGRP, include arthritis, skin conditions, diabetes, and obesity. It is concluded that CGRP is an important peptide in mammalian biology, but it is too early at present to know if new medicines for disease treatment will emerge from our knowledge concerning this molecule.

Potentiated adrenomedullin-induced vasorelaxation during hypoxia in organ cultured porcine coronary arteries

This study describes the effect of variable oxygen supply on relaxing responses induced by α-calcitonin gene-related peptide (CGRP) and adrenomedullin (AM) on isolated pig coronary arteries in vitro. Organ culture during normoxia (21% of O₂) and hypoxia (5% of O₂) induced a significant leftward shift of the AM concentration-response curves compared with fresh vessels altering the pEC₅₀ values from 6.9 ± 0.04 to 8.0 ± 0.04, whereas the potency (pEC₅₀) of αCGRP was attenuated from 8.8 ± 0.04 to 7.6 ± 0.04. AM₂₂₋₅₂ exerted significant antagonistic effect on AM-induced vasorelaxation in hypoxic and normoxic conditions (apparent pK(B) = 6.8-7.2), whereas no antagonistic effect was observed in fresh and hyperoxic (95%) organ cultured vessels. The antagonistic effect exerted by αCGRP₈₋₃₇ (10⁻⁶·⁵-10⁻⁵·⁵ M) on αCGRP-induced vasodilatation in fresh vessels (derived from Schild plot pA₂ = 7.4 ± 0.1) was unaltered during organ culture. The antagonistic effect exerted by αCGRP₈₋₃₇ (10⁻⁶ M) on AM-induced vasorelaxation in fresh vessels (apparent pK(B) = 7.4 ± 0.1) was absent during hypoxic organ culture. The receptor activity-modifying proteins 1 (RAMP1)/calcitonin-like receptor (CLR) messenger RNA ratio was reduced and RAMP2/CLR messenger RNA ratio was increased during hypoxic and normoxic organ culture compared with fresh vessels. Hypoxic organ culture for 24-72 hours potentiated the AM-induced vasorelaxation through an AM₂₂₋₅₂-sensitive receptor but attenuated the vasorelaxant effect of CGRP through the CGRP receptors. This could possibly be explained by relatively decreased levels of RAMP1, thus favoring RAMP2 + CLR complex (=AM receptor) formation during hypoxic organ culture.

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

OBJECTIVES

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

METHODS

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

KEY FINDINGS

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

CONCLUSIONS

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

CGRP in the trigeminovascular system: a role for CGRP, adrenomedullin and amylin receptors?

The neuropeptide calcitonin gene-related peptide (CGRP) is reported to play an important role in migraine. It is expressed throughout the trigeminovascular system. Antagonists targeting the CGRP receptor have been developed and have shown efficacy in clinical trials for migraine. However, no CGRP antagonist is yet approved for treating this condition. The molecular composition of the CGRP receptor is unusual because it comprises two subunits; one is a GPCR, the calcitonin receptor-like receptor (CLR). This associates with receptor activity-modifying protein (RAMP) 1 to yield a functional receptor for CGRP. However, RAMP1 also associates with the calcitonin receptor, creating a receptor for the related peptide amylin but this also has high affinity for CGRP. Other combinations of CLR or the calcitonin receptor with RAMPs can also generate receptors that are responsive to CGRP. CGRP potentially modulates an array of signal transduction pathways downstream of activation of these receptors, in a cell type-dependent manner. The physiological significance of these signalling processes remains unclear but may be a potential avenue for refining drug design. This complexity has prompted us to review the signalling and expression of CGRP and related receptors in the trigeminovascular system. This reveals that more than one CGRP responsive receptor may be expressed in key parts of this system and that further work is required to determine their contribution to CGRP physiology and pathophysiology.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

Direct interactions between calcitonin-like receptor (CLR) and CGRP-receptor component protein (RCP) regulate CGRP receptor signaling

Calcitonin gene-related peptide (CGRP) is a neuropeptide with multiple neuroendocrine roles, including vasodilation, migraine, and pain. The receptor for CGRP is a G protein-coupled receptor (GPCR) that requires three proteins for function. CGRP binds to a heterodimer composed of the GPCR calcitonin-like receptor (CLR) and receptor activity-modifying protein (RAMP1), a single transmembrane protein required for pharmacological specificity and trafficking of the CLR/RAMP1 complex to the cell surface. In addition, the CLR/RAMP1 complex requires a third protein named CGRP-receptor component protein (RCP) for signaling. Previous studies have demonstrated that depletion of RCP from cells inhibits CLR signaling, and in vivo studies have demonstrated that expression of RCP correlates with CLR signaling and CGRP efficacy. It is not known whether RCP interacts directly with CLR to exert its effect. The current studies identified a direct interaction between RCP and an intracellular domain of CLR using yeast two-hybrid analysis and coimmunoprecipitation. When this interacting domain of CLR was expressed as a soluble fusion protein, it coimmunoprecipitated with RCP and inhibited signaling from endogenous CLR. Expression of this dominant-negative domain of CLR did not significantly inhibit trafficking of CLR to the cell surface, and thus RCP may not have a chaperone function for CLR. Instead, RCP may regulate CLR signaling in the cell membrane, and direct interaction between RCP and CLR is required for CLR activation. To date, RCP has been found to interact only with CLR and represents a novel neuroendocrine regulatory step in GPCR signaling.

AM₁-receptor-dependent protection by intermedin of human vascular and cardiac non-vascular cells from ischaemia-reperfusion injury

Intermedin (IMD) protects rodent heart and vasculature from oxidative stress and ischaemia. Less is known about distribution of IMD and its receptors and the potential for similar protection in man. Expression of IMD and receptor components were studied in human aortic endothelium cells (HAECs), smooth muscle cells (HASMCs), cardiac microvascular endothelium cells (HMVECs) and fibroblasts (v-HCFs). Receptor subtype involvement in protection by IMD against injury by hydrogen peroxide (H₂O₂, 1 mmol l⁻¹) and simulated ischaemia and reperfusion were investigated using receptor component-specific siRNAs. IMD and CRLR, RAMP1, RAMP2 and RAMP3 were expressed in all cell types.When cells were treated with 1 nmol l⁻¹ IMD during exposure to 1 mmol l⁻¹ H₂O₂ for 4 h, viability was greater vs. H2O2 alone (P<0.05 for all cell types). Viabilities under 6 h simulated ischaemia differed (P<0.05) in the absence and presence of 1 nmol l⁻¹ IMD: HAECs 63% and 85%; HMVECs 51% and 68%; v-HCFs 42% and 96%. IMD 1 nmol l⁻¹ present throughout ischaemia (3 h) and reperfusion (1 h) attenuated injury (P<0.05): viabilities were 95%, 74% and 82% for HAECs, HMVECs and v-HCFs, respectively, relative to those in the absence of IMD (62%, 35%, 32%, respectively). When IMD 1 nmol l⁻¹ was present during reperfusion only, protection was still evident (P<0.05, 79%, 55%, 48%, respectively). Cytoskeletal disruption and protein carbonyl formation followed similar patterns. Pre-treatment (4 days) of HAECs with CRLR or RAMP2, but not RAMP1 or RAMP3, siRNAs abolished protection by IMD (1 nmol l⁻¹) against ischaemia-reperfusion injury. IMD protects human vascular and cardiac non-vascular cells from oxidative stress and ischaemia-reperfusion,predominantly via AM1 receptors.

Migraine is a neuronal disease

Migraine is a common, paroxysmal, highly disabling primary headache disorder with a genetic background. The primary cause and the origin of migraine attacks are enigmatic. Numerous clinical and experimental results suggest that activation of the trigeminal system (TS) is crucial in its pathogenesis, but the primary cause of this activation is not fully understood. Since activation of the peripheral and central arms of the TS might be related to cortical spreading depression and to the activity of distinct brainstem nuclei (e.g. the periaqueductal grey), we conclude that migraine can be explained as an altered function of the neuronal elements of the TS, the brainstem, and the cortex, the centre of this process comprising activation of the TS. In light of our findings and the literature data, therefore, we can assume that migraine is mainly a neuronal disease.

Calcitonin gene-related peptide receptor antagonists for migraine

IMPORTANCE OF THE FIELD

Migraine is a highly prevalent disabling condition, and the current treatment options are not satisfactory. The role of calcitonin gene-related peptide (CGRP) in migraine pathophysiology is well established. CGRP receptor antagonists address this new target and have the potential to improve therapy for both responders and non-responders to previous options.

AREAS COVERED IN THIS REVIEW

This review describes CGRP, its receptors and their role in the pathophysiology of migraine. CGRP receptor antagonists are a recent development; all reported antagonists are reported in chronological order. The experimental evidence, as well as all clinical trials since the first proof-of-concept study in 2004, is discussed.

WHAT THE READER WILL GAIN

An overview of the CGRP system and why it provides an attractive drug target for headache. The main focus is on the currently presented CGRP receptor antagonists and clinical evidence for this new therapeutic option.

TAKE HOME MESSAGE

CGRP receptor antagonists will provide an additional and valuable therapeutic option for the treatment of headaches.

Characterization of the calcitonin gene-related peptide receptor antagonist telcagepant (MK-0974) in human isolated coronary arteries

The sensory neuropeptide calcitonin gene-related peptide (CGRP) plays a role in primary headaches, and CGRP receptor antagonists are effective in migraine treatment. CGRP is a potent vasodilator, raising the possibility that antagonism of its receptor could have cardiovascular effects. We therefore investigated the effects of the antimigraine CGRP receptor antagonist telcagepant (MK-0974) [N-[(3R,6S)-6-(2,3-difluorophenyl)-2-oxo-1-(2,2,2-trifluoroethyl)azepan-3-yl]-4-(2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyridine-1-yl)piperidine-1-carboxamide] on human isolated coronary arteries. Arteries with different internal diameters were studied to assess the potential for differential effects across the coronary vascular bed. The concentration-dependent relaxation responses to human alphaCGRP were greater in distal coronary arteries (i.d. 600-1000 microm; E(max) = 83 +/- 7%) than proximal coronary arteries (i.d. 2-3 mm; E(max) = 23 +/- 9%), coronary arteries from explanted hearts (i.d. 3-5 mm; E(max) = 11 +/- 3%), and coronary arterioles (i.d. 200-300 microm; E(max) = 15 +/- 7%). Telcagepant alone did not induce contraction or relaxation of these coronary blood vessels. Pretreatment with telcagepant (10 nM to 1 microM) antagonized alphaCGRP-induced relaxation competitively in distal coronary arteries (pA(2) = 8.43 +/- 0.24) and proximal coronary arteries and coronary arterioles (1 microM telcagepant, giving pK(B) = 7.89 +/- 0.13 and 7.78 +/- 0.16, respectively). alphaCGRP significantly increased cAMP levels in distal, but not proximal, coronary arteries, and this was abolished by pretreatment with telcagepant. Immunohistochemistry revealed the expression and colocalization of the CGRP receptor elements calcitonin-like receptor and receptor activity-modifying protein 1 in the smooth muscle cells in the media layer of human coronary arteries. These findings in vitro support the cardiovascular safety of CGRP receptor antagonists and suggest that telcagepant is unlikely to induce coronary side effects under normal cardiovascular conditions.

CGRP receptor antagonists: A new frontier of anti-migraine medications

Migraine is a chronic pain condition that affects 12% of the population. Currently, the most effective treatments are the triptans, but they are limited in their efficacy and have potentially deleterious cardiovascular complications. Based on basic science studies over the past decade, a new generation of anti-migraine drugs is now being developed. At the forefront of these studies is a new calcitonin gene-related peptide (CGRP) receptor antagonist that is as effective as triptans in the acute treatment of migraines, without the cardiovascular effects. This review will address the likely mechanisms and therapeutic potential of CGRP receptor antagonists.

Experimental migraine models and their relevance in migraine therapy

Although the understanding of migraine pathophysiology is incomplete, it is now well accepted that this neurovascular syndrome is mainly due to a cranial vasodilation with activation of the trigeminal system. Several experimental migraine models, based on vascular and neuronal involvement, have been developed. Obviously, the migraine models do not entail all facets of this clinically heterogeneous disorder, but their contribution at several levels (molecular, in vitro, in vivo) has been crucial in the development of novel antimigraine drugs and in the understanding of migraine pathophysiology. One important vascular in vivo model, based on an assumption that migraine headache involves cranial vasodilation, determines porcine arteriovenous anastomotic blood flow. Other models utilize electrical stimulation of the trigeminal ganglion/nerve to study neurogenic dural inflammation, while the superior sagittal sinus stimulation model takes into account the transmission of trigeminal nociceptive input in the brainstem. More recently, the introduction of integrated models, namely electrical stimulation of the trigeminal ganglion or systemic administration of capsaicin, allows studying the activation of the trigeminal system and its effect on the cranial vasculature. Studies using in vitro models have contributed enormously during the preclinical stage to characterizing the receptors in cranial blood vessels and to studying the effects of several putative antimigraine agents. The aforementioned migraine models have advantages as well as some limitations. The present review is devoted to discussing various migraine models and their relevance to antimigraine therapy.

Pharmacological characterization of novel alpha-Calcitonin Gene-Related Peptide (CGRP) receptor peptide antagonists that are selective for human CGRP receptors

Human alpha-calcitonin gene-related peptide (CGRP) is a 37-residue neuropeptide that produces a variety of cardiovascular and other effects via activation of specific CGRP receptors that produce cAMP. Functional CGRP receptors are a heterodimeric complex composed of the heptahelical calcitonin receptor-like receptor and the single transmembrane receptor activity-modifying protein 1. Based on the known structures of the antagonist CGRP((8-37)) and the human CGRP receptor, we designed novel CGRP receptor peptide antagonists with modifications to promote high affinity and selectivity for human CGRP receptors. Antagonist affinity (K(B)) at CGRP receptors was determined using the mouse thoracic aorta and human SK-N-MC cells. In aorta, CGRP((8-37)), [N-alpha-benzoyl]human alpha-CGRP((8-37)) [bzl-CGRP((8-37))], and [N-alpha-benzoyl-His(10)-benzyl]human alpha-CGRP((8-37)) [bzl-bn-CGRP((8-37))] caused rightward shifts in the concentration-response relaxation curve for CGRP with K(B) values of 1000, 88, and 50 nM, respectively. In human SK-N-MC cells, CGRP((8-37)), bzl-CGRP((8-37)), and bzl-bn-CGRP((8-37)) caused rightward shifts in the concentration-response curve for CGRP-stimulated cAMP production with K(B) values of 797, 15, and 0.63 nM, respectively. Thus, CGRP((8-37)) had the same affinity for human and mouse CGRP receptors, whereas bzl-CGRP((8-37)) and bzl-bn-CGRP((8-37)) displayed 6- and 80-fold higher affinities, respectively, for human CGRP receptors. In addition, the selectivity of the antagonists for human CGRP receptors was highly correlated with the antagonist hydrophobicity index. These relatively high-affinity, species-selective peptide antagonists provide novel tools to differentiate structural and functional features that are unique to the human CGRP receptor. Thus, these analogs may be useful compounds for development of drugs to treat migraine headache and other cardiovascular diseases.

Critical role of calcitonin gene-related peptide 1 receptors in the amygdala in synaptic plasticity and pain behavior

The role of neuropeptides in synaptic plasticity is less well understood than that of classical transmitters such as glutamate. Here we report the importance of the G-protein-coupled calcitonin gene-related peptide (CGRP1) receptor as a critical link between amygdala plasticity and pain behavior. A key player in emotionality and affective disorders, the amygdala has been implicated in the well documented, but mechanistically unexplained, relationship between pain and affect. Our electrophysiological and pharmacological in vitro (patch-clamp recordings) and in vivo (extracellular single-unit recordings) data show that selective CGRP1 receptor antagonists (CGRP(8-37) and BIBN4096BS) in the amygdala reverse arthritis pain-related plasticity through a protein kinase A (PKA)-dependent postsynaptic mechanism that involves NMDA receptors. CGRP1 receptor antagonists inhibited synaptic plasticity in the laterocapsular division of the central nucleus of the amygdala (CeLC) in brain slices from arthritic rats compared with normal controls. The effects were accompanied by decreased neuronal excitability and reduced amplitude, but not frequency, of miniature EPSCs; paired-pulse facilitation was unaffected. The antagonist effects were occluded by a PKA inhibitor. CGRP1 receptor blockade also directly inhibited NMDA-evoked, but not AMPA-evoked, membrane currents. Together, these data suggest a postsynaptic site of action. At the systems level, the antagonists reversed the sensitization of nociceptive CeLC neurons in anesthetized rats in the arthritis pain model. Importantly, CGRP1 receptor blockade in the CeLC inhibited spinal (hindlimb withdrawal reflexes) and supraspinal pain behavior of awake arthritic rats, including affective responses such as ultrasonic vocalizations. This study provides direct evidence for the critical dependence of pain behavior on CGRP1-mediated amygdala plasticity.

Characterisation of CGRP receptors in human and porcine isolated coronary arteries: evidence for CGRP receptor heterogeneity

This study sets out to characterise calcitonin gene-related peptide (CGRP) receptors in human and porcine isolated proximal and distal coronary arteries using BIBN4096BS. Human (h)-alphaCGRP induced relaxations that were blocked by BIBN4096BS in all arteries studied. In contrast to the other vessels, the Schild plot slope in the human distal coronary artery segments (0.68 +/- 0.07) was significantly less than unity and BIBN4096BS potently blocked these responses (pK(b) (10 nM): 9.29 +/- 0.34, n = 5). In the same preparation, h-alphaCGRP(8-37) behaved as a weak antagonist of h-alphaCGRP-induced relaxations (pK(b) (3 microM): 6.28 +/- 0.17, n = 4), with also a Schild plot slope smaller than unity. The linear agonists, [ethylamide-Cys(2,7)]-h-alphaCGRP ([Cys(Et)(2,7)]-h-alphaCGRP) and [acetimidomethyl-Cys(2,7)]-h-alphaCGRP ([Cys(Acm)(2,7)]-h-alphaCGRP), had a high potency (pEC(50): 8.21 +/- 0.25 and 7.25 +/- 0.14, respectively), suggesting the presence of CGRP(2) receptors, while the potent blockade by BIBN4096BS (pK(b) (10 nM): 10.13 +/- 0.29 and 9.95 +/- 0.11, respectively) points to the presence of CGRP(1) receptors. Using RT-PCR, mRNAs encoding for the essential components for functional CGRP(1) receptors were demonstrated in both human proximal and distal coronary artery. Further, h-alphaCGRP (100 nM) increased cAMP levels, and this was attenuated by BIBN4096BS (1 microM). The above results demonstrate the presence of CGRP(1) receptors in all coronary artery segments investigated, but the human distal coronary artery segments seem to have an additional population of CGRP receptors not complying with the currently classified CGRP(1) or CGRP(2) receptors.

Lack of effect of the adenosine A1 receptor agonist, GR79236, on capsaicin-induced CGRP release in anaesthetized pigs

Migraine is a common neurological disorder that is associated with an increase in plasma calcitonin gene-related peptide (CGRP) levels. CGRP, a potent vasodilator released from the activated trigeminal sensory nerves, dilates intracranial blood vessels and transmits vascular nociception. Hence, inhibition of trigeminal CGRP release may prevent neurotransmission and, thereby, ameliorate migraine headache. Therefore, the present study in anaesthetized pigs investigates the effects of a selective adenosine A(1) receptor agonist, GR79236 (3, 10 and 30 microg/kg, i.v.) on capsaicin-induced carotid haemodynamic changes and on plasma CGRP release. Intracarotid (i.c.) infusion of capsaicin (10 microg/kg/min, i.c.) increased the total carotid blood flow and conductance as well as carotid pulsations, but decreased the difference between arterial and jugular venous oxygen saturations. These responses to capsaicin were dose-dependently attenuated by GR79236. However, the increases in the plasma CGRP concentrations by capsaicin remained essentially unmodified after GR79236 treatment. The above results suggest that GR79236 may have an antimigraine potential due to its postjunctional effects (carotid vasoconstriction) rather than to prejunctional inhibition of trigeminal CGRP release.

Increased alphaCGRP potency and CGRP-receptor antagonist affinity in isolated hypoxic porcine intramyocardial arteries

1. This study describes the effects of hypoxia on relaxing responses and cAMP production induced by the known vasodilator peptides: alphaCGRP, amylin (AMY) and adrenomedullin (AM) on isolated pig coronary arteries in vitro. 2. Hypoxic incubation increased the vasorelaxant effect of alphaCGRP (four-fold; P<0.05), AMY (3.2-fold; P<0.05), but not significantly for AM (two-fold; NS). 3. Whereas hypoxia had no effect on arterial cAMP levels, it significantly potentiated the production of cAMP stimulated of alphaCGRP and AMY, but not of AM. 4. The antagonist alphaCGRP(8-37) also exerted an increased effect in hypoxia. The Schild plot-derived pK(B) values revealed an increase in the apparent affinity of the antagonist for the CGRP(1) receptor from 7.0 to 7.2 under control conditions versus 8.0 in hypoxia. 5. Removal of endothelium, peptidase inhibitors, preincubation with the adenosine A(2A) receptor antagonist CSC (10(-3) M), the ATP-sensitive K-channel inhibitor glibenclamide (10(-5) M), the cyclooxygenase inhibitor indomethacin (10(-3) M) or NG-monomethyl-L-arginine (10(-4) M) had no effect on the alphaCGRP-induced vasorelaxation in hypoxia; neither did hypoxia influence the levels of CGRP and AM receptor mRNA. 6. We conclude that hypoxic incubation increases the relaxation and cAMP production induced by alphaCGRP and AMY in rings of porcine coronary arteries in vitro. A concomitant release of adenosine, a cyclooxygenase product, an endothelium-derived substance, activation of vascular ATP-sensitive K-channels, peptidase inhibitors or changes in CGRP and AM receptor mRNA cannot account for the changes observed in hypoxia. Moreover, alphaCGRP(8-37) showed increased affinity at the CGRP(1) receptor during hypoxia, possibly due to a conformational change at the CGRP(1) receptor site.

GPCR modulation by RAMPs

Our conceptual understanding of the molecular architecture of G-protein coupled receptors (GPCRs) has transformed over the last decade. Once considered as largely independent functional units (aside from their interaction with the G-protein itself), it is now clear that a single GPCR is but part of a multifaceted signaling complex, each component providing an additional layer of sophistication. Receptor activity-modifying proteins (RAMPs) provide a notable example of proteins that interact with GPCRs to modify their function. They act as pharmacological switches, modifying GPCR pharmacology for a particular subset of receptors. However, there is accumulating evidence that these ubiquitous proteins have a broader role, regulating signaling and receptor trafficking. This article aims to provide the reader with a comprehensive appraisal of RAMP literature and perhaps some insight into the impact that their discovery has had on those who study GPCRs.

Remote arteriolar dilations caused by methacholine: a role for CGRP sensory nerves?

Remote vasodilation caused by arteriolar microapplication of acetylcholine cannot be completely attributed to passive cell-cell communication of a hyperpolarizing signal. The present study was undertaken to ascertain whether a neural component may be involved in the remote response. In the cheek pouch of anesthetized hamsters, methacholine (100 μM) was applied to the arteriole by micropipette for 5 s, and the arteriolar responses were measured at the site of application and at remote locations: 500 and 1,000 μm upstream from the application site. Superfusion with the local anesthetic bupivacaine attenuated a local dilatory response and abolished the conducted dilation response to methacholine. Localized micropipette application of bupivacaine 300 μm from the methacholine application site also attenuated the remote dilation but did not inhibit the local dilation. Blockade of neuromuscular transmission with botulinum neurotoxin A (1 U, 3 days), micropipette application of calcitonin gene-related peptide (CGRP) receptor inhibitor CGRP-(8–37) (10 μM) 300 μm upstream from the methacholine application site, and denervation of the CGRP sensory nerve by 2 days of capsaicin treatment reduced the conducted dilation response to methacholine but did not affect the local dilatory response. Together, these data support involvement of a TTX-insensitive nerve, specifically the CGRP containing nerve, in vascular communication. Understanding the effect of regulation of a novel neural network system on the vascular network may lead to a new insight into regulation of blood flow and intraorgan blood distribution.

Calcitonin gene-related peptide antagonism attenuates the haemodynamic and glycaemic responses to acute hypoxaemia in the late gestation sheep fetus

The fetal defence to acute hypoxaemia involves cardiovascular and metabolic responses, which include peripheral vasoconstriction and hyperglycaemia. Both these responses are mediated via neuroendocrine mechanisms, which require the stimulation of the sympathetic nervous system. In the adult, accumulating evidence supports a role for calcitonin gene-related peptide (CGRP) in the activation of sympathetic outflow. However, the role of CGRP in stimulated cardiovascular and metabolic functions before birth is completely unknown. This study tested the hypothesis that CGRP plays a role in the fetal cardiovascular and metabolic defence responses to acute hypoxaemia by affecting sympathetic outflow. Under anaesthesia, five sheep fetuses at 0.8 of gestation were surgically instrumented with catheters and a femoral arterial Transonic flow-probe. Five days later, fetuses were subjected to 0.5 h hypoxaemia during either i.v. saline or a selective CGRP antagonist in randomised order. Treatment started 30 min before hypoxaemia and ran continuously until the end of the challenge. Arterial samples were taken for blood gases, metabolic status and hormone analyses. CGRP antagonism did not alter basal arterial blood gas, metabolic, cardiovascular or endocrine status. During hypoxaemia, similar falls in Pa,O2 occurred in all fetuses. During saline infusion, hypoxaemia induced hypertension, bradycardia, femoral vasoconstriction, hyperglycaemia and an increase in haemoglobin, catecholamines and neuropeptide Y (NPY). In contrast, CGRP antagonism markedly diminished the femoral vasoconstrictor and glycaemic responses to hypoxaemia, and attenuated the increases in haemoglobin, catecholamines and NPY. Combined, these results strongly support the hypothesis that CGRP plays a role in the fetal cardiovascular and metabolic defence to hypoxaemia by affecting sympathetic outflow.

Progression of vascular and neural dysfunction in sciatic nerves of Zucker diabetic fatty and Zucker rats

We have examined the progression of vascular and neural deficits in Zucker rats, Zucker diabetic fatty (ZDF) diabetic rats, and age-matched lean ZDF rats from 8 to 40 wk of age. Both the ZDF diabetic and Zucker rats were glucose intolerant at 8 wk of age. The Zucker rats did not become hyperglycemic but were hyperinsulinemic through 32 wk of age. All ZDF diabetic rats became hyperglycemic by 8 wk of age. Through their life span, serum free fatty acids and triglycerides levels were significantly higher in Zucker and ZDF diabetic rats compared with age-matched lean ZDF rats. After 24 and 28 wk of age, endoneurial blood flow was significantly decreased in ZDF diabetic and Zucker rats. Motor nerve conduction velocity was significantly decreased after 12-14 wk of age in ZDF diabetic rats and at 32 wk of age in Zucker rats. ACh-mediated vascular relaxation of epineurial arterioles of the sciatic nerve was impaired after 8-10 wk of age in ZDF diabetic rats and after approximately 16 wk of age in Zucker rats. In contrast, vascular relaxation mediated by calcitonin gene-related peptide was impaired significantly after 28 wk of age in ZDF diabetic rats but not impaired in Zucker rats up to 40 wk of age. Markers of oxidative stress were differentially elevated in ZDF diabetic rats and Zucker rats. These data indicate that vascular and neural dysfunction develops in both Zucker and ZDF diabetic rats but at different rates, which may be the result of hyperglycemia.

Calcitonin gene-related peptide and its role in migraine pathophysiology

Migraine is a common neurological disorder that is associated with an increase in plasma calcitonin gene-related peptide (CGRP) levels. CGRP, a neuropeptide released from activated trigeminal sensory nerves, dilates intracranial blood vessels and transmits vascular nociception. Therefore, it is propounded that: (i) CGRP may have an important role in migraine pathophysiology, and (ii) inhibition of trigeminal CGRP release or CGRP-induced cranial vasodilatation may abort migraine. In this regard, triptans ameliorate migraine headache primarily by constricting the dilated cranial blood vessels and by inhibiting the trigeminal CGRP release. In order to explore the potential role of CGRP in migraine pathophysiology, the advent of a selective CGRP receptor antagonist was obligatory. The introduction of di-peptide CGRP receptor antagonists, namely BIBN4096BS (1-piperidinecarboxamide, 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)-, [R-(R*,S*)]-), is a breakthrough in CGRP receptor pharmacology and can be used as a tool to investigate the role of CGRP in migraine headaches. Preclinical investigations in established migraine models that are predictive of antimigraine activity have shown that BIBN4096BS is a potent CGRP receptor antagonist and that it has antimigraine potential. Indeed, a recently published clinical study has reported that BIBN409BS is effective in treating acute migraine attacks without significant side effects. The present review will discuss mainly the potential role of CGRP in the pathophysiology of migraine and the various treatment modalities that are currently available to target this neuropeptide.

Calcitonin gene-related peptide contributes to the umbilical haemodynamic defence response to acute hypoxaemia

Despite clinical advances in obstetric practice, undiagnosed fetal hypoxaemia still contributes to a high incidence of perinatal morbidity. The fetal defence to hypoxaemia involves a redistribution of blood flow away from peripheral circulations towards essential vascular beds, such as the umbilical, cerebral, myocardial and adrenal circulations. In marked contrast to other essential vascular beds, the mechanisms mediating maintained perfusion of the umbilical circulation during hypoxaemia remain unknown. This study determined the role of calcitonin gene-related peptide (CGRP) in the maintenance of umbilical blood flow during basal and hypoxaemic conditions. Under anaesthesia, five sheep fetuses were instrumented with catheters and a Transonic probe around an umbilical artery, inside the fetal abdomen, at 0.8 of gestation. Five days later, fetuses were subjected to 0.5 h hypoxaemia during either i.v. saline or a selective CGRP antagonist in randomised order. Treatment started 30 min before hypoxaemia and ran continuously until the end of the challenge. The CGRP antagonist did not alter basal blood gas or cardiovascular status in the fetus. A similar fall in Pa,O2 occurred in fetuses during either saline (21 +/- 0.8 to 9 +/- 0.9 mmHg) or antagonist treatment (20 +/- 0.9 to 9 +/- 1.2 mmHg). Hypoxaemia during saline led to significant increases in arterial blood pressure, umbilical blood flow and umbilical vascular conductance. In marked contrast, hypoxaemia during CGRP antagonist treatment led to pronounced falls in both umbilical blood flow and umbilical vascular conductance without affecting the magnitude of the hypertensive response. In conclusion, CGRP plays an important role in the umbilical haemodynamic defence response to hypoxaemia in the late gestation fetus.

Peptidergic and non-peptidergic innervation and vasomotor responses of human lenticulostriate and posterior cerebral arteries

The aim of the present study was to compare in man the innervation pattern and the functional responses to neuronal messengers in medium sized lenticulostriate and branches of the posterior cerebral arteries (PCA). The majority of the nerve fibers found were sympathetic and displayed specific immunoreactivity for tyrosine hydroxylase (TH) and neuropeptide Y (NPY). Only few nerve fibers displayed vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP) and substance P (SP) immunoreactivity. In both arteries, the contractions induced by noradrenaline (NA), NPY and 5-hydroxytryptamine (5-HT) and the relaxant responses induced by acetylcholine (ACh), VIP and pituitary adenylate cyclase activating peptide-27 (PACAP) as well as CGRP and SP were compared in vitro. In conclusion, there was no major difference in innervation pattern or vasomotor sensitivity (pEC50 and pIC50 values) between the two vessels. However, the general pattern indicates stronger vasomotor responses (Emax and Imax) in the PCA branches as compared to the lenticulostriate arteries which may lend support for the clinical observation of a difference in stroke expression between the two vascular areas.

The pharmacology of CGRP-responsive receptors in cultured and transfected cells

Historically, CGRP receptors have been classified as CGRP(1) or CGRP(2) subtypes, chiefly depending on their affinity for the antagonist CGRP(8-37). It has been shown that the complex between calcitonin receptor-like receptor (CRLR or CL) and receptor activity modifying protein (RAMP) 1 provides a molecular correlate for the CGRP(1) receptor; however, this does not explain the range of affinities seen for CGRP(8-37) in isolated tissues. It is suggested that these may largely be explained by a combination of methodological factors and CGRP-responsive receptors generated by CL and RAMP2 or RAMP3 and complexes of RAMPs with the calcitonin receptor.

Adrenomedullin receptors: pharmacological features and possible pathophysiological roles

Three receptor activity modifying proteins (RAMPs) chaperone calcitonin-like receptor (CLR) to the cell surface. RAMP2 enables CLR to form an adrenomedullin (AM)-specific receptor that is sensitive to AM-(22-52) (AM(1) receptor). RAMP3 enables CLR to form an AM receptor sensitive to both calcitonin gene-related peptide (CGRP)-(8-37) and AM-(22-52) (AM(2) receptor), though rat and mouse AM(2) receptors show a clear preference for CGRP alpha-(8-37) over AM-(22-52). RAMP1 enables CRL to form the CGRP-(8-37)-sensitive CGRP(1) receptor, which can also be activated by higher concentrations of AM. Here we review the available information on the pharmacological features and possible pathophysiological roles of the aforementioned AM receptors.

Noncompetitive antagonism of BIBN4096BS on CGRP-induced responses in human subcutaneous arteries

We investigated the antagonistic effect of 1-piperidinecarboxamide, N-[2-[[5amino-l-[[4-(4-pyridinyl)-l-piperazinyl]carbonyl]pentyl]amino]-1-[(3,5-dibromo-4-hydroxyphenyl)methyl]-2-oxoethyl]-4-(1,4-dihydro-2-oxo-3(2H)-quinazolinyl) (BIBN4096BS) on the calcitonin gene-related peptide (CGRP)-induced responses by using isometric myograph and FURA-2 technique in human subcutaneous arteries removed in association with abdominal surgery. BIBN4096BS, at the concentration of 1 pm, had no significant effect on the CGRP-induced relaxation in these vessels. At the concentration of 10 pM, BIBN4096BS had a competitive antagonistic-like behaviour characterized by parallel rightward shift in the log CGRP concentration-tension curve with no depression of the E(max). At the higher concentrations (0.1 and 1 nM), BIBN4096BS had a concentration-dependent noncompetitive antagonistic effect on the CGRP-induced responses. The efficacy and potency of CGRP was significantly greater in the smaller (lumen diameter approximately 200 microM) human subcutaneous arteries compared to the larger ones. The apparent agonist equilibrium dissociation constant, K(A), for CGRP(1) receptors in the human subcutaneous arteries was approximately 1 nM. Analysis of the relationship between receptor occupancy and response to CGRP indicates that the receptor reserve is relatively small. Using reverse transcriptase-polymerase chain reaction (RT-PCR), the presence of mRNA sequences encoding the calcitonin receptor-like receptor, receptor activity modifying protein (RAMP1, RAMP2, RAMP3) and receptor component protein were demonstrated in human subcutaneous arteries, indicating the presence of CGRP(1)-like receptor and the necessary component for the receptor activation. In conclusion, the inhibitory action of BIBN4096BS at the low concentration (10 pM) on the CGRP-tension curve (but not intracellular calcium concentration ([Ca(2+)](i)) resembles what is seen with a reversible competitive antagonist. However, at the higher concentrations (0.1 and 1 nM), BIBN4096BS acts as a selective noncompetitive inhibitor at CGRP(1) receptors in human subcutaneous arteries.

Vascular Actions of Calcitonin Gene-Related Peptide and Adrenomedullin

This review summarizes the receptor-mediated vascular activities of calcitonin gene-related peptide (CGRP) and the structurally related peptide adrenomedullin (AM). CGRP is a 37-amino acid neuropeptide, primarily released from sensory nerves, whilst AM is produced by stimulated vascular cells, and amylin is secreted from the pancreas. They share vasodilator activity, albeit to varying extents depending on species and tissue. In particular, CGRP has potent activity in the cerebral circulation, which is possibly relevant to the pathology of migraine, whilst vascular sources of AM contribute to dysfunction in cardiovascular disease. Both peptides exhibit potent activity in microvascular beds. All three peptides can act on a family of CGRP receptors that consist of calcitonin receptor-like receptor (CL) linked to one of three receptor activity-modifying proteins (RAMPs) that are essential for functional activity. The association of CL with RAMP1 produces a CGRP receptor, with RAMP2 an AM receptor and with RAMP3 a CGRP/AM receptor. Evidence for the selective activity of the first nonpeptide CGRP antagonist BIBN4096BS for the CGRP receptor is presented. The cardiovascular activity of these peptides in a range of species and in human clinical conditions is detailed, and potential therapeutic applications based on use of antagonists and gene targeting of agonists are discussed.

Secretory and vascular effects of adrenomedullin in gastric ulcer: role of CGRP- and adrenomedullin-receptors

Adrenomedullin prevents damage of gastric mucosa in either reserpine-treated or pylorus-ligated rats. Pre-treatment with CGRP(8-37) resulted in a decrease of the gastro-protective effect of adrenomedullin in both models and reversed the inhibitory effect of adrenomedullin on gastric acid output in the pylorus-ligated rats. These adrenomedullin actions were less effectively modified by pre-treatment with adrenomedullin(22-52). These data suggest that the anti-ulcer effect of adrenomedullin is mainly related to its anti-secretory action, presumably mediated through CGRP-receptors.